微地震事件震源机制求解技术

微地震技术是通过监测致密储层压裂改造产生的微地震波,用于评价分析压裂效果、指导压裂工艺优化的地球物理技术。根据微地震事件的震源机制解可以描述压裂过程中裂缝破裂情况,能够更好地分析水力压裂裂缝的延伸和展布特征。利用纵波初至来估算震源机制解是一种比较直接的反推震源性质及破裂过程的方法,但该方法对微地震监测数据的品质要求较高,既需要足够多的台站监测纵波信号,又要求纵波初至具有较高的信噪比。针对常规方法的不足,采用纵波和横波的能量比计算微地震震源机制解,即通过纵横波能量比值来判定压裂震源点是剪切性破裂还是拉张性破裂。将纵横波能量比方法与常规矩张量反演方法进行对比,两者计算结果具有较高的相关性,微地震监测实际数据验证了该方法的可行性和有效性。

Determination Technique Study of Micro-seismic Event Focal Mechanism

Based on the waves generated by fracturing of tight reservoirs, microseismic monitoring is a geophysical technology that can be used to evaluate the fracturing effect and guide the optimization of fracturing technology. According to the focal mechanism solution of microseismic events, the fracture situation can be described, and the extension and distribution characteristics of fracturing cracks can be better analyzed. Using P-wave first arrival to estimate focal mechanism solution is a direct method to deduce source properties and rupture process. But the method requires high quality of monitoring data. It requires not only enough stations to monitor P-wave signals, but also high signal-to-noise ratio of P-wave first arrival. In order to overcome the shortcomings of conventional methods, the energy ratio of P-wave to S-wave is used to calculate the focal mechanism solution. The energy ratio of P-wave to S-wave is used to determine whether the fracturing focal point is shear fracture or tensile fracture. Comparing the P-S wave energy ratio method with the conventional moment tensor inversion method, the results of the two methods are highly correlated. The feasibility and validity of the method is verified by practical data.