Search

SUMMARY Economically viable natural gas production from the low permeability Mesaverde Formation in the Piceance Basin, Colorado requires the presence of an intense set of open natural fractures. Establishing the regional presence and specific location of such natural fractures is the highest priority exploration goal in the Piceance and other western U.S. tight, gas-centered basins. Recently, Advanced Resources International, Inc. (ARI) completed a field program at Rulison, Piceance Basin, to test and demonstrate the use of advanced seismic methods to locate and characterize natural fractures. This project, conducted jointly with Barrett Resources and supported by the USDOE/FETC, began with a comprehensive review of the tectonic history, state of stress and fracture genesis of the basin. A high resolution aeromagnetic survey, interpreted satellite and SLAR imagery, and 400 line miles of 2-D seismic provided the foundation for the structural interpretation. The central feature of the program was the 4.5 square mile multi-azimuth 3-D seismic P-wave survey to locate natural fracture anomalies. The interpreted seismic attributes are being tested against a control data set of 27 wells. Additional wells are currently being drilled at Rulison, on close 40 acre spacings, to establish the productivity from the seismically observed fracture anomalies. A similar regional prospecting and seismic program is being considered for another part of the basin. The preliminary results indicate that detailed mapping of fault geometries and use of azimuthally defined seismic attributes exhibit close correlation with high productivity gas wells. The performance of the ten new wells, being drilled in the seismic grid in late 1996 and early 1997, will help demonstrate the reliability of this natural fracture detection and mapping

Natural fracture intensity and diversity of orientation are requirements for commercial production from tight gas reservoirs. The ability to find and define these open natural fractures in advance of drilling represents the major challenge for continued development of these low permeability reservoirs. Since tectonic fractures are frequently caused by subtle basement structures, the Naturally Fractured Tight Gas Reservoir Optimization project is focused on techniques that can identify basement features and thereby locate the overlying fractured reservoirs.