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Seismic Characterization of Fractured Tight Gas Reservoirs, Piceance Basin, Colorado

Kyle T. Lewallen1, Ganglin Chen2, Xianyun Wu2, and Payson Todd3
1Technical Team Lead - Surface Geophysics, ExxonMobil Upstream Research Company, Houston, TX
2ExxonMobil Upstream Research Company, Houston, TX
3ExxonMobil Production Company, Houston, TX

The Piceance Basin, located in northwest Colorado, contains one of the largest gas accumulations in the U.S. This northwest trending asymmetrical, Laramide-age basin is composed of low porosity (1%-10%) and microdarcy-scale matrix permeability (1-60μD) sands and shales in the Upper Cretaceous Mesaverde Group. A west to northwest trending regional maximum horizontal compressive stress exists and aligned fractures have developed at depth. Since open fractures could have profound effect on the hydraulic behavior of this tight gas reservoir, the ability to reliably predict fracture anomalies is critical for reservoir characterization. Although numerous seismic studies of fractured rock exist, we extend previous work by investigating northern Piceance where the productive interval is thick (3000-5000 ft) and complicated by an additional 5000-8000 ft of overburden.

In this study we analyzed well logs, laboratory core measurements, numerical models, borehole seismic and surface seismic measurements to understand the relationship between reservoir fractures and surface seismic detection methods in the north Piceance basin. FMI and sonic logs were examined to observe the correlation between lithology, fractures and velocity anisotropy. An extensive borehole seismic program was collected to calibrate between downhole well measurements and surface detection methods. Several multi-component 2D surface seismic lines were acquired at different azimuths to measure fracture anomaly detection capabilities. Preliminary results suggest that fractures occur in sand intervals and seismic anisotropy has a positive correlation to fracture occurrence.

AAPG Search and Discovery Article #90092©2009 AAPG Rocky Mountain Section, July 9-11, 2008, Denver, Colorado