Chapter 7

DRILL FLUID

Topics examinedin this chapter are relevantto gravelenvelopewellsdrilled with direct and reverserotary equipment,with emphasison drillfluid propertiesandformationsampling.

7.1 Drill Fluid

A properly designeddrill fluid program is critical to construction ofwaterwells by therotarydrilling method.Useof thisprogramspeedscon-struction,minimizesaquiferdamage,andfacilitateswell development.

7.1.1Functions for DirectRotaryDrilling

In hydraulic rotary operations,the drill fluid systemperforms severalfunctions:

Cools and lubricatesthe drill bit.

. Removesdrill cuttingsusinga combinationof upwardvelocityandgel strength,density,andviscosity.The amountof work performedin drill cuttingsremovalis not alwaysrecognized. For example,awell with a36"conductorboreto adepthof 100feetanda28"wellbore to 1000feetwill requireexcavationof nearly170cubic yardsor about230tons of material.

*

Stabilizesthe boreholeby:

Exertingadifferentialhydrostaticpressurewhich tendsto holdlooselyconsolidatedformationsin place.

*Surroundingparticlesof formationwith mudgel.

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Limiting water intrusion in materialssuch as someshalesandclayswhich hydrate,swell,andslough.

Minimizesfluid migrationinto or from the boreholeby:

*

.*

Weightingthefluid sufficientlyto restrictwatermigrationfromanypermeablezone into the borehole.

Inhibiting outward flow by maintainingminimum practicalfluid densityand lining the boreholewith an impermeablefil-ter cakeformedfrom colloidalmaterial.

*

. Lubricatesthe borehole,drill pipe,andmudpump utilizing the gelandcolloidal propertiesof the drill fluid.

Suspendssolidsduringperiodsof noncirculationby combiningthenecessarygel strength,fluid weight andviscosity.

.

. Removescuttingsbeforerecirculation,by control of viscosityandgel strength,togetherwith properuseof settlingpits,shaleshakers,anddesanders/desilters.

. Aids interpretationof electric log and drilling samples,by mainte-nanceof proper fluid properties.

7.1.2Functions for ReverseRotary

The uses for and propertiesof the drill fluid systemin reverserotarydrilling are similar to those of direct rotary except that since cuttingsremovalis by high velocityfluid return,gel strengthand viscosityarenotas important. For this reason,manyreverserotary specificationssimplystatethat clear water alone shall be usedas the drill fluid. This standardmaybe unrealisticin manyformations,since contactof water with bore-hole walls and mixing of drill cuttingsas they are carried to the surface,immediatelycontaminatesthe water. The degreeof contaminationvarieswith the characterof formationsdrilled,but penetrationof certaintypesofclay and shalecan produce fluid propertiesof weight andviscositymorenearlyresemblingdrilling mudthanwater.The problemsof the useof drillfluid discussedbelow applyboth to reverseanddirect rotarymethods.

7.1.3Drill Fluid Problems

There areanumberof drill fluid problems.The mostusualare:

. Solidsbuildup

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. Lossof circulation

. Waterloss7.1.3.1Solids Buildup

Perhapsthe most common problem with the use of drill fluid is solidsbuildup andexcessivefluid densityresultingfromfailureto separatesolidsat the surface.Useof a shaleshakeranddesander/desilterand/or loweringof viscositywith water dilution and chemicaltreatmentis the usual solu-tion for directrotary.For reversedrilling,increasingpit sizeor the numberof pits lowers fluid velocityandlengthenssettlingtime,allowingthe solidsto drop out.

7.1.3.2Lossof Circulation

While loss of circulation is not usuallyencounteredIn wells drilled inalluvium,thereareexceptions.Theseareof concernto the engineer,sincedeep invasionof producing zonesby drill fluid mayinhibit proper devel-opment. The tendencyfor loss of circulationin sensitivezones maypre-clude useof drilling techniquesrequiringcirculatingfluid.

With direct rotary,lossof circulationis usuallyfirst counteredby increas-ing drill fluid colloidal content for thicker filter cakeand low water loss.Mud densityshould be lowered if possibleand viscosityincreased. Careshould be exercisedwhen pulling or installingdrill pipe to avoida swab-bing actionwhich would breakdown the filter cake. Mud pumps shouldbe startedslowly to preventpressuresurges. Use of loss circulationma-terialsshouldbe carefullyreviewed,sincesomecommonlyusedsubstanceswill plug off a producingzone,sour in thewell, or aretoxic.

When reverserotarydrilling operationspenetratelosscirculationzones,usuallythe amountof makeupwater is increasedin orderto keepboreholefluid level at groundlevel. This is effectiveif sufficientwater is available,and the thicknessof filter cake deposit is acceptable.Loss of circulationmayalsobe used

7.1.3.3WaterLoss

Another commonproblem is the swellingand/or sloughingof claysandshales,due to filtrateinvasion(high waterloss)causinghydrousdisintegra-tion. This happensmorefrequentlywith reversedrilling becausethe drillfluid is water,usuallywithout gel colloids or otheradditivesto retardfluid

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loss.

High water lossin permeablezonesresultsin excessiveinvasionanddrillcuttingsdeposition. This is a particularlysevereproblem in fine-grainedaquiferssuch asfme sandor sandstone's.In this situation,undersizebore-hole oppositepermeablezonesis frequentlynotedwhen pulling out of orreenteringthewell with drilling tools. Clayparticlesdepositedin the fineformationcannotbe easilyremovedduring development.

The correctiveactionnormallyconsistsof additionof colloidal materialand water loss inhibiting additives,and chemicaltreatmentfor dispersionof solidsandremovalof contaminants.Reversecirculationdrilling requiresextracarein properly designinga drilling fluid program.

7.1.3.4HighPressureAquifers

Occasionallywith direct rotary drilling,high pressureartesianaquifersarepenetrated.When thishappens,the pressureof the mud columnmustbe equalto or greaterthanthepressurein theaquifer,or thewell will flow.Use of weightingmaterialsto increasemuddensitycontrolsthis problem.

7.1.4DirectRotaryDrillFluid

Any drill fluid for direct rotaryuseconsistsof:

Wateris the major componentby volume.The suspendednon-colloidalsandandcuttingsarethe majorcomponentby weight. Colloidal solidsarethe mostimportantfactoraffectingmudpropertiesandperformance.Thisfraction is obtained from clays or organic (biodegradable) colloids.Inorganic clay colloids are generallymore influenced by chemical treat-mentthan organiccolloids.

