基于逆时成像的井中观测微地震定位精度分析

Accuracy analysis of borehole observation microseismic location based on time reverse imaging

微地震定位是非常规和低渗透油气勘探开发和地下工程安全监测的关键环节,其准确性是实现油气储层实时刻画和工程灾害监测预警的重要基础.由于微地震信号具有能量弱、频率高、信噪比低的特点,微地震定位精度易受到采集观测系统布设位置的影响,尤其在井下受限空间与高温高压环境中.基于此,本文提出了一种基于逆时成像的井下微地震采集定位精度分析方法,能定量预测实际采集观测系统布设方案在水平和深度方向上的定位偏差和不确定性.区别于传统定位精度分析方法,该方法基于波形而非走时,适用于复杂非均匀介质,同时考虑了信噪比和震源机制对定位精度的影响.均匀和非均匀介质下的实例应用结果均表明,该方法能有效评价微地震采集方案的预期定位精度,进而反馈采集参数设计,从数据采集的源头改善复杂介质条件下的微地震定位效果.

Microseismic location is a key step in exploration and development of unconventional and low permeability reservoirs or safety monitoring of underground engineering.Its accuracy is an important basis for realizing real-time characterization of reservoirs and engineering disaster monitoring and early warning.Due to the characteristics of weak energy,high frequency and low signal-to-noise ratio of microseismic signals,the accuracy of microseismic location is easily affected by the location of the acquisition and observation system,especially in the downhole confined space and environment with high temperature and pressure.Based on this,this paper proposes an analysis method for the location accuracy of downhole microseismic acquisition based on time reverse imaging,which can quantitatively predict the location bias and uncertainty in horizontal and depth directions of the actual acquisition and observation system layout scheme.Different from traditional location accuracy analysis methods,this method is based on waveform rather than travel time and is suitable for complex and inhomogeneous media.Meanwhile,the influence of SNR and focal mechanism on location accuracy is considered.The application results in both homogeneous and inhomogeneous media show that the proposed method can effectively evaluate the expected location accuracy of the microseismic acquisition scheme,and then feedback the design of acquisition parameters to improve the microseismic location effect in complex media from the source of data acquisition.