Cementing Best Practice Jorge Sierra

Cementing Best Practices

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Table of Contents


Table of Contents

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1Tips for Using This Document . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Reminders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2Time-Saving Navigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Engineering and Planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3Mud Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Drilling Fluid Conditioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3Pipe Movement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3Pipe Centralization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Spacers and Flushes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Operational Priorities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6Job Volume Excess . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6Flow Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6Downhole Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Centralizers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Wiper Plugs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Shoe Joint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Considerations for Liner Jobs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Cement Design Priorities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Priority No. 1—Density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Priority No. 2—Pump Time (Thickening Time) . . . . . . . . . . . . . . . . . . . . . . . . 9Priority No. 3—Mixability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Priority No. 4—Rheology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Priority No. 5—Fluid Loss Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Priority No. 6—Compressive Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Priority No. 7—Free Fluid and Settling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Cement Slurry Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Evaluation of Cementing Job Proposal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Data Review and Verification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Review of Cement Job Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12Interpretation of “Pilot” Test Results and Laboratory Reports . . . . . . . . . . . 12

Job Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14Monitoring and Recording . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Prejob Preparations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15Cement Design Verification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15Equipment / Materials Verification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15Wellbore Circulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Pumping Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17Pressure Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17Mixing and Pumping Cement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17Displacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Shallow Water Flow Cementing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19Wait on Cement (WOC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

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Table of Contents


Plug Cementing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22Engineering and Planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Placement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22Plug Length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22Cement Volumes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23Cement Slurry Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24Spacers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25Cement Slurry Displacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25Mechanical Tools for Supporting Cement Plugs . . . . . . . . . . . . . . . . . . . . . 26Waiting On Cement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Job Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Squeeze Cementing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29Engineering and Planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Placement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29Cement Volume . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30Slurry Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30Washes and Spacers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32Prejob Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Job Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34Bradenhead Cement Squeeze . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34Bull Head Cement Squeeze . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

Contractor Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36Cement Job Planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37Cement Job Mobilization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38Cement Job Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39Cementing Recommendation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40Reporting Responsibilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Cement Designs for “Pilot Testing” . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42Laboratory Testing Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43On-Location Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Cement Bulk Blending . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45Cement Load-Out for Land Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48Cement Loadout for Offshore Operations . . . . . . . . . . . . . . . . . . . . . . . . . . 50Prejob Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

Job Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

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isit the Engineering etwork LiveLink site ow by clicking on

his text link.

menting Best Practices

Introduction

PurposeThe purpose of this document is to teach and promote a “Best Practices” phi-losophy throughout the Unocal Global Drilling Community. Unocal spends millions of dollars each year on cementing operations. Poor planning and operational execution not only can lead to cement failure but can result in the loss of hydrocarbon recovery from the wellbore.

This document is a guide for planning and executing cementing operations for worldwide operations. It is realized that, in some well situations, the preferred Best Practice may not achieve the best results. Every cement job should be designed for the wellbore characteristics and the cementing objectives desired.

Promoting Best Practices is an ongoing effort throughout Unocal drilling operations. Given the wide variety of cementing operations going on through-out the Unocal drilling world, it is hoped that a collective sharing of Best Practices will help all areas obtain competent and economical cement jobs.

Visit the Casing, Liner Running and Cementing Network LiveLink site to view the network’s charter, goals, and members’ names and contact informa-tion. Access the Toolbox section for engineering tools, calculation work-sheets, and detailed job examples.

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Tips for Using This DocumentThis document is divided into seven main categories:

• Table of Contents

• Introduction

• Engineering and Planning

• Job Procedures

• Plug Cementing

• Squeeze Cementing

• Contractor Requirements

“Engineering and Planning” and “Job Procedures” cover all the basics involved in planning and executing a primary cementing job. “Plug Cement-ing” and “Squeeze Cementing,” as the names suggest, contain information specific to these techniques.“Contractor Requirements” provides information about contractors’ responsibilities in ensuring the job is carried out as planned.

Reminders

In many of the sections, you will find white text in the blue column at the left of the page, topped with an orange bar. These comments are emphasized to indicate their importance in the success of the job.

Time-Saving Navigation

This document is easily navigated from either the Table of Contents or the color tabs located at the right side of every page.

Table of Contents

The Table of Contents allows you to view the subtopics discussed within each major section. To navigate to a particular topic, just click on the entry.

Colored Tabs

The blue and orange tabs at the right of each page offer quick navigation to any major section of the document, including the Table of Contents, from any page in the document.

Where Am I?

The title of the section you are viewing is always located in the upper right hand corner of the page, in the same color as its corresponding tab.

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Engineering and Planning


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The cementing contractor’s role begins with the Engi-neering and Planning stage, and his work will parallel that of the Drilling Engineer. For details, see the Con-tractor Requirements section.

The condition of the drilling fluid is one of the most important variables in achiev-ing good displace-ment during a cement job.

Engineering and PlanningThe first step in Engineering and Planning for cementing is to identify the purpose of the cementing operation. Once the purpose is clearly defined, the wellbore conditions and casing design must be evaluated to determine the cement placement, hydrostatic constraints, and volumes. The cementing con-tractor must be involved in this stage, as detailed in the Contractor Require-ments section of this document.

Primary cement job failures are predominately due to a breakdown in the “displacement process,” which leads to channeling of the cement through the drilling fluid.

Application of the following guidelines for mud removal, cement and spacer design, in conjunction with a cementing software program, will enhance the displacement process and improve the probability of successful primary cementing. Cementing software can be used to help determine the optimum displacement parameters and safe operating equivalent circulating densities (ECD).

Mud RemovalMud removal is best achieved through proper drilling fluid conditioning, pipe rotation or reciprocation, pipe centralization, and the use of properly designed spacers and flushes.

Drilling Fluid Conditioning

The condition of the drilling fluid is one of the most important variables in achieving good displacement during a cement job. Regaining and maintaining good mobility is the key. An easily displaced drilling fluid will have low gel strengths and low fluid loss. Pockets of gelled fluid, which commonly exist following the drilling of a wellbore, make displacement difficult and must be broken apart.

Pipe Movement

Pipe rotation or reciprocation before and during cementing helps break up gelled, stationary pockets of drilling fluid and loosens cuttings trapped in the gelled drilling fluid. Pipe movement allows high displacement efficiency at lower pump rates because it helps to keep the drilling fluid flowing. If the pipe is poorly centralized, pipe movement can compensate by changing the flow path through the casing and allowing the slurry to circulate completely around the casing. The industry does not specify a minimum requirement for pipe movement, however it acknowledges that even a small amount of move-ment will enhance the displacement process.

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Drilling fluid displace-ment is best achieved when annular toler-ances are approxi-mately 1.5 to 2 in.

The industry bench-mark for standoff is approximately 70%.

In some instances, pipe movement is not recommended. For example, when equivalent circulating density and fracture pressure are very similar, or shal-low gas or water influx is critical, moving the pipe can induce surge and swab pressures that could promote pipe sticking and surface casing-head pressure. The use of mechanical devices, such as some models of liner hangers, may also prevent casing movement. All of these factors must be considered when designing the displacement program.

Pipe Centralization

Drilling fluid displacement is best achieved when annular tolerances are approximately 1.5 to 2 in. Centralization of very small annuli is very difficult, and pipe movement and displacement rates may be severely restricted. Very large annuli may require extreme displacement rates to generate enough flow energy to remove the drilling fluid and cuttings.

Centralizing the casing by placing mechanical centralizers across the intervals to be isolated is critical for effectively displacing the drilling fluid and placing cement all around the casing. In poorly centralized casing, cement will bypass the drilling fluid by following the path of least resistance; as a result, the cement travels down the wide side of the annulus, leaving drilling fluid in the narrow side.

Good pipe standoff ensures uniform flow around the casing and helps equal-ize the force that the flowing spacer and cement exerts around the casing, increasing drilling fluid removal. In a deviated wellbore, standoff is even more critical to prevent a solids bed from accumulating on the low side of the annulus. The industry benchmark for standoff is approximately 70%, how-ever the preferred standoff for a given well should be developed from com-puter modeling and will vary with well conditions.

To improve centralization of the casing, adhere to the following guidelines:

• Use cementing simulator runs to determine the standoff necessary to achieve complete flow around the casing.

• Run a centralizer calculation program and reference well deviation sur-veys to determine the number of centralizers necessary to achieve the rec-ommended standoff and their ideal placement.

• For liner jobs, include centralizers in the lap area to aid in the displace-ment of cement all around the casing perimeter either in the primary cement job or subsequent squeeze job.

• For highly deviated wells in which cuttings beds are likely, place the cen-tralizer on the lower joints to hold the landing shoe off of the bottom of the wellbore. This design will allow cuttings to pass underneath and help eliminate any snowplowing effect.

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Compatibility of the drilling fluid/spacer as well as the compatibility of the spacer/cement slurry is of prime importance.

Provide a contact time and volume of spacer that will pro-vide optimum amount of drilling fluid removal.

Spacer must be fully compatible with drilling fluid and cement.

For all liner and tie-back jobs, the spacer must be tested by “hot-rolling” at circu-lating temperature.

Spacers and Flushes

Spacers and flushes are effective displacement aids because they separate unlike fluids such as cement and drilling fluid, and enhance the removal of gelled drilling fluid, allowing a better cement bond. Spacers can be designed to serve various needs. For example, weighted spacers can help with well control, and reactive spacers can provide increased drilling fluid-removal benefits. Compatibility of the drilling fluid/spacer as well as the compatibility of the spacer/cement slurry is of prime importance. Application of the com-patibility procedures as outlined in the API SPEC RP10B, 22nd Edition, December 1997 is highly recommended.

