基于“剪切+张裂”一般位错模型频率域求解微震震源机制

研究微地震的震源机制，获得压裂区域的破裂方向、尺度和应力状态等信息，在非常规油气开采过程中具有重要意义.对于微震，通常采用剪切位错或者矩张量模型对震源进行描述.本文从其实际发震机制出发，使用了"剪切+张裂"的一般位错点源模型，并基于此模型发展了一种利用全波形信息，通过波形振幅谱相关和初至约束，在频率域求解微震震源机制的方法.该方法适用于地面和井中观测，能够在得到常规震源参数（断层走向、倾角和滑动角）的同时给出裂缝断层剪切和张裂错动的距离信息，更直观体现破裂程度.理论数值测试证明方法有效、可行，在未滤波的情况下，实际数据的波形拟和结果仍较为一致，同时还发现错动距离与应力降等常规破裂参数并不严格相关，说明剪切、张裂错距可作为独立的新参数来定量评估水压致裂效果，指导工程开发进行.

Microseismic focal mechanism inversion in frequency domain based on general dislocation point model

Fracture directionality, scale and stress state of hydraulic fracturing areas are extremely important for the exploration of unconventional oil and gas resources. These information can be obtained from the study of microseismic focal mechanisms. For microseismic events, double-couple or moment tensor models are usually used in focal mechanism inversion. In this study, a "Shear & Tensile" general dislocation point model is presented to describe the source of microearthquakes. Based on this model, we develop an approach to calculate microseismic focal mechanism using amplitude spectra fitting and simulated annealing technique in frequency domain. The new method takes account of full waveform information including phase and polarities of first P wave arrivals and can provide dislocation length along each direction as well as common source parameters (strike, dip and rake angles) in the study area. The synthetic tests on surface and borehole network and applications to real data show that our method is robust and efficient. We also find that shear and tensile dislocation lengths are independent of stress drop and can be used as new parameters for quantitative evaluation of hydraulic fracturing.