MI_Functions of Drilling Fluid

Functions of Drilling Functions of Drilling FluidsFluids

Functions of a Drilling FluidFunctions of a Drilling Fluid

Hole CleaningHole Cleaning

Pressure ControlPressure Control

Suspend SolidsSuspend Solids

Minimize Formation DamageMinimize Formation Damage

Isolate Fluids from FormationIsolate Fluids from Formation

Cooling and LubricationCooling and Lubrication

Functions of a Drilling Fluid Functions of a Drilling Fluid cont’ dcont’ d

Power Downhole ToolsPower Downhole Tools

EnvironmentEnvironment

Maximum Hole InformationMaximum Hole Information

CorrosionCorrosion

Support Part of DSSupport Part of DS

CostCost

Choice of Drilling FluidChoice of Drilling Fluid

Cost Cost


SafetySafety

SuitabilitySuitabilityInhibitionInhibitionRheologyRheologyFluid LossFluid LossTemperatureTemperature

Availability

Storage

Drilling Fluid SystemsDrilling Fluid Systems

Types of Systems:Types of Systems:

Spud Spud MudsMuds : : used to start the wellused to start the wellDrilling Fluids : Drilling Fluids : used to drill the wellused to drill the well

•• drill to top of the reservoirdrill to top of the reservoir•• drill through the reservoirdrill through the reservoir

Completion Fluids :Completion Fluids : used to complete the wellused to complete the well

Top Hole Drilling FluidsTop Hole Drilling Fluids

Requirements:Requirements:Fast drilling Fast drilling -- large hole size, 16” / 17 1/2” large hole size, 16” / 17 1/2” Young formation Young formation -- reactive or unconsolidatedreactive or unconsolidatedLow annular velocities Low annular velocities -- need need high pump rateshigh pump rates (1000 gpm)(1000 gpm)SCE may have difficulty in handling the flow, so use dump & diluSCE may have difficulty in handling the flow, so use dump & dilute method te method with with WBM’s WBM’s -- cheap system.cheap system.More problems with More problems with OBM’sOBM’s

–– reduce pump rates to avoid losses. reduce pump rates to avoid losses. –– fit coarser screens. fit coarser screens. –– need good shakers and centrifugesneed good shakers and centrifuges

Water Base Mud SystemsWater Base Mud SystemsCheap basic systems:Cheap basic systems:

Gel/Gel/Cmc MudsCmc MudsLime Lime MudsMudsGyp Gyp MudsMudsNonNon--Dispersed Polymer Dispersed Polymer mudsmuds

Expensive Inhibited systems:KCl/Polymer MudsHigh Temp MudsSpecial Mud Sytems>>QuadrillQuadrill>>VisplexVisplex>>SilicatesSilicates>>FormatesFormates

Advantages of OBMAdvantages of OBMGood Good penetration ratespenetration rates and prolonged bit life. (fewer trips, less bit balling)and prolonged bit life. (fewer trips, less bit balling)

Excellent Excellent inhibition inhibition of reactive of reactive shalesshales and clays.and clays.

Thermally Thermally stablestable..

Low damage factors to oil reservoir.Low damage factors to oil reservoir.

High High lubricitylubricity, low torque., low torque.

Good Good corrosioncorrosion protection, particularly for H2S.protection, particularly for H2S.

Gauge hole.Gauge hole.

Good Good fluid lossfluid loss control .control .

Less chance of stuck pipe.Less chance of stuck pipe.

High High solidssolids tolerance.tolerance.

Salt sectionsSalt sections not dissolved.not dissolved.

Good coring fluid.Good coring fluid.

