基于改进多模板快速行进法的井中微地震定位方法研究

Downhole microseismic event locating based on an improved multi-stencils fast marching method

1.成都理工大学地球物理学院,四川成都610059;2中油奥博(成都)科技有限公司,四川成都610041;
3.中国石油渤海钻探工程公司巴彦石油工程分公司,内蒙古巴彦淖尔015000

1. School of Geophysics,Chengdu University of Technology,Chengdu 610059,China;
2. Optical Science and Technology (Chengdu) Ltd.,CNPC,Chengdu 610041,China;
3. Bayan Petroleum Engineering Branch of CNPC Bohai Drilling Engineering Company Limited,Bayannur 015000,China

随着微地震监测的广泛应用,如何提升微地震的定位精度和效率成为重要的研究方向之一。目前,井下微地震定位多采用基于走时的线性反演定位方法。然而传统射线追踪方法在复杂非均匀介质中可能会存在阴影区、焦散等问题,导致定位结果存在一定误差。提出了一种基于改进多模板快速行进法的微地震定位方法,利用球面波近似算法计算震源附近网格点走时,再利用多模板快速行进法(MSFM)求解程函方程计算其余网格点走时,最后,采用走时差目标函数全局搜索事件位置。理论测试结果表明,该方法的计算走时优于快速行进法(FMM)和MSFM,具有较小的走时误差,尤其是在震源附近误差很小;且该方法可以对层状以及更复杂速度模型实现射线追踪以及准确定位。将该方法应用于四川盆地威远地区页岩气开发井下数据的处理,结果表明,所得到的定位结果比Geiger方法更加准确、合理,更加清晰地刻画了裂缝以及断层的形态分布。

How to locate microseismic events accurately and efficiently is an important problem in microseismic monitoring.However,the traveltime-based linear inversion,a routine method for event locating,suffers from some problems such as shadow area and caustics during ray tracing in complex heterogeneous media and thus fails to obtain accurate ray paths.Additionally,local minima in travel time calculation are also an obstacle to accurate positioning.We propose a method to locate microseismic events based on an improved multi-stencils fast marching (MSFM) algorithm.The approach utilizes a spherical wave approximation algorithm to compute the travel times at grid points near the seismic source,followed by solving the Eikonal equation using MSFM to calculate travel times at the remaining grid points.Finally,a global search of event positions is conducted using the travel time difference as the objective function.The model test results show that the improved method proposed in this paper outperforms the Fast Moving Method (FMM) and conventional MSFM in travel time calculation,especially in the vicinity of the source.This method can also achieve accurate ray tracing and positioning in layered and complex velocity models.The application to Weiyuan shale gas field in the Sichuan Basin shows more accurate results of event positioning and fracture delineation compared to the Geiger method.

10.12431/issn.1000-1441.2025.64.01.007