Devonian Shale Oil Production Analysis and Evaluation

Abstract

Abstract An analysis and evaluation of the Devonian Shale oil production's rapid decline rates and future potential production's rapid decline rates and future potential were performed. Various analysis techniques were employed to evaluate the performance of oil wells completed in the Lower Huron Member of the Devonian Shale in a seven-county area of western West Virginia and southeast Ohio. The analyses included material balance, and analysis of production data by a transient method and numerical simulation, together with statistical methods. Results of the evaluation showed that the coexistence of natural fractures and matrix permeability and porosity are necessary for oil production permeability and porosity are necessary for oil production from the Lower Huron in this area. Matrix permeability and porosity created by the inclusion of silt permeability and porosity created by the inclusion of silt in the shales are necessary for oil accumulation and production. Because the matrix permeability is production. Because the matrix permeability is extremely low, fractures are necessary to transmit the matrix production to the well bore. Although the cumulative oil volume is quite low, the recovery efficiency within the well drainage volume is significantly higher than expected for solution gas drive. A proposed explanation is that a mechanism of gas trapping is responsible for the high oil recovery efficiency. Another major finding of the study was that the methods of completion and stimulation had no effect on productivity. No major production problems except possible fracture closures were determined. The study also showed that the combination of the geologic features necessary for oil production from shale is unique to this area but is by no means consistent over the entire area. In fact, the probability of locating the geological conditions necessary for economic oil production is only about 4 percent with current methods. Although unlikely, even if the tech nology for finding and producing oil from the Devonian Shale is greatly improved, few opportunities for commercial wells remain since the area is already densely drilled. Also, restimulation of old wells does not appear promising because wells are usually too close to abandonment pressure for additional oil production. Introduction More than 2,000 wells have been drilled and completed in the Devonian Shale in a seven-county area of western West Virginia and southeast Ohio near the Burning Springs Anticline since the late 1970's (Figure 1). Most of the oil-producing wells experienced very rapid oil production decline rates during the first few months of production. During 1986, the U.S. Department of Energy initiated a geologic and engineering study to determine why the rapid oil production decline occurred. Other objectives were to production decline occurred. Other objectives were to determine what remedial action, techniques, or procedures which could be taken to increase production and procedures which could be taken to increase production and future potential, if any, for the area. Geologic, well, and production data were collected from various sources to get as complete a picture as possible of the overall oil production operations. possible of the overall oil production operations. The oil production performance was analyzed using material balance, transient flow, decline curve, and numerical simulation reservoir analysis techniques. Production methods for well completion and stimulation Production methods for well completion and stimulation were also analyzed. All of these analysis techniques employed statistical methods because of the wide variation in well completions and Production performance. The results were combined with the Devonian performance. The results were combined with the Devonian Shale geologic interpretations in this area of oil production to evaluate the future potential for production to evaluate the future potential for additional oil production. Geological and Reservoir Properties Lithology This study focused on oil production from Devonian Age rocks, including organic and inorganic shales and siltstones in a seven-county area. The counties are Wirt, Ritchie, Wood, and Pleasants in West Virginia, and Washington, Noble, and Monroe in Ohio. P. 327