地面微地震四维聚焦成像方法研究

As a new work way on microseism, surface microseismic technology has great prospects. The occurrence time and three-dimensional coordinates information of microseismic events are needed to confirm.Positioning exact locations of effective events is the key of microseismic monitoring method. The difficulty of surface microseismic monitoring technology lies in the extremely low SNR of surface datas.Unlike downhole microseismic data, it is impracticable to pick the arrival time of effective signal directly, and get source inversion based on the arrival time.However, it is an effective solution to image using surface microseismic data directly.At first, doing surface microseismic data preprocessing, most of noise can be removed by using single-channel SVD method.And then, according to time difference of arrival(TDOA) to directors, velocity field structure of medium under the ground can be acquired from perforating data. Finally, accroding to three-dimensional coordinates of surface detectors and velocity structure, seismic source images are acquired directly by using diffraction scanning migration method..The occurrence time and three-dimensional coordinates information of microseismic events are considered adequately in this method, we call it four-dimensional focus imaging method.Three-dimensional energy spectra acquired by four-dimensional focus imaging method, which reflects detailed information of cracks underground directly..Research results has important significances in theoretical and practical on promoting development of domestic oilgas field, especailly low permeability reservoir and shale gas.

地面微地震技术作为一种新型的微地震工作方式有着很好的发展前景。微震事件的产生时间，事件的三维坐标都是需要确定的。地面微地震监测技术最大的难点在于地面资料信噪比极低，无法像井中资料那样直接拾取有效信号到达时间，利用到达时间进行震源反演。针对这个问题，采用理论结合实际数据验证的方法，提出了直接使用地面微震资料进行偏移成像。方法首先对地面微震资料进行预处理，使用单道奇异值分解（SVD）方法去除噪音。然后利用射孔资料根据检波器到达时差求取地下介质的速度场结构。最后根据地表检波器的三维坐标和速度场结构通过绕射扫描偏移归位的方法直接对地下震源点位置成像，这种成像方法充分考虑了微震事件激发时间和微震事件地下三维坐标，称为四维聚焦成像法。这种方法获得的三维能量谱图直接反映了地下裂缝的具体信息。研究成果为地面微震处理奠定了基础，对促进国内油气田特别是低渗透油气藏和页岩气的开发有重要的理论和实际意义。

通过开展地面微地震四维聚焦定位方法的研究，建立了一套在低信噪比地面微地震资料情况下进行成像的处理方法和流程，该算法和流程能够适应中低信噪比的微地震资料成像定位。针对地面微地震资料信噪比极低、有效波难以识别、初至难以拾取的特点，进行了以下研究：1、研究了地面微地震资料的预处理方法，提出了压制野值及直流分量的处理方法；2、地面微地震资料的去噪方法研究，重点进行了周期性出现的机械干扰、线性分布的干扰波和随机噪音去噪方法研究，提出了以预测滤波、SVD分解、高阶累积量方法为系列的地面为地震资料去噪手段；3、研究了低信噪比微地震资料的速度反演方法，提出了基于检波器时差的叠加谱速度分析方法；4、提出了低信噪比情况下的微震成像方法，使用四维聚焦定位方式对有效波进行成像。