煤层气地球物理响应特征分析

煤层气与常规天然气的岩石物理特征不同，它以分子状态吸附在煤岩裂缝的内表面。该文将煤层气看作是煤岩所含矿物的组成部分，计算了甲烷吸附量引起的地震速度变化。结果显示，含气量变化引起的纵波速度降低为10%～16% 时，利用地震技术检测煤层气依然是乐观的。同时也证明了反射振幅对煤岩的速度变化有放大作用，这有助于利用振幅属性检测煤层气；利用叠前反演得到的纵、横波波阻抗计算孔隙流体的弹性参数，可提高煤层气的检测精度。

Geophysical response characteristics of coal bed methane

Coal bed methane has different petrophysics from conventional gas, and it absorbs in molecularity on the surface of coal. It is regarded as a component part of minerals contained in coal. The seismic velocity change resulted from methane adsorbance is calculated. The result shows that P-wave velocity declined to 10%~ 16% due to the change of gas content, so it is also feasible using seismic technology to detect coal bed methane. The reflection amplitude has amplification effect on velocity change of coal, which conduces to detecting coal bed methane by using amplitude attributes. Using prestack inversion P-wave and S-wave impedance to calculate the elastic parameters of pore fluid can improve the detection accuracy of coal bed methane.