Series Editor John Cubitt Holt, Wales Elsevier Radarweg29,POBox211,1000AEAmsterdam,Netherlands TheBoulevard,LangfordLane,Kidlington,OxfordOX51GB,UK 225WymanStreet,Waltham,MA02451,USA Firstedition2015 ©2015ElsevierB.V.Allrightsreserved. Nopartofthispublicationmaybereproducedortransmittedinanyformorbyanymeans, electronicormechanical,includingphotocopying,recording,oranyinformationstorageand retrievalsystem,withoutpermissioninwritingfromthepublisher.Detailsonhowtoseek permission,furtherinformationaboutthePublisher’spermissionspoliciesandourarrangements withorganizationssuchastheCopyrightClearanceCenterandtheCopyrightLicensingAgency, canbefoundatourwebsite:www.elsevier.com/permissions. Thisbookandtheindividualcontributionscontainedinitareprotectedundercopyrightbythe Publisher(otherthanasmaybenotedherein). Notices Knowledgeandbestpracticeinthisfieldareconstantlychanging.Asnewresearchand experiencebroadenourunderstanding,changesinresearchmethods,professionalpractices,or medicaltreatmentmaybecomenecessary. Practitionersandresearchersmustalwaysrelyontheirownexperienceandknowledgein evaluatingandusinganyinformation,methods,compounds,orexperimentsdescribedherein. Inusingsuchinformationormethodstheyshouldbemindfuloftheirownsafetyandthesafety ofothers,includingpartiesforwhomtheyhaveaprofessionalresponsibility. Tothefullestextentofthelaw,neitherthePublishernortheauthors,contributors,oreditors, assumeanyliabilityforanyinjuryand/ordamagetopersonsorpropertyasamatterofproducts liability,negligenceorotherwise,orfromanyuseoroperationofanymethods,products, instructions,orideascontainedinthematerialherein. ISBN:978-0-444-63533-4 ISSN:0376-7361 ForinformationonallElsevierpublications visitourwebsiteatstore.elsevier.com Series Editor’s Preface ThisisthefifthbookintheDevelopmentsinPetroleumScienceseriessinceit incorporatedtheHandbookofPetroleumExplorationandProductionin2013. After books on geophysics, stratigraphic reservoir characterisation, petrophy- sics and integrated sand management, we now switch our attention to core analysis. Intheongoingsearchforoilandgasaroundtheworld,muchofourunder- standing of the nature and distribution of hydrocarbon-bearing reservoirs is obtained through remotely sensing the subsurface. We are all familiar with the use of modern seismic, gravity, magnetic and electromagnetic techniques in the exploration for these reservoirs, but these techniques have also been enhanced to provide ongoing or time-lapse reservoir monitoring capabilities during production of reservoir fluids. These techniques for remote sensing are also used in drilling and petrophysics to understand the nature and distri- bution of various types of rocks and fluids. However, in the evaluation of oil and gas reservoir rock properties, there are no techniques that allow us to directly see or measure the properties of these subsurface reservoirs, with a single exception. Core analysis is the one and only method of quantitatively measuring reservoir properties at surface or simulated subsurface conditions by the rigorous laboratory testing of cores obtainedthroughdrilling,beitforconventionalorunconventionaloilandgas reservoirs.Itenablesbothexplorationgeoscientistsandreservoirdevelopment teams to provide quantitative control of their exploration or production mod- els and to determine the quantity of hydrocarbons in place and the speed that whichitcouldbeproduced.Ultimatelythiscanleadtoabetterunderstanding of commercial viability of the in-place hydrocarbons. This book reviews the vitally important area of core analysis and the best laboratory and field practices needed to obtain the highest quality data with minimal errors, thereby maximizing the value of the data to exploration geo- scientists and reservoir engineers. It should therefore be essential reading for those professionals active in hydrocarbon field exploration or production worldwide. In particular as the authors state, this book ‘should provide the foundation or ground truth upon which formation