Improve The Accuracy Of Microseismic Location By Relative Azimuth

Traditionally,for downhole microseismic location shot is often used to calibrate the sensors and calculate the orientation of sensors for further location.Due to the effects of the anisotropy of underground medium,it is possible that the ray path of shot and microseismic events bend.The possible errors on the calibration may cause errors on the location.We don't calibrate sensors by rotation matrix,instead we are enlighted by relative location to constrained the location of the event directly by relative azimuth.Considering the similarity between the ray path of two events,the difference between the azimuths of two events is nearly equal to the difference between the polar angle of two events on the condition that the two events are near.So it is important to get an accurate polar angle.We compared different methods to calculate polar angle.The analytical method seems unsuitable for those signal with low SNR.So we chose energy method to calculate polar angle.Finally We utilized the P and S waveform produced in weiyuan 10~thh stage fracture to locate the microseismic events.We chose gridsearch to locate these events.To some extent this method avoided under-determined.We simulated the relative location by relative azimuth in different level of HTI,the results show that relative location by relative azimuth can reduce the error by the change of velocity model.