Drilling Engineering Fall 2012Prepared by: Tan NguyenDrilling Engineering PE 311Chapter 2: Drilling FluidsIntrodution to Drilling FluidsDrilling Engineering Fall 2012Prepared by: Tan NguyenThe principal functions of the drilling fluid are1. Subsurface pressure control 2. Cuttings removal and transport3. Suspension of solid particles4. Sealing of permeable formations5. Stabilizing the wellbore. !reventing formation damage". Cooling and lubricating the bit and drill string#.Transmitting h$draulic horsepower to the bit%.&acilitating the collection of formation data1'. !artial support of drill string and casing weights11. Controlling corrosion12. (ssisting in cementing and completionPrinipal Funtions o! Drilling FluidsDrilling Engineering Fall 2012Prepared by: Tan Nguyen( column of drilling fluid e)erts a h$drostatic pressure that* in field units* is e+ual to! , '.'52 ) ) T-.where ! / h$drostatic pressure of fluid column in wellbore* psi0 / mud weight in pounds per gallon 1ppg2T-. / True -ertical .epth* ft / during normal drilling operations* this corresponds to the height of the fluid column in the wellbore. Prinipal Funtions o! Drilling FluidsSubsurface pressure controlDrilling Engineering Fall 2012Prepared by: Tan NguyenCirculation of the drilling fluid causes cuttings to rise from the bottom of the hole to the surface. 3fficient cuttings removal re+uires circulating rates that are sufficient to overridetheforceofgravit$actinguponthecuttings.4therfactorsaffectingthe cuttingsremovalincludedrillingfluiddensit$andrheolog$*annularvelocit$*hole angle* and cuttings/slip velocit$.5n most cases* the rig h$draulics program provides for an annular velocit$ sufficient to result in a net upward movement of the cuttings. (nnular velocit$ is determined b$ the cross/sectional area of the annulus and the pump output. Prinipal Funtions o! Drilling FluidsCuttings 6emoval and TransportDrilling Engineering Fall 2012Prepared by: Tan Nguyen7hentherig8smudpumpsareshutdownandcirculationishalted1e.g.*during connections* trips or downtime2* cuttings that have not been removed from the hole mustbeheldinsuspension.4therwise*the$willfalltothebottom1or*inhighl$ deviatedwells*tothelowside2ofthehole.Therateoffallofaparticlethrougha column of drilling fluid depends on the densit$ of the particle and the fluid* the size of the particle* the viscosit$ of the fluid* and the thi)otropic 1gel/strength2 properties of the fluid. The controlled gelling of the fluid prevents the solid particles from settling* oratleastreducestheirrateoffall.9ighgelstrengthsalsore+uirehigherpump pressuretobrea:circulation.5nsomecases*itma$benecessar$tocirculatefor several hours before a trip in order to clean the hole of cuttings and to prevent fill in the bottom of the hole from occurring during a round trip.Prinipal Funtions o! Drilling FluidsSuspension of Solid !articles Drilling Engineering Fall 2012Prepared by: Tan Nguyen(s the drill bit penetrates a permeable formation* the li+uid portion of the drilling fluid filters into the formation and the solids form a relativel$ impermeable ;ca:e; on the boreholewall.The+ualit$ofthisfilterca:egovernstherateoffiltratelosstothe formation..rillingfluids$stemsshouldbedesignedtodepositathin*low permeabilit$filterca:eontheformationtolimittheinvasionofmudfiltrate.This improveswellborestabilit$andpreventsanumberofdrillingandproduction problems.!otentialproblemsrelatedtothic:filterca:eande)cessivefiltration includeentoniteisthebestbasematerialfromwhichtobuildatough*low/permeabilit$ filter ca:e. !ol$mers are also used for this purpose.Prinipal Funtions o! Drilling FluidsSealing of permeable formationDrilling Engineering Fall 2012Prepared by: Tan NguyenTheboreholewallsarenormall$competentimmediatel$afterthebitpenetratesa section. 