Thesis (PhD (Geology))--University of Stellenbosch, 1997. / 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. / Digitized at 600 dpi grayscale to pdf format (OCR), using a Bizhub 250 Konica Minolta Scanner. / 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. / 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.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/4936 |
| Date | 12 1900 |
| Creators | Davies, Christopher Paul Norman, Rozendaal, A., Burger, B. V. |
| Contributors | University of Stellenbosch. Faculty of Science. Dept. of Earth Sciences, Jacobs, Ivan |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Rights | University of Stellenbosch |
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