Integrated Strategies for Carbonate Reservoir Reserve Growth: An Example from the Ellenburger Group, Permian Basin, West Texas

This study demonstrates the efficacy of using modern multidisciplinary analyses, including analysis of modern 3-D seismic data, to enhance natural gas reserve growth in Ellenburger Group reservoirs in Lockridge, Waha, and West Waha fields and parts of Worsham-Hayes and Coyanosa fields in the southern Delaware Basin, West Texas. Well log, 3-D seismic, structure, and pressure and production data indicate that the dominant control on Ellenburger production in this area is natural fractures, particularly fractures associated with faults and maximum flexure on positive structural features. Matrix porosity does not vary significantly in Ellenburger reservoirs within the study area and is not a significant factor in reservoir quality. Coherency analysis of the 3-D seismic data suggests that some features can be interpreted as paleokarst zones. Optimal gas production in Ellenburger, Devonian, and Mississippian reservoirs occurs in wells positioned close to faults, and production tends to increase as the fault displacement and structural distortion increase. Maximum production in the study area is associated with reverse faults and with overturned sections. Thus, the requirement for siting productive wells is to place the wellbore where it will penetrate the maximum amount of fractured rock, and any seismic attribute that shows where significant stratal movement and distortion have occurred is a valuable indicator of fracturing. Fusselman, Devonian, and Mississippian strata provide important opportunities for recompletion of Ellenburger wells in these shallower horizons.