7ellbore stabilit$ is a comple) balance of mechanical and chemical factors. Thechemicalcompositionandmudpropertiesmustcombinetoprovideastable wellboreuntilcasingcanberunandcemented.6egardlessofthechemical composition of the fluid and other factors* the weight of the mud must be within the necessar$ range to balance the mechanical forces acting on the wellbore. The other cause of borehole instabilit$ is a chemical reaction between the drilling fluid and the formations drilled. 5n most cases* this instabilit$ is a result of water absorption b$ the shale.5nhibitivefluids1calcium*sodium*potassium*andoil/basefluids2aidin preventing formation swelling* but even more important is the placement of a +ualit$ filter ca:e on the walls to :eep fluid invasion to a minimum.Prinipal Funtions o! Drilling FluidsStabilizing the 7ellboreDrilling Engineering Fall 2012Prepared by: Tan Nguyen(n$reductioninaproducingformation?snaturalporosit$orpermeabilit$is considered to be formation damage. 5f a large volume of drilling/fluid filtrate invades a formation* it ma$ damage the formation and hinder h$drocarbon production.There are several factors to consider when selecting a drilling fluid@A&luid compatibilit$ with the producing reservoirA!resence of h$dratable or swelling formation cla$sA&ractured formations AThepossiblereductionofpermeabilit$b$invasionofnonacidsolublematerials into the formationPrinipal Funtions o! Drilling Fluids!reventing &ormation .amageDrilling Engineering Fall 2012Prepared by: Tan Nguyen&riction at the bit* and between the drillstring and wellbore* generates a considerable amountofheat.Thecirculatingdrillingfluidtransportstheheatawa$fromthese frictional sites b$ absorbing it into the li+uid phase of the fluid and carr$ing it awa$.The la$ing down of a thin wall of ;mud ca:e; on the wellbore aids in reducing tor+ue anddrag.Theamountoflubricationprovidedb$adrillingfluidvarieswidel$and depends on the t$pe and +uantit$ of drill solids and weight material* and also on the chemicalcompositionofthes$stemase)pressedintermsofp9*salinit$and hardness.5ndicationsofpoorlubricationarehightor+ueanddrag*abnormalwear* and heat chec:ing of drillstring components.Prinipal Funtions o! Drilling FluidsCooling and Bubricating the >itDrilling Engineering Fall 2012Prepared by: Tan Nguyen.uring circulation* the rate of fluid flow should be regulated so that the mud pumps delivertheoptimalamountofh$draulicenerg$tocleantheholeaheadofthebit. 9$draulicenerg$alsoprovidespowerformudmotorstorotatethebitandfor Ceasurement7hile.rilling1C7.2andBogging7hile.rilling1B7.2tools. 9$draulicsprogramsarebasedonsizingthebitnozzles toma)imizetheh$draulic horsepower or impact force imparted to the bottom of the well. Prinipal Funtions o! Drilling FluidsTransmitting 9$draulic 9orsepower to the >itDrilling Engineering Fall 2012Prepared by: Tan NguyenThedrillingfluidprogramandformationevaluationprogramareclosel$related. (s drilling proceeds* for e)ample* mud loggers monitor mud returns and drilled cuttings forsignsofoilandgas.The$e)aminethecuttingsformineralcomposition* paleontolog$andvisualsignsofh$drocarbons.Thisinformationisrecordedona mud log that shows litholog$* penetration rate* gas detection and oil/stained cuttings* plus other important geological and drilling parameters. Ceasurement/7hile/.rilling 1C7.2 and Bogging/7hile/.rilling 1B7.2 procedures are li:ewise influenced b$ the mud program* as is the selection of wireline logging tools for post/drilling evaluation.Prinipal Funtions o! Drilling Fluids&acilitating the Collection of &ormation .ataDrilling Engineering Fall 2012Prepared by: Tan Nguyen7ith average well depths increasing* the weight supported b$ the surface wellhead e+uipmentisbecominganincreasingl$crucialfactorindrilling.