evaluation rests’. John Cubitt Holt, Wales xvii Preface In the evaluation of oil and gas reservoirs, core analysis provides the only direct and quantitative measurement of the reservoir properties and should providethefoundationorgroundtruthuponwhichformationevaluationrests. Geologists, reservoir engineers, and petrophysicists rely on accurate and rep- resentativecoreanalysisdatatoprovidekeydatainputforbuildingstaticand dynamic reservoir models. However, variable laboratory test and data report- ingstandardshaveresultedinvariabledataquality.Coupledwithaninconsis- tent and inexperienced approach to the design and management of the laboratory test programmes, this has led to a situation where, in the authors’ extensive global experience, around 70% of legacy special core analysis (SCAL) data are not fit for purpose. There are few books on core analysis and its applications, and only one industry-recognised recommended practice, which although largely still rele- vant and appropriate, does not fully cover SCAL and has not been updated foralmostover25years.Theobjectiveofthisbookistoprovidetheendusers of coreanalysisdata with the essentialinformation that they need toenable a more pro-active, more coherent, and more consistent approach to programme design,dataacquisition,andqualitycontrolofcoreanalysisdata.Theauthors are actively engaged in the design and management of laboratory core analy- sis programmes and in interpreting and using the data. Frustrated by the lack of standards and the often inadequate utility of core analysis data, we have written practical and pragmatic guidelines for core analysis best practice that shouldmaximisedataquality,encouragemoreeffectiveengagementbetween the end users and the data acquisition laboratories, and thereby add value to core analysis investments. Obtaining high-quality, undamaged core is the essential prerequisite for representativeandreliablecoreanalysisdata.Wethereforestartbydescribing theprincipalcoringsystemsandfluids,andhowtoidentifyandminimisedam- agetothecoreonitsjourneyfromthereservoirtothetestlaboratory.Analysis isusuallyperformedonplugsamplescutfromcore,sowediscussthemethods andequipmentusedtocutplugsandpreparethemforanalysisandtheirimpact on the measured properties. Specialist preparation methods for wettability conditioningandpreservationofdelicatemineralogiesaredescribed. Routine core analysis typically involves “as received” fluid saturation measurements, and porosity and permeability measurements on dry plugs, xix xx Preface which are used to characterise the reservoir properties and for log-core inte- gration.Asthetestequipmentandmethodsvarybetweenlaboratories,welist theadvantagesanddrawbacks/issuesassociatedwitheachtestandsummarise quality control checks and diagnostics. SCALmeasuresfundamentalstaticanddynamicreservoirrockproperties, oftenatreservoir-appropriatefluid,stress,andtemperatureconditions.Correct planning for SCAL tests is fundamental to the acquisition of high-quality, formation-representative data, so we focus on: the preparation and character- isation of test fluids; how to select and screen representative test plugs; and howtodeterminetheequivalentreservoireffectivestress.Formationwettabil- ity is a fundamental rock property. We describe laboratory wettability tests but, more importantly, the controls on native wettability and how wettability can bealteredduringcoring, core recovery,and core handling, andthe meth- ods used to try and restore native wettability conditions. We then focus on the principal SCAL tests: porosity and permeability at overburden stress; electrical properties for clean formations and shaly sands; capillary pressure; nuclear magnetic resonance (NMR); and relative perme- ability. We explain the various core test conditions, test methods, equipment, and procedures, and data reporting requirements. The advantages and draw- backs/issuesofeachsuiteoftestsaredescribed,andthequalitycontrolchecks and diagnostics are summarised. We clarify the corrections