Hydrocarbon-Related Diagenesis: The Key to Understanding Trap Integrity and Hydrocarbon Charge History in Australia's Timor Sea?

Geoffrey W. O'Brien, E. P. Woods, M. Lisk, and Melissa Fellows

In the Late Miocene, the effects of continental collision partially to completely breached many charged, Mesozoic traps in Australia's Timor Sea. An integrated geophysical and geochemical study has shown that the biodegradation of hydrocarbons leaking from these Mesozoic traps produced hydrocarbon-related diagenetic zones or HRDZs within overlying, Eocene aquifer sands. These HRDZs, which are principally defined by zones of intense carbonate cementation, are seismically-resolvable, with both their size and velocity being directly related to the amount of hydrocarbons that have passed through the aquifer sands. Consequently, the integration of observations on the seismic, velocity and isotopic characteristics of the HRDZs, the nature of present-day hydrocarbon seepage (as efined by sniffer and ALF data), and geometric relationships between the reactivation (Miocene) and trap (Jurassic) fault geometries, can provide a powerful predictive tool for evaluating and ranking undrilled structures and prospects within the Timor Sea.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California