>othdrillpipeand casingarebuo$edb$aforcee+ualtotheweightofthedrillingfluidthatthe$ displace.7henthedrillingfluiddensit$isincreased*thetotalweightsupportedb$ the surface e+uipment is reduced considerabl$.Prinipal Funtions o! Drilling Fluids!artial support of .rill String and Casing 7eightsDrilling Engineering Fall 2012Prepared by: Tan NguyenThedrillingfluidmustproduceawellboreintowhichcasingcanberunand cementedeffectivel$*andwhichdoesnotimpedecompletionoperations..uring casingruns*themudmustremainfluidandminimizepressuresurgessothat fracture/inducedlostcirculationdoesnotoccur.Themudshouldhaveathin*slic: filter ca:e. To cement casing properl$* the mud must be completel$ displaced b$ the spacers* flushes and cement. 3ffective mud displacement re+uires that the hole be near/gaugeandthatthemudhavelowviscosit$andlow*non/progressivegel strengths.Completionoperationssuchasperforatingandgravelpac:ingalso re+uire a near/gauge wellbore and ma$ be affected b$ mud characteristicsPrinipal Funtions o! Drilling Fluids(ssistance in Cementing and CompletionDrilling Engineering Fall 2012Prepared by: Tan Nguyen-ariousmaterialsma$beaddedatthesurfacetochangeormodif$thecharacteristicsofthe mud. &or e)ample@ 1.7eighting agents 1usuall$ barite2 are added to increase the densit$ of the mud* which helps to control subsurface pressures and build the wallca:e. 2.-iscosif$ingagents1cla$s*pol$mers*andemulsifiedli+uids2areaddedtothic:enthemud and increase its hole/cleaning abilit$. 3..ispersantsordeflocculantsma$beaddedtothinthemud*whichhelpstoreducesurge* swab* and circulating/pressure problems. "ud IngredientsDrilling Engineering Fall 2012Prepared by: Tan Nguyen4. Cla$s*pol$mers*starches*dispersants*andasphalticmaterialsma$beaddedtoreduce filtration of the mud through the borehole wall. This reduces formation damage* differential stic:ing* and problems in log interpretation. 5. Saltsaresometimesaddedtoprotectdownholeformationsortoprotectthemudagainst future contamination* as well as to increase densit$. . 4thermudadditivesma$includelubricants*corrosioninhibitors*chemicalsthattieup calcium ions* and flocculants to aid in the removal of cuttings at the surface. ". Causticsodaisoftenaddedtoincreasethep9ofthemud*whichimprovesthe performance of dispersants and reduces corrosion. #. !reservatives*bactericides*emulsifiers*andtemperaturee)tendersma$allbeaddedto ma:e other additives wor: better."ud IngredientsDrilling Engineering Fall 2012Prepared by: Tan Nguyen( water/base fluid is one that uses water for the li+uid phase and commercial cla$s for viscosit$. The continuous phase ma$ be fresh water* brac:ish water* seawater* or concentrated brines containing an$ soluble salt. The commercial cla$s used ma$ be bentonite*attapulgite*sepiolite*orpol$mer.Theuseofothercomponentssuchas thinners*filtration/controladditives*lubricants*orinhibitingsaltsinformulatinga particulardrillingfluidisdeterminedb$thet$peofs$stemre+uiredtodrillthe formations safel$ and economicall$. Some of the maDor s$stems include fresh/water fluids*brac:ishorseawaterfluids*saturatedsaltfluids*inhibitedfluids*g$pfluids* limefluids*potassiumfluids*pol$mer/basedfluids*andbrinesusedindrilling* completion or wor:over operations 1including single/salt* potassium chloride* sodium chloride* calcium chloride* and two and three/salt brines2.Drilling Fluid Classi!iations7ater/>ased .rilling &luidsDrilling Engineering Fall 2012Prepared by: Tan Nguyen5n man$ areas* diesels were used to formulate and maintain 4>Cs. Crude oils had sometimes been used instead of diesel but posed tougher safet$ problems. Thus* toda$*mineraloilsandnews$ntheticfluidsreplacedieselandcrudeduetotheir lower to)icit$. (dvantages of 4>Cs@ 1.Shalestabilit$@4>Csaremostsuitedfordrillingwatersensitiveshales.The whole mud results non reactive towards shales.2. 64!