and refinement protocols used to process laboratory data for static and dynamic model input. As core also supplies a source for geomechanical measurements for faster and safer drilling and better completions, we include a chapter on rock mechanics tests and particle size analysis tests. Finally, we provide generic examples of core analysis test programmes that the reader can use as guide or template to design and specify the workflow for core test programmes on oil and gas reservoirs. Followingthebestpracticeguidelinesinthisbookwillbenefitpetrophysi- cists,geoscientists,reservoirengineers,andproductionengineerswhousethe data but are often unaware of the uncertainty range. These are merely guide- lines,gainedfromyearsofexperience,andarenecessarilygeneric:eachreser- voirisdifferentandthedatarequiredtocharacteriseandaidfielddevelopment planningshouldbeconsideredanddiscussedwithrecognisedspecialistsbefore finalising the detailed experimental programme. Nevertheless, we hope the reader will gain a better understanding of core analysis procedures and meth- ods;bebetterplacedtojudgethequalityofcoreanalysisdata;andultimately beabletoreduceuncertaintyinstaticanddynamicreservoirmodels. This book is based on material from many sources including hundreds of laboratory reports; publications from the Society of Petroleum Engineers, the Society of Professional Well Log Analysts, the Society of Core Analysts; academic institutions; as well as oil company and service company websites. All reasonable effort has been made to trace and refer to the sources of these materials. Preface xxi We wouldliketorecognisethecooperationoftheoilcompanies andcore analysis laboratories who have helped us develop these best practice guide- lines. Labs aim to deliver excellent work often under trying circumstances. We are also indebted to the various companies and organisations who have given us permission to include their material in this work, and the manage- mentofLRSenergyfortheirsupport.Thisbookwouldnothavebeenpossible without the contributions, encouragement, and assistance of the following people: Mel Boulby, Mike Byrne, Tim Conroy, Gill Daniels, Bob Harrison, Lynne Harrower, Michelle Hubbard, Elise Johnston, Rick Lemanczyk, Michele Loseto, David Milton-Tayler, Iain Morrison, Phil McCurdy, Georgia McKendrick, Vivien MacKinlay, John Owens, Max Podolyak, Chris Reed, BethReid,YelitzaSorrentino,MariaVelazco,GrahamWebber,andPhanthip Wongtui. The authors thank their families for the patience and understanding they have shown duringpreparation of thisbook. Finally,we are thankful for the encouragement and patience of Elsevier editorial staff, particularly Derek Coleman and the series editor, John Cubitt. Colin McPhee Edinburgh, UK Jules Reed Aberdeen, UK Izaskun Zubizarreta Aberdeen, UK June 2015 Chapter 1 Best Practice in Coring and Core Analysis Chapter Outline 1.1 CoreAnalysisData:The 1.4 BestPracticeinCoreAnalysis: FoundationofFormation AnOverview 11 Evaluation 1 1.4.1 Coring,CoreHandling 1.2 CoreAnalysisDataUncertainty 4 andCoreProcessing 12 1.2.1 ReasonsandConsequences 4 1.4.2 SamplePreparation 12 1.2.2 ReducingUncertainty 8 1.4.3 RoutineCoreAnalysis 12 1.3 CoreAnalysisManagement 1.4.4 SpecialCoreAnalysis 12 Framework 8 1.4.5 GeomechanicsTests 13 1.3.1 CoreAnalysisPlanning 1.4.6 QualityControl andDesign 8 Proceduresand 1.3.2 ProgrammeDesign Diagnostics 13 Considerations 9 1.4.7 ExampleCoreAnalysis 1.3.3 CoreAnalysisFocalPoints 9 Programmes 14 1.3.4 Real-TimeQuality 1.4.8 Benefits 14 Control 11 References 15 1.1 CORE ANALYSIS DATA: THE FOUNDATION OF FORMATION EVALUATION The primary goal of geologists and petrophysicists is to estimate the volume of hydrocarbons initially in place in a reservoir. The primary goal of the res- ervoir engineer is to understand the physics of the reservoir-fluid system so thattheultimaterecoveryofhydrocarbonsismaximisedinthemosteconomic matter.Bothrequireadetailedknowledgeofthereservoirgeometry,structure and the interaction between the reservoir and the fluids, either in place, or which may be introduced into the reservoir. In reservoir modelling, a com- puter model of the reservoir is constructed by geologists, petrophysicists andgeophysiciststoprovideadescriptionofthereservoirwhichisprincipally used to determine the volumes of hydrocarbon in place. This is normally referred to as a static model. Reservoir simulation models are constructed DevelopmentsinPetroleumScience,Vol.64.http://dx.doi.org/10.1016/B978-0-444-63533-4.00001-9 ©2015ElsevierB.V.Allrightsreserved. 