煤层顶板砂岩富水性AVO预测技术

煤层顶板砂岩富水性预测是有待解决的重要问题。以实际测井曲线数据为输入，利用Gassmann方程和AVO（Amplitude Variation with Offset）技术探讨煤层顶板砂岩富水性的预测方法。首先，利用实际测井曲线计算顶板砂岩的纵波速度、孔隙度和泥质含量；其次，以Han经验公式为基础，曲面拟合纵波速度、孔隙度和泥质含量间的关系式，并导出砂岩骨架纵波速度；再次，利用Castagna经验公式计算砂岩骨架的横波速度，并建立14种顶板砂岩模型；最后，利用Gassmann方程进行流体替换，计算各模型的纵横波速度和密度，从而正演模拟顶板砂岩的AVO响应。结合理论分析和实例预测，发现截距-梯度交会图可以区分砂岩孔隙度和干湿性，是顶板砂岩富水性预测的一种有效手段。 

Water content prediction of roof sandstone using AVO technology

The purpose of this research is to discuss the water content prediction of roof sandstone using Gassmann equation and AVO(Amplitude Variation with Offset) modelling. First of all, we calculate P-velocities, porosities and clay contents using actual well logs as inputs. Then, we fit the P-velocity of sandstone matrix with Han's empirical equation. After that, we calculate the S-velocity of sandstone matrix and build 14 sandstone models to calculate corresponding velocities and densities following Gassmann's workflow. Finally, we calculate the AVO responses of roof sandstones with Zoeppritz equation. The results show the cross plot between intercept(P) and gradient(G) can differentiate roof sandstone with different porosity and wettability. In summary, AVO technology is a useful tool to predict water content of roof sandstone.