Disadvantages of OBMDisadvantages of OBMHigh initial well High initial well Cost.Cost.Some electric logs cannot be run.Some electric logs cannot be run.Can Can damage gas reservoirsdamage gas reservoirs due to water or emulsion blocks.due to water or emulsion blocks.Lost circulationLost circulation is expensive.is expensive.Greater chance of a poor cement bond.Greater chance of a poor cement bond.Detection of Detection of gas kicksgas kicks difficult due to solubility of gas in oil.difficult due to solubility of gas in oil.Logistic problemsLogistic problems (supply boats, storage tanks).(supply boats, storage tanks).Messy working environment., potential fire hazard can produce Messy working environment., potential fire hazard can produce carcinogenic fumescarcinogenic fumesDifficult to detect crude oil.Difficult to detect crude oil.Hole cleaning may be a problem. At high temperatures the viscosiHole cleaning may be a problem. At high temperatures the viscosity of ty of OBM is low..OBM is low..Fire Hazard.Fire Hazard.Environmental Environmental pollutionpollution -- fumesfumes

Oil Base Mud SystemsOil Base Mud Systems

Invert Oil Emulsion Invert Oil Emulsion mudsmuds: : INTERDRILL NT,INTERDRILL NT,INTERDRILL LORINTERDRILL LOR

RealtivelyRealtively cheap, recheap, re--usable, better usable, better enviromentalenviromental footprintfootprint

100% Oil 100% Oil MudsMuds: : TRUDRILLTRUDRILLbest inhibition, good for depleted gas reservoirs, poor best inhibition, good for depleted gas reservoirs, poor environmental impactenvironmental impact

Synthetic Oil Base Synthetic Oil Base mudsmuds: : ULTIDRILLULTIDRILLBest environmental footprint, can be used exactly as INTERDRILL Best environmental footprint, can be used exactly as INTERDRILL system.system.

Introduction to Drilling FluidsIntroduction to Drilling Fluids





Isolate Fluid From FormationIsolate Fluid From Formation


Remove Cuttings From the Remove Cuttings From the Well BoreWell BoreThe most important parameter is the The most important parameter is the Annular Velocity (A.V.)Annular Velocity (A.V.)

Where possible the annular velocity Where possible the annular velocity should be 100 ft/min, higher in deviated should be 100 ft/min, higher in deviated holes.holes.In large hole sections the A.V. can be as In large hole sections the A.V. can be as low as 20 ft/min. low as 20 ft/min.

If the A.V. is insufficient to clean the If the A.V. is insufficient to clean the hole the hole the viscosityviscosity must be increasedmust be increased

For top hole high viscosities must be For top hole high viscosities must be usedused

Cuttings removal is harder in deviated Cuttings removal is harder in deviated and horizontal holes as the vertical and horizontal holes as the vertical component of the mud is reduced.component of the mud is reduced.

A.V.(ft/min)

= Pump rate (bbls/min)Annular vol (bbls/ft)

Slip Velocity (ft/min)

=Cuttings velocity - A.V.






Isolate Fluid from FormationIsolate Fluid from Formation


Balancing SubBalancing Sub--Surface PressuresSurface PressuresThe pore pressure depends on:The pore pressure depends on:

The density of the overlying rockThe density of the overlying rockThe pressure of the interstitial fluidThe pressure of the interstitial fluidWhether the rock is self supporting or is supported Whether the rock is self supporting or is supported by the fluid.by the fluid.Tectonic activityTectonic activitySurface terrainSurface terrain

If the fluid hydrostatic pressure does If the fluid hydrostatic pressure does notnot balance the pore balance the pore pressure the following may occur:pressure the following may occur:

Influxes of formation fluid into the wellboreInfluxes of formation fluid into the wellboreLost circulationLost circulationHole InstabilityHole InstabilityStuck pipeStuck pipe

Balancing SubBalancing Sub--Surface PressuresSurface Pressures

The pressure balancing the The pressure balancing the formation pressure is composed formation pressure is composed from the hydrostatic pressure under from the hydrostatic pressure under static conditions:static conditions:

P = Depth (ft) x Density (ppg) x 0.052P = Depth (ft) x Density (ppg) x 0.052

Under circulating conditions the Under circulating conditions the effective pressure is increased by effective pressure is increased by the pumping pressure. This forms the pumping pressure. This forms the Equivalent Circulating density the Equivalent Circulating density (ECD):(ECD):

ECD = Density (ppg) + ECD = Density (ppg) + Ann Press LossAnn Press LossDepth x 0.052Depth x 0.052

