Table Of ContentPhilip Ringrose
Mark Bentley
Reservoir
Model Design
A Practitioner’s Guide
Second Edition
Reservoir Model Design
(cid:129)
Philip Ringrose Mark Bentley
Reservoir Model Design
’
A Practitioner s Guide
Second Edition
PhilipRingrose MarkBentley
EquinorASA TRACSInternationalLimited
NorwegianUniversityofScience Heriot-WattUniversity
andTechnology AberdeenandEdinburgh
Trondheim,Norway Scotland,UK
ISBN978-3-030-70162-8 ISBN978-3-030-70163-5 (eBook)
https://doi.org/10.1007/978-3-030-70163-5
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Preface
Thisbookisaboutthedesignandconstructionofsubsurfacereservoirmodels.
Intheearlydaysoftheoilindustry,oilandgasproductionwasessentiallyan
engineeringactivity,dominatedbydisciplinesrelatedtochemicalandmechan-
ical engineering. Three-dimensional (3D) geological reservoir modelling was
non-existent, and petroleum geologists were mostly concerned with the inter-
pretation of wire-line well logs and with the correlation of geological units
between wells. Two important technological developments – computing and
seismicimaging–stimulatedthegrowthofreservoirmodelling,withcomputa-
tionalmethodsbeingappliedtomapping,volumetricsandreservoirsimulation.
Geological or ‘static’ reservoir modelling was given further impetus from the
development of geostatistical techniques, allowing the reservoir modeller to
estimate inter-well reservoir properties and hence make statistical predictions.
3Dreservoirmodellinghasnowbecomethenorm.
Reservoirmodelsinthemselvesdonotgenerateprospectsordevelopment
scenarios, increase productivity or reduce risk and uncertainty. They are
simply tools which reflect our ability to achieve these goals. Advances in
reservoir modelling cannot therefore be compared to technology
breakthroughs such as 4D seismic imaging, horizontal drilling or EOR
methods. Reservoir modeling tools are, however, invaluable tools for
integratingknowledgeandformakingstrategicdecisions.
Astheworldmovesintotheenergytransitionandoilandgasproductionis
likely to decline, energy and transportation will be increasingly powered by
renewable or low-emissions technologies. In this new era, CO disposal and
2
subsurfaceenergystoragewillbecomeincreasinglyimportantandwillmake
new demands of subsurface modelling. The fluids used and stored in the
subsurface may change but the value of porous rock reservoirs will remain.
Wewillneverceasetoneedtoknowhowthesefluidsmoveinthesubsurface,
and modelling of subsurface reservoirs will remain a tool for building this
understandingandmakingusefulforecasts.
***
The explosion of reservoir modelling software packages and associated
geostatistical methods has created high expectations but also led to periodic
disappointments.Thishasgivenbirthtoanoftquotedmantra“allmodelsare
wrong.”
v
vi Preface
This bookemerged from a series of industry andacademic coursesgiven
bytheauthorsandaimedatguidingthereservoirmodellerthroughthepitfalls
andbenefitsofreservoirmodelling,inthesearchforareservoirmodeldesign
that is useful for forecasting. Reservoir modelling and simulation software
packagesoftencomewithguidanceaboutwhichbuttonstopressandmenus
touseforeachoperation,butlessadviceontheobjectivesandlimitationsof
the model algorithms. The result is that whereas much time is devoted to
modelbuilding,theoutcomesofthemodelsoftenfallshortoftheirobjectives.
Ourcentralcontentioninthisbookisthatproblemswithreservoirmodelling
tendnottostemfromhardwarelimitationsorlackofsoftwareskillsbutfromthe
approach taken to the modelling – the model design. It is essential to think
throughthedesignandtobuildfit-for-purposemodelsthatmeettherequirements
oftheintendeduse.Allmodelsarenotwrong,butinmanycasesmodelsareused
toanswerquestionswhichtheyweresimplynotdesignedtoanswer.
