Microseismic Event Location with Joint DAS and 3C Geophone Array

Fiber-optic distributed acoustic sensing (DAS) applied to microseismic has gained popularity in various microseismic monitoring applications. Compared to conventional geophone array based microseismic monitoring, DAS microseimsic has unique advantages in minimizing location uncertainties. However, if only one straight fiber were deployed on surface or in downhole, DAS may not be able to uniquely determine a microseismic event location without other constraints due to circular event location ambiguities. Since a standard DAS fiber cable usually can only record one component seismic wave data which is not able to provide source direction to reduce the circular ambiguities in event location, we developed a innovative joint DAS and 3C geophone array for microseismic monitoring and a three-step microseismic event location workflow to obtain a unique event location. First, we calculate source direction using P-wave first arrival on 3C geophone. Second, we calculate 2D semblance image along the source-geophone direction. Third, we extract the location of maximum semblance value in 2D semblance image as the event location. We presented a microseismic event location example which was obtained by applying the three-step location workflow on microseismic event dataset acquired by a field survey with joint DAS and 3C geophone array.