Hydrostatic Pressure (psi)= Height (ft) x Density(ppg) x 0.052

PorePressure(Not normally known)








Suspension of Solids Suspension of Solids Whenever the pumps are switched off solids will start to Whenever the pumps are switched off solids will start to settle.settle. This can result in:This can result in:

Bridging off of the wellboreBridging off of the wellboreStuck pipeStuck pipeHole fillHole fillLoss of HydrostaticLoss of Hydrostatic

A A gel structuregel structure is required to suspend the cuttings under is required to suspend the cuttings under zero shear conditions:zero shear conditions:

The gel structure is caused by time dependant attractive The gel structure is caused by time dependant attractive forces which develop in the fluid. forces which develop in the fluid. The longer the fluid is static the stronger these forces The longer the fluid is static the stronger these forces becomebecomeThe gel structure should be The gel structure should be easily brokeneasily brokenThe gel properties are especially important for The gel properties are especially important for deviateddeviated and and horizontalhorizontal wells as the distance solids have to settle is very wells as the distance solids have to settle is very smallsmall




Suspension of SolidsSuspension of Solids




Minimize Formation DamageMinimize Formation DamageDamage to the formation while drilling to the Damage to the formation while drilling to the reservoir:reservoir:

Formation swelling (Normally clay and Salt formations)Formation swelling (Normally clay and Salt formations)Washouts (Clay and Salt formations or any Washouts (Clay and Salt formations or any unconsolidated formation)unconsolidated formation)

This can result in:This can result in:–– Difficult directional controlDifficult directional control–– Poor zonal isolation Poor zonal isolation –– Excess mud and cement costsExcess mud and cement costs–– Poor Hole CleaningPoor Hole Cleaning–– Stuck PipeStuck Pipe–– Difficult fishing jobsDifficult fishing jobs

The Need For InhibitionThe Need For Inhibition

Minimize Formation DamageMinimize Formation DamageDamage to the reservoir will result in loss of production or Damage to the reservoir will result in loss of production or the need for remedial treatment. This can result from:the need for remedial treatment. This can result from:

Solids blocking reservoir poresSolids blocking reservoir poresEmulsion droplets blocking reservoir poresEmulsion droplets blocking reservoir poresSwelling claysSwelling claysIons from the formation and drilling fluid forming Ions from the formation and drilling fluid forming insoluble saltsinsoluble salts

Damage by Drilling MudsDamage by Drilling MudsMud damage can occur by:Mud damage can occur by:

Physical reduction of pore / pore throat sizePhysical reduction of pore / pore throat size

Mud solids invasionMud solids invasionFormation fines migrationFormation fines migrationClay swellingClay swellingAdsorption / precipitation of mud polymersAdsorption / precipitation of mud polymersReaction and precipitation (scale)Reaction and precipitation (scale)

Relative permeability reductionRelative permeability reductionWettabilityWettability changechangeEmulsion formationEmulsion formationFluid saturation change/fluid blockingFluid saturation change/fluid blocking

Formation Fines Migration Formation Fines Migration

Conglomeration of loose Conglomeration of loose material around pore throatmaterial around pore throat

KaoliniteKaolinite stack almost stack almost completely disaggregatedcompletely disaggregated

Depth of InvasionDepth of Invasion

Mud composition & reservoir characteristics influence the Mud composition & reservoir characteristics influence the degreedegree of damageof damage

DepthDepth of damage is influenced byof damage is influenced byMud formulationMud formulationTime in open holeTime in open holeMud overbalanceMud overbalance

Depth of damage is often less than the total depth of invasion dDepth of damage is often less than the total depth of invasion due ue to depletion of damaging speciesto depletion of damaging species








Isolate the Fluid From the Isolate the Fluid From the FormationFormation

The differential pressure forces fluid into the wellbore, The differential pressure forces fluid into the wellbore, resulting in whole mud or filtrate entering the formation. resulting in whole mud or filtrate entering the formation. Either, or both, of these is undesirable because:Either, or both, of these is undesirable because:

The loss of whole mud into the wellbore is The loss of whole mud into the wellbore is expensive expensive and damagingand damaging

The loss of filtrate into the wellbore may cause The loss of filtrate into the wellbore may cause formation damageformation damage

Isolate the Fluid From the Isolate the Fluid From the FormationFormation

The flow of fluid is affected by the formation of a filter cakeThe flow of fluid is affected by the formation of a filter cake

The filter The filter cake cake reducesreduces the flow of fluid into the formation.the flow of fluid into the formation.

