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不同的地震弹性阻抗反演软件计算弹性阻抗的方法不尽相同,地震弹性阻抗反演中尚有一些应用条件在没有详细讨论的情况下被简单地加以应用,这给实际生产带来了困难。有鉴于此,以典型的4种不同类型含气砂岩模型为基础,分析比较了弹性阻抗、反射阻抗和广义弹性阻抗在不同角度下的计算精度;并且基于Biot-Gassman理论,对Ostrander含气砂岩模型进行流体替代,探讨了含水饱和度由小变大时不同的弹性阻抗对流体的敏感性。通过4种不同类型含气砂岩模型计算可知:在第Ⅰ类和第Ⅳ类含气砂岩中,入射角不超过40°时,EI,RI和GEI均能替代Zoeppritz方程;在第Ⅱ类含气砂岩中,入射角不超过30°时,EI,RI,GEI也能替代Zoeppritz方程;这3种弹性阻抗无法应用于第Ⅲ类含气砂岩。将偏导的思想应用到Ostrander含气砂岩模型,计算结果表明,反射阻抗对流体的敏感性强于弹性阻抗和广义弹性阻抗,且入射角越大,这种敏感性越强。
Different seismic elastic impedance inversion softwares vary in their methods of calculating elastic impedance. Some of the application conditions of seismic elastic impedance inversion are simply applied without detailed discussion, which brings difficulties in actual production. In view of this, based on the typical four different types of gas-filled sandstone models, the computational accuracy of elastic impedance, reflection impedance and generalized elastic impedance at different angles are analyzed and compared. Based on the Biot-Gassman theory, The model is used to replace the fluid, and the sensitivity of different elastic impedances to fluids when water saturation increases from small to large is discussed. Computation of four different types of gas-bearing sandstone models shows that EI, RI and GEI can replace the Zoeppritz equation in gas-bearing type I and IV gas-bearing sandstones at angles of incidence of no more than 40 °; Sandstone, EI, RI, GEI can also replace the Zoeppritz equation when the incident angle does not exceed 30 °; these three kinds of elastic impedances can not be applied to the gas-bearing sandstone of type III. The partial derivative theory is applied to the Ostrander gas-bearing sandstone model. The calculated results show that the reflection impedance is more sensitive to fluid than the elastic impedance and generalized elastic impedance, and the greater the incident angle, the stronger the sensitivity.