基于快速模拟退火算法的井中微地震事件定位反演

Inversion of borehole microseismic event location based on fast simulated annealing algorithm

井中微地震监测技术被广泛应用于非常规油气储层压裂改造监测中,该技术的关键在于有效事件的准确定位.本文以实际测井资料为依据,建立水平层状模型,利用射线追踪模拟并获得微地震事件的传播路径及走时.在模拟退火法机理分析的基础上,引入非常快速算法(VFSA)进行微震事件定位反演,该算法依赖温度的柯西分布状态产生函数,在高温状态下可进行大范围的搜索,在低温状态下只对当前模型附近进行搜索,能够改进退火及抽样过程,提高模拟退火算法的定位效率与精度.最终,将该反演算法运用于实际井中水力压裂微地震事件定位,并描述其造缝空间产状及其发育过程.

During the exploration and development of unconventional oil and gas reservoirs, the precision of microseismic event location is very important for the evaluation of the reservoir reformation effect by hydraulic fracturing and the production guidance. Therefore, according to the practical log data, a layered geological model of oil and gas was established in this paper, and then the ray path and travel time of borehole microseismic was obtained by ray tracing simulation. Meanwhile, the microseismic events of the modeling record were identified and their first break was picked up. On this base, combined with the global convergence of simulated annealing algorithm, a very fast simulated annealing algorithm was put forward to invert the location of microseismic events. This algorithm produces functions depending on the temperature Cauchy distribution, which can search in a wide range at high temperature and search near the current model only at low temperature. Both the simulated annealing process and the sampling process are improved, which enhances the efficiency and accuracy of the simulated annealing algorithm. Besides, the research shows that, compared with the traditional linear inversion method, the very fast simulated annealing method does not depend on the initial value in the source location inversion and its characteristics of random searching solution space can acquire the global optimal solution rapidly. Finally, the inversion algorithm was applied to the microseismic event location of a practical borehole hydraulic fracturing, and the space occurrence and development process of the fracture made was described precisely.