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ABSTRACT: The prediction of sweet-spots using 2-D seismic data

Urosevic, Milovan1, Brian J. Evans1, and Jonathon D. Cocker2
(1) Curtin University, Perth, Australia 
(2) WA Petroleum, Perth, Australia

Coalseam methane 'sweet spots' are difficult to sense using seismic data, because the high reflectivity of coal does not allow the conventional methods of exploration, such as amplitude versus offset (AVO) application, which is commonly used for gas detection in other sedimentary structure.

The Bowen Basin of Queensland, Australia is said to contain more gas reserves adsorbed in coal than currently exists elsewhere within Australia. At Moura, a coalbed methane explosion killed a number of coal miners a few years ago, and any technique which could help locate sweet spots would not only be useful economically but would also help with hazard prediction.

This paper details a case history of using the conventional seismic technique at Kianga, an exploration site very close to Moura and containing similar geology to the Moura mine site. The paper explains how nine boreholes were drilled along a 2 km line, from which gas desorption tests were conducted. A seismic line was then recorded, following which a specialised seismic attribute approach was adopted, to tie-in the borehole data with the seismic section.

The end product was a seismic line which shows a number of faults and fractures, compartmentizing the sweet spots, and tieing-in with the gas desorption tests and borehole lithology. If such an attribute was produced at all mine sites, it would then be available for use thereafter for both the economic extraction of the gas and for improved hazard detection ahead of mining.

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