Microseismic Event Location using Multiple Arrivals: Demonstration of Uncertainty Reduction

Abstract

Author(s): Zhang, Z; Rector, JW; Nava, MJ | Abstract: Copyright 2015, Unconventional Resources Technology Conference. Event location is the basis of hydraulic fracture characterization using microseismic data. However, the traditional method of using direct arrival times and P-wave polarizations leads to increased error due to the large uncertainty in polarization. Due to shale's low velocity nature and the configuration of horizontal stimulation and monitoring wells, the head wave can often be the first arrival rather than the direct arrival. Finite difference modeling was used to validate the character of head waves in field data gathered from the Marcellus shale and the situations under which a head wave can be the first arrival were carefully analyzed. With careful processing, we reveal the presence of high number of head waves in the Marcellus Shale. Head wave and direct arrivals were used instead of the conventional P-wave polarization to estimate microseismic event location. A Bayesian inference program was also developed for joint event location and velocity model calibration. Validation of the developed method was performed on perforation shots and shows that using head waves instead of polarization can achieve much better resolution in microseismic event location. The application of the developed method on field data shows a more reasonable result than that provided by contractor. Our results show that the head wave can be a contributor instead of a detractor in the process of accurate event location. This will eliminate the necessity for polarization which has large uncertainty due to poor geophone-borehole coupling, multiple arrivals, and low signal to noise ratio. The developed method can effectively improve the accuracy of microseismic event location and proposes a better acquisition geometry and strategy to reduce microseismic monitoring cost and improve event location accuracy.