Geomechanical Impact on Gas Recovery from Marcellus Shale

The production rate from unconventional reservoirs declines more rapidly than conventional reservoirs. The production from the reservoir result in an increases in the net stress due to reduction in the pore pressure while the overburden pressure remains constant. This leads to formation permeability reduction, both for the matrix and the fissures, as well as and conductivity impairment in hydraulic fracures due to proppant embedment. Information relative to the impact of stress (geomechanical) on matrix permeability and porosity, hydraulic fracture conductivity, fissure permeability were obtained from published studies. The effects of stress on the matrix, and fissure permeability, and propped fracture conductivity were then incorporated into the numerical reservoir simulator to predict production performance.

The objective of this study is to investigate the impact of the net stress changes on gas production from the horizontal wells with multiple hydraulic fractures completed in Marcellus Shale. A commercial reservoir simulator was used to develop the base model for Marcellus shale horizontal wells. 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. 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 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. Shale petrophysical properties at this site were determined by Precision laboratory equipment. These laboratory measurments provided the impact of net stress on core plug permeability and porosity. Furthermore, these experimental results were utilized to determine the the fissure closure stress. The relation between the propped fracture conductivity with the net stress were obtained from published studies on cores plugs collected from Marcellus shale. The production data from two horizontal wells at MSEEL site, were utilized for history matching with the model first by inluding geomechanical effects and then by exdcluding them. This approach allowed the impacts of stress-dependent matrix permeability, fissure permeability, and hydraulic fracture conductivity on the gas production to be evaluated. The base model was finally used to perform a number of parametric studies. The inclusion of geomechanical effects in the model improved the model predictions particularly at the early stages of the production. The results indicated that fissure permeability reduction due to stress, compared to reduction in matrix permeability and propped fracture conductivity, has more impact on gas production when the pressure in the vicinity of the well has declined.