Investigating key pressure loss factors in the Wufeng-Longmaxi formation shale gas reservoirs, Southern Sichuan: A quantitative approach

Abstract

Pressure loss in the Wufeng-Longmaxi Formation shale gas reservoirs of the southern Sichuan Basin is a complex issue. This occurrence is influenced by several critical factors: faults, stratigraphic properties, fold structures, and the timing and magnitude of uplift events. While we know these factors are significant, their quantitative impact and individual contributions to pressure loss remain poorly understood. In this study, we integrate the burial and thermal history of the basin to reconstruct the evolution of key reservoir parameters, including formation temperature, hydrostatic pressure, overburden pressure, total porosity, water-filled porosity, and gas adsorption porosity. Using this framework, we simulate the effects of different preservation conditions on pressure loss within shale gas reservoirs and evaluate the relative contributions of these controlling factors. Simulation results revealed that the location of fault development, particularly its penetration through the caprock, is the predominant factor governing pressure loss in local shale gas reservoirs. In contrast, the scale of fault development has a relatively minor impact. Additionally, the thickness and vertical diffusion coefficient of the caprock, along with the time, emerged as secondary controlling factors that substantially influence the rate of pressure loss across the shale gas reservoirs. Furthermore, the dip angle of synclinal folds and the lateral diffusion coefficient act as accelerators of pressure loss, potentially leading to rapid depletion of reservoir pressure. Conversely, the properties of anticlines exhibit minimal influence on pressure loss. These findings provide valuable insights for the management and optimization of shale gas reservoirs in the Wufeng-Longmaxi Formation.