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. Water

. Non-ColloidalSolids

. Colloidal Solids

. DissolvedChemicals

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7.1.5Drill Fluid Composition

Direct rotary drill fluids are usuallyproduced as a mixture of potablewater andwesternbentoniteclay(sodiummontmorillonite).Additivesareused to counter adversesituations,usuallycausedby drilling formationswhich modify fluid properties. Common additivesarebarite(to increasedensity),viscosity thinners,hydratedlime (to increasegel strength),andsodaashfor water softening.

7.1.6AcceptableDrill Fluid Properties

As suggestedabove,the bestdrill fluid programdependsupon the typeof drilling equipmentand the formationsto be drilled. However the engi-neer can andshouldsetforth standardsfor acceptablefluid propertiesfordirect circulationdrilling. He shouldalsorealizethatunder somecircum-stances,reversecirculationconstructionwill requirea drill fluid.

Conformancewith mudspecificationsusuallyrequiresafew fairlysimplemeasurementsof mud properties. Field testsareconductedto determine:

7.1.6.1Density

Densityis commonlymeasuredwith amudbalancein unitsof lbsper gal-lon or lbsper cubic foot. For comparison,waterhasadensityof 8.3 lbspergallonor 62.4 lbs per cubic foot.

7.1.6.2Viscosity

Viscosityof a fluid is its internalresistanceto flow. One methodof com-paring fluid viscositymeasuresthe coefficientof viscosityin units of thepoise. Waterat room temperaturehasa viscosityof about0.01 poise,orone centipoise.

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. Mud density(or mudweight)

. Viscosity

. Filter CakeThickness

. 30-minutewater loss,API

. SandContent

DrillFluid

Measurementsof viscosityare complicatedby the distinction betweenNewtonian fluids, such aswater which startflowing with the applicationof the smallestforce;andnon-Newtonianfluids,suchastypical drill muds,which are thixotropic in natureand developa gel structurewhen quies-cent. Increasing gel strengthwith quiescent time is a characteristicofthixotropic fluids. They exhibithigh viscosityatinitial flow,but decreasingviscosityasflow continues.The coefficientof viscosityof mostdrilling flu-ids increaseswith quiescenttime.

Although the Marsh Funnel measuresa combination of viscosity andthixotropic gel effects,it is the standardinstrumentfor comparing drillfluid viscosity. Funnel viscosity is defined as the time required for onequartof fluid to flow throughthe funnel.For reference,thefunnel viscosi-ty of water is approximately26 seconds.

Other important flow characteristicsare plastic viscosity,yield point,apparentviscosity,andgel strength.Measurementsof thesecharacteristicsare complicated,and are usuallyonly performedand analyzedby a mudengineer.

7.1.6.330-MinuteWaterLoss and Filter CakeThickness

3D-minutewater lossandfilter cakethicknessaremeasuredusinganAPIstandardfilter press.A filter paperis supportedin the baseof a mud-filledstandardmetalcell to which 100psi is applied.The waterpassingthroughthefilter duringa3D-minuteperiodis collectedandmeasuredin cubic cen-timeters.To completethe test,the filter paperwith the mud filter cakeisremovedfrom the cell,and the cakethicknessis measuredto the nearestthirty-secondof an inch with a thin plasticrule.

7.1.6.4Sand Content

Sandcontent is found by diluting a known volume of mud with waterandfilteringit througha200meshscreen.The screenis thenflushedwithwater until the remainingparticles are too largeto pass. The screen isinvertedand the particlesarewashedinto a taperedgraduatedtube. Theheightto which thetubeis filled is takenasthevolumeof sandgrains.Thetube is markedto readthis volumeasapercentageof the original sample.

Circulationof largeamountsof sandresultsin excessivewear on pumps,drill pipe, andbits;causeslower penetrationrates,and depositsa thick fil-ter cakewhich impedeswell development.

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7.1.7TestingDrill Fluid

Procedures for measurementof drill fluid properties have been stan-dardizedby theAmerican PetroleumInstitute,and are describedin theirbulletinAPI RP 13B,'StandardField ProcedureforTestingDrilling Fluids'.

7.1.8Drill Fluid Engineers

Becauseof drill fluid programcomplexity,mostwell engineersdesigningevenrelativelysimpleand straight-forwarddirectcirculationwells requirethat a qualifieddrill fluid engineerbe availableto the contractorfor mudcontrol adviceduringthe drilling operation.

7.1.8.1Drill Fluid Specification

Drill Fluid

Drill fluid shallconsistof amixtureof waterandsodiumbasemont-morillonite (high grade bentonite) such as "Aquagel"or otherapprovedmaterial.It is desirableto maintainafluid systemof min-imum weight and low solids contentwhich depositsa thin easilyremovablefilter cakeon thefaceof the aquifers.If thereshouldbea conflict betweenthe drill fluid requirementsfor easeof drillingand drill fluid requirementsfor aquifer protection, the rulingrequirementsshallbe thosefor aquiferprotection.

The Contractorshallconsultaqualifieddrill fluids engineerregard-ing the proposeddrill fluid program.The programshallbe agreedupon andsubmittedto the Engineerfor approval.

During drilling operations,the fluid shallhavethe following prop-ertiesin accordancewithAPI CodeRP 13B,StandardProceduresforTestingDrilling Fluid".

1. Weight- A maximumof - Ibs/cu ft ( - Ibs/gal)

2. FunnelViscosity- A maximumOf- seconds

3. 30-minutewaterloss- A maximumof - cc whiledrillingpilotholeand- ccwhilereaming

4. Filter Cake- A maximumof /32"

5. SandContentof fluid enteringthewell bore- A maximum

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- of %by volume

The Contractor shall maintaincareful mud control and keep anhourly log of weight,funnel viscosity,30-minutewater 1088,filtercakethickness,and sandcontent.

Immediatelybefore the introduction of gravel,the drill fluid shallbe thinnedwith wateruntil it hasthe following properties:

1. Weight- a maximumof 68 lbs/cu ft

2. Funnel viscosity- A maximumof 28 seconds

3. Sandcontentof fluid enteringthewell bore- A maximumof - %by volume(Range1%to 3%,with the lower per-centagemore desirable)

The above fluid properties are to be maintainedthroughout thetime the gravelis installed.

