Sensitivity parameters of tight sand gas: A case study of Lower Cretaceous Yingcheng Formation of Yingtai gas field in Songliao Basin, NE China

Aiming at the difficulty in distinguishing gas-bearing layers and surrounding rocks due to the small differences between their impedance, the gas-bearing sensitivity parameters are studied in tight sandstone to identify thin layer tight gas accurately. According to elastic parameters sensitivity analysis of fluid in tight sandstone, a new combined elastic parameter is proposed, i.e. the ratio of the first Lame coefficient to S-wave velocity. Furthermore, considering different geological conditions, extending attribute (the ratio of Russell fluid phase to S-wave velocity) is deduced, and it can be simplified as the ratio of the first Lame coefficient to S-wave velocity in certain condition. Fluid replacement process is conducted by Gassmann equation and Brie empirical equation, and the new combined elastic parameter is more sensitive to gas saturation than common parameters such as the product of the first Lame coefficient and density, the ratio of P-wave to S-wave velocity, verifying the validity of the new combined elastic parameter. The pre-stack inversion is applied in the second member of Lower Cretaceous Yingcheng Formation in Yingtai gas field. Compared with section of the product of the first Lame coefficient and density, it shows that the new combined elastic parameter improves the accuracy of identifying gas-bearing layers, well conforms to the logging interpretation, and greatly enhances the identification ability and prediction accuracy towards gas-bearing layers. ©, 2014, Science Press. All right reserved.