The Impact of Stress on Propped Fracture Conductivity and Gas Recovery in Marcellus Shale

Abstract

Abstract It is commonly observed that the production rates from unconventional reservoirs decline rapidly as compared to conventional reservoirs. The net stress increases with the production because the pore (fluid) pressure decreases while the overburden pressure remains constant. This leads to the fracture compaction and conductivity impairment due to proppant embedment. Even though advances in technology have unlocked considerable reserves of hydrocarbon, the impact of the net stress changes on proppant conductivity, i.e. stress-dependent propped fracture conductivity, is not well understood. The objective of this study is to investigate the impact of the net stress propped fracture conductivity from the horizontal wells with multiple hydraulic fractures completed in Marcellus Shale. A commercial reservoir simulator was used to develop the base model for a Marcellus Shale horizontal well. The model incorporated various storage and production mechanisms inherent in Shales i.e. matrix, natural fracture, and gas adsorption as well as the hydraulic fracture properties (half-length and conductivity). The core, log, completion, stimulation, and production data from wells located at the Marcellus Shale Energy and Environment Laboratory (MSEEL) were utilized to generate the formation and completion properties for the simulation model. MSEEL is a Marcellus Shale dedicated field laboratory and a research collaboration between West Virginia University, Ohio State University, The National Energy Technology Laboratory, and Northeast Natural Energy. Precision laboratory equipment was utilized to determine rock petrophysical properties such as permeability and porosity. Additionally, the natural fracture closure stress values were determined by an innovative experimental technique using core plug samples. The relation between fracture conductivity and the net stress were obtained from published studies (SPE 181867) on core plugs collected from Marcellus shale at two different locations. This relation was incorporated in the model to investigate the geomechanical impact of hydraulic fracture on the gas production. The model was used to perform a number of parametric studies to investigate geomechanical effects for fracture conductivity on gas recovery from Marcellus shale. The production data from two horizontal wells at the MSEEL site, were utilized for production history matching both with and without geomechanical effects. The inclusion of the geomechanical effect in the model improved the predictions particularly at the early stages of the production. Simulation results show geomechanical effects of fracture conductivity on gas production performance for Elimsport and Allenwood samples, which were cut parallel and perpendicular to the bedding planes. Moreover, the results indicate that the geomechanical effects have a significant impact on gas production when the pressure in the vicinity of the well has declined.