10 - Drilling Fluids Design and Selection_Handout

8/22/2019 10 - Drilling Fluids Design and Selection_Handout

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Drilling Fluids:Drilling Fluids:

Design & SelectionDesign & Selection

Drilling Fluids:Drilling Fluids:

Design & SelectionDesign & Selection

Global Research & Technology Centre/ GRTC

Training Department

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Key elements of a successful DrillingFluid Operation

HS&E

Tender

Rig & Mud

Plant Specs

Quality

Control

Technical

Service

Personnel

Solids

Control

Drilling Fluid

Design &

Selection

Successful

Drilling Fluid

Process

Drilling Fluid

Design &

Selection


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There are only two reasons why wedrill a hole in the ground:

To collect geological and reservoir data

To successfully exploit and produce oil & gas

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Deliver quality geological and reservoir data

Minimise reservoir damage to optimise oil & gasrecovery

Achieve technical limit drilling performance

Note: The considerable reduction in operationalcosts as a consequence of technical limit drillingperformance is valid only to the degree that the

primary operational goals are successfully met!

Appropriate drilling fluid design and selection is a prerequisitein order to fully meet both our primary and secondary goals

Primary operational goals

Secondary operational goals


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Primary factors that impactdrilling fluid design & selection

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Primary functions of a drilling fluid

Lubricate & coolthe drill bit

Efficientlytransport

cuttings tosurface

Maximise Rate or

Penetration (ROP)

Lubricatethe drill string

Minimise shale

hydration &

dispersion

Minimise reservoir

damage

Maintain astable in gauge

well bore

Prevent the flowof oil and gaswhile drilling

Minimise fluidinvasion intoformations

Transmit Hydraulic

Horsepower (HHP)

to the bit


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Drilling fluid design & selectionconsiderations

Formation damage

Lubrication

Temperature and pressure

Do you want to be first to try somethingnew?

Waste disposal options

Cost of Fluid

What has worked before?

Company policy

Local regulations

Completion design

Who has the fluids contract?

Are mud losses expected?

Mud weight

Who needs to be involved?

Shale inhibition

Risk management

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Primary drilling fluid design andselection GOALS

To fully meet all regulatory and internal HSE guidelinesand goals.

To provide a stable wellbore to facilitate the successfulrunning / retrieval of quality geological and reservoirdata.

To minimise reservoir damage and thereby optimisewell productivity and profitability.

To optimise drilling performance and thereby reduceoverall drilling


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Framework for drilling fluid design,testing & selection

Test, evaluate and select drilling fluid systems that willfully meet all regulatory and internal HSE guidelines.This is especially applicable to synthetic oil basedmuds.

Test & analyse the physical & electro-chemicalcharacteristics of the clays, shales, mudstones andreservoir sequences to be drilled.

Design & test for the best synergy between the clays,shales or mudstones with various water based mud

system options in order to minimise hydration & controldispersion.

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Framework for drilling fluid design,testing & selection

Test various water based and / or synthetic oil basedmud formulations for their tolerance to:

Drill solids Barite weight upApplicable drilling fluid contaminants including

cement

Temperature stability at anticipated BHT

On the basis of the test results evaluate, optimise andthen select the appropriate water based or synthetic oilbased mud system to meet your well specificdrillingand reservoir challenges.


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Thoroughly review the following keyelements

Environmental regulations & guidelines. Offset well data, ie well programs / well summaries and

drilling fluid specific programs / summaries.

Reservoir data: offset reverse permeability test data mercury injection data for reservoir pore throat size

range

prognosed in-situ shales or shale beds present inreservoir sands

anticipated pore pressure gradient and temperaturegradient in the reservoir

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Logging plan, ie duration & prognosed maximum bottom holetemperature.

Testing plan, ie special fluid and kill pill requirements.

Development well - completion plan, ie perforated liner,expandable or fixed screens, sliding sleeve, etc. Well cleanup and fluid design program to be based on completiondesign criteria.


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Potential for the presence of acid gasses, CO2 & H2S.