Parameters governing a spacer’s effectiveness include flow rate, contact time, and fluid properties. To achieve maximum drilling fluid displacement, adhere to the following guidelines:

Density

Set spacer density 0.5 to 1.0 ppg above the drilling fluid weight and at least 0.5 ppg less than the cement slurry density. In situations that require the dif-ference between cement weight and drilling fluid weight to be less than 1.0 ppg, design the spacer density to be mid-way between the two densities.

Contact Time

Provide a contact time and volume of spacer that will provide optimum amount of drilling fluid removal. Typically 8 to 10 minutes contact time or 1,000 feet of annular space are adequate.

Rheology

Design spacer rheology that will provide turbulent flow where hole geometry allows. Turbulent flow of spacer is required on all liner jobs.

Compatibility

Spacer must be fully compatible with drilling fluid and cement. Contact with drilling fluid must not result in flocculation, settling, or excessive rheology. Contact with cement must not decrease pump time.

Stability

Spacer must remain stable with no excessive settling or separation. For all liner and tieback jobs, the spacer must be tested by “hot-rolling” at circulating temperature.

Wettability

When an oil-based or synthetic-based drilling fluid is in the hole, the spacer must also be capable of converting the pipe and hole to a “water wet” condi-tion.

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High-energy displace-ment rates are most effective in ensuring good displacement.

Operational PrioritiesDetermining how the cement will be placed in the hole is as important as the design of the cement itself. This section discusses the operational factors that should be determined in planning a successful job.

Job Volume Excess

Unless caliper data is available or excess volume is otherwise specified, use the recommended percentages in the following table to calculate cement slurry volume requirements across an open hole.

For cementing operations on offshore wells that use subsea housing, try to plan the well’s programs so that cement returns are not transported through the subsea housing. In such cases, the surface casing is usually cemented only to 500 ft above the conductor shoe. The presence of cement in the recesses of subsea housing can cause great difficulty in setting subsequent hangers or packoffs.

Flow Rate

Cement flow is characterized by three flow rate regimes: turbulent flow, lam-inar flow, and plug flow. High-energy displacement rates are most effective in ensuring good displacement. Turbulent flow conditions are desirable, but are not required. When turbulent flow is not a viable option for a formation, use the highest pump rate that is feasible for the wellbore conditions. The best results are obtained when the spacer and/or cement is pumped at maximum energy, the spacer or flush is appropriately designed to remove the drilling fluid, and a good competent cement is used.

To maximize displacement, adhere to the following guidelines:

• Design spacer to be in turbulent flow as it rounds the shoe and passes the sections to be isolated.

• Mix and pump cement as fast as density control, pumping equipment, material supply, and wellbore conditions allow.

Calculations of Volume Excess

Depth (ft) % Excess with Water-Based Mud

% Excess with Oil-Based Mud

0 to 4,000 100 50

4,000 to 8,000 75 25

8,000 to 10,000 50 15

10,000 to 18,000 35 15

Greater than 18,000 25 15

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Ceoi

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Tcopj

hoose all downhole quipment for fit, peration, and proper

nstallation.

owspring-type entralizers provide n acceptable alance between cost nd standoff for most tandard cementing perations.

op and bottom ement plugs are rec-mmended for every rimary cementing

ob, when possible.

m
enting Best Practices
• Displace at high rates (8 bbl/min and higher) without exceeding the for-mation breakdown pressure.

Downhole Equipment

Choose all downhole equipment (float collars, shoes, guide shoes, centraliz-ers, liner hanger systems, and wiper plugs) for fit, operation, and proper installation.

Centralizers

• Determine which type of centralizer is best for a particular application by evaluating the centralizer’s suitability for the specific application, its abil-ity to mitigate exposure for problems in the running of casing due to its design, and to provide centralization cost-effectively.

• Select appropriate centralizer types, stop rings, and casing connections to minimize the risk of centralizers sliding and stacking-out.

Bowspring-type centralizers provide an acceptable balance between cost and standoff for most standard cementing operations.

• If centralizers are at risk of becoming smashed when running through existing liner tops or downhole components such as wellhead housings, choose a durable centralizer such as solid integral centralizer subs that can withstand these conditions.

• For highly deviated wellbores, evaluate the use of double bowspring or solid body centralizers to centralize the casing and to maintain or improve running force requirements. Tight clearances and holes drilled with bi-center bits may require the use of bow spring centralizer subs.

Wiper Plugs

Top and bottom cement plugs are recommended for every primary cementing job, when possible. The bottom plug minimizes contamination of the cement as it is pumped. The top plug prevents contamination of the cement slurry by the displacement fluid and provides a positive indication that the cement has been displaced. Use composite body plugs that are easy to drill out with PDC bits.

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A shoe joint is recommended for all primary casing/liner jobs.

Shoe Joint

A shoe joint is recommended for all primary casing/liner jobs. The length of the shoe joint will vary. The absolute minimum length is one joint of pipe. If a bottom plug is not required, a minimum of two joints are required.

Considerations for Liner Jobs

A liner hanger must be designed for the combined loading of the liner weight to be hung off and the mud weight differential on the slip area to avoid exceeding the elastic limit on the ID of the casing in which the slips are engaged.

• Ensure that the liner hanger set pressures are well above the circulation pressures that could be required while running the liner to prevent prema-ture setting of the liner hanger.

• On all liner float shoes, verify that holes exist on the side of the float shoe, allowing circulation and preventing a hydraulic lockup in the event that the liner hanger fails and the liner lands on the bottom of the hole.

• Use or design autofill float equipment that can be activated without set-ting the liner hanger, should a well control condition arise while going in hole.

• Design liner hanger systems with a tieback sleeve length that allows the bottom of the tieback stem to be partially stung into the tieback sleeve when cementing the tieback casing. This will enhance the process of slacking off the tieback casing after the cement job has been completed. Buckling of the lower portion of the tieback casing after cementing can make it difficult to stab the tieback stem into place.

• For ultradeep liners on directional wells with relatively high torque and drag, use a pressure-indicating method to verify that a liner is released from the running tool. The actual liner weight may be small in compari-son to the drag forces, making it difficult to determine if the liner is actu-ally released.

Recommended Shoe Joint Lengths

Casing Size (in.) No. of Pipe Joints

> 18 5/8 Tag in

> 13 3/8 2 joints

> 9 5/8 3 joints

> 7 5/8 6 joints

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Cement slurry density must be within range to maintain well control.

The pump time should include the estimated job time plus a safety factor.

Cement Design PrioritiesA slurry design must address a broad assortment of well conditions and well-control parameters. To maximize the performance of a slurry, adhere to these seven guidelines, listed in the order of importance:

Priority No. 1—Density

Cement slurry density must be within range to maintain well control. If hole conditions allow, cement slurry density should be a minimum of 1.0 ppg greater than drilling fluid weight and 0.5 ppg greater than the spacer weight.

Priority No. 2—Pump Time (Thickening Time)

The pump time should include the estimated job time plus a safety factor. The safety factor must be based on wellbore parameters, operational objectives and limitations, and the accuracy of expected temperatures to which the cement slurry will be exposed during the cementing process as compared to the laboratory testing conditions.

Keep the following in mind when specifying and evaluating thickening time:

• The first sack or leading edge of the cement is exposed to different tem-perature conditions and will require a different placement time than the last sack of cement.

• Consider the total placement time for the lead slurry (mixing and pumping of lead + mixing and pumping of tail + displacement).

Recommended Safety Factors

• For surface and intermediate strings where cement placement is relatively easy and minimal WOC is the objective, allow a 1-hr safety factor.

• For HPHT liner cementing where cement placement is critical, allow a minimum safety factor of 2 hours or 50% of the calculated job time, whichever is greater.

Priority No. 3—Mixability

Cement must be easy to mix at the cementing unit in order to achieve density control at a mixing rate that allows cement slurry placement within the avail-able pump time.

Priority No. 4—Rheology

The cement slurry must be pumpable, and the cement slurry rheological prop-erties must allow effective placement, with a PV and YP as low as possible, but higher than that of spacer or drilling fluid.

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The minimum require-ment is a WOC time of less than 12 hours.

Priority No. 5—Fluid Loss Control

Design fluid loss control to specification. Excessive loss of fluid from the cement slurry has negative impact on other slurry properties.

Priority No. 6—Compressive Strength

The goal is to achieve rapid compressive strength development after place-ment. The minimum requirement is a WOC time (time to achieve 500 psi) of less than 12 hours and 24-hr strength greater than 1,000 psi.

Priority No. 7—Free Fluid and Settling

Cement slurry must remain stable (free water within specification and no sig-nificant settling or separation) while fluid. Design and test for given hole con-ditions, i.e. for directional well test at appropriate angle.

Cement Slurry Specifications

Slurry Properties

Conductor and Surface

Casings

Intermediate Casings and

Drilling Liners

Production Casings and

Liners

Deep Production

Liners and for Gas Control

Density + 1 ppg > drilling fluid density

< Equivalent Circulating Density (ECD) to fracture formation

Thickening Time

Job time plus at least one hour for safety factor

For production casings or for gas control, the TT chart should display a right angle set (transition from 40 to 100 Bc in less than 15 minutes)

Free Water < 1.0% < 0.5 % 0 % 0 %

Fluid Loss NA < 250 < 100 < 50

Rheol. (PV) < 150 < 150 < 100 < 100

Rheol. (YP) < 50 < 40 < 25 < 20

Comp. Strength

WOC (hr to 500 psi)

< 12 < 8 < 8 < 8

24-hr Comp. Strength (psi)

1,000 2,000 2,000 2,000

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Do not proceed until well data have been confirmed.

Evaluation of Cementing Job ProposalEvaluation and quality control of the service company’s job plan, simulator runs, slurry design, and laboratory test results is necessary to ensure that the cement slurry design fits the planned operation.

Data Review and Verification

1. Check the accuracy of Subject, Field, Well and Rig entries. Well data include the following:

• hole and pipe sizes

• hole and pipe weights

• annular, hole, and pipe volumes

Caution—Do not proceed unless these data are confirmed.