Wecannothopetocoverallthepossiblemodeldesignsandapproaches,and
wehaveavoidedasmuchaspossiblereferencetospecificsoftwaremodelling
packages.Ouraimistoshareourexperienceandpresentagenericapproachto
reservoir model design. Our design approach is geologically based – partly
because ofour inherentbiasasgeoscientists – but mainlybecause subsurface
reservoirsarecomposedofrocks.Theporespacewhichhousesthe‘blackgold’
ofthe oil age,the ‘goldenage’ ofgas orthefluidsdisposedandstoredinthe
new‘ageofsustainability’,hasbeenconstructedbygeologicalprocesses–the
depositionofsandstonegrainsandclaylayers,processesofcarbonatecemen-
tation and dissolution, and the mechanics of fracturing and folding. Good
reservoirmodeldesignisthereforefoundedongoodgeologicalinterpretation.
Thereisalwaysabalancebetweenprobability(theoutcomesofstochastic
processes)anddeterminism(outcomescontrolledbylimitingconditions).We
developtheargumentthatdeterministiccontrolsrootedinanunderstandingof
geologicalprocessesarethekeytogoodmodeldesign.Theuseofprobabilis-
ticmethodsinreservoirmodellingwithoutthesegeologicalcontrolsisapoor
basis for decisionmaking, whereas anintelligent balancebetweendetermin-
ismandprobabilityoffersapromisingpath.
We also discuss the decision-making process involved in reservoir
modelling.Human beingsarenotoriously badatmakinggood judgements–
athemewidelydiscussedinthesocialsciencesandbehaviouralpsychology.
Thesameappliestoreservoir modelling–howdoyouknowyouhaveafit-
for-purpose reservoir model? There are many possible responses, but most
commonly there is a tendency to trust the outcome of a reservoir modelling
processwithoutappreciatingtheinherentuncertainties.
We hope this book will prove to be a useful guide to practitioners and
students of subsurface reservoir modelling in the fields of petroleum geosci-
ence, environmental geoscience, CO and energy storage and reservoir
2
engineering – an introduction to the complex, fascinating, rapidly-evolving
andmulti-disciplinaryfieldofsubsurfacereservoirmodelling.
Trondheim,Norway PhilipRingrose
Edinburgh,UK MarkBentley
Tenby,UK
Prologue: Model Design
Successful Reservoir Modelling
This book offers practical advice and ready-to-use tips on the design and
construction of reservoir models. This subject is variously referred to as
‘geological reservoir modelling,’ ‘static reservoir modelling’, ‘3D reservoir
modelling’ or ‘geomodelling’, and our starting point is very much the geol-
ogy.However,theendpointisfundamentallytheengineeringrepresentation
of the subsurface and in this sense these notes will deal with the important
interfacewiththeworldofdynamic,simulationmodelling,withwhichstatic
modellingisintrinsicallyintegrated.
Our central argument is that whether models succeed in their goals is
generally determined in the higher level issue of model design – building
modelswhicharefitforthepurposeathand.
Basedonourownexperiencesandthoseofcolleaguesandgroupswehave
workedwithoncoursesandinreviews,wedistinguishfiverootcauseswhich
commonlydeterminemodellingsuccessorfailure:
1. Establishingthemodelpurpose
Whyareweloggedoninthefirstplaceandwhatdowemeanby‘fit-for-
purpose’?
2. Buildinga3Darchitecturewithappropriatemodellingelements
Thefluid-dependentchoiceonthelevelofdetailrequiredinamodel
3. Understandingdeterminismandprobability
Ourexpectationsofgeostatisticalalgorithms
4. Modelscaling
Reconcilingthejumpbetweenthescaleofdataandcellularresolutionof
our models, and how to represent pore-scale fluid flow reasonably at a
reservoirscale
5. Uncertainty-handling
Movingfromsingletomulti-modelsandwherethedesignbecomessubject
tobias
Strategies for addressing these underlying issues will be dealt with in the
following chapters under the thematic headings of model purpose, the rock
model, the property model, upscaling flow properties and uncertainty-
handling.
vii
viii Prologue:ModelDesign
In the later chapters we focus on specific reservoir types, as there are
generic issues which predictably arise when dealing with certain reservoirs.
