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《Journal of China Coal Society》 2015-S2
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Requirements of seismic offset data for CBM AVO analysis

GAO Yang;FENG Xi-hui;ZHU Fang-xiang;CHEN Xin-ping;CHEN Fu-yi;WANG Jun;School of Geophysics and Information Technology,China University of Geosciences(Beijing);Key Laboratory of Coal resource Exploration and Comprehensive Utilization,Ministry of Land and Resources,Shaanxi Coalfield Geophysical Prospecting and Surveying Group Co.Ltd.;Shaanxi Coal Geology Group Co.Ltd.;Geomodulus Energy Technology Co.Ltd.;School of Information,Xi'an University of Finance and Economics;  
In order to determine the optimal offset for CBM AVO( amplitude versus offset) analysis,the variation of Pwave reflection coefficient R( θ) versus θ,the average of incidence and transmission angles,the top boundary of a CBM( Coalbed Methane) reservoir and its derivative d( R( θ)) /dθ are explored with the help of geomodulus approximation of Zoeppritz equations,and compared with their counterparts of a C-gas( conventional gas) reservoir. d( R( θ)) / dθhas extreme value for the top boundary of a CBM reservoir,while R( θ) at the top boundary of a C-gas reservoir varies monotonously with increment in θ. Thus,the requirement for maximum offset by CBM AVO analysis is different from that required by C-gas AVO analysis,the rule for C-gas AVO analysis,i. e.,"the bigger the maximum offset the better the AVO analysis achievements",is not applicable for CBM AVO analysis,and the small offset can be used for CBM AVO. It is suggested that the optimal offset for CBM AVO analysis be determined according to the extreme value of d( R( θ)) /dθ. Three methods for determining the optimal offset for CBM AVO analysis are proposed in this study.
【Fund】: 国家自然科学基金资助项目(U1261111)
【CateGory Index】: P631.4
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