Abstract

Mathematical modeling and fluid inclusion data analysis are used to reconstruct the petroleum hydrogeology of the Australian Cooper and Eromanga basins. Our analysis focuses on the development of topography- and compaction-driven groundwater flow systems and their role in heat redistribution, petroleum generation, and oil and brine migration during basin evolution. Finite-element models of basin transport processes are constructed along northeast-southwest (AA') and northwest-southeast (BB') cross sections that generally follow the present-day groundwater flow patterns through these basins. Numerical results are presented in the form of three-dimensional evolving geologic fence diagrams. The most significant feature of basin paleohydrology was the development of topography-driven flow systems associated with two separate mountain-building events during the Tertiary and Pliocene-Holocene. Computed convective heat transfer effects resulting from these paleogroundwater flow systems produced thermal anomalies as high as 40 degrees C in recharge and discharge areas, causing source beds to attain peak oil generation in some areas. Computed oil heads also suggest that the Tertiary flow system may have focused oil migration in Eromanga carrier beds for hundreds of kilometers toward structural traps overlying the southern end of the Cooper basin. Computed saltwater heads indicate that the Tertiary and, to a lesser extent, the Pliocene-Holocene topography-driven flow systems probably also were responsible for flushing basinal brines out of the Cooper basin. Quantitative results are consistent with 36 Cl groundwater age measurements, vitrinite reflectance data, present-day geothermal gradient and groundwater salinity data, fluid inclusion paleosalinity data, and the location of proven oil reserves in the southern Cooper basin.

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