We look specifically at how our experiences from modelling hydrocarbon
reservoirscanbeappliedtomodellingreservoirs(andtheiroverburdens)for
disposal and storage of CO or hydrogen. We share our experience, gained
2
frompersonalinvolvementinoverahundredmodellingstudies,significantly
augmented by the experiences of others shared in reviews and reservoir
modellingclassesoverthepast30years.
Beforeweengageintechnicalissues,however,areflectiononthecentral
themeofdesign.
Reservoirmodellersinfrontofrocks,discussingdesign(PhotographbyPhilipRingrose)
Design in General
Designisanessentialpartofeverydaylife,compellingexamplesofwhichare
to be found in architecture. We are aware of famous, elegant and successful
designs, such as the Gherkin – a striking feature of the London skyline
designed for the Swiss Re company by Norman Foster and Partners – but
we are more likely to live and work in less glamorous but hopefully fit-for-
purpose buildings. The Gherkin, or more correctly the 30 St. Mary Axe
building,useshalftheenergytypicallyrequiredbyanofficeblock,optimises
the use of daylight and natural ventilation (Price 2009) and embodies both
innovativeandsuccessfuldesign,althoughwithsignificantcomplexity.
Prologue:ModelDesign ix
There are many more examples, however, of office block and accommo-
dation units that are unattractive and plagued by design faults and
inefficiencies–thecarbunclesthatshouldneverhavebeenbuilt.
This architectural analogy gives us a useful setting for considering the
moreexclusiveartofconstructingmodelsofthesubsurface.
NormanFosterbuilding,30St.MaryAxe(PhotographfromFosterandBlaser(1993)–
reproducedwithkindpermissionfromSpringerScience+BusinessMediaB.V.)
Whatconstitutesgooddesign?Inourcontextwesuggesttheessenceofa
good design is simply that it fulfils a specific purpose and is therefore fit for
thatpurpose.
The Petter Daas museum in the small rural community of Alstahaug in
northernNorwayoffersanotherarchitecturalstatementondesign.Thisfairly
smallmuseum,celebratingalocalpoetanddesignedbythearchitecturalfirm
Snøhetta,fitssnuglyandconsistentlyintothelocallandscape.Itiselegantand
practical giving both light, shelter and warmth in a fairly extreme environ-
ment.AlthoughlackingthecomplexityandscaleoftheGherkin,itisequally
fit-for-purpose.Significantly,inthecontextofthisbook,itrisesoutfromand
x Prologue:ModelDesign
fitsintotheNorwegianbedrock.Itisanengineeringdesignclearlyfoundedin
thegeology–theessenceofgoodreservoirmodeldesign.
Whenwebuildmodelsoffluidresourcesinthesubsurfaceweshouldnever
ignore the fact that those resources are contained within rock formations.
Geologicalsystemspossesstheirownnaturalformsofdesignasdepositional,
diagenetic and tectonic processes generate intricate reservoir architectures.
Werelyonafirmreservoirarchitecturalfoundation,basedonanunderstand-
ing of geological processes, which can then be quantified in terms of rock
propertiesandconvertedintoaformusefultopredictfluidflowbehaviour.
ThePetterDassMuseum,Alstahaug,Norway(ThePetterDass-museum,#PetterDass-museum,
reproducedwithpermission)
Good reservoir model design therefore involves the digital representation
ofthenaturalgeologicalarchitectureanditstranslationintousefulmodelsof
subsurface fluid resources. Sometimes the representations are complex –
sometimestheycanbeverysimpleindeed.
References
FosterN,BlaserW(1993)Normanfostersketchbook.Birkhauser,Basel
Price B (2009) Great modern architecture: the world’s most spectacular
buildings.CanaryPress,NewYork
