Elastic impedance modeling of tight sandstone gas reservoir
Jin Jineng1, Pan Renfang1,2, Zhu Zhengping1, Zhang Liping2
1. Key Laboratory of Oil and Gas Resources and Exploration Technology of Ministry of Education, Yangtze University, Wuhan, Hubei 430100, China;
2. College of Geoscience, Yangtze University, Wuhan, Hubei 430100, China
Abstract：In order to analyze fluid sensitivity characteristics of elastic impedance for tight sandstone gas reservoir identification and its model response trend, an elastic impedance modeling in tight sandstone gas reservoir is conducted. Based on well data statistics of He 8 sandstone in Sulige Gasfield, rock physical model of tight sandstone gas reservoir is established and used in fluid replacement simulation to do the modeling. As the study shows, four types of elastic impedance characteristics for gas reservoirs have been found: Class Ⅰ, positive high elastic impedance difference decreases with incident angle increase; Class Ⅱ, near zero elastic impedance difference decreases from positive to negative with incident angle increase; Class Ⅲ, negative high elastic impedance difference decreases with incident angle increase; and Class Ⅳ, negative high elastic impedance difference increases with incident angle increase. For Classes Ⅰ,Ⅱ, and Ⅲ, the elastic impedance of reservoirs decreases and that of cap rocks increases with incident angle increase while the reflection coefficient decreases with incident angle increase. But for Class Ⅳ, the elastic impedance of reservoirs increases and that of cap rocks decreases with incident angle increase while the reflection coefficient increases with incident angle increase. The elastic impedance and reflection coefficients of the four types of tight gas sandstone reservoirs all show a decreasing trend with gas saturation increase. Larger decreases appear with gas saturation range between 0 and 0.1. In addition, amplitude response characteristics of elastic impedance model can well reflect elastic impedance variation with incident angle and gas saturation, which can serve as a guide for tight gas sandstone reservoir prediction.
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