Special additives are added to improve the cake quality:Special additives are added to improve the cake quality:–– Bridging materialBridging material–– Plate like materialPlate like material–– Plugging materialPlugging material

The filter cake should be The filter cake should be thin with a low permeabilitythin with a low permeabilityThis avoids reducing the effective hole diameterThis avoids reducing the effective hole diameterIt also reduces the chance of differential stickingIt also reduces the chance of differential stickingMinimises filtrate penetration into formationMinimises filtrate penetration into formation








Cooling and LubricationCooling and LubricationThe drilling fluid removes heat from the bit which is then The drilling fluid removes heat from the bit which is then dispersed at the surfacedispersed at the surface

Fluid formulations are not changed to improve this Fluid formulations are not changed to improve this functionfunctionVery occasionally the temperature of the fluid exceeds Very occasionally the temperature of the fluid exceeds the flash point. In this case it is necessary to improve the flash point. In this case it is necessary to improve surface coolingsurface cooling

Extra lubrication may be required between the drill string Extra lubrication may be required between the drill string and the casing or wellbore, especially in directional wellsand the casing or wellbore, especially in directional wells

Liquid additives are used, or Oil based mudLiquid additives are used, or Oil based mudSolid additives are sometimes used such as glass Solid additives are sometimes used such as glass beads, plastic beads, graphite or nut plugbeads, plastic beads, graphite or nut plugDrill pipe rubbers are sometimes added to reduce wear Drill pipe rubbers are sometimes added to reduce wear between the casing and drill pipebetween the casing and drill pipe

Other ConsiderationsOther Considerations




CorrosionCorrosion

Support Part of the DSSupport Part of the DS

CostCost

Other FunctionsOther Functions

Power Downhole motorsPower Downhole motors

Turbines to turn the bit or power MWD / LWD Turbines to turn the bit or power MWD / LWD equipmentequipment

Transfer information from measurement equipment Transfer information from measurement equipment to the surfaceto the surface

This is done with a pressure pulseThis is done with a pressure pulse





CorrosionCorrosion


CostCost

Environmental Impact Environmental Impact -- OffshoreOffshore

AlgaeAlgae((SkeletonemaSkeletonema sp.)sp.)

SedimentSediment ReworkerReworker((CorophiumCorophium sp.)sp.)

ZooplanktonZooplankton((AcartiaAcartia sp.)sp.)

ManMan

ShrimpShrimp((MysidopsisMysidopsis spsp..))

MusselMussel((MytilusMytilus sp.)sp.)

FishFish((ScophthalamusScophthalamus sp.)sp.)

BioaccumulationBioaccumulation

TaintTaint

DischargeDischarge

BiodegradationBiodegradation

Environmental Impact Environmental Impact -- LandLand

Drilled Drilled CuttingsCuttings

LiquidLiquidWasteWaste

DischargeDischarge-- ChloridesChlorides-- Heavy metalsHeavy metals-- pHpH-- TDSTDS-- BOD, COD BOD, COD -- ClarityClarity

DisposalDisposal-- ToxicityToxicity-- ChloridesChlorides-- Heavy metalsHeavy metals-- Oil contentOil content-- Solids contentSolids content

TreatTreat

RecycleRecycle-- Solids contentSolids content





CorrosionCorrosion


CostCost

Secure Maximum Hole InformationSecure Maximum Hole Information

The operator will always require the following The operator will always require the following information:information:

Rock type being drilledRock type being drilledThe cuttings should not dissolve or disintegrateThe cuttings should not dissolve or disintegrate

Analyses of gasesAnalyses of gasesThe gases should separate easily from the mudThe gases should separate easily from the mud