2. Review the BHST and BHCT; if any deviation or uncertainty exists, investigate further.

3. Review the Cement Slurry Formulation to verify that it matches the slur-ries tested in the laboratory.

4. Read the Density, Yield and Mix Water requirement.

• Mix Water—Use this value to calculate the volume of water needed for the job.

• Density—Mix the cement slurry to this value

• Yield—Use this value to calculate the number of “sacks” required for the job.

5. Review the Cement Job Simulation as follows:

a. Check inputted values.

b. Review the following data output against the job plan.

• pumping rates

• ECDs

• placement pressure at the pump

• spacer contact time

c. Change planned pumping rates as necessary.

6. Review the centralization program, taking note of

• centralizer placement and type

• minimum standoff across zones of interest

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Review of Cement Job Simulation

Although gas flow may not be apparent at the surface, it may occur between zones, damaging the cement job and eventually leading to casing pressure at the surface. A cementing simulator program can be used to determine the gas flow potential for any primary cement job, and to identify possible solutions that are tailored to the severity of the possible gas flow.

Run the simulator to test equivalent circulating densities (ECD), flow regime of the different fluids, required rheological properties of the fluids, maximum pumping rates, centralizer standoff requirement, displacement efficiency, anticipated pumping pressures at surface, pressure to shear or bump plugs, BHCT, etc. Using this tool will aid in job design and will help identify any potential problems with the design.

Interpretation of “Pilot” Test Results and Laboratory Reports

1. Check cement slurry formulation for the following information:

• Cement type

• Additive types and concentrations

• Water source and concentration

2. Check cement slurry “pilot” test results against specifications as listed in the following table.

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Slurry Property Task Notes

Density Check test value. —

Thickening Time Check times and test temperature.

Test temperature must be at BHCT.

Time must be within the specified range.Use 70 Bc for liner and narrow clearance jobs.Use 100 Bc for surface and intermediate jobs.

Attach strip chart for the thickening time test.

—

Check time reported vs. times read from chart.

—

Fluid Loss Check value and test temperature.


Rheology Check PV, YP and test temperature.

PV and YP must be reported.

Test temperature must be at BHCT, 194F maximum.

CompressiveStrength

Check the time for WOC (500-psi) and check 24-hr strength.

Test temperature must be at the requested value.

Free Water Check value and test temperature.


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m enting Best Practices
Job ProceduresThis section contains basic procedures for every step of a job, from prejob preparations to pumping and displacement. Throughout each phase, it is very important to monitor and record various measurements, times, and events. This information allows the job to be tracked as it is carried out, and is invalu-able in troubleshooting an unexpected problem.

Monitoring and Recording

Use the following checklist to ensure that all pertinent job data is captured at the appropriate time as each job is executed.

Prejob Preparations

• Loading of wiper plugs or darts

• All volume calculations

• Circulation of hole till clean

Pumping Operations

• Pressure testing

• Start and stop of each fluid pumped

• Pumping rates for each fluid

• Any pumping rate changes

• Any pressure changes

• Volume of spacer pumped

• Dropping any plug, dart or ball

• Start of cement slurry mixing

• Cement slurry density

• Mix water volume

• Start of displacement

• Surface pressures

• Displacement rate

• Landing of plugs

• Pressure to release liner wiper plugs

• Pressure to bump top plug

• Reverse circulation

• Total displacement

• Job time

• Returns

• Any shutdown

• Safety issues or incidents

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Prejob Preparations

Cement Design Verification

1. Verify that the following cement design and test conditions coincide with current well conditions.

a. BHCT and BHST

b. Thickening time and job time

c. WOC time

2. Verify the following calculations.

a. Volumes for all fluids to be pumped

b. Hole and pipe volumes

c. Total displacement volume to bump plugs and correction factor as applicable

d. Pressure to bump plug

e. Volume to catch liner wiper plugs, and displacement volume from that point

3. Review the cement job simulator.

4. Review pumping rates for wash/spacer, cement slurry and displacement.

5. Review pumping pressures expected during the job.

6. Review ECD’s at shoe and zones of interest.

7. Review the returns expected during the job.

Equipment / Materials Verification

1. Check the bulk tanks for proper contents.

2. Confirm that all equipment (include a complete list) is on location and in good working condition.

3. Check operational features, ensure that the float backpressure valve is operational, and that the plugs are of the correct type and fit.

4. Check wiper plugs, the bottom plug (hollow), and the top plug (solid).

5. Witness the loading of plugs.

6. Confirm the delivery rates for water and mud.

7. Confirm what type of displacement fluid will be used and the parties responsible for routing and pumping downhole.

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8. Confirm that all density devices have been calibrated properly with fresh water.

Wellbore Circulation

1. Clean and stabilize the wellbore by circulating during wiper trips, before and after logging.

2. Run the casing at a controlled rate, and circulate drilling fluid at intervals.

If there is known potential for lost circulation, run the casing at less than 1 minute per stand.

3. Condition the drilling fluid until drilling fluid properties are optimized (PV < 15; YP < 10).

4. Move the pipe via reciprocation or rotation during conditioning.

5. Circulate the wellbore until clean, using a minimum of two bottoms-up.

Total conditioning time is determined by drilling fluid properties and the circulatable hole volume.

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Pumping Operations

Pressure Testing

1. Pump wash or spacer to the cement head.

2. If running two bottom plugs, load the first bottom plug into the casing at this time.

3. Connect (reconnect) the cement head. The bottom and top plugs should have already been loaded during prejob preparations.

4. Clear the rig floor and the area surrounding the lines.

5. Pressure-test the lines as follows:

a. Increase pressure to a predetermined level.

b. Hold the pressure for 5 min.

c. Release the pressure.

Mixing and Pumping Cement

1. Drop the bottom plug (the first one, if using two).

2. Pump the wash or spacer. Standard pumping rates are 6 to 8 bbl/min.

Caution—Never open the cement head once pumping has begun.

3. Drop the second bottom plug (if running two bottom plugs).

4. Start to mix and pump the cement slurry. The standard pump rate is 5 to 8 bbl/min, depending upon the specific job.

5. Measure the mix water for the cement slurry through the displacement tanks and record the measurement.

6. Control the density within 0.2 lb/gal accuracy throughout the job.

7. Check the cement slurry density with a pressurized balance to calibrate the densitometer.

8. Confirm slurry density by monitoring the pressure (downhole) readings of the densitometer.

9. Continue to mix and pump cement.

Important—Never compromise slurry density to maintain the scheduled pump rate.

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Caution—Near the end of the job, bulk delivery may decline. Never sacrifice density control to use up the cement. If the designed density cannot be main-tained, discontinue cement slurry mixing.

10.After the cement is pumped, drop the top plug.

11.Displace the top plug out of the cementing head with minimal down time.

12.Do not open the cementing head to drop the top plug.

13.Begin displacement.

Displacement

Measure the displacement volume with the cementing unit displacement tanks or rig pumps. DO NOT use a “barrel counter.”

1. Maximize displacement with a pump rate of 8 to 12 bbl/min. Limit the rate only if necessary to prevent excessive ECD’s.

2. Maximize the pump rate as spacer passes zones of interest.

3. Begin decreasing the pump rate as the final displacement volume nears.

4. Displace to bump the top plug at 1 to 2 bbl/min. Never overdisplace.

5. After displacement is completed and the plug has been bumped, relieve surface pressure and check for flowback.

Important—Do not hold pressure inside the pipe unless operations will be compromised by flowback.

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Shallow Water Flow CementingConsider the following standard shoe track, centralizer, and wiper plug requirements for use in shallow water flow cementing:

• a stab-in float shoe

• one joint with two bow-spring centralizers

• one bow-spring centralizer per joint to the drive pipe

• one centralizer per joint between casing and casing

To cement casing in a shallow-water-flow formation, use the following proce-dure.

1. Drill the conductor hole section with MWD so that sand depths are known.

2. Set the conductor casing above potentially flowing sands.

3. Cement the conductor pipe, using centralizers, etc. to achieve complete coverage.

4. Drill with controlled drilling fluid.

5. Once the casing point is reached, pump out of hole with kill-weight mud

that has low gel strength (i.e. yield point of 8 to 10 lbf/100 ft2, 10 ft, 10 in.

and 30 in. gels flat and < 25 lbf/100 ft2).

6. After pulling out of hole before running casing, observe for flow.

If flowing, increase the mud weight in the hole.

Caution—Conducting a cement job with the well in flowing condition will most likely result in channeling, causing the job to be unsuccessful.

7. Run the casing, maintaining kill-weight mud in the hole at all times.

8. Design a program to eliminate seawater in the drillpipe and casing below the stinger.

9. Before running in hole, displace the drillpipe and casing below with the same mud weight as that in the hole.

10.Circulate in hole and fill the drillpipe with the same mud weight as that in the hole.

11.Pump the required spacer system weighted to a density between that of the mud in the hole and that of the lead cement slurry.

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12.Run the designated cement system with a foamed lead slurry (1.0 ppg heavier than the drilling mud) and a non-foamed tail slurry.

13.Pump the cement and allow it to set to 500-psi compressive strength before drilling out.

See API RP 65 for further recommendations.

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K(cp

Wait on Cement (WOC)For operations, waiting on cement (WOC) is the waiting time required after cementing in order to safely remove well control equipment or to allow the well to be underbalanced.

For a cement slurry, WOC is the time necessary for the cement to solidify and attain a compressive strength of 500 psi. This is most effiiciently determined through laboratory testing with a UCA, which plots strength development vs. time.

To maximize the efficiency of WOC, adhere to the following guidelines.

• Know the well conditions before, during, and after the cement job.

• Know the WOC (500-psi time) for the cement slurries pumped.

• Never allow the well to be underbalanced during WOC.

• Minimize WOC by using the correct cement systems that develop strength quickly after placement.