1 2 CoreAnalysis:ABestPracticeGuide by reservoir engineers to describe and map the hydrocarbon recovery pro- cesses under different production mechanisms. These dynamic models are principally used to determine reserves and recovery factors and to predict hydrocarbon production profiles for economic analysis. Both static and dynamic reservoir models draw on a variety of disparate datasourcesincludingregionalgeology,seismic,sedimentologicalmodelling, drilling data, wireline and logging/measurement while drilling data, fluid pressures and rock and fluid property data. The nature and quality of the model input data change throughout the lifetime of a field, so it is important toconstantlyreviewdataqualitytominimiseuncertaintiesandtoincludedata quality assessment in reservoir modelling. The quantity and quality of data used for both static and dynamic reservoir modelling must always be fit for purpose and match the field development objectives. Coreisnormallytheonlypartofthe(relatively)undisturbedreservoirfor- mation we can actually see, touch and feel at the surface. Consequently, core analysis data should be the “ground truth”, or the foundation upon which integrated formation evaluation and reservoir characterisation rest. All other data sources are essentially remote, so reliable and representative core analy- sis data are essential to calibrate and validate other data. Forexample,thevolumeofstocktankoilinitiallyinplace(OIIP)inares- ervoir can be determined from (cid:1) (cid:3) N 1 OIIP¼GRV fð1(cid:2)SwÞ (1.1) G B o Determinationofthegrossrockvolume(GRV)andgrossfactor(G)inthe net/gross ratio (N/G)isthe primaryresponsibilityof geophysicistsandgeolo- gists. The reservoir engineer is responsible for oil formation volume factor (B )frompressure,volumetemperature(PVT)experiments.Thepetrophysicist o is responsible for net (N), porosity (f) and water saturation (Sw) where data input relies principally on logs. Reservoir net thickness is normally defined byapermeabilitycut-off,andhigh-resolutionpermeabilitydataareonlypossi- blefromcore.Porosityinterpretation(e.g.fromdensitylogs)shouldbeverified by,orcalibratedagainst,stressedcoreporosities.Resistivityloginterpretation requires core electrical property measurements to quantitatively determine watersaturationincleanformations,andnormalisedcationexchangecapacity isrequiredtocorrectformationresistivityresponseforthepresenceofconduc- tive clays. Water saturation can be determined directly by extracting water fromcoreusingDeanStarkorretortmethodsorindirectly,fromprimarydrain- agecapillarypressuremeasurements. Thetypicalcoreanalysistestswhichareofferedbycommercialcoreanalysis vendors and used as data input in petrophysical static models are summarised inTable1.1.Historicallythesetestswerecarriedoutonlyatambientconditions (lowornoconfiningstress;ambientlaboratorytemperature),butmostcommer- cial laboratories can now provide these tests at more representative reservoir- appropriatestress,fluidandtemperatureconditions. BestPracticeinCoringandCoreAnalysis Chapter 1 3 TABLE1.1 TypicalCoreAnalysisDataInputtoVolumetricCalculations (StaticModels) Parameter DataSource TestMethods Net Permeability Airpermeability(ambientorreservoirstress) Klinkenbergpermeability(ambientor reservoirstress) Brine(water)permeability(ambientor reservoirstress) Probepermeability(ambientconditions) Porosity Densityporosity Heliumporosity(ambientorreservoirstress) Resaturationporosity(ambientorreservoir