7.1.8.2Typical Drill Fluid Properties

Drill fluid standardscan vary dependingupon local conditions and for-mations encountered. However,propertieswhich have produced goodresultsin mostcasesare:

. Weight,A maximumof85lbs/cuft (11.4lbs/gal)

. FunnelViscosity,amaximumof 40 seconds30-minuteWaterLoss,amaximumof 15cc.

. FilterCake,amaximumof3/32"

. SandContent,amaximumof3%

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7.1.9 Mud Pit Size

Most expertsagreethat maintenanceof good fluid properties requiresuse of a mud pit or pits with combinedvolumetwo to threetimesthat ofthe theoreticalvolume of the final borehole. Smallpits complicatemudcontrol,andfrequentlygreaterchemicaluseis required.

7.2 BiodegradableDrill Fluids

A growing number of well engineersbelieve that use of an organicbiodegradable,polymer-baseddrill fluid speedsthe drilling process andsimplifieswell development,makingits extracost and complexityworth-while.An acrylicpolymer,suchasSodiumPolyacrylamide,replaceswesternbentoniteasthe fluid base.

Organicpolymersarebeneficialin severalways:

. They areeffectivethickeners.They reducefiltrationandform thin filter cakes..

. They stabilizeclays,resultingin recoveryof largersizecuttingsandbetter surfaceseparation.

They lower systemfriction... Only smallamountsareneeded,simplifyingstorageandhandling.

7.2.1Guar-GumBased Drill Fluid

Problems have been encounteredwith use of biodegradableguargumbasedorganicdrill fluid in water wells. This fluid lacks thixotropic prop-ertieswhich permitpassagethroughavibratingscreen,andmuch is lost inthe cuttingpits if a shaleshakeris used. Gasproducedby the decompos-ing guar gum has confused results of tests for coliform bacteria.Consequently,engineersspecifyinguseof biodegradabledrill fluid shouldneveruseguar-gumbasedfluid.

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7.2.2 Toxic Additives

It is prudent for the well engineerto incorporateinto his specificationsa statementthatwhile drilling into aquifersthe drill fluid shallnot containany substancein toxic concentrations,or material which imparts (ordecomposesto produce) objectionableodors,colors,bacterialactivity,ortastesto thewaterproduced.The additivesemployedwith both bentonite-basedandpolymer-basedfluids areso numerousthatonly a qualifiedmudengineercan assesstheir possibletoxicity.

7.2.3 Influence of Water on Biodegradable Fluids

Proper compositionand useof biodegradabledrill fluids requireschem-ical analysisof the makeupwater,with adjustmentmadeto the program.

7.2.3.1BiodegradableDrill Fluid Specification

BiodegradableDrill Fluid

All water used during drilling shall meetDepartmentof Healthstandardsfor safedrinkingwater.

The drill fluid shall be mixed and maintainedto ensureoptimumdrilling conditions,protect the water bearingformations,supportthe walls of the borehole during drilling,and permit recovery ofrepresentativeformationcuttingsamples.The drill fluid shall alsopossesssuchcharacteristicsthatit canbe easilyremovedfrom thehole during placementof the filter pack, and well development.The Contractorshouldnote thatclayzonesmaybe encounteredofsuchnaturethathigh water lossmayleadto swelling,reductionofshearstrength,andsubstantialcaving.The drilling fluid shouldbedesignedto mitigatethesepotentialproblems.

State

The drill fluid shall be of the biodegradabletype.Bentoniteshallnot be used.Additivesmaybe usedto maintainfluid propertiesorcorrect deficiencies.

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However,approvalfor all additivesthe Contractorproposesto usemustbe obtainedprior to use,andpreferablybeforestartof work.In no caseshalltoxic materialsbe introducedinto thedrill fluid sys-tem.

Drill fluid propertiesshallbe maintainedto the satisfactionof theEngineer.The Contractorshallat his expenseprovide the serviceof anexperienced,qualifiedmudengineerto design,superviseandmaintaindrill fluid characteristics.This requiresclose monitoringof fluid parametersincluding,but not limitedto,viscosity,pH, sandcontent,water 1088,weight,and cakethickness.These propertiesshallbe measuredandrecordedat leasteveryfour hours in accor-dancewith proceduresshown inAPI Code RP 13B"RecommendedProcedureforTestingDrilling Fluid."

A shaleshakeranddesalterscapableof handlingthecapacityof thefluid systemshall be installedbetweenthe drill rig and mud pits.This equipmentmust keep the drill fluid sandcontentbelow 1%andtotalsolidsbelow 5%atall timesduringthe drilling process. Ifthese limits are exceeded,the Contractor shall immediatelysus-pend drilling operationsand recondition the drill fluid until thisstandardis met.

Use of lost circulationmaterialis to be avoided,and will only beallowedwhen fluid is being lost from thebore at a rateexceeding50 GPM with thefluid weight maintainedatno morethan9 lbspergallon (67.3 lbs per cubic foot). No lost circulationmaterialswillbe addedwithout the approvalof the Engineer.Type of lost circu-lation materialwill be selectedby the mud engineerafterconsid-ering boreholeconditions.

The drill fluid mud pit shall have a volume at least three timesgreaterthanthefinalwell-borevolume.The pit will be cleanedoutaftercompletionof drilling operations.All fluids andcuttingsshallbe removedfromthesiteandlegallydisposedof attheContractor'sexpense.

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7.3 ReverseRotary Drill Fluid

A specificationcoveringdrill fluid for reverserotarydrilling is relativelysimple,usuallyonly statingthatclearpotablewaterwill be used. In situa-tionswhere the formationspenetratedareprimarilysandandgravel,this isalmostalwaysadequate.Complicationsoccur when lessfavorableforma-tions,suchashydratingclaysor shales,or losscirculationzones,arefound.Under these conditions,the drill fluid specificationshould be similar tothatfor directrotary.However,efficiencyof thereversesystemdependsoncuttingsremovalthrough the drill pipe by high upward velocityof a rela-tively low densityfluid, and direct rotary fluid loss control methodsareoften not practical.Thereforesomeexpertsspecifywater lossesof 10,00or less.

