Shale Oil Production Performance from a Stimulated Reservoir Volume

Abstract

The horizontal well with multiple transverse fractures has proven to be an effective strategy for shale gas reservoir exploitation. Some operators are successfully producing shale oil using the same strategy. Due to its higher viscosity and eventual 2-phase flow conditions when the formation pressure drops below the oil bubble point pressure, shale oil is limited to lower recovery efficiency than shale gas. However, the recently discovered Eagle Ford formations is significantly overpressured, and initial formation pressures is well above the bubble point pressure in the oil window. This, coupled with successful hydraulic fracturing methodologies, is leading to commercial wells. This study evaluates the recovery potential for oil produced both above and below the bubble point pressure from very low permeability unconventional oil formations.Relative permeability behavior, including the critical gas saturation, is likely to be quite different in created fractures from that of the shale matrix, and technology for laboratory multiphase flow measurements has not been developed for such low absolute permeability values as are found in shale formations. Further, propent embedment and expected multi-phase flow in the created hydraulic fractures can lead to actual values of fracture conductivity in the created fractures order of magnitude lower than the values reported in the laboratory.As with shale gas, high recovery in shale oil wells will require that created hydraulic fractures are spaced close enough to result in interfracture interference during the time the well is on production. This study investigates the role of the fracture spacing, fracture conductivity, fracture half-length, critical gas saturation, flowing bottom-hole pressure and matrix permeability in the well economics and the ultimate recovery efficiency considering flow both above and below the bubble point pressure and using known properties of successful shale oil plays. Simulations show that results are strongly dependent on assumed relative permeability behavior, and sensitivity studies provide considerable insight about the long term production behavior than can be expected in these wells.