Prognosed fractured and / or faulted zones with thepotential for lost circulation

Maximum prognosed temperature for each hole section.

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Deep water wells: Seabed depth

Seabed temperature

In-situ gas hydrates

potential for formation of gas hydrates

Drilling fluid lubricity: A key element in terms of potential torque& drag limitations when planning to drill a long reach step out

well. Note: Lubricity is also a significant factor when drilling

deviated wells through hard rock, eg granite.


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Exploration well, ie wildcat or mature exploration area.

Detailed lithology profile.

Casing design options.

Hole sizes / depths MD & TVD as applicable.

Directional plan inclination & azimuth.

Wellbore stress modeling data, ie in-situ vertical stress &minimum / maximum horizontal stress prediction.

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Pore pressure prediction, ie mud weight range for each holesection. Data sources used to predict pore pressure gradient: Sonic / resistivity logs, seismic data analysis, micro

hydraulic fracturing (MDT), drilling records and bore holemodeling.

Offset well leak off & F.I.T. test data.

Mud plant capacities / warehouse facilities, product availabilityand lead times.

Rig specifications / limitations, ie tank capacities, solids controlequipment and rig mixing / delivery systems.


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Risk management in drilling fluiddesign & selection

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Risk management in drilling fluid design & selection

Overall well costs

Management of risk

Evaluate risk ie potential value of success vs the potential cost of failure

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Risk HigherLower

Inhibitive propertiesHigher Lower

Choice of drilling fluid systems:

Synthetic oil based mud

Enhanced KCL / Polymer / Glycol

& Surfactants

Silicates

Bentonite muds / spud muds

Brine systems

Fully dispersed fresh water /

lignosulfonate / Lime / gyp muds

KCL / Polymer / Glycols

Lower Higher

Poor shale inhibition

Hole stability problems

Stuck pipe

Low ROPs

Consequences of poor

drilling practices

Failure to run & retrieve

quality logging data

Reservoir damage, etc

Exception:

Dispersed muds are often the

most economical low risk

option for drilling shallow,

young, weakly consolidated

shales

SW / viscous sweeps

Dispersed muds


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Management of risk

The cost of failure !

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Hours

Example

lost time analysis for

an offshore well

Risk management in drilling fluid design & selection

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Advantages & disadvantages ofSBM & WBM


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Advantages & disadvantages of SBM& WBM

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SBM WBM

EnvironmentalEnvironmental

Moderate to significant environmental impact,

however this impact can be managed, e.g.

cuttings re-injection, ship to shore, etc.

Moderate environmental impact. Dependant

upon type of WBM system.

Hole stability & hole gauge Hole stability & hole gauge

Open hole stability sustainable for long periods of

time.

Close to gauge well bore.

Open hole stability very time dependent.

From close to gauge to out of gauge well bore

dependent upon appropriate water based mud

system design & selection requirements.

Accretion / bit balling Accretion / bit balling

Minimal to zero ac cretio n / bit balling. Severe to minimal accretio n/ bit balling

problems. Dependant upon appropriate water

based mud system design & selection.

Advantages & disadvantages of SBM & WBM


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SBM WBM

ROPs

Higher ROPs in most drilling environments.

Torque & drag

Lower torque & drag values.

Temperature stability

High thermal stability 450F +

ROPs

Lower Rops in most drilling environments.

Torque & drag

Higher torque & drag values.


Lower thermal stability, ie above 280 F require

special H.T. products for thermal stability to +/-

400 F. Potential problems maintaining stable

mud properties at very high temperatures.


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SBM WBM

ROPs

Higher ROPs in most drilling environments.

Torque & drag

Lower torque & drag values.


High thermal stability 450F +

ROPs

Lower Rops in most drilling environments.

Torque & drag

Higher torque & drag values.


Lower thermal stability, ie above 280 F require

special H.T. products for thermal stability to +/-400 F. Potential problems maintaining stable

mud properties at very high temperatures.



