S-Wave azimuthal anisotropy: an effective tool for stress monitoring
T.L. Davis and S.L. Roche
Journal name: First Break
Issue: Vol 37, No 2, February 2019 pp. 45 - 50
Special topic: Reservoir Monitoring
Info: Article, PDF ( 812.13Kb )
Reservoir monitoring is required in understanding reservoir behaviour under dynamic conditions associated with enhanced oil recovery processes related to carbon dioxide injection and shale reservoir development through multistage hydraulic fracturing. Geochemical and geomechanical changes associated with these processes may affect reservoir permeability both positively and negatively. These changes need to be monitored to understand the causative mechanism of these changes and to mitigate potential harmful effects including damage to our reservoirs. Completion and production processes cause dynamic changes in reservoir properties. The most accurate geophysical tool for monitoring these changes is time-lapse, multi-component seismology, specifically enabling the use of shear wave azimuthal anisotropy for reservoir monitoring of effective stresses in the reservoir. Studies over the past 23 years by the Reservoir Characterization Project (RCP) document the power of shear wave azimuthal anisotropy to observe and quantify stress changes in our reservoirs. Our studies focus on carbonate and clastic rocks where changes in rigidity, detected using measurements of shear wave azimuthal anisotropy, are the primary observations to infer reservoir processes. All projects are full waveform data volumes utilizing both vertical and horizontal vibrators as P- and S-wave sources recorded by multi-component geophones. This paper portrays results of time-lapse, multi-component studies at Vacuum, Weyburn, and Wattenberg Fields conducted by the Reservoir Characterization Project. Both Vacuum and Weyburn Fields are carbonate reservoirs undergoing tertiary recovery using CO2 injection. Wattenberg Field is a mixed carbonate/shale reservoir undergoing horizontal drilling and multistage hydraulic fracturing. Results show that stress changes associated with the reservoir processes involving enhanced oil recovery and hydraulic fracturing result in shear wave azimuthal anisotropy changes detected using time-lapse, multi-component seismic data.