@ allowing to drill faster than 7>Cs* still providing e)cellent shale stabilit$3.9ighTemperature@candrillwherebottomholetemperaturee)ceeds7>Cs tolerances0 can handle up to 55' '&.Drilling Fluid Classi!iations4il/>ased .rilling &luidsDrilling Engineering Fall 2012Prepared by: Tan Nguyen4. Bubricit$@ 4>Cs has a thin filter ca:e and the friction between the pipe and the wellbore is minimized* thus reducing the ris: of differential stic:ing.5. Bow pore pressure formation@ Cud weight of 4>Cs can be maintained less than that of water 1as low as ".5 !!E2. Corrosion control@ corrosion of pipe is controlled Since oil is the e)ternal phase. ".6e/use@4>Csarewell/suitedtobeusedoverandoveragain.The$canbe stored for long periods of time since bacterial growth is suppressed.Drilling Fluid Classi!iations4il/>ased .rilling &luidsDrilling Engineering Fall 2012Prepared by: Tan Nguyen(noil/basedrillingfluidisoneinwhichthecontinuousphaseisoil.Thetermsoil/basemudandinvertedorinvert/emulsionmudsometimesareusedtodistinguish among the different t$pes of oil/base drilling fluids. Traditionall$* an oil/base mud is a fluidwith'to5Fb$ volume ofwater*whileaninvert/emulsion mudcontains more than 5F b$ volume of water. 9owever* since most oil muds contain some emulsified water*haveoilastheli+uidphase*and1ifproperl$formulated2haveanoilfiltrate* wedonotdistinguishamongtheminthisdiscussion.S$ntheticmudsma$include esters* olefins* and paraffin.Drilling Fluid Classi!iations4il/>ased .rilling &luidsDrilling Engineering Fall 2012Prepared by: Tan Nguyen(irdrillingisusedprimaril$inhard/roc:areas*andinspecialcasestoprevent formationdamagewhiledrillingintoproductionzonesorto circumventseverelost/circulationproblems.(irdrillingincludesdr$airdrilling*mistorfoamdrilling*and aerated/mud drilling. 5n dr$ air drilling* dr$ air or gas is inDected into the standpipe at avolumeandratesufficienttoachievetheannularvelocitiesneededtocleanthe holeofcuttings.Cistdrillingisusedwhenwateroroilsandsareencounteredthat produce more fluid than can be driedup using dr$ air drilling. ( mi)ture of foaming agent and water is inDected into the air stream* producing a foam that separates the cuttings and helps remove fluid from the hole. 5n aerated mud drilling* both mud and air are pumped into the standpipe at the same time. (erated muds are used when it isimpossibletodrillwithairalonebecauseofwatersandsandGorlost/circulation situations.Drilling Fluid Classi!iations!neumatic &luids 1(ir* Eas* Cist* &oams* Easified Cuds2Drilling Engineering Fall 2012Prepared by: Tan NguyenDrilling Fluid Classi!iations!neumatic &luids 1(ir* Eas* Cist* &oams* Easified Cuds2Drilling Engineering Fall 2012Prepared by: Tan NguyenTheph$sicalpropertiesofadrillingfluid*particularl$itsdensit$andrheological properties*aremonitoredtoassistinoptimizingthedrillingprocess.Theseph$sical properties contribute to several important aspects of successful drilling* including@A!roviding pressure control to prevent an influ) of formation fluidA!roviding energ$ at the bit to ma)imize 6ate of !enetration 164!2A!roviding wellbore stabilit$ through pressured or mechanicall$ stressed zonesASuspending cuttings and weight material during static periodsA!ermitting separation of drilled solids and gas at surfaceA6emoving cuttings from the wellDrilling Fluid PropertiesDrilling Engineering Fall 2012Prepared by: Tan NguyenTheconceptsofshearrateandshearstressappl$toallfluidflow*andcanbe describe in term of two fluid la$ers 1( and >2 moving past each other when a force 1&2 has been applied.Drilling Fluid Properties-iscosit$Drilling Engineering Fall 2012Prepared by: Tan Nguyen7hen a fluid is flowing* a force e)ists in the fluid that opposes the flow. This force is :nownastheshearstress.5tcanbethoughtofasafrictionalforcethatarises whenonela$eroffluidslidesb$another.Sinceitiseasierforsheartooccur betweenla$ersoffluid than between theoutermost la$er offluid andthe wall of a pipe*thefluidincontactwiththewalldoesnotflow. Therateatwhichonela$eris movingpastthene)tla$eristheshear rate. Theshear rate is therefore a velocit$ gradient. The formula for the shear rate is Drilling Fluid Properties-iscosit$Drilling Engineering Fall 2012Prepared by: Tan Nguyen5nthemostgeneralsense*#isositydescribesasubstance?sresistancetoflow. 