煤储层各向异性地震波场模拟

SEISMIC WAVE SIMULATION OF ANISOTROPY IN COAL-BED MEDIA

对中国煤层的裂隙系统进行了系统分类;阐述了各类裂隙的主要成因。基于二维二分量各向异性弹性波方程交错网格高阶有限差分法数值模拟,对各向同性介质模型和高裂隙密度(含干裂隙和饱和水裂隙)煤层的二维层状模型进行了弹性波场数值模拟。结果表明:煤层含裂隙后与不含裂隙时相比,反射时差的变化已不足以识别,但由于波速的改变会使煤层顶底、界面的波阻抗发生变化,从而引起波的动力学特征的改变,AVO现象尤其明显。含气和含水裂隙煤层中在x分量和z分量表现为极性相反,而且含水裂隙煤层中的波速比含气裂隙煤层的波速要快。因此,应用各向异性理论研究煤层裂隙的特征是可能的。

In this paper,systematic classification was conducted for the fissure systems of China＇s coal seams,and the main causes for the different types of fissures were described.Based on 2-D,2-C anisotropic elastic wave-equation staggering grid high-order finite-difference numerical simulation,the authors carried out the numerical simulation of elastic wave field for the isotropy model and the water-saturated and dry media 2-D layered model with fracture-bearing coal seams of high fracturing density.The results show that,in comparison with the fractures-free coal-seam,the fractures-bearing coal-seam has the following characteristics： the surge impedance of the boundary plane at the top and the bottom is changed due to the change of wave velocity,causing the change of dynamic characteristics of the wave.The AVO phenomenon is especially obvious.The characteristics of x component and z omponent are opposite in dry fractural media and in water-saturated fractural media,and the velocity of wave is faster in water-saturated fractural media than in dry fractural media.It is thus thought that coal-seam fractures are detectable by using anisotropy theory.