Microseismic Monitoring Using a Borehole Geophone Array at Farnsworth CO2-EOR Field

Abstract:

Since December 2010, anthropogenic CO2 has been actively injected into the Pennsylvanian Morrow B formation of the Farnsworth CO2-enhanced-oil recovery field located in the Anadarko Basin in Ochiltree County, Texas. This field serves as a large-scale carbon storage demonstration for Phase III of the Southwest Regional Partnership on Carbon Sequestration project. Detecting and locating microseimic events induced by fluid injection is crucial for ensuring the safe storage of CO2. The project deployed a borehole geophone array consisting of 16 levels of three-component geophones into the vertical well 13-10 for microseismic monitoring. The project also acquired offset vertical seismic profiling (VSP) data using the borehole geophone array for check-shot points located at different azimuthal directions around well 13-10. We use hodogram analysis of the VSP data for 15 check-shots with offsets greater than 600 m to determine the horizontal orientations of the 3-component borehole geophones. We first employ spectrogram analysis to detect microseismic events. We then employ a combination of a migration method and a polarization method to locate the detected events. We do not find any induced microseismic events in the Morrow B reservoir layer. We find two distribution peaks in the histogram of microseismicity along the depth. The upper peak coincides with a geologic formation containing strong horizontal transverse isotropic properties revealed from well-log analysis, while the lower peak lies within a different geologic formation. We use focal mechanisms to study of the possible different mechanisms of the induced microseismic events around those two peaks.