The fluid should have a defined resistivityThe fluid should have a defined resistivityFormation resistivity measurements need to be madeFormation resistivity measurements need to be made





CorrosionCorrosion


CostCost

Control CorrosionControl Corrosion

The fluid should be The fluid should be non corrosivenon corrosive to the:to the:

Drill stringDrill string

CasingCasing

Surface equipmentSurface equipment

Corrosion can lead to:Corrosion can lead to:

Wash outsWash outs

Twist offsTwist offs

Pump failurePump failure

Surface LeaksSurface Leaks

&

Corrosion leads to loss of





CorrosionCorrosion


CostCost

Support Part of the Tubular Support Part of the Tubular WeightWeight

Aids in supporting part of the weight of the drill string and Aids in supporting part of the weight of the drill string and casingcasing

The degree of buoyancy is directly proportional to the The degree of buoyancy is directly proportional to the density of the fluid.density of the fluid.

The fluid density is The fluid density is never never changed to changed to increase the buoyancyincrease the buoyancy





CorrosionCorrosion


CostCost

5 10

Maximize Penetration RatesMaximize Penetration RatesThe fluid properties greatly influence penetration rates by:The fluid properties greatly influence penetration rates by:

Removing cuttings from below the bit and wellboreRemoving cuttings from below the bit and wellboreReducing the cushioning effect of solids between the bit Reducing the cushioning effect of solids between the bit teeth and the formationteeth and the formationReducing the hydrostatic differentialReducing the hydrostatic differentialIncreasing the jet velocityIncreasing the jet velocity

Solids Content (%volume)

Bits

Rig days

Ft/Bit

Rig days, Bits,Ft/Bit.

Well CostWell Cost

WellWellCostCost

($)($)

== DailyDailyCostCost

(days x $/day)(days x $/day)

++ FootageFootageCostCost

(ft x $/ft)(ft x $/ft)

++ Once off andOnce off andOther CostsOther Costs

($)($)

DFSDFSCostCost($)

FluidsFluidsEngineeringEngineering(days x $/day)

DrillingDrillingFluidFluid

(ft x $/ft)

CompletionCompletionFluidFluid

($)($)(days x $/day) (ft x $/ft)

–– DFS direct cost is relatively small (5 to 10% of well cost)DFS direct cost is relatively small (5 to 10% of well cost)–– Greatest savings achieved by improving Drilling EfficiencyGreatest savings achieved by improving Drilling Efficiency

($)== ++ ++

Key Drilling Fluid IssuesKey Drilling Fluid Issues

Lubricatethe drill string

Controlformationpressure

Removedrilling cuttings

from the hole

Minimiseloss of fluid

to the formationSuspend barite

under static anddynamic conditions

Maintainborehole stability

Provide hydraulichorse power

to the bit

Building blocksBuilding blocks

There are two basic building units from which all the different There are two basic building units from which all the different clay minerals are constructed :clay minerals are constructed :

The Octahedral LayerThe Octahedral Layer

This consists of two sheets of closely packedThis consists of two sheets of closely packed oxygensoxygens or or hydroxides in whichhydroxides in which aluminiumaluminium (Gibbsite), iron or magnesium (Gibbsite), iron or magnesium ((brucitebrucite) ions are embedded.) ions are embedded.


The tetrahedral LayerThe tetrahedral Layer

In each tetrahedral unit, a silicon atom is located in the centrIn each tetrahedral unit, a silicon atom is located in the centre of e of the tetrahedron, equidistant from the four oxygen atoms.the tetrahedron, equidistant from the four oxygen atoms.

Note that whenNote that when viewdviewd from above this gives a hexagonal opening.from above this gives a hexagonal opening.

(A) (B)


Tetrahedral andTetrahedral and octrahedraloctrahedral sheets may combine in sheets may combine in different combinations to form over 26 different clay different combinations to form over 26 different clay mineralsminerals

The type of clay mineral will depend on The type of clay mineral will depend on the ratios of the silica to octahedral layer .the ratios of the silica to octahedral layer .The nature of ionsThe nature of ions inbededinbeded in these structures.in these structures.Other ions associated with the structures. Other ions associated with the structures.

