Table Of ContentSeries Editor
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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,
