As Ton Sun Um

8/6/2019 As Ton Sun Um

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SPE DISTINGUISHED LECTURER SERIES

is funded principally

through a grant of the

SPE FOUNDATION

The Society gratefully acknowledgesthose companies that support the program

by allowing their professionals

to participate as Lecturers.


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Selecting the Right

Drilling Fluid

Dr. Mark AstonDrilling Fluids Specialist

BP Exploration, UK

Email: [email protected]

Telephone: 44 1932 739506


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Outline

Introduction to drilling fluids Technical challenges

The bigger picture selecting theright fluid


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Requirements of a Drilling Fluid (Mud)

Lubricatethe drill string

Removedrill cuttings

Seal rocks toprevent loss offluid

Prevent holecollapse

GQS37586_11

Prevent the flowof oil and gaswhile drilling

Prevent rockdispersion

Avoid damageto the

productionzone


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Other Important Requirements

Not too expensive

Easy to use Environmentally friendly

$$


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Water Based and Oil Based

Muds

They look similar but are very different

WBM OBM


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Water Based Mud (WBM)

Simple WBM contains 3 components:

Water Barite (BaSO4) dense powder for mud weight

Clay as a thickener

Many variations: Salts and other chemicals for shale inhibition

Polymeric viscosifiers (xanthan)

Starch and polymers for reducing fluid loss

Bridging solids like calcium carbonate

Lubricants

Thinners

High temperature systems

Dense brines to replace barite


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Oil Based Mud (OBM)

Oil mud is an emulsion system Oil

Water phase containing salt (CaCl2)

Emulsifier

Barite powder for density

Wetting agent

Thickener (organoclay)

Variations: Oil type: diesel, mineral oil, synthetic oil Bridging solids and chemicals for reducing fluid loss

Barite-free muds

Flat rheology muds for deepwater


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To Summarise

Drilling muds can be complex There are many different formulations

available We need to design the mud to suit the

application


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Technical Challenges

Shale Stability - improving the performance

of water based muds Wellbore Sealing

Wellbore Strengthening

3 technical areas:

Bigger picture


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Shale Stability

Up to 80% of the rocks we

drill are shales (clay-richrocks)


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Shale exposed to oil and water

We can predict what will happen in the field:

Oil Water


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Drilling a Short Vertical Section

OBM Simple WBM

Poor holecondition but this may

not be aproblem

Mud weightis less

important!

We can use a simple water based mud such as a gel mud

Mud weightmust behigh enough

to prevent

tight hole


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Drilling Deviated Hole

OBM Simple WBM

difficult to steer

poor hole cleaning

hard to run casing

poor cement job

In this application we need a WBM that stabilises the shale


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Measuring Shale Dispersion


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Shale Dispersion Results

010

20

30

40

50

60

70

80

90

100

%s

hale

recovered

A B C D E F

A: Gel mudB: NaCl/polymer mud

C: KCl/polymer mud

D: KCl/glycol mud

E: KCl/silicate mud

F: Oil mud

The best water based muds contain salt a problem for land based drilling?


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Land-Based Drilling - WBMs

Mud Disposal

Contamination offreshwater aquifers


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Shale Dispersion in Salt-Free WBMs

0

10

20

3040

50

60

7080

90

% Shale

Recovered

Gel

Polymer

Glycol

New


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Wellbore Sealing

For water based or oil based muds

Wellbore strengthening Bigger PictureShale dispersion


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Sealing Permeable

Formations

We should seal permeableformations such as sandstones to

avoid: mud losses, differentialsticking, damage to the production

zone, and to preserve core qualitywhen coring

Bridging Particles can Help to Seal


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Bridging Particles can Help to Seal

Permeable Formations

mechanical sealingby calcium carbonate particles


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What size particles do we need?

ShalesConsolidated

SandsSilts

UnconsolidatedSands

Darcy10-3 Darcy10-6 Darcy10-9 Darcy

10s - 100smicrons

millimetres< micronsnanometers

Polymers/clay fines Barite

Permeability:

Pore Size:

Mud Sealants:

Forgotten?special case

Typical mud particle size distribution


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Typical mud particle size distribution(barite oil mud)

Clay fines Barite

too small forsome

applications?


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To Design the Mud for Bridging

Estimate the maximum pore size in the rock Pore size ~ sq root (permeability in mD)

Ensure the mud contains particles of this size, plus arange of smaller ones.

Ground marble is effective and acidisable, avoid soft

solids like chalk Run large shaker screens if required to keep the

solids in the mud

Replace the large solids during drilling as they grinddown. Maintain a low API fluid loss


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Particle size Definitions!

The industry uses terms like fine, medium, coarse,and extra coarse

These terms are not defined and can be misleading.

Always check the actual size distribution

Be aware that fibres and carbonates have differentdefinitions of fine, medium and coarse.

