发展全波形震源定位和震源机制反演算法及对页岩气水力压裂诱发地震的研究

With recent surge in unconventional shale gas production in the Sichuan Basin, the induced seismicity occurring during hydraulic fracturing has drawn increasing attention from the public. Accurate location of the earthquakes and reliable determination of their source mechanisms can help understand the cause for induced earthquakes, and mitigate the risks for inducing larger ones. This project proposes to develop a new method that simultaneous determines the location and source mechanism of an earthquake based on full waveform matching. Then we will apply it to the microseismic data from hydraulic treatments to analyze the characteristics of the induced seismicity in an area with widely distributed blind and critically stressed faults. Using the surface microseismic data from a hydraulic treatment in the Pengshui area, we will first build a 3-D velocity model for a small region around a hydraulic treatment well using the double-difference tomography method. With the derived 3-D velocity model, we will compute the corresponding Green’s function library, which will be used in the newly developed full waveform matching algorithm to accurately locate the events and determine their source mechanisms. This project will also develop a new full-waveform based double-difference method to further improve the relative locations of induced earthquakes in clusters. To further understand the characteristics of induced seismicity in hydraulic fracturing and the correlation between hydraulic treatments and reactivation of surrounding faults, we will deploy 200 3-C integrated short-period seismometers to monitor another 1-2 hydraulic fracturing sites in the Shangluo area in the Sichuan Basin. With additional analyses, we will further mature the full-waveform based workflow for microseismic and induced seismicity characterization, and as a result, we will develop an interactive software package for the workflow.

随着四川盆地页岩气的大规模开采，水力压裂诱发地震引起了越来越多的关注。准确地定位地震及确定其震源机制有助于理解诱发地震的成因，降低诱发较大地震的风险。本课题拟发展新的全波形地震定位及震源机制反演算法，并将其应用于压裂井的微震监测数据，详细分析在断层广泛分布、地质应力积累强度大的该地区水力压裂过程中诱发地震的特征。本课题拟先基于彭水地区某压裂井地面微震数据，利用双差成像法构建井周围三维速度模型，并计算对应的理论波形格林函数库，以便利用新的全波形匹配算法准确反演压裂产生的地震位置及其震源机制。本课题还将发展新的全波形双差定位法改进地震定位精度。为更进一步理解四川地区水力压裂诱发地震的特征，分析水力压裂与周围断层活动之间的联系，本项目拟部署200套一体式地震仪，对上罗地区1-2个页岩气压裂平台进行监测并分析采集的数据，进一步发展微地震和诱发地震的全波形分析工作流程，以及开发交互式全波形反演软件。

随着四川盆地页岩气的大规模开采，水力压裂诱发地震引起了越来越多的关注。依托该项目资助，我们对四川盆地一页岩气开发区的诱发地震发震情况和机理开展系统研究，包括对开发区地下精细速度结构进行刻画，并系统开展地震定位、震源机制反演等方面的工作和方法研究。具体而言，本项目对四川长宁页岩气国家级示范区开展了系统研究，布设了由近200套短周期节点式检波器组成的国内第一个页岩气开发区微地震和诱发地震密集观测台阵，监测到了海量的微地震和诱发地震事件，并获得了地下的精细三维横波速度结构；提出了四种先进的主、被动源地下结构成像方法，发展了软硬件一体化的基于深度学习和4G实时地震仪地震实时监测系统，发展了基于全波形匹配的地震定位和震源机制反演方法，同时还研发了实时、自动的地震震源机制反演软件，并与地震局相关研究所和地方局开展合作，投入了实际应用。项目有多项相关科研成果产出，除了对四川长宁页岩气开发区的诱发地震问题和机理有了系统、深刻的认识之外，新发展的多项技术方法也在不同地区的实际问题中得以广泛应用，很好地服务了国家的实际需求。