基于跟踪分量扫描的井中微地震定位方法

常规的井中微地震定位方法主要利用的是初至旅行时和偏振信息,如果信噪比较低则方法不再适用。理论研究表明,各检波器X分量和Y分量记录在其水平面内沿着任意方向可合成为一个新的向量,当该向量为质点振动的跟踪分量时,其能量最强且在各检波器间波形一致性最好。根据三分量微地震记录的这一性质,将地面微地震定位常用的叠加能量扫描方法引入井中微地震定位中,将检波器X和Y分量记录在水平面内沿着假想震源与检波器连线方向进行合成,对所有检波器的合成向量经时差校正后进行波形叠加计算能量值E₁,再计算各检波器合成向量的能量值并求和得到能量值E₂,以E₁+E₂作为目标函数,通过网格搜索方法得到累加能量最大的网格即为震源位置。该方法不需要拾取初至信息,通过模型数据和实际资料验证了该方法的定位精度和抗噪能力,可用于信噪比较低的井中微地震事件定位。

Locating borehole microseismic events based on the tracking component scanning

Conventionally,locating borehole microseismic events is based on first arrivals and polarized information. However,if the SNR is low,they can't work well. Theoretical studies show that the X and Y components of a borehole detector can be synthesized into a new vector in any direction on the horizontal plane of the detector. When the vector is the tracking component of microseismic events,it has the strongest energy and the best waveform consistency among all detectors. According to the nature of three-component microseismic record,this paper introduces the stacked energy scanning method commonly used in surface microseismic location into borehole microseismic location. First compose the X and Y components of a detector into a new component in the horizontal plane along the direction from an imaginary source to the detector. Second,stack the waveforms and calculate energy E₁ after NMO correcting the vectors of all detectors,then taking the sum of the energy of the synthetic vector of all detectors to get E₂,and finally,taking the sum of E₁ and E₂ (E₁+E₂) as an objective function,find the grid with the largest cumulative energy,which is the location of the source point. It is not necessary to pick up first arrivals. Model and real data have proved the method is accurate to locate microseismic events and strong to resist noises. It can be used to locate microseismic events in the environment where the SNR is low.