Time-lapse characterization of the Niobrara reservoir from multicomponent seismic data, Wattenberg field, Colorado

Abstract

The Niobrara Formation has been responsible for the majority of oil production from the Wattenberg Field since its discovery in 1974 (Higley and Cox (2007)). Due to the low porosity and permeability associated with this tight formation, horizontal drilling and hydraulic fracturing has been the standard completion strategy in the field since 2010. The main areas of focus in this thesis include characterizing the natural fracture network within the Niobrara which contributes to permeability, the induced fracture network created through hydraulic stimulation, and the in-situ stress state which influences the hydraulic stimulation. Fracture characterization of the Niobrara Formation is based on time-lapse multicom- ponent seismic surveys acquired before and after hydraulic fracturing. Since azimuthal anisotropy and shear-wave splitting (SWS) are exhibited due to the presence of fractures, the SWS phenomenon was studied in poststack and prestack shear volumes. A quick and simple poststack methodology for extracting time-lapse changes in SWS utilizing both traveltime and amplitude variations was demonstrated to provide an estimated volume that relates to the stimulated reservoir volume (SRV). SWS was also studied in terms of the azimuthal variation of the AVO response in the fast and slow prestack shear volumes. Azimuthal trav- eltime variations in radial and transverse shear volumes were analyzed as an independent methodology to investigate its feasibility for fracture characterization in comparison with the AVO approach. Although they face unique challenges and display varying degrees of sensitivity to azimuthal anisotropy, the two prestack methodologies are in good agreement in terms of final results and interpretations. Azimuthally varying moveout velocities were studied in the compressional baseline survey through which the residual interval traveltime variations with azimuth were used to identify the orientation and elongation of NMO ellipses. Differential azimuthal traveltimes appear to relate to the current day stress state as verified by production logs and microseismic events.