In a few instances,someengineerswill not allow reverserotarydrillingwhen circulation is induced by airlift pumping. There is evidence thatwells constructedin somesandstoneaquifersusingthis drilling techniqueare lower producers than similarwells drilled by other methods. This isapparentlydueto air-locking,causedby lossinto the aquiferof higher-headfluid carryingresidualair. Constructionof wells by the cabletool methodmaybe requiredin such fragilezones,sinceremovalof colloidal drill fluidand air from sandstoneis difficult.

7.3.1ReverseRotaryCuttings Recirculation

In reverserotaryoperations,a lower densityandviscosityfluid is circu-lated facilitatingrelativelyrapid dropout of drill cuttings. Therefore con-tractorssometimesusea singlesmallpit, particularlyif makeupwater canbe supplied by a float-controlledhigh capacitywater line. Under theseconditions,frequentandthoroughremovalof cuttingsfrom the pit is nec-essary to avoid recycling, particularly since shale shakers anddesander/desiltersare not usually used in reversecirculation well con-struction.

Since reversecirculation equipmentis usuallyset at ground level,trip-ping drill pipe, installingcasing,etc.,areconductedwith thecrew workingon the ground around the well. In order to increaseworking spaceandkeep the work areadry,manycontractorslaya large-diameterreturn flowpipe below ground surface,from the pit to the borehole. Unfortunately,this systemtendsto recirculatedrill cuttingswhich havesettledin the pit.If a below ground return flow pipe is used,precautionssuch as using amuch largerpit, a two-pit system,or a seriesof baffles in the pit to holdback drill cuttingsshouldbe taken.

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7.3.1.1ReverseRotaryDrill Fluid Specification

Drill Fluid

Potablewateraloneshallbe utilizedasdrilling fluid. Shouldlossofcirculation or other drilling problemsrequirethe additionof ben-tonite or othermaterial,it shallbe addedonlywith the approvalofthe Engineer,and developmentproceduresshall insure the com-plete removalof the additives.

In constructionof deeperwells or other circumstanceswhere bentoniteor other additivesto thewatercirculationsystemmaybe needed,the engi-neer shouldcontrol fluid propertieswith a similarspecificationto that fordirect rotary.This is particularlypertinentfor gravelinstallation.A specifi-cation suchasshown in 7.1.8.1maybe used.

7.4Sampling

Samplingand analysisof cuttingsgeneratedby direct or reverserotarydrilling requirescare in the samplingoperationand understandingof thelimitationsof theresultsobtained.Directrotarysamplesareoftenobtainedfrom the materialretainedas the returning mud flow crossesthe shaleshakerscreen.The fmersegmentswhich passthroughthe screencustom-arily areremovedfrom the fluid by a desanderfdesilter.However,the for-mation gradationis difficult to determinefrom observationof theseseg-mentsseparately.Samplesmayalsobe obtainedfrom a samplecatcher(abox with severalbaffleplatesplacedin thereturnmudflow), but againthefiner formationparticlesareusuallyretainedin the drill fluid.

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7.4.1 Formation Sampling Specification

Following is a typical specificationfor obtaining samplesfor analysiswhen direct rotaryconstructionis used:

Sampling

When instructedby the Engineer,the Contractorshalldrill from 3to 5 feetof pilot bore,raisethebit from thebottomof thehole,andcontinue circulationuntil all cuttingsfrom the intervalareclearedfrom thehole andcaughton the shaleshakerscreenor in the sam-ple catcher.This operationwill be repeatedas required.Samplesobtainedfrom eachinterval shall be thoroughlymixed and quar-tered until an approximate two-quart representative sampleremains.The sampleshall then be placedin a five-gallonpail,andwater addedto fill it.After thorough stirring,the contentsshallbeallowed to settle and the muddy water decanted. The sampleremainingin the bottom of the pail shallbe placedin two I-quartcontainers,both clearlymarkedto show the well number,sampledepth,and date.

7.4.2 Reverse Drilling Sampling

With reverserotary drilling,cuttingsarebrought to the surfaceat highvelocity,and it is usuallynot necessaryto raisethe bit from the bottom ofthe hole and circulate. However,the generalpracticeof putting a straineror bucketin thereturnflow andgrabbingasampleis not reliablesincethefmer portion is lost. This shouldnot be permitted.

A more reliable procedure uses a sampler(splitter box) in the returnflow from the drill pipe. The splitterbox containsa centerdivider. Fluidpassingonesideof thedividerflows directlyto themudpit. The othersidecontainsa control gatewhich when opened,divertsa portion of the flowinto a containersuchasa 5-gallonpail. By havingseveralpails available,asamplecanbe obtainedfrequently.The cuttingsareallowedto settleto thebottom.After decanting,the cuttingsremainingarethoroughlymixed,andone-quartsamplesaretakenandlabeled.

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7.4.3Sample Limitations

Regardlessof the care exercisedin obtainingsamplesof cuttingspro-ducedby eitherdirector reverserotarytechniques,the engineershouldbeawarethatthey maynot be representativeof the formation. Hole erosioncausedby fluid flow, mechanicalenlargementcausedby rotation of thedrill pipe, and sloughingcontribute to sampleunreliability. In addition,finer formationparticlesusuallyarelost into thefluid. This maskingof trueaquifergradationoftencausespotentialwaterbearingformationsto appearmore productivethanthey eventuallyprove to be,andmayresult in filterpack designerrors.

The engineermaywish to havea moreprecisesampleanalysisdone bya geologist,particularly if correlation to known aquifers is needed. Onoccasion,authoritiescontrollinggroundwateruselimit well production todesignatedaquifersandrequirepositiveidentification.

It is dangerousto rely on samplesobtainedfrom circulatingdrill fluid asthe sole criterion for determiningplacementof screen,screen aperturesize,or filter pack gradation.The engineershould evaluateall pertinentinformation.

7.5 Drill ProgramSubmittal

Togetherwith other submittals(5.2.1),engineersfrequentlyrequire thesuccessfulbidder for gravelenvelopewell constructionto submitan oper-ations program prior to commencingoperations. This program usuallyincludesbrief resumesof the personnelwho will do thework, aproposedtime scheduleof the drilling phases,anda detaileddescriptionof the con-templatedwell developmentprogram. With direct rotary drilling, a com-plete descriptionof the drill fluid programis alsoincluded.

