Risk Reduction for Prospecting in the Unconventional Niobrara Play.
Tony Rebec and Alvano Chaveste
Major interest in the Niobrara has been spurred by the latest recovery techniques in sub-surface simulation as is typically of all unconventional plays. The Niobrara, of mid-upper Cretaceous age, was strongly influenced by the late Cretaceous Laramide Orogeny, and located in what is now Colorado, Wyoming and Nebraska. The seismic characterization of the Niobrara presented here is based on the Geokinetics/Geophysical Pursuit Multi-Client 3D survey recently acquired in Weld County, NE Colorado, and publically available well data for calibration within the 3D area. The presentation starts with the location and geologic setting of the Niobrara and it's vertical reference to the seismic response. An association is made using geometric attributes relating the complex subtle faulting to the Laramide Orogeny, which occurred in a series of pulses with intervening quiescent phases, possibly influencing hydrocarbon production. This sets the local structural framework for using fracture anisotropy and related rock properties for locating possible areas of significant interest. A methodology is presented to reduce risk in identifying sweet spots within the local structural framework using the full azimuth 3D seismic and well logs for calibration. Prospect identification in this play requires characterizing the formation properties not commonly used for conventional plays. While a trap within a porous permeable formation is required for a conventional reservoir, the unconventional reservoir is engineered, based on locating sweet spots. For the Niobrara, these sweet spots are associated with carbonate content, brittleness, natural fractures and total organic content (TOC) or a combination of these. Risk reduction is performed through the estimation of both, isotropic and anisotropic rock properties calibrated to their equivalent from well-logs. Fracture density and orientation are qualitatively estimated from elliptical inversion of sectored S-impedances derived from pre-stack simultaneous elastic inversion. Carbonate content is derived from isotropic P and S impedances calibrated to wells, and brittleness through a combination of elastic properties (Poisson's ratio and Young's modulus). Based on the Multi-Client full azimuth 3D seismic data, processed through OVT migration, elliptical and pre-stack simultaneous elastic inversion with well to seismic correlation, areas of potential high interest can be differentiated.
AAPG Search and Discovery Article #90156©2012 AAPG Rocky Mountain Section Meeting, Grand Junction, Colorado, 9-12 September 2012