Research On Microseismic Location Based On Multi-mode Wave And Multi-component Information

Microseismic monitoring technology is widely used in unconventional oil and gas exploration,and it is currently the most effective way to evaluate hydraulic fracturing.The forward modeling,three-component signal processing,microseismic event detection,and source location methods related to microseismic monitoring have been systematically studied in this paper.In this paper,the wave field excited by the shear-fracture source are simulated based on the standard staggered-grid finite difference technique.The numerical simulation results are compared with the source theory to verify the rationality of the finite difference double couple model.Two ray tracing methods were then studied: one is a two-point ray method dedicated to horizontal layered media,and the other is the fast marching method(FMM)based on point expansion.Tests show that the two-point ray method is faster,and the travel time and path of the seismic wave can be obtained.However,this method is only suitable for horizontal layered media.The fast marching method is more adaptable.Even FMM is applied to a spherical model,it still has excellent convergence.But this method can only calculate the travel time and cannot get the seismic trace.When these two methods are applied to the same model,the maximum difference in the calculated travel time is less than 80?s.Various three-component data processing techniques and some special physical quantities involved in microseismic monitoring are studied.Firstly,the corresponding filtering methods are studied according to the characteristics of different noises,such as FIR bandpass filter(group),notch filter,LMS adaptive filter and so on.Three-component detector has been widely used in microseismic monitoring.This paper implements a stable and efficient polarization analysis technique based on singular value decomposition algorithm.The stability and reliability of this method are illustrated by examples throughout the text.The attitude correction of the downhole three-component detectors is realized by polarization analysis of the P-waves excited by perforation.After the rotation of the detector coordinate system is completed,the polarization directions are no longer random,but appear consistent.Based on the concept of instantaneous polarization direction,this paper proposes a method for calculating the comprehensive energy ratio of three-component data.From the application results of field data,the integrated energy ratio method has a stronger amplitude than the traditional STA/LTA method.And can realize the separation detection of the P-and S-wave.The surface of the earth approximates the free boundary,and the vibration of the particle on the boundary is the result of the interaction of the incident wave and the reflected wave.Therefore,the ground detector records is the vibration signal of the free boundary particle.In this paper,the total displacement vector expression of the particle on the boundary is derived,and a method of separating the reflected wave from the incident wave is proposed.From the application effect of the forward data,the separation method is effective.Based on the comprehensive semblance and comprehensive amplitude of threecomponent waveforms,a weighted semblance location method is proposed.This method does not need to pick the first arrival of the signals,and simultaneously uses the P-and S-waves to perform the source imaging with amplitude-weighted similarity.From a large number of test results,the weighted semblance method has lower location uncertainty and stronger adaptability than the traditional migration-based method(semblance method and amplitude stacking method).In order to test and compare the source localization methods used in microseismic monitoring,a corresponding physical simulation study was carried out.Taking a huge cement block as the experimental sample,and use a metal hammer to strike on the surface of the experimental sample to excite the sound source,and four three-axis accelerometers were arranged in a line array on the surface of the experimental sample to receive the three-component data.Processing the recorded multi-channel experimental waveform with combine the coherence scan image with the polarization direction to determine the three-dimensional space coordinates of the sound source.The simulation results show that,under the same error condition,the weighted semblance method has the highest localization accuracy,and the comprehensive amplitude stacking method has the lowest localization accuracy.The physical simulation experiment further verifies the reliability and applicability of the new location method.