Hydrocarbon evolution of the Bredasdorp Basin, offshore South Africa : from source to reservoir

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dc.contributor.author Davies, Christopher Paul Norman
dc.contributor.author Rozendaal, A.
dc.contributor.author Burger, B. V.
dc.contributor.other University of Stellenbosch. Faculty of Science. Dept. of Earth Sciences
dc.contributor.other Jacobs, Ivan
dc.date.accessioned 2010-12-06T13:26:14Z
dc.date.available 2010-12-06T13:26:14Z
dc.date.issued 1997-12
dc.identifier.uri http://hdl.handle.net/10019.1/4936
dc.description Thesis (PhD (Geology))--University of Stellenbosch, 1997. en_ZA
dc.description 1123 leaves printed on single pages, preliminary pages and numbered pages 1-286. Includes bibliography, list of figures and tables and explanation of abbreviations used. en_ZA
dc.description Digitized at 600 dpi grayscale to pdf format (OCR), using a Bizhub 250 Konica Minolta Scanner. en_ZA
dc.description.abstract ENGLISH ABSTRACT: This first comprehensive study of the petroleum geochemistry of the Bredasdorp Basin, and the adjacent Southern Outeniqua Basin, documents the characteristic large number of hydrocarbon shows and the four regionally distinctive marine source rocks. Detailed correlation of reservoired hydrocarbons with source rock bitumens shows that two source rocks have expelled oil in commercial quantities and two others have expelled commercial quantities of wet gas/condensate. In contrast with earlier studies which indicated that thermal 'gradualism' prevailed, this study indicates that the post-rift thermal history of the basin is very complex. Post-rift cool-down is punctuated by periods of rapidly increasing heat flow resulting in much of the maturation being localised in time. These periods of increased heating coincide with regional plate tectonism. The associated thermal uplift and downwarp effects govern the periods of trap formation and control the hydrocarbon migration direction. Migration distances of these hydrocarbons are described and show inter alia that oil migrates no more than -7-10 km but gas migrates regionally. Two regional episodes of meteoric water flushing reduce sandstone cementation in palaeo-highs forming potential reservoirs at specific times. The unusually low salinity of remnants of this water in some sandstones help characterise these two main migration conduits. A highly detailed hydrocarbon correlation scheme derived from gas, light oil and biomarker data has been established which differentiates products of the four active source rocks and helps characterise the oil-oil, oil-source and source-source pairs. It is evident from these correlations that two periods of migration and reservoiring occurred at 50-60 Ma and 0-10 Ma. As a result, source-reservoir plays which characterise certain areas of the basin as predominantly oil or gas prone can be described. These correlations also highlight areas where mixtures of hydrocarbons are common and where some of the early reservoired oil has been displaced to new locations, constituting potential new exploration plays. Source rocks for some of the analysed hydrocarbons have yet to be found and may not even have been drilled to date. One such source rock appears to be located in the Southern Outeniqua Basin, making that area a potential target for further exploration. This study resolved the common heritage of the source rocks and reservoir sandstones which form part of the Outeniqua petroleum system. The hydrocarbon volumes available to this system show that by world standards it is indeed significant. en_ZA
dc.description.abstract AFRIKAANSE OPSOMMING: Die groot aantal koolwaterstof voorkomste asook vier streekskenmerkende mariene brongesteentes word in hierdie eerste omvattende studie van die petroleumgeochemie van die Bredasdorp-kom en die aangrensende Suidelike Outeniqua-kom saamgevat. Gedetaileerde korrelasies van die opgegaarde koolwaterstowwe met brongesteente bitumen, dui daarop dat twee van die vier geidentifiseerde brongesteentes olie in kommersiele hoeveelhede uitgeset het. Die ander twee het kommersiele hoeveelhede nat gas-kondensaat uitgeset. In teenstelling met vroeer studies wat daarop gedui het dat termale 'gradualisme' voorgekom het, dui hierdie studie daarop dat die na-riftermale geskiedenis van die kom baie meer kompleks is. Verskeie periodes van versnelde toename in hittevloei het voorgekom in die na-rifse verkoeling. Dit het daartoe gelei dat veroudering plaaslik binne 'n beperkte tydsverloop plaasvind. Hierdie periodes van hittetoename stem ooreen met die regionale plaattektoniek. Die geassosieerde termiese opheffing en afwaartse vervormingseffek, beheer die totstandkoming van opvanggebiede en die migrasierigting van die koolwaterstowwe. Migrasie-afstande van die koolwaterstowwe word bespreek en wys inter alia daarop dat olie nie verder as -7-10 km beweeg nie, maar gasmigrasie vind regionaal plaas. Twee kort episodes van meteoriese wateruitsetting, het sandsteensementasie in palaeohoogsliggende gebiede verminder wat potensiele reservoirs gevorm het op spesifieke tye. Die ongewone lae soutvlakte van oorblyfsels van die water in sekere sandstene help om die twee vernaamste migrasieroetes te kenmerk. 'n Hoogs omvattende koolwaterstof-korrelasieskema wat van gas, ligte olie en biomerkerdata verkry is, is opgestel. Die skema het onderskei tussen produkte van die vier aktiewe brongesteentes en help om die olie-olie, olie-bron en bron-bron pare te karakteriseer. Dit is duidelik van die korrelasies dat twee periodes van migrasie en opgaring plaasgevind het ongeveer teen -50-60 Ma en 0-10 Ma. Gevolglik kan bronreservoir omskrywings wat sekere dele van die kom karakteriseer as grotendeels olie of gas-ontvanklik beskryf word. Hierdie korrelasies beklemtoon ook areas waar mengsels van koolwaterstowwe algemeen voorkom en waar sekere van die vroeer opgegaarde olie verplaas is na nuwe lokaliteite, wat nuwe eksplorasieteikens daarstel. Brongesteentes vir sekere van die ge-analiseerde koolwaterstowwe, moet nog gevind word en is tot op hede nog nie raakgeboor nie. Een so 'n brongesteente kom voor in die Suidelike Outeniqua-kom, wat daardie area 'n potenslele teiken vir verdere eksplorasie maak. Die studie het die gesamentlike oorsprong van die brongesteente en reservoirsandsteen, wat deel is van die Outeniqua Petroleumsisteem, geidentifseer. Die koolwaterstofvolumes wat beskikbaar is vir die sisteem wys dat, gemeet teen wêreldstandaarde, dit wel beduidend is. en_ZA
dc.language.iso en_ZA en_ZA
dc.publisher Stellenbosch : University of Stellenbosch en_ZA
dc.subject Petroleum -- Geology -- South Africa -- Southern Cape en_ZA
dc.subject Petroleum -- Geology -- Indian Ocean en_ZA
dc.subject Geochemistry -- South Africa -- Southern Cape en_ZA
dc.subject Geochemistry -- Indian Ocean en_ZA
dc.subject Geological modeling en_ZA
dc.title Hydrocarbon evolution of the Bredasdorp Basin, offshore South Africa : from source to reservoir en_ZA
dc.type Thesis en_ZA
dc.rights.holder University of Stellenbosch en_ZA


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