煤储层裂隙参数正演分析

Forward modeling of fracture parameters in coal reservoir

以TTI煤层的二维三分量各向异性弹性波方程为基础,推导Lebedev网格的有限差分格式,对不同裂隙参数的TTI介质进行数值模拟,分析裂隙参数对地震波场的影响,建立3层介质模型,获得不同裂隙密度和裂隙填充物的理论模型,正演得到煤层的AVO记录。通过对模拟结果的分析可知:(1)当煤层介质为干裂隙时,纵波的速度各向异性对裂隙反应敏感,当煤层介质为含流体裂隙时,横波的速度各向异性对裂隙反应敏感;(2)煤层顶板的反射系数为负值,底板为正值,煤层顶底板反射系数受多种因素的影响;(3)在煤层裂隙介质为干裂隙时,裂隙密度的变化对于反射系数曲线的截距影响较大,而对斜率的影响较小,在煤层裂隙介质为含饱和流体时,裂隙密度对于煤层反射系数基本无影响;(4)随着裂隙密度的增大,裂隙填充物对于反射系数的影响也相对增大。

Based on the three components of TTI coal seam by two-dimensional anisotropic elastic wave equation,the finite difference scheme of Lebedev grid was derived,and the numerical simulation of TTI medium on different fracture parameters were carried out,the impact of fracture parameters on the seismic wave field was analyzed,the three layer model was established,and the different theoretical models of crack density and crack filling were obtained.Also,the AVO records were obtained by forward modeling.The simulation results show that（1）When the coal seam medium is a dry fracture,the velocity anisotropy of the compressional wave is sensitive to the fracture.When the coal seam medium is fluid fracture,the velocity anisotropy of the shear wave is sensitive to the fracture;（2）The reflection coefficient of coal seam roof is negative,the bottom plate is positive,and the reflection coefficient of coal seam is affected by many factors;（3）When the coal seam fracture medium is dry,the change of fracture density to intercept the reflection coefficient curve has a great influence and the effect on slope is small.When the fractured medium is saturated fluid,the fracture density has no influence on the reflection coefficient of coal seam;（4）With the increase of the fracture density,the influence of the filling material on the reflection coefficient is relatively larger.