S li Sh l


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Sealing Shales

OBM does notpenetrate, pressure

support is maintained

WBM canpenetrate, pressure

support is lost

Pore sizes are very small (nanometre size)

Sh l Diffi lt t S l i


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2+

Shales are Difficult to Seal using

WBMs - Research Continues

Polymers orglycol droplets?

special salts like silicate can work

Na+

SiO3

Ca2+

Mg 2+

Insoluble gel

Bridging solids like finecalcium carbonates orclays are not effective


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For Depleted Reservoirs

Wellbore sealingShale dispersion Bigger Picture

Depletion Weakens the Rock


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FractureGradient

Depletion Weakens the Rock

Formations

1.80 0.30

Pore Pressure Poissons Ratio

s.g.

Pore

Pressure

Overburden

0.5 1.0 1.5 2.0 2.3

ECD Range

H S h h


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How can we Strengthen the

Formations?

Pump cement or resin treatments Slow, expensive, have to drill the section first, onlyworks for short sections

Design muds that can strengthenformations as you drill Can it be done?

Concept to Strengthen Rocks


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Concept to Strengthen Rocks

t

Hoop Stress Increase(stress cage)

Bridging Particles

Wellbore

P

Designer Mud Concept

D i M d T i l


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Designer Mud Trial

ELoT - Designer Mud Trial

0

200

400600

800

1000

1200

1400

1600

1800

2000

2200

2400

2600

0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00

time/mins

Surface

Pres

sure

(psi)

Initial

formation

beakdown

Designer

mudbreakdown

838 PSI5 ppg


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The Bigger Picture

Selecting the right fluid

Things To Consider


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Things To Consider

Formation damage

Lubrication

Temperature andpressure

Do you want to be first to trysomething new?

Waste disposal options

Cost of Fluid

What has worked before?

Company policyLocal regulations

Completion design

Who has the fluids contract?

Are mud lossesexpected?

Mud weight

Who needs to beinvolved?

Shale inhibition

Rheology

Fluids Design Process


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Fluids Design Process

This process needs the involvement of manypeople a team approach

Well designand objectives

Environmentalissues

Review offsetwell experiences

Assessavailable technology

Perform

Risk assessment

Mud Program


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Example

Offshore Gas Development (10 wells) 300ft water depth

Deviated wells (80 deg), 7000ft MD BHT 200 F, Max mud wt. 12 ppg

Open Hole (OHGP) Completion

Well Design


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Well Design

24

13 3/8

9 5/8

5 1/2

limestone

17 1/2 hole

12 1/4 hole

8 1/2 hole

ft

ft

Environmental


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Environmental

Many things to consider, e.g.

Seabed surveys (e.g. presence of corals)

Environmental regulations

Can we achieve low oil on cuttings levels?

Cuttings re-injection

Onshore disposal

Technical requirements (e.g. formation damage)

Use water based muds Use oil based muds

Offset Experiences


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Offset Experiences

30 cond.

13 3/8 casing

8 hole

9 5/8 casing

Lithology Mud Issues

Soft

Sediment

Shale &limestone

Shale &sandstonestringers

Sandstone &Interbedded

shale

KClmud

9.3ppg

SW/Gel

500 ft

2000 ft

3500 ft

4400 ft

KClmud9.3

9.6ppg

Driven

Lost 200bbls,sticky shale

Mud Rings,tight trips

Pack-offcavings

backreaming

17

12 1/4

8 1/2

Risk Matrix 17


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Risk Matrix 17

Low

Medium

Medium

Probability

Run LC50 toxicitytests

ReputationCannotDischargeWBM Waste

Use inhibitiveKCl/polymer mud,monitor cuttingscondition whilst

drilling

Balling, cannotsteer, poor holecleaning

ShaleInhibition

Prepare lossesdecision tree

Lost time, lost mud,well control?

Losses

Action

(Mitigation)

OutcomeRisk

Risk Matrix 8


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Risk Matrix 8

Perform wellborestability study Use at

least 10ppg mud weight

MediumTight Hole, Cavings, lossof well

Mud weight toolow

Use a water based mud

for open hole gravelpack

HighImpacts productionMud not

compatible withcompletiondesign

Low solids mud, correctbridging particles. Runlab tests

HighImpacts productionFormationdamage

Medium, have

interbedded shales

High

Probability

Use inhibitive mud, test

in lab if possible

Impacts drilling and

production

Shale Inhibition

Perform T&D study, testlubricants in lab

Cannot get WOB,cannot get completion tobottom

Torque & Drag

Action

(Mitigation)

OutcomeRisk

Af h Ri k M i


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After the Risk Matrix

Work on the actions

Produce the mud program

Decide how to measure performance in

the field and record the lessons learned(measure non-productive time and well

productivity) Apply learning to the next well

Conclusion


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Conclusion

Technical challenges Shale stability

Wellbore sealing


Selecting the right fluid follow a careful planning process

produce a risk table with actions

measure the performance of the fluid to identifyareas for improvement

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