The Impact of the Net Stress on Gas Recovery from the Marcellus Shale

摘要

Unconventional reservoirs have high initial production rates followed by a steep decline as compared to conventional reservoirs.The increase in the net stress with the production results in matrix and fissure permeability reduction and hydraulic fracture compaction and conductivity impairment due to proppant embedment.At the same time,the pressure decline will result in gas slippage and matrix permeability enhancement.The impact of the net stress and pore pressure changes are often neglected when evaluating the production performance of the shale wells.The objectives of this study are to investigate the impacts of net stress changes(geomechanical)and pore pressure changes(gas slippage)on the gas production from horizontal wells with multiple hydraulic fractures completed in the Marcellus Shale.Laboratory measurements on Marcellus shale core plugs provided the foundation for evaluating the impact of pore pressure and net stress changes on the matrix permeability.Additionally,these laboratory measurements on Marcellus shale core plugs provided the fissure closure stress.The results of the published studies on Marcellus shale core plugs were also utilized to develop relationships for hydraulic fracture conductivity and the fissure permeability as a function of the net stress in the shale.Core,log,completion,stimulation,and production data from the wells located at the Marcellus Shale Energy and Environment Laboratory(MSEEL)were utilized to generate the formation and completion properties for the base model for a horizontal well completed in Marcellus Shale.The results of the laboratory measurements and published studies were then incorporated into the base model to account for the impact of the stress on the matrix,fissure,and hydraulic fracture permeability(conductivity),and consequently on the production performance.The model was utilized to determine the effective properties of the hydraulic fractures by history matching the production data from two horizontal wells at MSEEL site.For the comparison purposes,the geomechanical effects were excluded from the model,individually and all combined,to history match the same production data from the horizontal wells.The results indicated that the geomechanical effects for fissure permeability have a significant impact on gas production as compared to geomechanical effect for matrix permeability and hydraulic fracture conductivity.The gas slippage was found to have an insignificant impact on the production.The base model was finally used to perform a number of parametric studies to investigate the impact of fracture half-length,initial fracture conductivity,and fracture stages spacing on the stress-dependent fissure permeability.