• WOC cannot be accurately determined from thickening time alone.

• In some areas, regulations specify minimum WOC times that may exceed, and thus supercede, these guidelines.

• During the WOC period, perform operations that can help minimize the time and cost of WOC, such as

• Pick up drillpipe for the next hole section.

• Run any required surveys.

• Clean up the mud by circulating it over shakers.

• Rigup equipment that may be required for the next hole section.

now the WOC 500-psi time) for the ement slurries umped.

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Tubing diameters of 2 7/8 in. should be used in slim holes of 8 1/2 in. or less; 3 1/2-in. tubing should be used for larger hole sizes.

Plug CementingPlug cementing is the process of placing a column of cement in casing or an openhole to isolate or “plug” a section of the wellbore. This best practice pro-vides important guidelines that must be considered when designing a plug job, as well as a detailed procedure for carrying out a plug cementing opera-tion to ensure proper placement of the plug and adequate zonal isolation.

Engineering and PlanningPlan a plug job based on hole conditions to pull out of cement. Many methods are available and consideration should be given to prevention of contamina-tion, risk exposure, environmental spill considerations, etc. The well depth, the mud type, and many other factors will determine which procedure should be used.

Placement

Use a small workstring to balance cement plugs for optimal displacement. The length of the tail pipe must be at least equal to the plug length with tubing in place.

Tubing vs. Drillpipe

Run the tail pipe to the planned bottom of plug depth. Tubing diameters of 2 7/8 in. should be used in slim holes of 8 1/2 in. or less; 3 1/2-in. tubing should be used for larger hole sizes. Tubing is preferred over drillpipe in plug jobs because the displacement of the tubing reduces swabbing and reduces the weight of pipe to be pulled. For 17 ½-in. or larger open plugs, this is not criti-cal and thus, they can be set using drillpipe. Coupling OD’s of the tubing should be minimized. If no tubing is available, 3 ½-in. drillpipe may be used. If a stinger is to be run through open hole or in casing after a milling opera-tion, break circulation every 5 to 10 stands to prevent plugging of the stinger.

Diverter Sub

A diverter sub can improve the success of cement plug setting by directing the flow and preventing the jetting of cement downhole. Use a distribution (diverter) tool to direct flow up the annulus, such as a bull plug with four to eight small (approximately 1-in.) horizontal side holes greater than the flow area of tailpipe and at 90-degree phasing. If a wiper plug catcher is used, place it below the holes.

Plug Length

Assume that the top and bottom 100 ft of cement will be contaminated with spacer.

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Minimize your risk by making sure plug lengths are adequate. Never use a cement plug of less than 20 bbl set through a drill-pipe for a 6-in. or larger open hole.

If large quantities of cement are observed above the top of cement when cir-culating the well clean, channeling has likely occurred, and the area contami-nated by the spacer will be larger than normal. This will increase the risk for failing to tag the plug and/or for obtaining a pressure test.

Cement plugs set across perforations should be set from 100 ft below the per-forations to 200 feet above the perforations.

Recommended plug lengths are as follows:

• Plugs of 300 to 600 ft have been used for 8 ½-in. to 36-in. open holes for abandonment, suspension and sidetracking in wells that are less than 14,500 ft deep and have less than a 45° inclination.

• For recovery of oil-based and synthetic-based mud, 1,500-ft abandonment plugs have been set in 12 ¼-in. open holes with thickening times exceed-ing 10 hr.

• In 8 1/2-in. and smaller open holes, plugs of up to 800 ft have been set and successfully tagged to ensure a minimum volume criterion is met.

• Plugs in extended reach wells are special cases and where plug setting depth exceeds 14,500 feet and hole angle exceeds 45°, plug length should be 600 to 750 ft, with 300 ft of contamination allowance on top of the plug.

Caution—Minimize your risk by making sure plug lengths are adequate. Drilling out excess cement is normally far less expensive than setting a sec-ond balance plug to accomplish required objectives. No cement plug of less than 20 bbl should be set through drillpipe for a 6-in. or larger open hole.

Caution—If there is a risk of lost circulation, do not place more than two plugs in a row without waiting the time required for the first plug to attain 500-psi compressive strength.

Cement Volumes

Whenever possible, use a caliper log to determine the cement volumes and to help determine where to set a plug. Setting a plug in a section of the hole that is near gauge will increase the chances for success.

If no caliper is available, refer to the following table for recommended per-centages of excess volume.

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Make sure the BHST and BHCT are accurate for proper job design.

For Class G cement, use 16.2 to 16.5 ppg densities.

For Class H cement, use 17.0 to 17.2 ppg densities.

Always consider the particular area and hole conditions such as sloughing shales or losses when determining the actual excess to be used.

Cement Slurry Design

Temperature

Make sure the BHST and BHCT are accurate for proper job design.

Select the temperature for your design on the basis of deviation, operation, and local experience.

Wherever hole angle exceeds 60°, perform a temperature simulation.

In water depths exceeding 1,500 ft, predict cooling in the riser.

Allow some safety margin for slurry test temperatures; if no local expertise is available, allow a 10°F margin.

Slurry Properties

For kick-off plugs, the density of the slurry is important for rapid, high strength development.

• For Class G cement, use 16.2 to 16.5 ppg densities.

• For Class H cement, use 17.0 to 17.2 ppg densities.

• Add a dispersant and/or retarder as needed to densify and to provide the required pump time.

Plug and abandonment plugs and squeeze plugs are generally designed at nor-mal density for the cement available, but may be adjusted for specific well conditions. Dispersants and retarders are the most common additives used. A fluid loss control additive may also be required for some open hole and squeeze operations.

Calculation of Volume Excess

Hole Size (in.) % Excess (Water-Based Mud)

% Excess (Synthetic-Based Mud)

30 to 36 200 —

24 to 30 100 —

14 3/4 to 17 1/2 50 20

12 1/4 30 20

6 to 8 1/2 30 20

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40 Bc time (in the lab report) must be greater than or equal to job pump time + time to pull out of plug + 1 hr (safety factor).

Fluid loss is required in plugs set across permeable formations; a fluid loss less than 150 ml is adequate for abandonment / suspension plugs. However, squeeze slurries should have less than 75 ml.

Thickening Time

For all cement plugs that are to be spotted and balanced, the required thicken-ing time is based on the calculation:

40 Bc time (in the lab report) must be greater than or equal to job pump time + time to pull out of plug + 1 hr (safety factor).

Calculated pump time is based on time cement is moving, and does not include static time.

The recommended pulling rate is 30 to 50 ft/min.

Spacers

Separate mud and cement with adequate spacer/wash.

• For sea-water mud, pump water as a spacer/wash.

• For synthetic-based mud, pump a weighted chemical wash system or spacer system to displace mud and provide a water-wet surface for bond-ing.

Calculate the volumes of spacer/wash as follows.

• The volume of spacer/wash ahead of the cement should equal 500 ft of annular fill.

• The volume of spacer/wash behind the cement should be calculated to balance.

• Always calculate the loss in hydrostatic pressure ahead of a cement plug.

Cement Slurry Displacement

Use a cement unit to displace the cement slurry to ensure accurate control over displacement volume.

The displacement can be accurately determined with an indicator sub, usually positioned in the drillpipe above the balance point. The tool used will provide a positive indication of displacement volume when it makes contact with the plug catcher sub.

When an indicator sub is not used, a slight under-displacement, typically 1 to 3 bbl, is recommended in order to pull dry. For deep plugs, the average pipe ID should be determined to ensure a correct displacement volume.

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Kick-off plugs require a compressive strength of 3,000 psi.

Mechanical Tools for Supporting Cement Plugs

Mechanical tools should be used only where necessary. Setting a reactive pill may be more economical and easier, if support is necessary. The simplest tool is a small sub run on the end of the tubing stinger that holds a short “umbrella” like tool. When a ball is dropped, the umbrella extrudes and then springs open to an approximate 20-in.diameter. This tool can be run in open hole and casing. In casing, inflatable packers or mechanical bridge plugs set on wireline can be used.

Inflatable packers and mechanical bridge plugs are not suitable for use in open holes.

Waiting On Cement

Plugs should not be tagged until they have at least 1,000-psi compressive strength. A total of 1,500-psi compressive strength is required for pressure-testing the plug.

Kick-off plugs require a compressive strength of 3,000 psi. Deep kick-off plugs (placed at depths of 10,000 ft or more) across hard formations will require 4,000-psi compressive strength.

Compressive strength should be determined at a temperature mid-way between static temperature and the temperature used for designing the pump-ing time, unless more precise values are available.

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Plug Cementing


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Job Procedure 1. Make sure the stinger is run at least 300 feet below the plug-setting depth.

Note—In an openhole situation, consider jetting across the interval.

2. Pull back to plug-setting depth, condition the mud, and circulate the annu-lus clean a minimum of one bottoms-up while moving pipe.

3. Pump 500 ft (up to 50 bbl) of spacer/wash ahead of cement. As in primary cementing, the weight of the spacer/wash should be halfway between mud weight and cement weight.

4. Pump cement.

a. Check the density using a pressurized mud balance.

b. Control the mixing rate at 2 to 4 bbl/min.

c. If the cement is mixed with a jet mixer, dump the first quantities of cement overboard until a consistent slurry is obtained.

d. If a batch mixer is used, disregard Step 4c.

5. Pump a volume of spacer/wash behind the cement to balance the spacer ahead of cement. Rotate pipe (approximately 20 rpm) to improve cement displacement into the annulus in deviated wells.

6. Displace at a maximum rate (limited by ECD) to improve gelled mud removal; then reduce the displacement rate according to the following guidelines:

• For hole sizes less than 12 1/4-in, pump at 2 bbl/min for the last 20 bbl.

• For hole sizes greater than 12 1/4-in, pump at 3 bbl/min for the last 40 bbl.