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SBM WBM

Lubricity Lubricity

Lower coefficient of friction = good lubricity Higher coefficient of friction = poor lubricity

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0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

SBM WBM with lubricant

CoefficientofFriction

Metal to sandstone Metal to shale

SBM WBM + lubricant


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SBM

Risk of unscheduled events

Low risk of costly unscheduled events, e.g. hole

stability problems, stuck pipe, etc. Subject to good

drilling practices due to close to gauge hole.

Long reach step out wells

Extended long reach step out range (distance) due

to the lower co-efficient of friction ie lubricity

significantly reduces torque & drag values.

WBM

Risk of unscheduled events

Much higher risk of costly unscheduled events, e.g.

hole stability problems, stuck pipe, etc.

Long reach step out wells

Diminished long reach step out range (distance) due

to the higher co-efficient of friction ie higher torque &

drag values and potential hole stability problems

related to time!

Stuck pipe

Generally easier to recover from mechanically stuck

pipe and twist off type incidents, i.e lubricious,

stable & close to gauge well bore conducive to more

successful jarring/ fishing operations.

Generally more difficult to recover from mechanically

stuck pipe and twist off type incidents, i.e less

lubricious, hole stability time dependant and

possibility of out of gauge well bore results in a more

challenging jarring/ fishing environment.

Stuck pipe



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SBM

Fluid loss

Low invasion rates ( fluid loss properties) moderate

the rate at which the rock matrix weakens followed

by hole stability problems.

Extended time period before the onset of hole

instability problems. Especially significant when

unscheduled events are encountered, eg pipe twist

off, rig shut down for cyclones, etc.

Hole stability (time)

WBM

Fluid loss

Higher invasion rates ( fluid loss properties) accelerates

the rate at which the rock matrix weakens followed by

hole stability problems.

Limited time period before onset of open hole

stability problems. High risk of unscheduled events

resulting in stuck pipe and probable requirement to

side track.

Hole stability (time)

Tools Corrosion & frictional wear

Minimal corrosion and frictional wear of tools &equipment due to a lower co-efficient of friction and

the preferential oil wetting of steel surfaces.

Tools Corrosion & frictional wear

Increased corrosion rates and higher frictional wear ontools and equipment due to a higher co-efficient of

friction and a water / seawater environment.


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SBM

Fluid loss

Low invasion rates ( fluid loss properties)

moderate the rate at which the rock matrix

weakens followed by hole stability problems.

WBM

Fluid loss

Higher invasion rates ( fluid loss properties)

accelerates the rate at which the rock matrix

weakens followed by hole instability problems.

HtHp fluid loss graphs

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FLValue,

dP500p

si@300F-cc

SBM WBM

PPA spurt loss & total fluid loss SBM vs WBM

Bridging agent PSD optimised to minimise invasion at assumed 60 micron pore throat size

0.2

16.8

3.2

0.6


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0

2

4

6

8

10

12

FLValue,dP

500psi@250F-cc


SBM

Fluid loss

Low invasion rates ( fluid loss properties)

moderate the rate at which the rock matrix

weakens followed by hole stability problems.

WBM

Fluid loss

Higher invasion rates ( fluid loss properties)

accelerates the rate at which the rock matrix

weakens followed by hole instability problems.

SBM WBM

HtHp fluid loss SBM vs KCL / Glycol / polymer WBM

Mud weight 10 ppg - High-mod prima clay 35 ppb Hot rolled @ 250 deg F for 16 hrs

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1.0

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SBM

Inhibition & dispersion properties

Continuous oil phase is non-polar, ie does not react

with clays, shales and mudstones.

WBM

Inhibition & dispersion properties

Continuous water phase does react with clays, shales

and mudstones, resulting in significant hydration and

dispersion. The degree of hydration and dispersion

depends upon the type of WBM system selected.

Shale in oil Shale in fresh water



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WBM

Logging

Enhanced petrophysical log evaluation. However,

out of gauge hole & higher invasion / filter cake

thickness requires careful and rigorous correction

& correlation of log data, e.g. neutron density,

gamma ray, resistivity, sonic, etc. * Hole gauge

depends upon type of WBM system used.

