Quantitativemaps ofthe reconstructed oilandgaspotentialofthe DraupneandHeatherFormation in the SouthVikingGrabenwereproduced inordertoimprovethe understandingoflateralandverticalvariations in the typeoforganic matter. For thispurposethe DraupneFormation wassubdivided into alowersynriftandan upperp ostriftp art (UpperandL owerDraupneF ormation,respectively). Bothsections show large lateral variability insource rock quality andoilandgaspotential. The totalTOC distribution isstrongly related to the depositionalenvironment andalso to the preservation oforganic matter. The UpperDraupneFormation exhibits equally high amounts ofoil-andgas-proneorganic matter. The LowerDraupneFormation shows aconsiderably higheramount ofland-derived TypeIII organic matter,which decreasesupwardsandtowardsthe UtsiraHigh. The marineTypeIImaterialinthe synriftsection isless abundant,becauseofdilution ofthe marinematerialby terrestrialm aterialt ransported bym ass flows from the surroundingh ighs. Thesefi ndingsaresupported by environmentalm oleculardata.The HeatherFormation isamixtureoftype-III and-II kerogenandshows moderateto goodg asp otential. The source rock sections werea lso correlated usingthe relativeoccurrence of bisnorhopaneint he rock extracts.Keywords: source rock, organofacies,mapping, oilpotential,gaspotential,NorthSea, Norway,hydrocarbon system,bisnorhopaneThe NorwegianSouthern VikingG raben,f rom the Frigg to the SleipnerFields,i saprolific hydrocarbon province with 255.2 £ 10 6 Sm 3 oiland4 29.7 £ 10 9 Sm 3 gasr ecoverablei nt he NorwegianSector. Although amatureexploration area, anumber ofundrilled leadsandprospects remainwithconsiderablereserve potential. Animproved quantified understandingofthisarea will be animportant tool ins olvinge xploration andproduction problems,will uncovernewplays andbringnewlife to exploration int he area.Thiss tudyisp art ofa'Petroleum SystemAnalysis' project inwhich the understandingofhydrocarbon generation,migration, filling-andloss-historiesisemphasized.The aimist oimprove the fundamentalu nderstandingofthe processescontrolling the accumulation ofh ydrocarbons andtheirq uality int he South VikingG raben. Whilst the reservoirs on the eastern side ofthe basin( NorwegianSector) ared ominated bygasdiscoveries, oilist he dominant hydrocarbon phaseon the western side (UK sector) (Eriksen etal .2 003). Thisdistribution ofpetroleum int he asymmetric Southern VikingG rabens eems primarily to be af unction ofthe tectonostratigraphicd istribution of source rocks,c arrierbedsandtraps and, secondarily,the organic faciesv ariations ofthe UpperJurassic Draupnea ndH eather Formations.Thisv ariation oforganofaciesandsource rock potentialint he GreaterBalderArea wasinvestigated bydetailed source rock analysisandsubsequent mappinga ndi nterpretation. The quantitativemaps ofoilandg asp otentialp roduced canbe used for calculations ofthe hydrocarbon volumesp roduced ande xpelled, andhence charge-to-trapcalculations.Various The UpperJurassic shalesareoftenr egarded ashomogeneous anda ss uch not furthe...
Source facies and quality of the Late to Middle Jurassic source rock system in the South Viking Graben between 58°N and 60°15'N are highly variable both regionally and stratigraphically. In order to assess the degree of variability and to create a model of source rock quality and potential, isochore maps of the syn‐ and post‐rift sections of the Upper Jurassic Draupne Formation and underlying Heather Formation were generated from seismic and well data, and maturity‐corrected Rock‐Eval data were used to generate quantitative maps of oil and gas potential. The thin post‐rift section at the top of the Draupne Formation is a rich oil‐prone source, while the up to 1,600 m thick syn‐rift section contains a mixture of Type III and Type II material with substantial amounts of gas‐prone and inert organic matter. The Heather Formation, which reaches modelled thicknesses of up to 930 m, is a lean source and is generally gas‐prone. Detailed analyses and interpretations of biomarker and isotopic characteristics support this upward increase in oil‐prone Type II material. The analytical parameters include increasing relative amounts of C27 regular steranes; decreasing ratios of C30 moretane relative to C30 hopane; and an increasing predominance of short chain n‐alkanes and progressively lighter isotopic values for saturate and aromatic fractions of source rock extracts. In addition, increasing amounts of 17α(H),21β(H)‐28,30‐bisnorhopane and decreasing amounts of C34 homohopanes relative to C35 homohopanes, as well as decreasing Pr/Ph ratios, suggest a general decrease in oxygenation upwards. Maps of average Pr/Ph ratios for the syn‐ and post‐rift Draupne Formation and for the Heather Formation are consistent with permanent water column stratification and gradual ascent of the O2:H2S interface from the Callovian to the Ryazanian. Interpretation of oil and gas potential maps, molecular parameters and estimates of sediment accumulation rates in combination suggest that the source facies of the upper, post‐rift Draupne Formation is controlled by widespread anoxia, reduced siliciclastic dilution and reduced input of gas‐prone organic and inert material; by contrast, the potential of the lower, syn‐rift Draupne Formation is strongly controlled by dilution by gas‐prone and inert organic matter resulting from mass flows and also by varying degrees of oxygenation. The oil and gas potential of the Heather Formation is mainly controlled by the degree of oxygenation and siliciclastic dilution.
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