9enceahigh/viscosit$drillingmudma$becharacterizedas;thic:*;whilealow/viscosit$ mud ma$ be described as ;thin.; -iscosit$ 12* b$ definition* is the ratio of shear stress 12 to shear rate 12@Hnit@ !aS* ISGm2* :gGms* cp* d$neSGcm2* lbfSG1''ft2 Drilling Fluid Properties-iscosit$Drilling Engineering Fall 2012Prepared by: Tan NguyenThesimplestclassoffluidsiscalledNe$tonian.Thebasefluids1freshwater* seawater*dieseloil*mineraloilsands$nthetics2ofmostdrillingfluidsare Iewtonian. 5n these fluids* the shear stress is directl$ proportional to the shear rate. Thepointslieonastraightlinepassingthroughtheorigin1'*'2ofthegraphon rectangular coordinates. The viscosit$ of a Iewtonian fluid is the slope of this shear stressGshearrateline.The$ieldstress1stressre+uiredtoinitiateflow2ofa Iewtonianfluidwillalwa$sbezero.7hentheshearrateisdoubled*theshear stressisalsodoubled.7henthecirculationrateforthisfluidisdoubled*the pressure re+uired to pump the fluid will be s+uared 1e.g. 2 times the circulation rate re+uires 4 times the pressure2.Fluid TypesIewtonian &luidsDrilling Engineering Fall 2012Prepared by: Tan NguyenThe shear stress at various shear rates mustbemeasuredinorderto characterizetheflowpropertiesofa fluid.4nl$onemeasurementis necessar$sincetheshearstressis directl$proportionaltotheshearrate foraIewtonianfluid.&romthis measurementtheshearstressatan$ other shear rate can be calculated from the e+uation@Fluid TypesIewtonian &luidsDrilling Engineering Fall 2012Prepared by: Tan Nguyen7hen a fluid contains cla$s or colloidal particles* these particles tend to ingham!lasticmodelhasbeenusedmostoftentodescribetheflow characteristics of drilling fluids. 5t is one of the older rheological models currentl$ in use.Thismodeldescribesafluidinwhichafiniteforceisre+uiredtoinitiateflow 1$ieldpoint2 and which then e)hibits a constant viscosit$ with increasing shear rate 1plastic viscosit$2. Fluid Types>ingham !lastic &luidsDrilling Engineering Fall 2012Prepared by: Tan NguyenThetwo/speedviscometerwasdesignedtomeasurethe>ingham!lastic rheologicalvaluesfor$ieldpointandplasticviscosit$.(flowcurveforat$pical drillingfluidta:enonthetwo/speed&ann-Emeterisillustratedin&igure below. The slope of the straight line portion of this consistenc$ curve is plastic viscosit$.Fluid Types>ingham !lastic &luidsDrilling Engineering Fall 2012Prepared by: Tan NguyenCostdrillingfluidsarenottrue>ingham!lasticfluids.&orthet$picalmud*ifa consistenc$ curve for a drilling fluid is made with rotational viscometer data* a non/linearcurveisformedthatdoesnotpassthroughtheorigin*asshowninFlow diagramofNewtonianandtypicalmud.Thedevelopmentofgelstrengthscauses the$/intercepttooccuratapointabovetheoriginduetotheminimumforce re+uiredtobrea:gelsandstartflow.!lugflow*aconditionwhereinagelledfluid flows as a ingham !lastic &luidsDrilling Engineering Fall 2012Prepared by: Tan NguyenFluid Types>ingham !lastic &luidsDrilling Engineering Fall 2012Prepared by: Tan NguyenThe!owerBawmodelattemptstosolvetheshortcomingsofthe>ingham!lastic modelatlowshearrates.The!owerBawmodelismorecomplicatedthanthe >ingham!lasticmodelinthatitdoesnotassumealinearrelationshipbetween shearstressandshearrate.9owever*li:eIewtonianfluids*theplotsofshear stress vs. shear rate for !ower Baw fluids go through the origin.Fluid Types!ower Baw CodelDrilling Engineering Fall 2012Prepared by: Tan NguyenThis model describes a fluid in which the shear stress increases as a function of the shearratemathematicall$raisedtosomepower.Cathematicall$*the!owerBaw model is e)pressed as , Kn 7here@, Shear stressK, Consistenc$ inde), Shear raten, !ower Baw inde)Fluid Types!ower Baw CodelDrilling Engineering Fall 2012Prepared by: Tan Nguyen!lottedonalog/loggraph*a!owerBawfluidshearstressGshearraterelationship formsastraightlineinthelog-logplot.The