7. Under-displace by 1 to 3 bbl, excluding the volume of surface lines, unless using a latchdown sub, to ensure the plug is not contaminated and that the pipe pulls dry.

Note—For ultradeep jobs, a ball catcher sub and wiper plugs may be required to effectively verify displacement.

8. Pull out of the plug at a controlled rate (approximately 25 stands/hour) to prevent swabbing and contamination.

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Minimize any unnec-essary time from shutdown to pullout. The thickening time estimate is based on moving cement. Once the cement is static, this time allowance is reduced.

Reverse circulation can only take place if the ECD would not induce losses.

Do not run back into a cement plug with the stinger until the cement has set. When the plug has been tagged, do not run back into the cement without circulation.

Caution—Minimize any unnecessary time from shutdown to pullout. The thickening time estimate is based on moving cement; once the cement is static, this time allowance is reduced.

Note—Step 9 below does not pertain to intermediate plugs set in series.

9. If ECD’s allow reverse circulation, pull back to approximately 500 ft above the top of any cement plug that is not to be tagged, otherwise go to the TOC; then, reverse circulate clean.

Caution—Reverse circulation can only take place if the ECD would not induce losses.

If reverse circulation is not possible due to losses or differential sticking, perform the following steps before POOH:

a. Flush the pipe clean.

b. Displace 150% of the pipe’s contents at maximum rate.

c. Drop a dart or pump 50 bbl of 50 pp. Nutplug in active mud to clean pipe of cement rings. In the latter case, the size of openings in diverter tool needs to be considered.

10.When going in hole to tag a cement plug, start washing down and rotating pipe at the previous depth of last bottoms-up circulation or 500 to 1,000 ft above the calculated top of cement.

Where a plug is being tagged with a kick-off assembly, use minimum flow rates.

Caution—Do not run back into a cement plug with the stinger until the cement has set. When the plug has been tagged, do not run back into the cement without circulation.

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Squeeze CementingSqueeze cementing is the process of placing cement into a confined area with hydraulic pressure. Often this cementing process does not attempt to “squeeze” or dehydrate the slurry at all but to place high quality, noncontami-nated cement in the proper location to provide isolation or achieve other objectives.

Engineering and PlanningBefore a squeeze cement job is designed, it is important to identify the objec-tives to be met and to perform a risk analysis.

Some of the more common objectives include:

• Repair a failed primary cement job.

• Add to the height of the cement column in place to produce upper zones.

• Eliminate water from above, below, or within the hydrocarbon zone.

• Reduce the producing gas:oil ratio.

• Repair a casing leak.

• Seal the annulus of a liner top or casing shoe.

• Plug all, or part, of one or more zones in a multi-zone injector or produc-tion well.

A risk analysis should include:

• Well control considerations.

• Pore, fracture and planned squeeze pressures.

• Work-string and displacement accuracies.

• U-tube effect, hydrostatic pressure, and location of cement.

• Casing condition, especially for old wells.

• Ability to contend with unexpected events.

• Worst-case pressures for circulating out.

Placement

There are two basic squeezing techniques: the Bradenhead squeeze and the Bull Head squeeze.

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The properties of the cement slurry must be tailored according to the characteristics of the formation to be squeezed and the technique that will be used.

“Bradenhead” is the technique whereby the cement slurry is pumped down tubing or drillpipe and circulated to the surface. Once the cement is spotted or balanced, the tubing is pulled above the cement, the blowout preventers are closed, and the slurry is pumped into the target zone. No packer is required, and the hesitation squeeze method is often used. The Bradenhead squeeze is recommended when the casing can withstand the pressure and the target zone is effectively isolated.

“Bull Head” or “Non-Bradenhead” is the technique whereby the cement is pumped down tubing or drillpipe and the wellhead annulus simultaneously. The preferred method is to design a placement schedule that allows at least half of the slurry to be pumped into the formation and leaves the remainder of the slurry in the tubing or casing. When the Bull Head technique is used with a packer, slurry can be placed with greater precision and higher injection pres-sures can be run.

Cement Volume

The volume of slurry depends on the length of interval to be cemented, the pipe size, placement technique, formation characteristics, and the amount of excess slurry desired. Formation characteristics are especially important. To accurately calculate the cement slurry volume required, the job designer must know the fracture pressure of the formation, the permeability of the selected zone, and whether or not the zone(s) are fractured.

For squeeze cement jobs in which the cement is to be held in place, a total slurry volume of approximately four times the volume of casing below the work string is recommended. This should represent 60 to 80% of the work string volume.

For squeeze jobs in which the operator plans to “squeeze” away the cement into the formation, the total slurry volume should equal the amount to be squeezed, so that only a minimal volume of excess cement will have to be cir-culated out.

Slurry Design

The properties of the cement slurry must be tailored according to the charac-teristics of the formation to be squeezed and the technique that will be used.

Low-pressure squeezes do not exceed formation fracture pressures. They are recommended for depleted wells with low bottomhole pressures and for squeezing existing voids in any well where cement is not desired within the formation.

High-pressure squeezes have no pressure limitations other than that of the casing or tubing. Final squeeze pressure is either the maximum that can be

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Fluid loss is extremely important when a low-pressure squeeze is used against high-permeability zones.

obtained or a predetermined value based on experience and calculations. Depending on the type of squeeze job performed and operational objectives, the formation fracture pressure may or may not be exceeded.

Fluid Loss Control

Fluid loss is extremely important when a low-pressure squeeze is used against high-permeability zones. If fluid loss is too low, it will leave non-dehydrated cement in the perforations, which could be removed during reversing or when a negative differential pressure is created. Excess fluid loss could allow pre-mature dehydration of a slurry to the extent that a zone is not completely cov-ered. Optimum fluid loss varies with the permeability of the zones.

• For a low-pressure squeeze in a low-permeability formation, use a slurry with fluid loss of 100 to 200 ml/30 min.

• For a low-pressure squeeze in a high-permeability formation, use a slurry with fluid loss of 50 to 100 ml/30 min.

• For a high-pressure squeeze, use a slurry with fluid loss of 200 to 500 ml/30 min.

• Use a slurry with high fluid loss for fast cake buildup in a fracture. A fluid loss of 300 to 800 ml/30min at 1,000-psi differential pressure is recom-mended.

• In a fractured limestone or dolomite, the addition of a lost circulation material may help form a bridge on the formation to prevent cement dehy-dration.

Dispersion

Slurries with a low yield point, or thin slurries, are preferred for most squeeze jobs. Thin slurries can flow into narrow cracks or channels. Thick slurries are more useful when cementing large voids.

Thickening Time

Accelerators and retarders are used as necessary to overcome the effects of depth, temperature, and squeeze technique on the slurry’s thickening time. The thickening time must be sufficient to mix the slurry, pump the slurry, pull the workstring, reverse any excess slurry, and squeeze the slurry away.

Compressive Strength

Cements with high compressive strength may be desirable, but compressive strength should not be the primary concern. Normally, the dehydrated cake of slurries made with cements of moderate compressive strength will attain the compressive strength necessary to accomplish the job and in a shorter time than that required for cements with high compressive strengths.

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Always perform a pre-liminary prejob analy-sis and calculations to assure the planned procedure fits actual hole conditions.

Help prevent flowback due to the U-tube effect by planning procedures to hold the cement in place and eliminate the risk of cement being where it is not wanted.

Washes and Spacers

As in primary cementing, washes and spacers are normally recommended for two reasons:

• to clean the perforation and surrounding voids of mud so that the cement can get to the formation face and dehydrate properly

• to prevent contamination of the cement slurry

Prejob Considerations

• Plan the job in detail with the service contractor to define the objectives and operational procedures and pressures.

• Always perform a preliminary prejob analysis and calculations to assure the planned procedure fits actual hole conditions. All pressures, volumes, pumping times, injection rates, and fracture gradients must be within acceptable limits.

• Plan a pump-in test to determine the injection rate.

• Reduce the risk for cement contamination by using spacers, plugs, excess cement or other tools.

• Estimate the fracture gradient at depth.

• Estimate the pressure differential between the fracture gradient and the mud weight at depth.

• Help prevent flowback due to the U-tube effect by planning procedures to hold the cement in place and eliminate the risk of cement being where it is not wanted.

• Calculate what the hydrostatic pressures will be once cement is in place and determine whether or not over-displacement will occur. A water col-umn may need to be included in displacement pumping schedule for well to remain static once cement is in place. (This is especially important if squeezing is being performed due to the loss of returns or when the liner laps right at the fracture gradient.)

• Plan displacement procedures to help compensate for the U-tube effect that can occur when mixing heavy cements slurries relative to light mud weights. For example, when mixing 300 sk (63 bbl) of 15.6 ppg cement slurry on a well with 12.0 ppg mud and a 5-in. drillpipe, the level in the drillpipe will fall 18.8 bbl. You will recover 18.8 bbl more volume from the annulus while mixing cement since it is being slugged. The cement is 18.8 bbl ahead of surface displacement volumes in the drillpipe.

• Make calculations to set the bottom of the drillpipe or work string off bot-tom by 15 to 20% of work string volume below the drillpipe.

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Allow for a 10% error in displacements based on the volume of the work string, unless some mechan-ical devices are used to calculate displace-ments more accu-rately.

Never circulate out cement the long way if it cannot be reversed.

When unexpected problems arise in performing a squeeze cementing job, reverse out the cement and start over.

• Plan the displacement volumes necessary to under-displace the leading edge of the cement slurry by 20% and over-displace the tail edge of cement slurry by 10 to 15%.

• In planning cement squeeze jobs, always allow for a 10% error in dis-placements based on the volume of the work string, unless some mechan-ical devices are used to calculate displacements more accurately.

• Determine the expected worst-case pressure to reverse out.

• Plan to test the casing with worst-case pressure to reverse out excess cement or develop a contingency plan that can be used if reversing out is not practical.