Excellent image log quality.

SBM

Logging

Petrophysical log evaluation more demanding.

However gauge hole & minimal invasion / filter cake

thickness requires less rigorous correction &

correlation of log data, e.g. neutron density, gamma

ray, resistivity, sonic, etc.

New logging tools have been successfully developed

to provide reasonable image log quality.

Mud weight

Generally lower mud weight overbalance required to

maintain well bore pressure support o ver time.

Minimal invasion = low pore pressure penetration.

Mud weight

Generally higher mud weight overbalance required

to maintain well bore pressure support over

time, ie higher invasion rates = higher pore

pressure penetration. Invasion rates are dependant

upon type of WBM system.


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GassesGasses

High hydrocarbon gas solubility in oil at down hole

pressures. Minimal reaction time due to rapid

expansion of gas near surface.

H2S soluble in oil but comes out of solution when mud

alkalinity is depleted, ie excess lime content. Serious

health & safety implications for rig personnel if H2S is

not managed properly at surface.

Hydrocarbon gasses insoluble. Acid gasses H2S &

CO2 soluble in water, resulting in serious mud

problems together with H2S health and safety

implications for rig personnel.

WBMSBM

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1000

1200

1400

1600

0 2000 4000 6000 8000 10000 12000

Pressure (psi)

GasOilRatio(scf/stb)

Gas solubility in mineral oil, ester & olefin

Bubble point, ie gas

coming out of solution

near the surface as the

pressure diminishes

EsterOlefin Mineral oil



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SBM

Identifying hydrocarbons

Some difficulty identifying hydrocarbon shows but

can be managed with preparatory GC scan and

analysis of synthetic oil properties.

Elastomers (rubber parts)

Low elastomer resistance to solvents in SBM.

Requirement for rigorous testing of selected base

oil at maximum prognosed BHT.

Temperature conductivity

Temperature conductivity high. Significant mud

temperature increases when drilling and

circulating mud at high pump rates for long periods

of time.

WBM

Identifying hydrocarbons

Less difficulty identifying hydrocarbon shows but

some WBM additives can interfere with hydrocarbon

analysis.

Elastomers (rubber parts)

Higher elastomer resistance to most WBM additives.

Temperature conductivity

Temperature conductivity lower. Not as significant

when drilling and circulating at high pump rates for

long periods of time.


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SBM WBM

Drill solids tolerance

High tolerance to drill solids.

Drill solids tolerance

Low tolerance to drill tolerance.

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SBM drill so lids contaminatio n test WBM d rill so lids co ntamination test

PVYP PV

YP

PV

YP

PV

YP

Base mud + 45 ppb Drill Solids Base mud + 45 ppb Drill Solids



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WBM

Sensitivity to common

drilling fluid contaminants

High, but dependant upon type of WBM

selected.

Examples:

Reaction to clays, shales and mudstones

- Potential for clays, shales and mudstones to

hydrate and disperse

Calcium contamination (eg cement, anhydrite)

- Retards performance of most polymers

- Flocculates Bentonite based systems

Carbonate/bicarbonate contamination

- Flocculates Bentonite based systems

SBM

Sensitivity to common

drilling fluid contaminants

SBM impervious to most common contaminants.

Exceptions:

- Ester oil / cement contamination will cause the

ester to hydrolise ie waxing out

- Substantial / rapid influx of water can lead to severe

water wetting of drill solids and barite as a

result of severe emulsion instability.


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SBM

Optimum drilling performance

Lower overall risks and well costs in

challenging drilling environments

Potentially good drilling performance.

Hole stability time dependant &

dependant upon appropriate mud

system design

Moderate to significant environmental

impact. Various options available to manage

environmental impact, eg dependant upon

type of base oil and physical environment, ie

seawater temperature, seawater current

activity, depth of deposition, etc

WBM

Higher overall risks and well costs in

challenging drilling environments

Moderate environmental impact

dependant upon type of WBM system

used

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10 - Drilling Fluids Design and Selection_Handout