This chapterhasemphasizedthe complexityof drilling fluid technologyand the difficulty facing the engineerattemptingto write a specificationanticipatingall contingencies.With the increasinguseof biodegradableflu-ids and additives,it is nearly impossibleto adequatelyspecify what hasbecome a completeand unique discipline,with its own terminologyandexpertpractitioners.

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DrillProgramSubmittal

Specificationswhich incorporate an organic colloidal (biodegradable)drill fluid (7.2) frequentlyrequirethe drill programto be preparedin col-laborationwith a mud engineerexperiencedwith organic-colloidalfluids.This individualis usuallyanemployeeof amajormanufacturerof materialsused to preparedrill fluid. The designengineershould approvethe sub-mittalbeforeallowingwork to commence.Dependingupon the expecteddrilling complexity,thespecificationsmaystatethatthemudengineerwhoassistedin the programpreparationbe eitheron site or availableon shortnotice.

7.5.1 Drill Program Submittal Specification

Drill Program Submittal

Within 15 daysafter notice of award,the successfulbidder shallsubmit his detaileddrill program. Notice to Proceedwill not beissued until a program containingthe following information hasbeenreceivedand approvedby the Engineer.

1. A list of key personnelto be employedin the executionofthework, togetherwith abriefbiographicalindividualworkhistory. This list shall include the Contractor'sresponsiblerepresentative,on-sitesupervisors,drillers,developmentrigoperators,andtestpumpers. laborers neednot be listed.

2. A time schedule,showing the anticipateddatesof com-mencementand completion,andmajorstepsin the execu-tion of the work.

3. The proposed drill fluid system,covering major featuressuchassizeandplacementof pits,etc.A full descriptionofthe methodof establishingandmaintainingdrill fluid qual-ity conforming with specification requirementsshall begiven,includingtradenamesof all materialsplannedto mixand makeup the fluid. The nameandqualificationsof thedrill fluid engineershallbe stated.Contractoris informedthat full-timeavailabilityof a qualifiedmud engineersatis-factoryto the Engineeris a contractrequirement.The pro-posedsystemshallbe capableof meetingall drill fluid stan-dards required by the specifications,and shall be com-patible with the quality of makeupwater availableat thesite. (This paragraphis not usuallyrequiredfor reversecir-culationdrilling)

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4. Detailsof the proceduresthe Contractorproposesfor drillfluid treatmentduringgravelling,preliminarywell develop-mentwith the drill rig,subsequentwell developmentwithother equipment, final development by pumping, andpump testing.

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Chapter 8

DRILLING AND LOGGING

Although fromthecontractorswork viewpoint,drilling is themajorworkcomponent,the specificationcoveringit is relativelysimple. This chaptercovers direct rotary,reversecirculation rotary,and cable tool boreholedrilling andconcurrentactivities.

8.1 DirectRotary Drilling

Most direct rotarydrilling equipmentis designedto completethe bore-hole in a seriesof passes,with thenumberrequireddependenton drillingequipmentcapacityandfinalboreholediameter.The engineerusuallydoesnot designatethe numberof passes,andonly considersthepilot bore,log-ging,andthe fmalboreholediameter.

8.1.1Pilot Bore

The pilot bore servesseveralfunctions in the construction of a gravelenvelopewell. The drillers log, formation samples,and electric logs areobtainedfrom the pilot bore. Since pilot bore drilling is relativelyinex-pensive,it maybe continuedto greaterdepthsto obtain additionalinfor-mation.

8.1.1.1Pilot Bore Specification

A typicalspecificationfor drilling pilot bore follows:

Drilling pilot Bore

The pilot bore shallbe drilledto the depthof - feet.Thediam-eter of the pilot bore shallbe not greaterthan 15 inches nor less

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than 8 inches.

Thepurposeofthepilotboreis tofindthethicknessandnatureofall materialspenetrated,the location of water bearing strataandother hydrologicaland geologicalinformation. To obtain reliablecuttingssamples,the Contractorshallcomplywith the following:

1. Maintainreasonablyconstantweight on bit and consistentdrilling fluid properties.

2. Maintainadequatefacilitiesfor collectionof drill cuttings.

3. Equip the drill stringwith drill collarsof appropriatediam-eter,weight,and length.

8.1.2Geophysical Logs

Geophysicallogsarerun in the completedpilot bore.The following logscan be made:

.Singlepoint resistivity

Long andshort normalresistivity

. Lateralresistivity

. Spontaneouspotential

. Gamma-rayneutronCaliper Survey

. Sonic

. TemperatureFlow meter.Density

The requirementsfor and analysisof theselogs is beyond the scope ofthis publication,and expertsareusuallyemployedto assessand interpretthe logs neededfor a particularproject.

.

For mostwells,the electric logs run arespontaneouspotentialand longand short normal resistivity.A caliper survey is often taken in the finaldiameterborehole,to check its conditionandestimatethe quantityof grav-

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el to be placed(8.1.5.1).

8.1.2.1GeophysicalLogging Specification

Geophysical Logging

Geophysicalwell logs shall be taken in the pilot bore. Logs runshall be . Loggingapparatusshallbe ScWumbergerorapprovedequal. The logs shall haverecorded on them the welllocation and elevation;type,weight,resistivity,and temperatureofdrilling fluid; boreholediameter,and anyother informationneces-sary for proper interpretation.- copies of the loges) withreproducibleif desiredshallbe handedoverto the Engineer.

8.1.3Test Bore Water Sampling

It is difficult andexpensiveto obtainreliablewater samplesfrom directrotarypilot bore holes,and it is rarelyrequired. If needed,they arebetterobtainedfrom a separatetestbore.The full depthtestbore is geophysical-ly loggedandis reamedif necessaryto aminimum12"diameterto thebot-tom of the deepestzone to be sampled.Any boreholebelow the zone,notfilled with cuttings,is filled with gravel.

A screen is installedon drill pipe or line pipe of diameteradequatetoallow installationof a smallsubmersiblepump. The screenis a minimum4-112"00 pipe, 20' long,with approximately3/32"wide milled slots,or apipe basescreen. It is set into the zone to be sampled,and gravelforma-tion stabilizer(9.1) is tremiedinto theannulusto anelevationabout20feetabovethe top of the screen.The well is pumpedfor a sufficientperiod ortime to assurea reliable sample(usuallya minimum of eight hours). Apumping rate of ten to ftfteengallonsper minuteis sufficientunder mostconditions. Heavydrilling fluid (85 to 95 lbs per cubic foot) is maintainedin the testbore while pumping.