• Establish a plan for circulating out cement. Never circulate out cement the long way if it cannot be reversed. Leaving cement on the inside of a work string is not advised, but a cemented-up work string on the rig’s pipe rack is better than cementing up a drillstring in an active well that’s being drilled.

• When unexpected problems arise in performing a squeeze cementing job (mechanical failure of equipment, losing track of cement displacement, pressure loss indicating a possible washout, etc.), reverse out the cement and start over.

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Ce

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hen the cement olume in the casing s used, STOP pump-ng.

m
Job Procedures

Bradenhead Cement Squeeze

1. Pump 300 ft (up to 30 bbl) of spacer/wash ahead of cement. Pump spacer/wash behind the cement at a volume calculated to balance.

2. Use a cement stinger to place the abandonment plug were possible.

3. Place a minimum of 300 to 500 ft of cement slurry on bottom, ensuring that the slurry has a greater density than the mud weight.

4. Pull two to three stands above the plug and reverse out the excess.

5. Pump away 1/3 of the cement volume while monitoring for pressure increase as the cement feeds into the formation.

6. Wait for 15 minutes and pump 1/6 of the cement volume – again while monitoring for pressure increase.

7. Again, wait for 15 minutes and then pump 1/6 of the cement volume – while monitoring for pressure increase.

8. Let the well remain static until the cement sets up.

Hesitation Squeeze Technique

Hesitation Cycle

• When stabilized pressure does not increase, lengthen the hesitation cycle.

• When stabilized pressure increases, the hesitation cycle can be shortened.

Pump Cycle

• Pump at the slowest rate possible.

• Never pump a predetermined volume of fluid.

• As pressure increases, continue to pump.

• When pressure breaks back, drops, or shows any indication of pumping into formation (including gut feeling), STOP pumping.

Potential Squeeze Endpoint

• When the cement volume in the casing is used, STOP. This is all the squeezing possible for the volume of cement selected. NEVER overflush perforations.

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hen maximum llowable pressure is ttained without sig-ificant leak-off, TOP.

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• When maximum allowable pressure is attained without significant leak-off, STOP. This is all the squeezing possible within the preset pressure limit.

Bull Head Cement Squeeze

For best results, use a slurry design with a fluid loss of less than 100 cc/30 min, and perform the following steps:

1. Pump adequate wash ahead of the cement to remove mud cake.

2. Mix enough cement so that you can squeeze ½ the volume into the forma-tion on the first squeeze. Use excess.

3. Stop and wait 15 minutes; then, pump ½ the remaining volume in the tub-ing and/or drillpipe while monitoring for a pressure increase.

4. Let the well remain static until the cement sets up.

5. Pull two to three stands above the plug and reverse out the excess.

Cement Retainer

The decision of whether to use a squeeze tool or cement retainer is usually determined by wellbore integrity, as defined by the answers to these ques-tions:

• Is the well relatively old or new?

• How recently was the casing tested?

• Do we know where we are pumping in?

• What are the wellbore conditions (mud weights and fracture gradients)?

Squeezing a deep intermediate casing shoe with a low mud-weight may require a very high injection pressure. Very high pressures may also be required to reverse out with a particular work string in certain conditions, which could “junk” the well}.

To use a cement retainer for a squeeze job, set the cement retainer close to the squeeze interval (40 to 60 ft above the interval) to minimize cement contami-nation. A lesser volume of cement slurry can be used since less contamination will take place below the work string (usually 40 to 50% of the work string volume). The pumping schedule should allow the cement slurry to be under-displaced by 10% of the work string volume to avoid over-displacement with the excess cement slurry reversed out.

3535

Contractor Requirements

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Contractor RequirementsThe following information is provided to ensure a thorough understanding of the job process as it pertains to both Unocal staff and contractors.

Included in this section are:

• flowcharts illustrating the roles and responsibilities of various parties dur-ing the job planning, mobilization, and implentation

• instructions for preparing a cementing recommendation

• procedures for pilot-testing cement designs

• laboratory test requirements

• on-location procedures for cement bulk blendng and loadout

• prejob and job procedures

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Cement Job Planning

Unocal Drilling Engineer defines cement job well data and applicable well conditions.

Cementing contractor receives and reviews cement

job data.Cementing

contractor conducts cement job simulation, centralizer

placement, etc.

Cement contractor and Unocal Drilling Engineer

check if cement job specifications are covered

in the Engineering and Planning section of this

Best Practices document.

OFFICE LAB

Unocal Drilling Engineer reviews

output, verifies input data and updates

cementing contractor as appropriate.

Simulation OK?

No

Unocal Drilling Engineer approves simulation output.

Yes

Need a new cement slurry

design?

Cementing contractor

conducts "new" slurry design pilot testing using lab materials.

Yes

Pilot test design check.

PASS

Unocal Drilling Engineer approves selected

cement slurry design.

No

FAIL

Cementing Best Practices 3737


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Cement Job Mobilization

Unocal Drilling Engineer orders materials / authorizes

materials movement.

Cementing contractor conducts lab pilot test

using actual materials to be used for the job.

Pilot test results

acceptable?

Adjust slurry design.

No

Unocal Drilling Engineer issues

bulk blending order.

Yes

Cementing contractor prepares blending facility and determines

volume of bulk blends.

Unocal Drilling Engineer and/or Drilling Supervisor checks and approves blending

volume.

Cementing contractor blends dry materials. Unocal Drilling Engineer or Supervisor

witnesses.

Cementing contractor samples blend and conducts confirmation test to

QC blend.

Confirmation test check

FAIL

REBLEND

Unocal Drilling Engineer approves completion of bulk blending and load out.

Unocal Drilling Engineer or Supervisor provides final well data.

A



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Cement Job Implementation

A

Cementing contractor performs final job calculations.

Unocal Drilling Engineer or

Supervisor approves job calculations.

Cementing contractor conducts all tasks on

prejob checklist.

Cement job performed.

Cementing contractor completes post job lab

test and job report.

Unocal Drilling Engineer approves

job report.




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Always use the standard UNOCAL laboratory report form for submitting labora-tory reports.

Cementing RecommendationThe Cementing Coordinator is responsible for preparing a Cementing Recom-mendation as requested for upcoming wells, and communicating with the UNOCAL Engineer as required to obtain all necessary information for prepa-ration of this document.

The Cementing Coordinator be fully capable of running the simulator, analyz-ing the output data and making the appropriate job recommendations, and must use standardized software for generating this recommendation.

Contents

The Cementing Recommendation should contain the following:

• detailed objectives of the cement job(s)

• cementing operation issues and detailed solutions

• thickening time requirement for the cement slurry(s)

• detail of well geometry, including hole, casing, and annular volumes, and pore and fracture pressures

• required cement slurry volumes

• BHST and detail on the method of calculation

• proposed cement and spacer formulations with details as to how they meet the job objectives; this proposal should include the following

• densities, yield and material requirements of the proposed slurries and spacers

• “pilot” laboratory test results for the cement slurry formulation(s)

Important—Always use the standard UNOCAL laboratory report form for submitting laboratory reports.

• operational details, pump rates for each fluid and shear or bumping pres-sures for wiper plugs

• a computer-generated simulation of the cement job(s) that is based on the proposed cement slurries, well information and geometries, with clear and accurate inputs. The output shall include:

• centralization (centralizer spacing for inputted stand-off, and stand-off for inputted spacing, both in tables and graphs)

• flow regime of each fluid (for each wellbore geometry based on input-ted pump rate and rates for achieving turbulent flow for each fluid

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Well control exceptions must be clearly highlighted and brought to UNOCAL Engineer’s attention.

• U-tube simulation for the cement job under dynamic conditions (tables and graphs of free-fall vs. time)

• temperature simulation profile of cement slurry temperatures, bottom-hole circulating temperatures (BHCT) and a graph of particle temper-ature profile at depth

• well security and control (equivalent circulating densities at total depth and at other selected points, graphed against pore and fracture pressures)

Important—Well control exceptions must be clearly highlighted and brought to UNOCAL Engineer’s attention.

• displacement volumes

• tabular and graph of fluids fill level and placement

• cost estimates for service and materials

Reporting Responsibilities

Presentation of this report must include a hard copy and an electronic file in either Microsoft Word or Excel format. Graphs may be generated to supple-ment the reports.

Prior to each cementing job the Cementing Coordinator shall update the respective portion of the recommendation. Updates must be referenced to ini-tial recommendation and pertinent lab testing.

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No slurry design will be sent to the rig with-out signoff by the UNOCAL Drilling Superintendent or Engineer.

Cement Designs for “Pilot Testing”Pilot testing (laboratory testing to develop cement designs that meet the required criteria for the given well parameters) is required for all cementing operations and shall include thickening time, rheologies, free fluid, fluid loss (when fluid loss additive is included in formulation), 24-hour compressive strength and WOC (time to 500 psi) by UCA for tail slurries and kick-off plugs.

• Clearly reference all “pilot testing” data to the appropriate cementing rec-ommendation with a unique project or “job” number.

• Use the standard Unocal laboratory report form when submitting labora-tory reports.

• Conduct all laboratory testing in a timely and accurate manner.

• Incorporate sufficient lead-time into the testing program so that the designs are ready well in advance.

• Conduct testing with the representative samples of materials that will be used on the job (bulk plant or rig samples) as appropriate.

• For liner jobs, isolate critical additives such as retarders.

• Conduct all laboratory testing in accordance with UNOCAL-designated procedures and report the required test results.

• Incorporate contingency planning into the testing program, taking into account variations in well parameters that may require adjustments in density or thickening time.

• Perform compatibility tests between the cement and spacer and between the spacer and drilling fluid for all jobs in which oil-based or synthetic-based drilling fluids are in the hole.

• For all liner and tieback jobs, test the spacer for stability by “hot-rolling” at circulating temperature.