stress) Water Electrical Formationresistivityfactor(ambientor saturation parameters reservoirstress) Resistivityindex(ambientorreservoir- appropriateconditions) Wetchemistrycationexchangecapacity (CEC)forshalysands(ambientconditions) Multiple-salinitytests(normalisedCEC)at ambientorreservoirstress Primarydrainage Low-pressuremercuryinjection(ambientor capillarypressure reservoirstress) High-pressuremercuryinjection(ambient conditions) Gas–wateroroil–waterporousplate (ambientorreservoir-appropriateconditions) Gas–wateroroil–watercentrifuge(ambient conditionsorlimitedreservoirstress) Direct Retortextraction(ambientconditions) measurement Dean-Starkextraction(ambientconditions) As Dake (1991) points out, “determination of the recovery factor is the most important single task of the reservoir engineer”. Recovery factors may bedeterminedonpurelytechnicalcriteria,but,moreprobably,oneconomic or environmental terms. For example, hydrocarbon recovery efficiency in a waterfloodinanoilreservoirislargelygovernedbythemobilityratio: M krwm M¼ rw¼ w (1.2) M krom ro o where M and M are the relative mobilities of water and oil, respectively. rw ro The parameters kro and kro are the relative permeabilities to oil and water, 4 CoreAnalysis:ABestPracticeGuide and m and m are water and oil viscosities, respectively. If kro and krw are w o relative permeabilities at residual phase saturations (kro at irreducible water saturation, Swir, and krw at residual oil saturation, Sro), then M is defined as the endpoint mobility ratio. If this value is (cid:3)1, then in a waterflood, oil cantravelthroughthereservoirataspeedgreaterthanorequaltowater.This “piston-like” displacement results in a sharp interface between the fluids whichminimisesoilbypassandresultsinaveryefficientdisplacement.How- ever,ifMis>1,watercantravelfasterthanoilleadingtoearlierwaterbreak- through at producers, and a poor or unstable displacement resulting in oil bypass. It may take injection of several barrels of water to recover one barrel of oil. Relative permeabilities of oil, gas and water therefore provide key input data in reservoir dynamic modelling. Thetypicalcoreanalysistestswhichareofferedbycommercialcoreanal- ysis vendors and used as data input in dynamic reservoir models are sum- marised in Table 1.2. This is not meant to be exhaustive—rather it lists the principal tests to determine the key modelling parameters. Combinations of twoormoretestsarenormallyrequiredtofullydefinetheparametersrequired to predict recovery factors under different drive mechanisms and to describe fluidmovementforsaturated andunder-saturatedoilreservoirs,leanand rich gasreservoirsandgascondensatereservoirs.Historicallythesetestswerecar- ried out only at ambient (low or no confining stress; ambient laboratory tem- perature) conditions using synthetic fluids, but many commercial laboratories now provide these tests at more representative reservoir-appropriate stress, fluid and temperature conditions. 1.2 CORE ANALYSIS DATA UNCERTAINTY Potentially, core analysis is the only direct and quantitative measurement of the“intact”reservoirpropertiesandshouldunderpinstaticanddynamicmod- elling. Harrison (2009) argues that taking and analysing core in increasingly more complex reservoirs have never been more important. Core and core analysis data confirm lithology and mineralogy; calibrate estimates of funda- mental rock properties; show how fluids occupy and flow in pore space; and supply a source for geomechanical measurements for faster and safer drilling andbettercompletions.Harrisonpointsoutthat“logsalonecannotcharacter- ise the reservoir if knowledge of the rock is absent so subsequent modelling must rely on un-calibrated and unverified log-derived correlations”. The pre- dictable consequence of not having core analysis data is greater uncertainty. 1.2.1 Reasons and Consequences Basedontheauthors’extensiveexperienceintheacquisition,verificationand interpretationofcoreanalysisdataofdifferentvintagesfromacrosstheworld,