If additionalsamplesare needed at higher elevations,the apparatusispulled,and the borehole is back filled,usually with gravel,to the bottomof the next zone to be sampled. The procedure outlined above is thenrepeated.

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8.1.3.1TestBoreWaterSamplingSpecification

WaterSampling

Afterthetestborehasbeendrilledandlogged,theEngineershallselectthezoneor zonesfromwhichwatersamplesareto betaken.

Any unfilledboreholebelow the lowestzoneselectedshallbe filledby tremieing an approved mixture of sand and gravel.TheContractor shall reamthe testbore if necessaryto a diameterofapproximately12inchesto the bottomof the zoneandconstructatemporarygravelenvelopewell with screensetin the zone.

The screenshallbe 4-112"OD pipe,slottedwith a- inch open-ing and with - slotsper foot. The bottom of the screenshallbe closed. The screenshallbe set on pipe with a minimuminchinside diameter.Before and during settingcasingand screen,thedrill fluid level shallbe at ground surface.The casingand screenshall be set in the hole to the required depth, and the annulusbetween the screenand bore shall be filled with selectedgravelthroughatrestlepipe to atleast20feetabovethetop of thescreen.

If necessary,the screensectionshallbe developedby washingandpumpingwith air.However,airliftpumpingto producethesamplesis not allowed.

A pump shallbe installedandoperatedataminimumrateof -gallonsper minute for at least- hours,or as directedby theEngineer. Following approvalof the operationby the Engineer,awater sampleshallbe obtainedandplacedin a containerfurnishedby the Owner.

If directed by the Engineer,samplingwill be repeatedat higherzones.The casingandscreenshallbepulledfrom thetestbore,andthe well filled asbeforeto the bottom of the next zone to be sam-pled.The operationaboveshallbe repeated.

Following all sampling,the testbore will be abandonedin accor-dance with procedures approved by the Board ofHealth (or governingagency).

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8.1.4Dual-TubeTestBore

A procedurefavoredby manyengineersfor determiningaquiferpotentialandwater qualityutilizesa drilling methodknown asdual-tube.

In the dual-tubesystem,the drill pipe consistsof two concentric tubes.The drilling fluid is air under at least250psi pressurewhich flows downthe annulusbetweenthe tubespast the drill bit. It returnsto the surfacethroughthe inner tubeatanapproximatevelocityof 3000feetper minute.Very accurateformation samples,uncontaminatedby contact with theborehole walls, are supplied continuously.At ground surface,the returnsaredirectedthrougha centrifugesimilarto acycloneseparator.In the sep-arator,the heavierdrill cuttingsandwater aredischargedout the bottom,andthe air is exhausted.

In most dual-tubeoperations,the outsidediameterof the outer tube is4-1/2", and the bit diameteris approximately5". Becauseof this tight fit,the drill bit essentiallyacts as a packer,assuringreliable water samples.Drilling is stoppedat the point where a sampleis desired,and the well isairlift pumpedfor approximatelyone-halfhour.

In alluvium,formationstend to close on the drill pipe during drilling,makingit difficult to drill deeperthan 1200feet.

Although formationsamplesareexcellentwith this system,the engineershouldrememberthatwater samplesmaybe distortedby airliftpumping.Any volatile contaminantsin the water will be removed by the air.However,for most purposes,formation and water samplingare nearly asgood andarefar lesscostlythanwith anyothermethod.

8.1.5SpecificationforReamingBorehole

Thespecificationforreamingfinaldiameterboreholeis brief.Thenum-berof passesmadeby thecontractoris notspecified.A typicalspecifica-tionis:

Reaming Borehole

The pilot bore below the surfacecasingshallbe reamedto -inch diameterand to - foot depth,or other depth as directedby the Engineer.

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8.1.5.1Considerationof OversizeBorehole

A calipersurveyis oftenrun aftercompletionof thefinal-diameterbore-hole. It evidencesthe existenceof oversizeborehole,andis usedto calcu-latethe amountof envelopematerialneeded.Someengineersbelievethatif the calipersurveyshowsexcessiveoversizeborehole,poor drilling tech-niques or fluid control are indicatedand reservethe right to stop work.Such beliefs usually stem from the poor performanceof nearby wellsattributedto oversizeborehole. If the engineercontemplatesstoppingwork under these circumstances,he should carefullyspell it out in thespecifications.

8.1.5.2RejectionSpecification

If the engineerreservesthe right to rejectoversizeborehole,a specifica-tion sectionsuchasthe following shouldbe added.

Possible Rejection of Oversize Borehole

Following reaming,a caliper surveyshallbe conductedto permitassessmentof the boreholecondition and possiblezones of over-breakage.If, in the judgementof the Engineer,the caliper surveyIndicates oversize borehole, or excessive overbreakagewhichcould jeopardize successfullanding of casing,filter pack place-ment,or well development,theContractormaybe requiredto drilla replacementwell atno additionalcost to the Owner.

After acceptanceof the reamed borehole by the Engineer,theContractor shall submit an estimate of the volume of gravelrequiredto completethe well.

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8.2 Reverse Rotary Drilling

Reverserotary is especially suited for shallow to medium depth drillingin unconsolidated alluvial formations. Proper removal of drill cuttings forreverse circulation drilling requires high return velocity in the drill pipe(usually 6 feet or more per second). Down-hole annular velocity must berestricted to a few feet per minute to limit erosion. Since the larger diam-eter drill pipe increases velocity, it is difficult to construct bores smallerthan 18" and pilot holes may no be drilled. Therefore selection of screenopening and gravel gradation must be made prior to drilling, based onexpected conditions. In many areas, aquifer characteristics are so wellknown that this presents no difficulty. Otherwise, a test bore may be drilledby another method.

8.2.1Geophysical Logs

With reverse rotary equipment the [mal diameter borehole may not bedrilled in one pass. Geophysical logs are not ordinarily run. If these logs areneeded, either a test bore should be drilled and logged, or a logging engi-neer consulted to determine if useful logs for the purpose can be obtained.