• Whenever possible, design the cement job to achieve turbulent flow of the spacer in the open hole.

Important—No cement slurry is considered “approved and finalized” until the UNOCAL Drilling Superintendent or Engineer signs off on it. No slurry design will be sent to the rig without this approval.

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Laboratory Testing RequirementsUnless otherwise specified, all laboratory testing of cement slurries for UNO-CAL operations must be performed in accordance with the latest revision of API RP10B. The following are the required minimum laboratory testing pro-cedures for cement slurry designs, as applicable.

Mixing

Mix slurry as per standard API procedure (4000 rpm for 15 seconds and 12000 rpm for 35 seconds). If the slurry contains microspheres, the 12000 rpm requirement may be replaced by 4000 rpm.

Density

Measure density with a pressurized mud balance.

Free Fluid Test

Follow API RP10B Section 15, with the following exceptions:

• Conditioning in an atmospheric consistometer is acceptable.

• Time–to-temperature of 6 minutes is not required.

Conduct tests with a heated static period at BHCT or 194°F, whichever is lowest. Place the graduated cylinder at an inclination of 45°.

API Static Fluid Loss at BHCTs less than 193°FUse an atmospheric consistometer for conditioning, and test at BHCT and 1000 psi.

API Static Fluid Loss at BHCTs 194°F or Greater

Condition the slurry in a pressurized consistometer at BHCT and pressure. Follow API procedures for heating the fluid loss cell to BHCT and for testing.

Rheology at 80°F and the lessor of BHCT or 194°FAccording to API RP 10B method, include 10-second and 10-minute gel strength values.

Thickening Time at BHCT and BHP

Test as per the appropriate API RP 10 B Schedule or as per a calculated tem-perature and pressure schedule using the equations in sections 9.5.3.2 and 9.5.3.4 through 9.5.3.7 of the API RP 10B. Report the time required to reach 40 Bc, 70 Bc, and 100 Bc.

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Compressive Strength at BHST and 3000 psi

Attach documented results of UCA testing required for WOC 500-psi values and UCA charts to the slurry test result sheets. A crush test is required for 12-hr or 24-hr compressive strength. Cure and test according to API RP 10B, excluding section 7.6.

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Never use previously opened sacks.

Discard any substan-dard or suspect material (chunks, lumps, rocks, wet).

On-Location ProceduresThe cement bulk blending and loadout procedures that are performed on loca-tion are an integral part of quality control, and must be

Cement Bulk Blending

The following procedure is required for all blended cements containing fluid loss, retarder or silica additives.

For smaller jobs (400 sk or less), consider the use of 220-ft3 portable tanks for loading, transporting and pumping the job. This will place the final quality control point at the bulk plant, eliminating the need for quality control checks between the bulk plant and the rig and consequently, the lead time required for those checks.

Validating Materials

Verify that the following criteria are met for all materials to be blended:

• Lot numbers of bulk cement and all additives are recorded on the blend sheet.

• Only one batch number of cement is used per job.

• This batch number coincides with that used in laboratory testing.

• Additives are of the same lot or batch number used in laboratory tests.

• Only one lot number is used per each critical additive, i.e., fluid loss addi-tives, retarders.

Important—NO exceptions are permitted.

Caution—Never use previously opened sacks.

Caution—Discard any substandard or suspect material (chunks, lumps, rocks, wet).

Calculating Blend Volumes

The UNOCAL Drilling Engineer and Foreman will approve the volume of cement to be blended for the job.

If a UNOCAL representative cannot be present for the blending operation, the bulk plant operator with primary responsibility for the blending operation must verify the blend volumes with the UNOCAL drilling office.

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The bulk volume of each batch of cement and additives must not exceed 60% of scale tank capacity.

Important—The bulk volume of each batch of cement and additives must not exceed 60% of scale tank capacity.

To determine the total volume of cement and additives required:

1. Based on total volume of cement blend required, bulk load factor, and blending capacity, determine the batch size and quantity.

2. Use the cement blend formulation to calculate total cement and additives required.

Preparing Equipment

1. Verify that the additive scale is clean and operating properly.

2. Check the scale tank balance for proper operation.

3. Verify that the scales have been calibrated and certified within the past six months. A certification stamp must be on the scale.

4. Check air compressor and/or vacuum system for proper operation, and drain of any moisture.

5. Record lot numbers of bulk cement and all additives to be used.

Preparation for Liner Job Blends

1. Empty, clean, and inspect all blending equipment, including cutting pods, scale tanks, boxing tanks, silos and sampling devices.

2. Open and visually inspect all tanks immediately prior to the job to ensure that they are empty and clean.

3. In addition to blowing down, sweep down and clean out tanks.

4. Follow all appropriate regulations and requirements prior to entry into a tank.

5. Check aeration pads for moisture; if wet, blow air through until dry.

6. Inspect air-jets for build-up. Clean or replace jets and rubbers as neces-sary.

7. Purge, empty, and clean all transfer lines.

8. Clean or replace dust sacks.

Weighing

1. Make sure calibration and certification records for all weighing devices are available.

2. Zero the scale tank prior to the blending operation.

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Weigh all additives into the bulk tank. Never use the weight indicated on the bag for calculations.

3. Once the scale is zeroed, this same zero point MUST be maintained dur-ing the entire blending operation.

4. Cement and additives are to be layered into the scale tank in the following order:

• 1/3 of the cement

• 1/2 of the additives


• 1/2 of the additives


5. DO NOT exceed 60% capacity of the scale tank.

6. Calculate weights of cement and additives for each step. Double check calculations.

7. Weigh all additives into the bulk tank.

Caution—NEVER use the weight indicated on the bag for calculations.

8. Take into account bag weight or weight of any other weighing container. Example: For small amounts of additives, the material should be weighed using a clean plastic or steel container (bucket, garbage can, etc.) after adjusting (tarring) the scale for the weight of the container.

9. Calculate “target” cumulative weight of scale tank at each step.

10.Record scale tank readings after each step, “actual” cumulative weight.

11.During the weighing process, document and compare the “target” and “actual” cumulative weights after each addition of additives or cement to the blend.

12.For large volume additives such as silica sand, the weigh tank scale may be used to measure the weight of the material. Example: 3700 lbs. silica flour, record current scale tank weight, add 36 sacks of 100 lbs. net (labeled) each, check scale tank weight, weigh out and add any additional silica flour to bring weight added up to 3700 lbs.

13.Shake dust socks regularly during the blending operation to minimize accumulation of materials in them.

14.Purge the lines of all material after each transfer of material (cement or additives). Repeat this purging procedure if it is suspected that some of the material is remaining in the line.

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Five complete pneu-matic bulk plant transfers are required on all blends.

The weight of the material remaining in the scale tank after the transfer must be recorded. This weight will be added to the cumulative weights of the next batch of blended material.

Blending

Important—Five complete pneumatic bulk plant transfers are required on all blends. Percolating air through the blend WILL NOT be accepted as a replacement method.

1. After all cement and additives have been placed in the scale tank, use approximately 30 psi to transfer the material to the blend tank. If extremely light additives are being used (microspheres, silica fume, etc.) the transfer pressure should be reduced to 6 to 8 psi to minimize segrega-tion and losses of these light additives through the vents.

2. Box a minimum of five times. Example:

a. scale tank to blend tank

b. blend tank to scale tank

c. scale tank to blend tank

d. blend tank to scale tank

e. scale tank to holding tank, truck or portable tank.

3. During the last transfer, take bulk blend samples as detailed in the follow-ing section on sampling.

4. Check and record weight of blend each time it comes back into the scale tank.

Important—The weight of the material remaining in the scale tank after the transfer must be recorded. This weight will be added to the cumulative weights of the next batch of blended material.

Cement Load-Out for Land Operations

The bulk plant operator is responsible for visually inspecting through open hatches all transport pods to ensure that they are clean and dry.

For intermediate and deeper casings, a UNOCAL representative or designated third party inspector is required to inspect tanks prior to loading.

1. Blow or sweep down any residual cement in the pods as necessary.

2. Blow clean all transfer lines.

3. Check the air system and drain any water from the traps.

4. Transfer cement through a weigh tank to determine an accurate weight and volume.

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Always take samples for lab analysis and confirmation testing.

Sampling

Always take samples for lab analysis and confirmation testing. A sample MUST be taken for each batch blend when it is transferred from the scale tank to the holding tank prior to load-out.

An automatic or manual sampling valve may be used. A pneumatic inline sampler is operated through the complete transfer. A manual 1- or 2-in. valve sampler located on the discharge line, should be opened intermittently throughout the transfer.

The minimum total sample quantity is three gallons (three plastic sample bags)—two to send to the lab and one to keep at the bulk plant.

To take a sample, perform the following steps:

1. Purge the sample line/valve.

2. Take a sample in a new plastic bag.

3. Force out any excess air.

4. Seal the bag with a wire tie.

Important—The minimum volume for any single bag is 1 gal.

5. Label the sample containers and storage tanks with the following informa-tion:

a. date

b. formulation

c. quantity

d. batch number

e. bulk plant operator

f. well number

g. cementing job

In some cases sampling should be witnessed by a UNOCAL representative or designated third party inspector.

Bulk Blend Testing

Bulk blend testing is required for application of dry-blended bulk blends for all casing strings.

Bulk blend testing is to include the following, as a minimum:

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The Cementing Contractor must not load out a dry cement blend until approved by a UNOCAL representative.

• thickening time test at BHCT

• compressive strength test, 24 hr (WOC, if specified) at BHST (and TOL if requested)

• rheologies at 80oF and BHCT

• free fluid and solids settling, at temperature

• fluid loss at BHCT

The Cementing Contractor shall ensure that there is sufficient time between field blending and the actual cement job to allow for blending, testing, and when necessary, modifications, re-blending, and re-testing, without jeopardiz-ing the execution of the cement job itself.

