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Drilling Fluids

Offshore Drilling Operations Agenda

Monday Tuesday Wednesday Thursday Friday

AM

Introduction

HSEMetocean

Geology

Rig Typesand

Wellbore Construction Sequences

Casing and Cementing

Design

Drill Strings and Bits

Lunch Exercise Exercise Exercise Exercise Exercise

PM

Offshore Systems

and Structures

Well PlanningAnd Rig Selection

Wellbore Stability

and Drilling Fluids

Directional Drilling

MacondoReview

Exam

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Why WBM or OBM?

• Cost benefit ratio.

• Temperature.

• Formation reactivity.

• Required additives.

• Environmental sensitivity.

• It is important to look at the big picture when choosing a fluid type. What problems are expected.

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Water Based Mud Advantages Disadvantages

Higher frac pressure / frac gradient than OBM

Good fracture sealing & healing ability

Low gas solubility, promoting detection & handling of kicks

“Typically” cheaper than OBM

Perceived to be more environmentally friendly than OBM

Rheology / gels / density not as strongly affected by Temperature & Pressure.

More accretion and bit-balling tendencies –slower ROP

Shale & borehole instability as a function of open-hole time

Less lubricating than OBM More differential sticking

potential (fluid loss control more difficult to manage)

Hole cleaning in deviated wells not as good as OBM

Oil or Synthetic Base Muds (NAFs)ADVANTAGES

Excellent ROP

Excellent shale & hole stability

Thermally stable Excellent fluid loss

control / low differential sticking tendencies

Excellent lubricity & tubular wear characteristics

No hydrate formation problems

DISADVANTAGES

Low frac pressure & poor fracture healing ability

Fluid Rheology strongly dependent on P,T

Poor borehole stability when formations are fractured in-situ

High gas solubility, complicating kick detection & handling

Expensive if losses are heavy

Compliance requirements of new NPDES permit

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Measurable Working Fluid Properties

• Density• Viscosity• Filtration• pH• Temperature stability• Chemical and physical composition• Corrosivity• Additive compatibility• Formation compatibility• Environmental compatibility

Density

• Mass per unit volume.– ppg, g/cc, kg/m3, lb/ft3

• Important to wellbore stability.– Pressure Control– Formation Stability

• Measured With:– Mud Balance– True Mud Balance– Hydrometer

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Mud Density Measurement• In the field, mud density is measured with

a mud balance.

Electrostatic Charges on Clay Platelets

• Clays have (+) charges on platelet faces and (-) charges on platelet edges

• Face-to-face and edge-to-edge repel

• Edge-to-face attracts

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Structures and Behaviors of Clay•Clay (shale rock) is sedimentary

•Layers deposited in water

•Water is baked and squeezed out of clay structure with deeper burial

•When exposed to water, clay draws water back into structure

Yield Point (YP)

• YP driven by electrostatic structure• Particle charges• Concentration

• More charged particles means more structure

• More internal resistance to shear

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Other Fluids

Drill-in fluids• Designed to drill into and through

productive zones.

• Formulated to have;– Very low solids

– Limited fluid loss

– Acidizable components

– Usually water-based with a polymer viscosifier

– Good flow back characteristics of filter cake

• Displace the mud system currently in use and are only used for drill-in.

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Completion Fluids• Contacts a producing formation after the well

is drilled.– Perforating

– Gravel packing

– Pay-zone drilling or underreaming

– Casing repair

– Zone-sensitive operations

– Chemical treatments

– Cleanout of sand and foreign objects,

– Well killing

– Tubing and hardware replacement

Packer Fluids

• Fluid placed in the tubing annulus.

• Purpose– Inhibit Corrosion and other production chemistry and

temperature issues.

– High enough density to assist in controlling wellbore pressure.

– Low enough density to prevent a differential packer failure at late stages of production.

• Usually a salt based solution.