8.2.1.1ReverseRotary DrillingSpecification

Drilling Borehole

The- inch boreholeshallbe drilled with diligenceandwith-outunduedelaysin a continuousoperationto - feet or otherdepth directedbytheEngineer.TheEngineerwill approvethecas-ing andscreenprogram,or orderchangespromptlyto avoiddelaysin installation.

If the engineerwishes to havethe right to reject oversizeborehole,aspecificationsectionsimilarto Section8.1.5.2shouldbe added.

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8.2.2 Reverse Rotary Water Sampling

Watersamplescan be obtainedwith reverserotaryconstructionfollow-ing a procedure similar to that usedfor testbore sampling. Samplingiscostly becauseof the rig time required. Since reverserotary drilling israpid,the engineermustinformthecontractorin advancetheapproximatedepthsfrom which sampleswill be required.

One operationrequiresthe contractorto drill approximately20 feetintothe zone to be sampled.A 4-1/2"to 6"OD well screen(eitherslottedpipeor pipe basescreen)about20feetlong,is setin the zone.Gravelis treatedinto the annulusuntil it extendsabout20 feetabovethe screen. Sincetheamount of water produced is small,formation stabilizermaterial(9.1) issatisfactory.Slot sizevariesfrom 1/16"to 3/32",accordingto the gravel.

Three to five feetof fine sandis treatedon top of the gravel,followed bya heavydrill mud to sealthe sand.The well canbe developedwith air,butthe samplesareobtainedwith asubmersiblepumpto avoidaffectingwaterquality.

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8.2.2.1ReverseRotaryWaterSamplingSpecification

Water Sampling

Water samplesshall be taken from aquifers as directed by theEngineer. It is anticipatedthat - sampleswill be required,atapproximatedepthsof - feet,- feet,(etc.).

When an aquiferis encounteredat or lower than the highestele-vation specifiedabove,the Contractorshalldrill into it a sufficientdistance to determine its character,stop drilling and notify theEngineer.

If directedby the Engineer,the Contractorshallinstallanapproved- inch diameterwell screen,approximately- feet inlength,completewith endplug. The screenmaybe seton the drillpipe or minimum6"diameterthreadedandcoupledpipe,andshallbe centeredin thezoneto be sampled.If it is run connectedto thedrill pipe, the Contractormayinstallseverallengthsof blank pipeof the samediameteras the screenbetween the drill pipe andscreen,to preventgravelfrom sensingthe drill pipe flanges.

Gravelapprovedby the Engineershallbe treatedinto the annulusbetweenthescreenandborehole,to alevelabout20feetabovethescreen.Fine sandshall then be treatedto fill the annulusat leastthreefeet.A quantityof heavydrill mudsufficientto displaceaboutten feetof annulusshallthen be treateddirectlyabovethe sand

The well maybe developedwith airliftpumping.To obtainthe sam-ple for analysis,an electricallypoweredsubmersiblepump shallbeplacedin the drill pipe andoperatedfor - hours,or as direct-ed by the Engineer.

When a sampleis obtainedandapproved,the Contractorshallpullthe drill pipe andscreen,cleanout thegravelandsandfill, andcon-tinue drilling until the next zone to be sampledis encountered.Atthattime,the procedureshallbe repeated.

Sinceplacementof screenandfinalwell designmaybe affectedbythe water sampleanalysis,the Contractor is informed that whileanalysiswill be expeditious,theremaybe a short delayin notifica-tion of well completiondetails.

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8.3 Under-Reamed Borehole

As discussedin Chapter 2,one gravelenvelopewell designrequiresanenlarged(under-reamed)borehole under the pump housing casing. Thespecification for this well is similar to other designs,except for theunder-reamingprocess.

8.3.1Under-ReamedBoreholeSpecification

Drilling Under-Reamed Borehole

The borehole below the pump housing casing shall be un-der-reamedto a minimumof - inches,to a depth at leasttenfeetbelow the lowestproducingzonein thewell,asdesignatedbythe Engineer.The under-reamingshall be done with a Bakerhydraulicunder-reameror approvedequal.After the hole hasbeenunder-reamedto the total depth,its wall shallbe scrapedthrough-out its entire length with a Baker hydraulic under-reamerorapproved equal. After scraping,a Schlumberger(or approvedequal) section gaugelog (hole caliper log) shall be made of theunder-reamedborehole. If the sectiongaugelog shows the diame-ter of theunder-reamedboreholeis lessthanspecifiedatanypoint,the Contractorshallagainscrapethe entireunder-reamedsection,and run a new sectiongaugelog. This procedurewill be repeateduntil the section gaugelog shows the under-reameddiameteratleastequalto thatspecified.All costsof under-reamingandloggingwill be at the expenseof the Contractor.

If the work is done by reverserotary equipment,a mechanicalunder-reamermaybe used,andthespecificationmustbe modified.

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8.4 Drillingthe NaturallyDevelopedWell

With the naturallydevelopedcabletool well asfrequentlydrilled in thealluvialaquifersof theWesternUnited States,casingis installedcoincidentwith drilling. Consequently,the drilling specification includes casingassemblyandinstallation.

8.4.1 Drilling Specification - Cable Tool Well

Drilling and Installing well Casing

The Contractorshalldrill thewell andinstallthe casingusingcabletool drilling methodsapprovedby the Engineeras circumstancesmayrequire.The Contractorshallinstallhydraulicjacksif he findsit necessary,or if in the opinion of theEngineer,furtherdrivingwillresult in damageto the casing.

The doublewell casingsectionsshallbe joined by welding the cir-cumferentialseams.A gapof approximatelyl/8th inch shallbe setbetweenthe outer casingjoints prior to welding in order thattheouter andinner jointsmaybeweldedtogether.Weldingshallbe bythe electricarcprocess.

If practicalthe casingshallbe landedin a hard imperviousforma-tion. A cementplug shallbeplacedon bottomby meansof adumpbaileror other effectiveprocedure.

No reduction in casing diameter shall be permitted above thedepth of - feet.

Formation samplesshall be taken at five-rootintervalsor at eachchangeof formation.Samplesshallbetakendirectlyfrom thescowor bailerandplacedin approvedjarsor containerslabeledwith thedepth from which the samplewas taken. Sampleswill not bewashedbeforebeingexaminedby the Engineer.

