Impact of relative permeability hysteresis on pressure transient behavior and storage capacity in underground gas storage with well interference

Abstract

Underground gas storage (UGS) plays a critical role in addressing both regional and temporal discrepancies in energy supply and demand, and is a key strategy for optimizing the energy structure and achieving carbon neutrality. The presence of groundwater, coupled with simultaneous high-speed injection-withdrawal from multiple wells, leads to significant relative permeability hysteresis (RPH) and well interference effects. Here, a high-precision numerical model is developed to explore the impact of well interference and gas-water flow on pressure transient behavior (PTB). The model employs unstructured Voronoi grids for accurate mesh discretization and utilizes a discrete fracture network (DFN) model to simulate natural fractures in the formation. The results indicate that the PTB during gas-water injection-withdrawal is positively correlated with the number of cycles, and is reflected in phenomena such as skin effects, radial flow, matrix-fracture flow, well interference flow, and total radial flow. When the gas relative permeability at irreducible water saturation (G-IWS) increases from 0.4 to 0.7, the gas storage capacity (GSC) increases by a factor of 5.9. By contrast, increasing the water relative permeability at residual gas saturation (W-RGS) by 4-fold only results in a 2.05-fold increase in GSC. Moreover, when the residual gas saturation (RGS) increases from 0.10 to 0.30, the GSC decreases by a factor of 1.41. By fitting to field data from China's largest UGS site at Hutubi, the reservoir permeability, initial water saturation, initial pressure, skin factor, and well storage coefficient were estimated to be 8.5 mD, 0.3, 30 MPa, −3, and 0.32 m³/MPa, respectively.