Contractor’s Cementing Supervisor shall monitor bulk blending and coordi-nate the lab testing.

The Cementing Contractor must not load out a dry cement blend until approved by a UNOCAL representative.

Documentation

The following documentation must be provided directly to the UNOCAL office after completion of every bulk blending operation.

• quantities and batch/lot numbers of cement and additives

• copy of laboratory cement slurry formulation sheet

• weight calculation and recording sheets

• final quantity and the number of the storage tank into which it was loaded

Cement Loadout for Offshore Operations

The bulk plant operator is responsible for loading out cement and must ensure that cement quality is not diminished during or because of this operation. On the rig, the cementer is responsible for the preparation and execution of cement offloading procedures from the boat onto the rig. They must promptly report any problems to UNOCAL.

In the event bulk trucks are used to transport the cement blend to the boat dock, a bulk plant operator shall accompany the trucks and uphold responsi-bilities.

Preloading

1. Prepare a load ticket detailing type, content, volume, and weight and bulk load factor of each cement or blend to be loaded.

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The bulk plant operator or other approved service company representa-tive must visually inspect all tanks that are to be loaded.

2. Prior to loading or inspecting tanks, present a copy of the load ticket to boat captain and discuss which tanks are to be loaded.

3. Verify tank volumes and calculate cement volume to be loaded into each tank.

4. Verify hose hookup and valve alignment with boat captain or designated representative.

5. Install a rock catcher between bulk facility and boat.

Boat / Tank Inspection

The bulk plant operator or other approved service company representative must visually inspect all tanks that are to be loaded.

Follow all appropriate regulations and requirements prior to entry into a tank.

1. In addition to blowing down the tanks, any tanks containing barite, bento-nite, or cement must be swept down and cleaned out.

Tanks containing any other type of material require steam or pressure cleaning.

2. Check aeration pads for moisture; if they are wet, blow air through them until they are dry.

3. Inspect air-jets for cement or other buildup; if found, clean or replace the jets and their rubbers.

4. Drain water and moisture from bulk air systems.

5. Blow air through all purge lines until they are dry.

6. Pressurize tanks that are to be loaded to 10 psi and check for leaks.

7. Blow down tanks through discharge and hoses that will be used at the rig.

8. Install and seal hatch covers after inspection is completed.

Loading Cement

1. Monitor vent line for overfilling of tanks.

Important—Do not change tanks without verifying hose hookup and valve alignment with the boat captain or the designated representative.

2. After loading, request the boat crew to open hatches and verify the amount of cement in each tank, reseal hatch covers, pressure check seal, and then vent pressure.

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Caution—Leave pressure off tanks until preparing to off-load cement at the rig.

3. Verify that the boat crew caps and stows the cement discharge hoses before getting underway.

Offloading Cement at Rig

The cementer is responsible for overseeing offloading of cement blends onto the rig, including tank inspection, rigging up, volume calculations, and sam-pling.

1. Calculate available rig tank capacities based on bulk load factor of cement to be loaded.

2. Meet with the company man to discuss volume calculations for the cement and verify the rig tanks into which cement is to be loaded.

3. Conduct a visual inspection of the rig tanks prior to loading. and make sure that any necessary cleanup or repair operations are witnessed.

4. For a liner job, sweep down the rig tank and completely clean it out prior to loading. Inspect all air pads and jets and replace them as necessary.

5. Go on board the boat to inspect the air system and to verify the location and type of cement or blend in each tank. Check the hose hookups, valve alignment, and hoses and capped hoses and lines.

6. Install a rock catcher in-line between the boat and the rig tank. The rock catcher should be positioned on the rig.

Rigsite Sampling

During the loading, catch two sets of samples by taking two 1-gal samples at the beginning, middle, and end of each tank load for a total of six samples.

Cement Sampling Equipment

For critical jobs, a Gustafson inline sampler is required.

If an inline sampler is not available, use a portable cement tank to collect samples as follows:

a. Transfer the loaded cement from the rig tank to a portable cement tank (pod).

b. Open the access hatch on the top and open the lower feed line from the bottom of the tank; take three 1-gal samples from each, labeling them as top and bottom.

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Labeling Samples

1. Place the samples of cement blend in the standard sample bags that are prelabeled with the date, job type, formulation, amount, rig tank number, and at what interval the sample was taken during the loading process—beginning, middle, or end.

2. Take two 5-gal samples of mix water and two 2-gal samples of drilling fluid in clean, sealable containers that are labeled with date, rig, and source.

3. Send one set of samples (three cement samples, one mix-water sample, and one drilling fluid sample) to the laboratory and retain the other set on the rig.

Prejob Procedures

The cementer is responsible for execution of all on-location procedures, as described below and in the following “Job Procedures” section.

1. Prior to the cement job, obtain up-to-date well information and cementing objectives from the UNOCAL Drilling Supervisor. This information should include

• hole size with caliper data or required excess factor

• casing length, size, and weight

• drill pipe length, size, and weight

• shoe track dimensions

• required length of tail cement

• desired top of cement

• liner hanger configuration

• any other pertinent information

2. Conduct a prejob meeting for all service personnel (mud loggers, etc.) to provide information or add value to the process.

3. Verify equipment and material requirements and confirm that they will be on location for the job.

4. Review cement and spacer formulations with the cementing coordinator.

5. Review laboratory test results from the rig samples with the cementing coordinator, paying special attention to the thickening time (available pumping time) and the required WOC (wait on cement time, time to 500-psi).

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6. Calculate cement volumes in barrels, in cubic feet, and in sacks of cement required for the lead and tail formulations. Include a breakdown of these volumes showing cased hole, open hole, and shoe track volumes.

7. Calculate the mix water requirement, additive requirements, and the resultant mix fluid volume for both lead and tail cement slurries.

8. Calculate spacer volumes and material requirements, taking into account available mixing space.

9. Check the available water supply and verify that sufficient quantities of water will be available for the job.

10.Verify that the suction rates required for the job can be achieved with both drilling fluid and water.

11.Calculate displacement volumes for the casing or liner and drillpipe as required.

12.Develop a pumping schedule based on the cement job simulator output.

13.Determine whether the available pumping time as indicated by the labora-tory thickening time test result is sufficient for the planned job.

Note—The cementing contractor’s equipment will be used for all mixing and pumping.

14.Prepare a job plan that includes the following.

• rig-up procedure

• safety concerns

• pressure testing procedure

• spacer type, density, and volumes to be pumped

• wiper plugs, dart- or ball-dropping sequence and procedure

• cement slurry formulation(s) densities and volumes

• conversion factors for calculating sacks per barrel of slurry and barrels of slurry per barrel of mix water

• pumping schedule indicating rates, volumes, and times for pumping and displacing each fluid

• total job time including time to drop plugs and flush lines

• anticipated job pressures during pumping, shearing or bumping of plugs and darts

• in-hole hydrostatic pressures of each fluid after placement

• personnel requirements for the job

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Load the wiper plugs in the presence of the UNOCAL Drilling Supervisor.

• contingency plans for the unexpected: liner top packer fails, float equipment fails, loss of returns while going in the hole, etc.

• WOC criteria prior to rigging down any well-control devices

15.If supplying the wiper plugs and cementing head, verify that the correct equipment is on location and that the cementing head and associated con-nections have been tested.

16.Load the wiper plugs in the presence of the UNOCAL Drilling Supervi-sor.

17.Review checklists, laboratory test results (available pumping time and WOC time), and job plan with the UNOCAL Drilling Supervisor.

18.Prepare spacer as required and check the weight with a pressurized drill-ing fluid balance.

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Maintain an open line of communication to rig floor at all times.

The cementer is responsible for seeing that wiper plugs darts or balls are released at appropriate times.

Job Procedure 1. Hold a safety meeting on the rig floor to review the job procedure and

address safety concerns.

Note—Maintain an open line of communication to rig floor at all times.

2. Pump spacer to break circulation.

3. Pressure test the lines and the operating system to a pressure above that expected during the cementing operation.

4. Pressure up the bulk tanks.

5. Pump the job according to the job plan.

Note—The cementer is responsible for seeing that wiper plugs darts or balls are released at appropriate times.

6. Use a data acquisition system to record pressure, rate, density and vol-umes pumped during job.

7. Manually record the following events during the job.

• pressure test, psi and time

• start time for job

• dropping of any plug, darts or ball

• start and stop time for each fluid pumped

• start of displacement

• landing or shearing of any plug or dart and the observed pressure

• any unexpected pressure changes and any unscheduled shutdowns

• top plug bumping pressure and whether or not floats held

• cement in place

8. Count and record the volume of mix water by the number of displacement tank volumes used.

9. Measure the cement slurry density with a pressurized drilling fluid bal-ance.

10.Take cement slurry cup samples throughout the job.

11.Take three separate one-gallon mix water samples from the displacement tank and three separate one-gallon dry cement samples from the surge can or a transfer line after the job.

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Do not pump anyfluids lighter in weight than the drilling fluid in the hole, unless previously agreed upon by respective parties that a lighter-weight spacer or flush is to be used.

Do not open the cement head after a cementing fluid has been pumped down-hole, until after the job is completed.

Do not sacrifice cement slurry density for pump rate.

12.Label and retain samples for possible laboratory testing until the well is completed.

Caution—Do not pump any fluids lighter in weight than the drilling fluid in the hole, unless previously agreed upon by respective parties that a lighter-weight spacer or flush is to be used.

Do not open the cement head after a cementing fluid (spacer or slurry) has been pumped downhole, until after the job is completed.

Do not sacrifice cement slurry density for pump rate.

Do not over-displace past the calculated displacement plus 50% of the shoe track volume.

13.Prepare a job ticket, a printout of the data acquisition output and chart, and any incident reports, and present them to the UNOCAL Drilling Supervisor.

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Documents

Cementing Best Practice Jorge Sierra