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ABSTRACT: Fluid and lithology prediction using seismic amplitude analysis: A deepwater exploration program case study, Northwest Shelf Australia

Criddle, D. S.1, D. M. Sibley2, and E. F. Herkenhoff3
(1) West Australian Petroleum Pty. Limited (WAPET), Perth, Australia 
(2) West Australian Petroleum Pty. Limited (WAPET) 
(3) Chevron

In 1996, WAPET acquired the WA-267-P permit located on the Northwest Shelf of Australia. The permit area covers over 5000 square kilometres and contains water depths ranging from 1000-1300 metres. Work commitments include drilling 6 wells in the first three permit years (1999-2001) at an approximate cost of A$25 MM per well. The primary objective of the program is to add significant gas reserves to WAPET's nearby gas resources which include Gorgon (1987-1999), Chrysaor (1995) and Dionysus (1996).

Seismic interpretation within WA-267-P revealed several prospects as structurally controlled 3 way or 4 way closures at key target horizons. Some of the prospects exhibited anomalous amplitude responses at potential reservoir objectives and were flagged as possible DHIs. However, seismic and rock property data in the area revealed high porosity brine bearing sands and low impedance coals could also yield anomalous seismic amplitude responses. It became clear that more information was needed to verify the causes of the seismic amplitude responses, and further refine the exploration risk associated with each prospect and reservoir objective. A solid amplitude analysis workflow was developed enabling confident seismic based fluid and lithology predictions for each prospect and reservoir objective within WA-267-P.

The pre-drill amplitude analysis process has successfully predicted the fluid and lithology type of every potential reservoir interval drilled in the program to date. This has included 3 separate gas bearing sands and one brine bearing sand encountered at Geryon (1999) and one gas bearing sand and one brine bearing sand encountered at Orthrus (1999).

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia