A multidisciplinary reservoir-characterization study of the Ellenburger Group was conducted over a 176-mi2 3-D seismic grid in Pecos, Reeves, and Ward Counties in the southern Delaware Basin of West Texas. The study area covered Lockridge, Waha, and West Waha fields and parts of Worsham-Bayer and Coyanosa fields, which have produced 1.3 trillion standard cubic feet of natural gas since their discoveries in the 1960's. Seismic time-structure and depth maps were generated for the tops of the Bone Spring-3, Mississippian, Devonian (Woodford), and Ellenburger. The focus of the study was to determine whether productive Ellenburger facies could be detected and mapped by using surface-recorded seismic data. No seismic attribute could be found, however, that exhibited any significant correlation with Ellenburger production. Systems of complex faults were interpreted across the 176-mi2 3-D image space.
The structural maps that were created are thought to be some of the most accurate depictions of the subsurface structure that are publicly available in this area of the Delaware Basin. Particular attention was given to documenting the overturned bedding and repeated sections that are associated with the interpreted fault systems. Both well log and 3-D seismic evidence of these tectonic folds and repeated reverse faults is presented. Natural gas production in the Lockridge-Waha region seems to be directly related to fracturing. The best gas production in Ellenburger, Devonian (Thirtyone), and Mississippian reservoirs in this study area occurs where wells are positioned close to faults and tends to increase as fault displacement and stratal distortion increase. The best production in the Lockridge-Waha region seems to be associated with reverse faults and with overturned sections. Wells should therefore be sited where they will penetrate the maximum number of fractured strata. From a 3-D seismic interpretation perspective, the requirement for siting productive wells is to place the well bore where seismic data allow an interpreter to infer that significant stratal movement and distortion have occurred because these rock deformation processes are indirect, but valuable, indicators of fracturing.