12. Introduction to Drilling Fluids PDF

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Introduction to Drilling Fluids

Circulating Syst System: em: Sur Surface face

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Mud handling syst system em

Bourgoyne,etal.

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Functions of Drilling/Completion Fluids 1) 2) 3) 4) 5) 6) 7)

Control formation pressures. Remove cuttings from the well. Suspend and release cuttings. Seal permeable formations. Maintain wellbore stability. Minimize reservoir damage. Cool, lubricate, and support the bit and drilling assembly.

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Functions of Drilling/Completion Fluids

8) Transmit hydraulic energy to tools and bit. 9) Ensure adequate formation evaluation. 10) Control corrosion. 11) Facilitate cementing and completion. 12) Minimize impact on the environment

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Drilling Mud’s Beginning • Spindletop – Drilling encountered “quick sand” – very permeable, low stability formation – Could not drill ahead – Cpt. Anthony Lucas – engineer – Curt Hamill – driller

• Herded cattle through a long shallow pit – Muddied up water with clay – Lost circulation zone “healed”

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Objectiv Objectives es of Monit Monitoring oring Fluids • • • •

Establish a baseline or trend Identify potential hole problems & causes Solve problems through drilling fluid properties Ideally PREVENT hole problems from starting

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Introduction to Drilling Fluids Part 2

Basic Mud Properties: MW • Mud weight (MW) is the density of the drilling fluid • Measured in: – – – –

Lb/gal (ppg) Lb/cubic ft SG Pressure gradient (psi/ft)

• Measured with mud balance

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Basic Mud Properties: MW Equiv Equiva alent Density Concept • Equivalent mud weight is the total pressure imposed at a given depth expressed in ppg equivalent – I.e. - If you had a gauge at a given depth that read in lb/gal (ppg), what would it say?

• EMW = Pressure/ (0.052 x TVD) • For example: For 5946 psi at 10,000’: 5946/ (0.052 x 10000) = 11.43 ppg

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Fu Fun nnel Viscosity • • • • •

Quick test of viscosity Run by rig crew Measured in sec/quart Water is 28 sec/quart What does it really mean? Marsh Funnel

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Shear Stress & Shear Rat Rate e • Shear Stress: – Force required to sustain the shear rate – Alternatively: internal resistance of a fluid to flow at a given shear rate.

• Shear Rate: – Function of the fluid velocity (and therefore flow rate).

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Rheological Models • In drilling fluids, the flow behavior of the fluid must be described using rheological models and equations before hydraulic equations can be applied. • Models are created which describe the relationship between shear stress and shear rate Harold Vance Department of Petroleum Engineering

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Fluid Models • • • •

Newtonian Model Bingham Plastic Model Power Law Model Herschel-Bulkley Model (Current API recommended model)

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Rheological Models

Herschel‐ Bulkley

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Newt Newtonian onian Model • Shear Stress, , is proportional to the Shear Rate,  • Plot intersects at the origin

 

–  –  = Viscosity, centipoise = 300 reading

300 rpm 

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Bingham Plastic Model • Shear Stress, , is proportional to the Shear Rate,  • Plot intersects at the Yield Point (not 0) – py – p = PV – y = YP

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Pow owe er La Law w Model

• Shear Stress, , is a non-linear function of the Shear Rate,  • Plot intersects at the origin • Described with variables K, n – K is a measure of the thickness of the fluid – n is a measure of the deviation from Newtonian fluid behavior.

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Modif Modified ied P Po ower Law or HerschelBulkle Bulkleyy • Shear Stress, , is a non-linear function of the Shear Rate,  • Plot does NOT intersect at the origin

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Viscosity • • • • • • •

Funnel Viscosity – Marsh Funnel Apparent Viscosity Effective Viscosity Plastic Viscosity Yield Point Low-shear viscosity and Low-shear-rate viscosity Gel Strengths

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What Rheology Measurements Mean

bob

A “bob” is immersed in mud in a cylinder. The cylinder can be rotated at different speeds. The torque the fluid applies to the bob when the cylinder is rotated provides an indication of the resistance of the fluid to movement at at different “shear rates” Fann 286TM Rheometer Harold Vance Department of Petroleum Engineering

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Rot Rota ati tio ona nall Visc sco ometer

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Gel Strengths • Most drilling muds are designed to be thixotropic (shear-thinning). – Therefore we need a measurement of the static behavior

• Measure the gel structure that develops when the mud is not flowing. • Shows fluid’s ability to suspend solids, surge and swab issues, pump startup pressures • Maximum shear stress at 3 RPM – After mud is static for a specified amount of time (10 sec and 10 minute are the most common).

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Gel Strengths

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Filt Filter er Press – Filter cake thickness – Filter cake consistency – Fluid loss

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Diagnostic ttests ests • pH Determination • Chemical Analysis - Test for: – Chlorides: salt content – Hardness: Ca, Mg, and Fe ions

• Alkalinity - Pf, Pm, Mm, Mf – Designed to establish the concentration of hydroxyl, bicarbonate, and carbonate ions in the aqueous phase of the mud.

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Diagnostic tte ests: Solids Analysis • Mud Retort: volume fraction of oil, water, and solids in mud • Sand content • MBT (CEC of clays): volume fraction of low gravity solids

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Diagnostic tte ests: Solids Analysis • Two primary types: – HGS (2.6 SG and higher) • Barite • Hematite • Sand

– LGS (2.6 SG and lower) • Drill solids • Clay

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LGS solids over time

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Desander

Rigsit Rigsite e solids contro controll can make or break a w well… ell… Shaleshaker Desilter

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Composition • Continuous Phase – Flows – Transports

• Discontinuous Phase – Non-flowing – Transported

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Phase Example: WBM

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Wat ate er based muds • Water is the basic component • Clays are added for viscosity – Yield of clay is defined as the number of bbls of mud that can be produced using 1 ton of clay if the mud has an apparent viscosity of 15 cp at 600 rpm.

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Wat ate er based muds • Wyoming bentonite is the most common used in fresh water muds and is considered high yield clay - mostly sodium montmorillonite.

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Wat ate er based muds • Barium sulfate - barite is most common solid added to muds to increase density. • Hematite (iron ore) is sometimes used also

CourtesyAESDrillingFluids

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Inhibitiv Inhibitive ew wate ate aterr based muds • A mud in which the ability of active clays to hydrate has been reduced greatly. • Used to prevent drilled clays from disintegrating into very small particle and entering the mud. • Used to stabilize high clay content formations • Created with addition of calcium, lignosulfonate or salt

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Oil based muds (Ak (Aka a NAF) • Continuous phase is composed of diesel or mineral oil. • Emulsifiers are added to prevent water droplets from coalescing and settling out of the mud • Water droplets are used to build viscosity and for filtrate control, as is asphalt, polymers, etc

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Mud and drilling success Thesuccessofawellisdirectlydependenton thequalityofbothdrillingfluiddesignand implementation.Failuretodoeitherproperly resultsinalmostguaranteeddrillingproblems and/orcostincreases.

Harold Vance Department of Petroleum Engineering

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