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Detection of gas reservoirs by the joint use of P- and PS-waves: A case study on the Ordos basin, China |
Xiucheng Wei1, Xiangyang Li2, Yang Liu3, Songqun Shi4, Weidong Jiang5 |
1 Petroleum Exploration and Production Institute, China Petroleum and Chemical Corporation, Beijing 100083, China
2 Edinburgh Anisotropy Project, British Geological Survey, Edinburgh EH9 3LA, UK
3 Faculty of Resources and Information, China University of Petroleum, Beijing 102249, China
4 Changqing Research Institute, China National Petroleum Corporation, Xi’an 710021, China
5 Changqing Institute of East Geophysical Company, China National Petroleum Corporation, Xi’an 710021, China |
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Abstract We present an example of using converted-waves for characterizing onshore gas reservoirs in the Ordos basin in Northwest China. The Ordos basin is the largest gas province in China. The main gas reservoirs (about 3 300 m in depth) are in upper Paleozoic sandstone that has low or reversed P-wave impedance and is immediately above a coal seam. This makes it very difficult to image the gas reservoirs using conventional P-wave data. Analysis of core, log and VSP data shows a weak PP reflection but a relatively strong PS-converted wave reflection, or both strong PP- and PS-reflections but with opposite polarity from the gas bearing sands, which indicates the potential of using PS-waves to image the gas reservoirs in the Ordos basin. Subsequently, thirteen seismic lines were acquired, processed and interpreted to verify the PP- and PS-responses, and two corresponding attributes (PP- and PS- amplitude ratio and polarity ratio) are used to map the reservoirs through joint PP and PS analysis.
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Received: 24 September 2008
Published: 10 June 2009
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Corresponding Authors:
Xiucheng Wei
E-mail: weixc@pepris.com
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