Oil Well cementing

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WELL CEMENTING

Well CementingIntroduction to Drilling

Learning Objectives

Explain the main reasons for cementing wells Describe slurry properties that must be controlled Describe slurry thickening time Explain API classes of cement commonly used Explain various cement additives and their function Describe methods of evaluating a cement job

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Well CementingIntroduction to Drilling

Reasons for cementing

Achieve Zonal Isolation

Provide Casing Support

Protect Casing

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Well CementingIntroduction to Drilling

Casing

Casing Support

Casing bonded withformation rockssupports its ownweight andload of surfaceequipment that ismounted on it

Cement

Zonal Isolation

Properly cementedcasing preventscommunicationbetween zonesof differingcharacteristics toenable drillingdeeper

Low pressureloss zone

Higherpressurepermeablezone

Reasons for cementing

Casing ProtectionSome formations contain fluids that can attack casing

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Well CementingIntroduction to Drilling5

Slurry Design

Density Solids/water ratio

Thickening Time Fluid Loss Free Water Rheology Compressive Strength

Future? Tensile Strength Young’s Modulus Poisson’s Ratio

Well CementingIntroduction to Drilling

Slurry Density Hierarchy

Spacer at least one-half ppg heavier than mud

Lead slurry at least one-half ppg heavier than the spacer

Tail slurry always heavier than the lead slurry

Example

Mud to surface12.0 ppg

Spacer12.5 ppg

Lead Slurry13.0 ppg

Tail Slurry15.8 ppg

Casing Shoe

** When pumping “normal” circulation, not reverse circulation

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Well CementingIntroduction to Drilling

Pressurized Mud Balance

Eliminates the effect of air in the cement slurry

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Well CementingIntroduction to Drilling

Slurry Thickening Time

The time available to place a slurry before it becomes too thick to pump.

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Well CementingIntroduction to Drilling

Thickening Time Test

Consistometers are used to measure the thickening trendof a slurry under simulated conditions of temperature and pressure

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Well CementingIntroduction to Drilling

Consistometer Slurry Cup

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Well CementingIntroduction to Drilling

Thickening Time Requirements

The thickening time should equal job time (mix, pump, displace) plus a reasonable safety factor such as 1 to 2 hours.

A slurry exhibiting a “right-angle set” rather than a “gel set”, is generally preferred. In actual well, slurry is static when set occurs, not

continuously sheared until set as in consistometer.

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Well CementingIntroduction to Drilling

API Classification for Oil Well Cements

Class A: Ordinary cement intended for use from surface to 6,000 ft.Class B: Sulfate resistant, intended for use from surface to 6,000 ft.Class C: High early strength, intended for use from surface to 6,000 ft.Class D: Intended for use from 6,000 ft. to 10,000 ft.Class E: Intended for use from 10,000 ft. to 14,000 ft.Class F: Intended for use from 10,000 ft. to 16,000 ft

Class G & H: Intended for use as a basic cement from surface to8,000 ft. as manufactured, or can be used for a wide range of welldepths and temperatures with suitable additives. Class G iscommonly used in California and Rocky Mountains and overseas, and Class H in Oklahoma and Texas as well as the Gulf Coast.

Manufacture and testing conforms to API Specification 10 12

Well CementingIntroduction to Drilling

Cement Slurry Additives

ACCELERATORS: To shorten the thickening time

RETARDERS: To lengthen the thickening time

EXTENDERS: To lighten slurry density

DENSIFIERS: To increase slurry density

FLUID LOSS CONTROL: To reduce loss of filtrate into

formation

FRICTION REDUCERS: To improve flow properties

HIGH TEMPERATURE: To prevent the cement from losing

strength under high temperature conditions over time

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Well CementingIntroduction to Drilling

Conventional Primary Cementing

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Well CementingIntroduction to Drilling

Good Cementing Practices

Casing Movement Centralizers Scratchers and Wipers Casing Wiper Plugs Two Floats Adequate Shoe Joint

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Well CementingIntroduction to Drilling

Centralizers

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Well CementingIntroduction to Drilling

Centralizers

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Well CementingIntroduction to Drilling

Float failure means pressure must be held on the casing until the cement sets. Can cause micro-annuli

Use a float shoe and a float collar for redundancy.

FloatCollar

FloatShoe

Casing

Two Floats

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Well CementingIntroduction to Drilling

The length of casing between the float collar and float shoe. Also called the “shoe track”

The purpose of the shoe joint to to contain contaminated or lightweight cement

Use at least two joints - more in larger casing

ShoeTrack± 80’

Adequate shoe joint

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Well CementingIntroduction to Drilling

Evaluating the Job

Temperature Survey Leak-off Test Bond Logs

Sonic Tools: CBL, CBT, SBT etc.Ultrasonic Tools: CET, PET, USIT

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