1-Functions of the DF

Functions of the Functions of the Drilling FluidsDrilling Fluids

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

Introduction to Drilling FluidsIntroduction to Drilling Fluids





Isolate Fluid From FormationIsolate Fluid From Formation


Remove Cuttings From the Remove Cuttings From the WellboreWellbore

The 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 increased must 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 Sub-Surface PressuresBalancing Sub-Surface Pressures The pore pressure depends on:The pore pressure depends on:

The density of the overlying rockThe density of the overlying rock The pressure of the interstitial fluidThe pressure of the interstitial fluid Whether the rock is self supporting or is supported by the Whether the rock is self supporting or is supported by the

fluid.fluid. Tectonic activityTectonic activity Surface 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 wellbore Lost circulationLost circulation Hole InstabilityHole Instability Stuck pipeStuck pipe

Balancing Sub-Surface PressuresBalancing Sub-Surface Pressures

The pressure balancing the formation The pressure balancing the formation pressure is composed from the pressure is composed from the hydrostatic pressure under static hydrostatic pressure under static conditions: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 the effective pressure is increased by the pumping pressure. This forms the pumping pressure. This forms the Equivalent Circulating density (ECD):Equivalent Circulating density (ECD): ECD = Density (ppg) + ECD = Density (ppg) + Ann Press LossAnn Press Loss

Depth x 0.052 Depth 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 wellbore Stuck pipeStuck pipe Hole fillHole fill Loss of HydrostaticLoss of Hydrostatic

A A gel structuregel structure is required to suspend the cuttings under zero is required to suspend the cuttings under zero shear conditions:shear conditions: The gel structure is caused by time dependant attractive forces The gel structure is caused by time dependant attractive forces

which develop in the fluid. which develop in the fluid. The longer the fluid is static the stronger these forces becomeThe longer the fluid is static the stronger these forces become The gel structure should be The gel structure should be easily brokeneasily broken The 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 small wells as the distance solids have to settle is very small




Suspension of SolidsSuspension of Solids




Minimize Formation DamageMinimize Formation Damage Damage 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 Damage Damage 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 pores Emulsion droplets blocking reservoir poresEmulsion droplets blocking reservoir pores Swelling claysSwelling clays Ions from the formation and drilling fluid forming Ions from the formation and drilling fluid forming

insoluble saltsinsoluble salts

Damage by Drilling MudsDamage by Drilling Muds

Mud damage can occur by:Mud damage can occur by:

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

Relative permeability reductionRelative permeability reduction

Damage by Pore / Pore Throat Damage by Pore / Pore Throat Size ReductionSize Reduction

Mud solids invasionMud solids invasion Formation fines migrationFormation fines migration Clay swellingClay swelling Adsorption / precipitation of mud polymersAdsorption / precipitation of mud polymers Reaction and precipitation (scale)Reaction and precipitation (scale) Wax formation (paraffin, Asphaltene)Wax formation (paraffin, Asphaltene) Sludge formation (e.g. by reaction of crude & mud acid)Sludge formation (e.g. by reaction of crude & mud acid) Stress-induced permeability changeStress-induced permeability change Perforation pluggingPerforation plugging

Bold type denotes mud-induced damage mechanismsBold type denotes mud-induced damage mechanisms

Formation Fines Migration Formation Fines Migration

Kaolinite stack almost Kaolinite stack almost completely desegregatedcompletely desegregated

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

Damage Due to Relative Permeability Damage Due to Relative Permeability ReductionReduction

Wettability changeWettability change Emulsion formationEmulsion formation Fluid saturation change/fluid blockingFluid saturation change/fluid blocking Water coningWater coning

Gas breakoutGas breakout

Condensate bankingCondensate banking

Bold type denotes mud induced damage mechanismsBold type denotes mud induced damage mechanisms

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 by of damage is influenced by

Mud formulationMud formulation Time in open holeTime in open hole Mud overbalanceMud overbalance

Depth of damage is often less than the total depth of invasion due Depth of damage is often less than the total depth of invasion due 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 cake The filter cake reduces reduces 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 permeability This avoids reducing the effective hole diameterThis avoids reducing the effective hole diameter It also reduces the chance of differential stickingIt also reduces the chance of differential sticking

Cooling and LubricationCooling and Lubrication The 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 functionFluid formulations are not changed to improve this function Very occasionally the temperature of the fluid exceeds the Very occasionally the temperature of the fluid exceeds the

flash point. In this case it is necessary to improve surface flash point. In this case it is necessary to improve surface coolingcooling

Extra lubrication may be required between the drill string and Extra lubrication may be required between the drill string and the casing or wellbore, especially in directional wellsthe casing or wellbore, especially in directional wells Liquid additives are used, or Oil based mudLiquid additives are used, or Oil based mud Solid additives are sometimes used such as glass beads, Solid additives are sometimes used such as glass beads,

plastic beads, graphite or nut plugplastic beads, graphite or nut plug Drill 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 to Transfer information from measurement equipment to the surfacethe surface

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