横波分裂裂缝检测方法在川西深层气藏中的应用

Application of fracture detecting methods by shear wave splitting at the depth gas reservior in west Sichuan

由横波分裂原理可知,当横波(或转换横波)在裂缝介质中传播时,横波将分裂成平行裂缝走向的快横波和垂直裂缝走向的慢横波.基于此,求取裂缝走向的问题可以转化为求取快横波的偏振方位角度的问题;由于快、慢横波的传播时差与裂缝发育密度密切相关,因而裂缝发育密度的预测问题可以转化为快、慢横波的传播时差求取问题.根据快、慢横波在径向分量和横向分量上的振幅、能量、相位、传播速度、走时等差异,可从不同的角度着手,建立不同的横波分裂裂缝检测技术.如R/T能量比值法、T分量极性反转法、最小二乘拟合法、传播矩阵法、Alford正交旋转法等.随着多波多分量地震勘探技术的快速发展,这些方法日趋成熟,正扮演着越来越重要的角色.实践表明,它们对四川盆地新场地区深层裂缝性气藏的勘探开发提供了重要的支撑.

It can be understood from the theories of shear wave splitting, that shear wave（or conversion shear wave） transmits in fracture medium may split into fast shear wave which transmits parallelly the frcature orientation and slow shear wave which transmits vertically the frcature orientation. Based on these theories, the computing problems about fracture orientation can be transformed into the computing problems about polarizing angles of fast shear wave. Because of the affinities between the transmitting time delay between fast and slow shear wave and the fracture density, the predicting problems about growing fracture density can be transformed into the computing problems about the transmitting time delay between fast and slow shear wave. By the difference of amplitude, energy, phase, velocity, tranmitting time and others between radial and transverse components, the different fracture detecting technologies on shear wave splitting can be established by different methods. They are energy ratio between R and T components, reversal polarity of T components, least-squares fitting, transmitting matrix, Alford orthogonal rotation and so on. Following the rapid development of multi-wave and multi-component seismic prospecting technology, these methods are becoming more and more mature and it will play important role. Indicating by the practice, they have been providing important supports when the deep fracure gas reservoir are explored and developed in Xingchang area in the west of Sichuan.