Note thatthe specificationdoesnot requirecertifiedwelders for joiningdouble well casing. Becauseof the inherentmechanicalstrengthof thejoint,welding by experiencedrig personnelis usuallysufficient.

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8.4.2PerforatingDoubleWell Casing

Wellsdrilledwith cabletool equipmentusingdoublewell casingareper-foratedin place with a down-the-holeperforator.The intervalsto be per-foratedand the opening size areselectedby the engineerin consultationwith the contractorafterexaminationof thesamplestakenfrom ascow orbailer. Samplingwhen casingis carriedcoincidentwith drilling is veryreli-ableandmuch more representativeof trueconditionsthansamplingfromcirculatingfluid.

8.4.2.1PerforatingSpecification

Perforating Well Casing

The Contractor shall perforatethe casingat the direction of theEngineer. The size, spacingand location of perforationsshall bedeterminedfrom analysisof the formation samples. The casingshall be perforatedwith a perforator having positive action andconstructedto preventdistortionof thecasing.The openingsshallbe of horizontallouver shapewith the aperturefacingdownward.The bidder shall submitwith his bid a sampleof No. - gaugedoublewell casingof themanufactureandperforatedwith thetypeperforatorhe intendsto usein the performanceof this contract.

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8.4.3 Swaging Double Well Casing

Cable tool wells with double well casing are often drilled under condi-tions where the casing is subject to roll-ins or becoming out-of-round. Inaddition, the perforating process may slightly separate the two plies of cas-ing where the inside joints butt. Therefore, most engineers require that thecasing be swaged after perforating with a hydraulic expanding tool.

8.4.3.1Specification

A typical specification example for this operation follows:

Swaging

After perforating and sand pumping and prior to developmentpumping, the roundness and smoothness of the well casing shall beensured by passing a suitable hydraulic expanding tool throughoutthe entire well. The design of the expanding tool shall be such thatthe well casing will be stressed circumferentially to it's yield point.The surface of the tool will form a true cylinder in the expandedposition.

8.4.4 Water Sampling with Cable Tool Drilling

Where casing is installed as the well is drilled, water sampling is moreaccurate than with any other drilling procedure, particularly in alluvium.Even closely spaced alluvial aquifers often contain waters with consider-able quality variation. They may be the result of man-caused contamina-tion, usually found in the upper zones. In some areas,natural contaminantsare encountered randomly. Cable Tool sampling procedures are explainedin the following specification example.

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8.4.4.1WaterSamplingSpecification-CableTool Drilling

WaterSampling

To avoid perforating zones containing water unsuitable for theintendedwell use,the Contractorshallbe requiredto obtainwatersamplesasdirectedby the Engineer.It is anticipatedthatthe ques-tionableaquifer(s) arelocatedfrom - feetto - feet.

Successfulwater samplingrequiresthatthe easingshoe be seatedin clay or other aquiclude materialoverlayingthe questionableaquifers.The Contractoris cautionedthatin thosepartsof thewellwhere samplesmay be required,the casing shoe must be keptabovethe bottom of the boreholeto avoidprematurelyenteringazonewhich maybe sampled.

When sandor gravelindicatingthetop of anaquiferis encounteredin a potential samplinginterval,the Engineer shall be informed.After examiningtheformationsamples,theEngineerwill advisetheContractorwhether a sampleis required.

When orderedto takeawater sample,the contractorshallseatthecasingshoefirmly in the aquicludematerialnot lessthan five feetabovethe zone,and shalldrill up to 15feetof open hole into theaquifer,if practical.

If the Engineerdecidesthatonly a bailedwater sampleis needed,the Contractor shall bail the well until the calculatedvolume ofwater inside the casingand bore hole has been replacedat leastfour times.Following this, water shall be poured from the bailerinto cleanquartcontainerssuppliedby the Owner. Careshall betakenthat no contaminantsare introducedwhile pouring. Whenrolled, the containersshall be turned over to the Engineer. TheContractoris cautionedto with draw the bailer slowly as it clearsstaticwater level,to avoidcollapsingthe openhole.

If the Engineerdirectsthe Contractorto takeapumpedwater sam-ple, the following procedureshallbe followed. An inflatablepack-er furnishedby theContractorshallbe installedIn thewell on min-imum 6"- diameterpipe. The packershallbe placedin the easingstartersection,and inflatedsufficientlyto sealthewell.

After the packeris inflated,the Contractorshallfurnish andinstallinside the6"pipe a submersiblepump capableof producing-

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GPM. The pump shallbe operatedaminimumof eighthours (or asdirected by the Engineer).At the end of the pumping period,Owner supplied sanitarycontainersshallbe filled from the pumpdischargeIn amannerassuringthatno extraneoussubstanceentersthe samples.

After satisfactorysamplesare obtained,the sampling apparatusshallberemoved,anddrilling shallcontinue.When thenextaquiferis reached,the aboveprocedurewill be repeated.

It is anticipatedthataminimumof- andamaximumof -sampleswill be required.

Certain contaminantsare removed if air is mixed with water.

Becauseof the importanceof accurateinformation,airliftpumpingto obtain thewater sampleswill not be permitted.

8.5 WaterAnalysis Specification

The specificationsmayplacetheresponsibilityfor water sampleanalysison the Contractor.A typicalspecificationsectioncoveringthis follows:

Testing Water Samples

The samplesshallbe takenand testedat Contractor'sexpensebyan approved independentlaboratoryselectedby the Contractor.The Contractorshallmakearrangementsin sufficienttimeto avoiddelays.Watersamples shallbe collectedin new,unusedpolyethyl-ene"cubitainers"or in glasscontainerswith teflon-linedcaps.Theglasscontainersshallbe chemicallycleanedby the laboratory.Thecollected water samplesshall be analyzedat the laboratory asquickly aspossible.

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WaterAnalysisSpecification

Testsshallbe madefor the following:

Inorganic Chemicalsand WaterQuality

ArsenicBariumCadmiumMercurySeleniumSilverSodium

AlkalinityCalciumCopperMagnesiumManganeseSulphateZinc

FluorideHardnessIronNitratepHSilicon

Total dissolvedsolids

Radiological Contaminants

GrossAlpha

Volatile Organic Chemical Analysis

For Contaminantscontrolled by the Stateof California,tests asrequiredbyAB 1803.

Other Contaminants

Coliform Organism

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