Application of time-lapse multi-component seismic inversion to characterize pressure and stimulation in the Niobrara and Codell Reservoirs, Wattenberg Field, Colorado
The Wattenberg field is the fourth-largest oil and ninth largest gas field in the United States (EIA, 2015). A multi-component time-lapse seismic study has been conducted by RCP and Anadarko Petroleum Corporation in the Wattenberg field. This study includes an integrated dataset with seismic, microseismic, FMI log interpretations, and completion information. As part of a horizontal drilling programme, the Niobrara and Codell formations were targeted. P-wave seismic and S-wave seismic were analysed as part of the time-lapse study before and after the completion of 11 horizontal wells in the study area. Time-lapse P-wave pre-stack inversion was able to identify pressure compartments in the different reservoir intervals that were able to be distinguished by the pre-stack data. The inverted P-impedance percentage difference volume allows for identification of pressurized zones and whether the faults are acting as seals or conduits for the hydrocarbons. S-wave data provides a subset of the pressure compartmentalization that encompasses the stimulated reservoir volume. Time-lapse post-stack inversions of the shear wave datasets provide insight into how the shear impedance is affected by hydraulic fracturing through the work of time-lapse shear wave splitting. The inversions show an increase in fast shear wave velocity and a decrease in slow shear velocity after stimulation. The sensitivity of both the fast and slow shear seismic to stimulation correlates with the net pressure trends at each stage as well as base map microseismic patterns. The stimulated volume for the Niobrara and Codell reservoir intervals are now more accurately defined. Timelapse shear wave splitting is able to define the stimulated rock volume and reveal areas that are not being accessed by the wells currently drilled. These areas are now detected within the Wishbone section, and may be candidates for future re-completion.