Numerical Simulation Of Microseismic And Study On Source Location Method

In recent years, microseismic monitoring technology has gained increasing attention, andis widely used in many fields. It can be used for fracture dynamic imaging and fluid drivenmonitoring in low permeability reservoir during hydraulic fracturing, which can optimize thehydraulic fracturing well network design and layout, enhance oil recovery. In addition, with apreventive effect in mine disaster, this technology can monitor mine water inrush and rockpressure bump in mining. The cores of microseismic monitoring include well data acquisitionand processing technology of real time, automatic, high-precision. Here, we have studiednumerical simulation, pre-processing, automatic picking of microseismic event,high-precision source positioning, geophone network performance evaluation andoptimization layout in detail, the specific contents and innovations are as follows:(1)Numerical simulation of microseismic wavefield. Three-component elastic waveforword numerical simulation of3D microseismic wave field is carried out using piecewiseiterative ray tracing method and high-order staggered-grid finite difference techniques. Forviscoelastic medium, the attenuation theory for one-way is applied to ray tracing, so thatviscoelastic medium ray tracing simulation method is produced. According to thecharacteristics of hydraulic fracture that the fracture is an elongated self-similar expansionellipsoid, a mathematical model of microseismic source distribution is established, bycontrolling model parameters, different forms of hydraulic fracture microseismic crack issimulated.(2)Study on filtering method for microseismic data. The geophones in microseismicmonitoring are less than usual(usually10in borehole), it is difficult that using coherentmulti-channel filtering criterion to suppress noise. So Hankel matrix filtering algorithm basedon single channel signal is used in adaptive processing of microseismic data. The filteringmethod has better fidelity of the signal while attenuating the random noise, it can applies toreal time auto-processing of microseismic monitoring.(3)Many different existing method for picking microseismic event have been studied, and the two-step method based on after-term average over before-term averageratio(ATA/BTA) and the Akaike information criterion(AIC) is developed taking advantage ofthe existing methods. The two-step method avoids the disadvantage that the accuracy ofpicking is dependent on length of time window.(4)The paper studied common objective functions and proposed two new objectivefunctions: the vector objective function and the energy flow objective function. Theseobjective functions used the travel time and amplitude information of microseismic data,combined with three-component data, so that they play an important role in reducing multiplesolutions and improving the utilization of geophones. An improved Geiger microseismicsource location algorithm by combining vector objective function with classical Geigerlocation algorithm is obtained. Testing by the model data shows that the method is sensitive toazimuth information of source, and has higher positioning accuracy. By means of analysis ofclassical double-difference earthquake location algorithm, combined with improved Geigerlocation algorithm, a hybrid difference location algorithm is developed. This approachreduces the amount of data stored and sensitiveness to initional source location, and alsogreatly improves the computational efficiency.(5)It discussed the sensitivity of source location, location error and multiple solutions oflocation theoretically in detail. By testing with different arrays of receivers, criteria has beenobtained for optimal arrangement of the receivers. Furthermore, an objective function isestablished for optimal receivers arranged network, so that an optimal receivers layoutnetwork is estimated for a given source area.(6)Simulated hydraulic fracturing microseismic data, illegal mining of small coal minepassive seismics data and actual hydraulic fracturing microseismic data with horizontaldrilling well have been tested by proposed processing technology to verify the effectivenessand practicality of the proposed method.