Evaluation of CBM reservoir fracture characteristics by azimuthal AVA inversion

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• 作者：Yiming Zhuang ; Shouhua Dong ; Haibo Wu ; Yaping Huang
• 关键词：Fracture density ; Fracture strike ; HTI medium ; Azimuthal AVA ; Azimuthal gathers
• 刊名：Arabian Journal of Geosciences
• 出版年：2017
• 出版时间：February 2017
• 年：2017
• 卷：10
• 期：3
• 全文大小：
• 刊物类别：Earth and Environmental Science
• 刊物主题：Earth Sciences, general;
• 出版者：Springer Berlin Heidelberg
• ISSN：1866-7538
• 卷排序：10

文摘

Exploitation of coalbed methane (CBM) is directly affected by the strike and density of fractures, particularly because fractures can act as conduits for water and gas (after desorption). To realize the azimuthal amplitude versus angle (AVA) inversion for a CBM reservoir, we treated reservoirs whose fractures are aligned vertically as being equivalent to a horizontal transverse isotropic medium and simplified the P-P wave reflection coefficient formula to an approximately linear equation. Then, we adopted a modified damping least squares algorithm to solve the azimuthal AVA inversion problem. With edited macro-bins, corrected residual moveout, and normalized amplitude, the azimuthal gathers exhibited unambiguous azimuthal AVA characteristics. The #3 CBM reservoir in the Qinshui Basin was selected for a case study. The density and strike of the reservoir fractures were obtained and analyzed, and the reservoir was divided into three classes according to fracture density. Finally, in comparison with the gas production data, we confirmed that the inversion results and reservoir classification were both reasonable and credible.