Arrival picking and global refinement for microseismic events based on waveform similarity

Arrival picking of microseismic events is a fundamental step in processing of downhole microseismic monitoring data. The errors in the arrival times may lead to significant bias in the estimate of hypocenter locations and thus the interpretation of hydraulic fractures. Due to the difference of energy, focal mechanisms, propagation paths and the presence of ambient noise, the arrival results show significant distinction with the same method in conventional picking workflow. We have developed a new method based on waveform similarity in arrival picking and refinement to increase the consistency of arrival picking criteria. This method performs moveout correction for the microseismic records based on cross -correlation functions, the records after moveout correction are superposed and the arrival times are obtained by pick the arrivals for the stack traces. Global refinement is applied to the stack waveforms of different events to calculate the interevent arrival time difference. Finally, the arrival results of each microseismic events can be obtained by adding the arrival information and relative time differences. The proposed method considers the arrival data as a whole and compares recordings from different events, which can overcome the shortcoming of the conventional algorithms in terms of the identic picking criteria. The processing results of microseismic events recorded by borehole array indicate the method can improve the accuracy of the arrival and event location results compared to the traditional processing method.