The Maturity And Hydrocarbon Prospectivity Of Mesozoic Source Rocks In The Vlaming Sub-Basin, Perth Basin, Western Australia.
Eldridge, Martin J
Honours Degree, 1992
University of Adelaide
The Vlaming Sub-basin of the Perth Basin is considered to be a region of high future prospectivity, containing several regional seals, proven reservoir units and complex structure conducive to the entrapment of hydrocarbons.
The aim of this study is principally to assess the source intervals within the Mesozoic sequence of the Vlaming Sub-basin, those likely to charge reservoirs within the practical range of drilling operations (<3500m).
A burial and hydrocarbon generation model was created to predict depth to, and time of, onset of hydrocarbon generation and to produce depth-maturity curves for the calibration of the D log R software package. The D log R method has been applied with some success but problems with it's application include baselining and the sensitivity of calculations to the maturity profile used.
Of the three source intervals central to this study, the Otorowiri Member of the Parmelia Formation is considered to hold the greatest potential, with average maturity equivalent to Rv = 0.65%, average TOC of 3.5% and a wide distribution across the sub- basin. The Carnac Member of the Parmelia Formation is only marginally mature, if not immature with an average maturity equivalent to Rv = 0.52%. TOC values are low for the Carnac Member averaging 1.3%. The South Perth Shale of the Warnbro Group is immature in all wells and considered to be so over the majority of the sub-basin. Low organic content, average TOC of 1.1%, lessen the source potential of this unit.
The D log R technique developed by Passey and co-workers at Exxon (1990) was used to assess the organic richness of three source intervals in terms of total organic carbon (TOC). The assessment of the future application of the D log R method as an alternative to generally costly evaluation of source richness by geochemical methods was the secondary aim.
A "dummy" well location, Pseudo #1, situated in what is considered to be one of the more prospective parts of the sub-basin, the western flank of the Rottnest Trough, was assessed in terms of source richness, maturation and hydrocarbon generation.
This location was judged to have good potential for exploration, with the Otorowiri Member within the hydrocarbon window. The undifferentiated sandstones of the Parmelia Formation (a known reservoir unit) immediately overlies the source to be sealed by the thick shales of the Carnac Member.