beyond fault seal analysis - Force

Reservoir compartmentalisation inHTHP reservoir: beyond fault sealanalysisQuentin FisherCentre for integrated Petroleum Engineering and GeoscienceUniversity of Leeds, UKE:-mail: q.fisher@see.leeds.ac.ukCiPEG

Outline• Impact of faults on petroleum production• Incorporating of fault properties intoproduction simulation models• Examples of successful and unsuccessfulfault seal analyses• Other causes of reservoircompartmentalisation• ConclusionsCiPEG

Impact of faults on gas productionCiPEG(From van der Molen et al., 2003)

Fault Seal Types in SiliciclasticsJuxtaposition seal(by far the mostcommon type ofbarrier toproduction)CiPEGFault rock seal(fault seal sensustricto)- This appears to be thecase for Rotliegendexample

CiPEGFault rock seals

CiPEGCalculation of transmissibilitymultipliersjfjffifiijktLktktLTrans22TM =jjiiijkLkLTrans2

Extensive databases on faultproperties are now availableRotliegendBrent 3500 mBrent 2500 mCiPEG

Standard fault seal analysis workflowMap faultsEstimate faultrock propertiesSimulationmodelCiPEGCalculate faulttransmissibility multiplierEstimate claycontent of fault

Simulation model using singlephasefault permeabilitiesvan der Molen et al., (2003)CiPEG

BHP (psi)History match from HTHP reservoir4000350030002500200015001000500No TMTM = 0.1TM = 0.01BHP00 50 100 150 200 250Time since start of production (days)CiPEGFault TMs altered on a trial and error basis until a historymatch is achieved

Fault rock permeability needed forhistory matchRotliegendJurassicCiPEGFault TMs required to achieve history match are oftenequivalent to permeabilities that are far lower than aremeasured

So why are fault permeabilitiesneeded for history matches often farlower than measured in core?CiPEG

Relative permeability of faults321CiPEG

Lossiemouth Fault: Hopeman sandstoneHostFaultCiPEG

Capillary pressure (psi)Gas relative permeability – Hopeman fault600.00500.00400.00300.00200.00100.00CiPEGAl-Hinai et al, 20080.000.00 0.20 0.40 0.60 0.80 1.00Water saturation

Fault-related barriers to gasproductionCiPEG

CiPEGMiri cataclasite

Oil-water relative permeability – Miricataclasite/pffrCiPEG

Variation in clay content between differentinterpretations of log dataSponsor ASponsor BSponsor CSponsor DCiPEGFrom Fisher et al. 2003

Stress sensitivity of fault rockpropertiesCiPEG

Permeability (mD)Stress dependence of permeability andPermeability ratioKrgrelative permeabilityDry Mam Tor samplesStress dependence of relative permeability duringloading0.00350.003100.00250.0020.00150.001K1D1A1110.1Sw = 44.4%Sw = 40.5%Sw = 66%0.000500 500 1000 1500 2000Effective stress (psi)0.010 500 1000 1500 2000 2500Effective stress (psi)1614121086Partially saturatedDry420900 1100 1300 1500Difference in effective stress (mD)

Stress dependence of absolutepermeabilityFrom Cluff et al., (2009) Tight Gas SPE Forum• Stress dependence ofabsolute permeability oftight gas sands• No stress dependenceabove 10 mD• Suggests publisheddatabases of permeabilityof low permeability faultrocks should be treatedwith caution• Doesn’t help explainMiddle Jurassic historymatches

Stress dependence of Hg injection data• Stress dependence ofabsolute permeability of tightgas sands• No stress dependence above1 mD• Suggests publisheddatabases of Hg-injectiondata from low permeabilityfault rocks should be treatedwith caution• Doesn’t help explain MiddleJurassic history matchesFrom Cluff et al., (2009) Tight Gas SPE Forum

So why are such low faultpermeabilities needed to historymatch some reservoir models?It’s not the faults fault• Other possibilities include:-– Lack of sediment connectivity– Misrepresentation of three phase flow properties insimulation models– Overestimation of sediment permeabilityCiPEG

Reservoir quality in HTHP reservoirs• Rapid decrease inpermeability below12000’ due to quartzcementation and illiteprecipitation etc.• Larger uncertainties incore analysis due tostress dependency,failure to reach capillaryequilibrium, damage ofillite etc.CiPEG(from Giles et al. 1992)

Diagenetic compartmentalisationCiPEG1 mD difference in thepermeability of thereservoir can have thesame impact as a partiallysealing fault

CiPEGConclusions• To gain history match of many HTHP reservoirs far lower faulttransmissibility multipliers are used than can be justified based onpublished fault rock permeability data• Taking into account problems with existing databases on faultrock properties does not provide good explanation for why suchlow TM values are needed for history match• Overestimation of sediment connectivity or failure to properlymodel 3-phase flow may be an issue• Diagenetic alteration maybe responsible for poor communicationbetween injectors and producers– Potentially reservoir permeability is slightly overestimated– Transition zone forms a permeability jail: consistent with lackof aquifer support in many HTHP reservoirs

Acknowledgements• BG, BP, Chervron, ExxonMobil, Petrobras, Total, Shell, Statoil forsponsoring research• Roxar for providing Tempest TM license• Schlumberger for providing Eclipse TM licenseCiPEG