Shale ShakerShale Shaker

The Shale Shaker performance determines the The Shale Shaker performance determines the total efficiency of the complete solids control total efficiency of the complete solids control package.package.

Poor performance here cannot be rectified Poor performance here cannot be rectified laterlater !!

Overhead Manifold DesignOverhead Manifold Design

Screen BlindingScreen Blinding• Blinding can be due to

solids jamming the openings.

• The usual remedy is to remove the screen and jet wash it from the rear of the screen.

• Fitting finer screens may allow the solids to pass over the openings, if not then the only answer is to fit coarser screens

Screen Plugging

DegasserDegasserGas cut mud is :Gas cut mud is :

DamagingDamaging to rig equipment,to rig equipment,A potential A potential well controlwell control problem,problem,LethalLethal if Sour or Flammable.if Sour or Flammable.

Common with high viscosity / heavy Common with high viscosity / heavy mudsmuds..Centrifugal pumps, Centrifugal pumps, hydrocycloneshydrocyclones and the rig pumps loose and the rig pumps loose efficiency if the mud is gas cut.efficiency if the mud is gas cut.The degasser should be installed between the sand trap The degasser should be installed between the sand trap and the first and the first hydrocycloneshydrocyclones..

Degasser

Operation of a degasser

Mud Input

HydrocyclonesHydrocyclones

A general view of a Desander and Desilter

Mud CleanerMud Cleaner

The purpose of the mudThe purpose of the mud--cleaner is to screen the cleaner is to screen the underflow of the underflow of the hydrocycloneshydrocyclones in order to:in order to:

Reclaim base liquid.Reclaim base liquid.Reclaim discarded Reclaim discarded barytesbarytes..Produce relatively dry cuttings.Produce relatively dry cuttings.

MudcleanerMudcleaner

Note that a Mudcleaner is basically a combination of a hydrocyclone and a shale shaker.

Hydrocyclone use has diminished rapidly with the introduction of better shakers and centrifuges.

CentrifugesCentrifuges

Centrifuges are usually the last piece of solids control Centrifuges are usually the last piece of solids control equipment. equipment. They process about 10% of the flow. They process about 10% of the flow.

The capacity for separation is approx. 95% for 20 micron and The capacity for separation is approx. 95% for 20 micron and 50% of 10 micron particles. 50% of 10 micron particles.

Due to the high G forces, ultraDue to the high G forces, ultra--fine particles (as small as 3 fine particles (as small as 3 microns) can be removed form the mud.microns) can be removed form the mud.

CentrifugesCentrifuges

Solids Solids discharge withabsorbed liquid only

Colloidal liquid discharge

Feed inlet

Colloidalliquid discharge

Pool level controlledby weir settings

Feed ports Beach

Gearbox

ApplicationsApplicationsThe centrifuge is used for the separation of solids and for reclThe centrifuge is used for the separation of solids and for reclaiming aiming fluid. It is extremely useful to remove ultrafluid. It is extremely useful to remove ultra--fine solids especially from fine solids especially from more expensive fluids such as more expensive fluids such as KClKCl--polymer mud or OBM. polymer mud or OBM.

The removal of The removal of ultrafineultrafine drilled solids (LGS) will enhance viscosity and drilled solids (LGS) will enhance viscosity and weight control without excessive dilutions being required. weight control without excessive dilutions being required.

In weighted In weighted mudsmuds the centrifuges can be useful to lower the mud weight the centrifuges can be useful to lower the mud weight by removing the weighting material (HGS) for the following reasoby removing the weighting material (HGS) for the following reasons:ns:

During a pressure differential stuck pipe situation.During a pressure differential stuck pipe situation.During lost circulationDuring lost circulationWhen the next hole section is scheduled to be drilled with lightWhen the next hole section is scheduled to be drilled with lighter er mud.mud.

Another application is the recovery of oil from oilAnother application is the recovery of oil from oil--contaminated cuttings. contaminated cuttings.

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MI_Functions of Drilling Fluid