Analysis of Reservoir Parameters in Relation to Optimal Well Spacing in the Marcellus Shale Formation

Abstract

Abstract. Optimizing well spacing is an underutilized solution to low recovery rates in unconventional reservoirs, allowing for higher extraction efficiencies while avoiding complex recovery techniques and added operational presence. However, defining the optimal spacing will necessarily be influenced by inherent reservoir heterogeneities. The primary objective of this study is to understand the influence of critical reservoir parameters on optimal well spacing and associated production increase in unconventional gas reservoirs, using a representative unit of the Marcellus shale as a model system. Numerical reservoir simulation models were developed to evaluate the distinct influence of matrix permeability, matrix porosity, fracture conductivity, and pore pressure on the optimal spacing between identical wells. Cumulative production was also quantified for each configuration to understand where well spacing contributes to production loss, either due to interference (spacing too close) or unstimulated reservoir volume (spacing too wide, leaving gas that would require subsequent infilling or restimulation to obtain). For wells with a fracture half-length of 300 ft, increasing well spacing from 200 ft to 600 ft increased the 10-year cumulative production by approximately 28%. The optimal spacing, however, was found to be highly dependent on the obtained fracture half-length. It was also determined that fracture conductivity had a maximum, effective limit of 2 mD · ft, where any further increase provided a minimal benefit of less than 5%. Understanding the effects of fracture half-lengths and reservoir parameters leads to development in shale gas reservoirs that is more efficient and generates an optimized yield of natural gas over its production lifetime.