Study on the Mechanism of Stress Sensitivity and Retrograde Condensation Coupling Effect on Reservoir Depletion Development in Fractured-Vuggy Carbonate Rocks

Summary Deep and high-pressure carbonate gas condensate reservoirs develop a large number of cracks and holes, with strong interlayer heterogeneity and complex mechanisms. To clarify the fundamental reasons that affect the development efficiency of such condensate gas reservoirs, we take the typical fractured and vuggy carbonate rock reservoirs in China’s S condensate gas field as the object of study, and conduct experiments such as X-ray computed tomography (X-CT) scanning, high-temperature and high-pressure stress-sensitivity testing, and long-core depletion development experiments. From multiple parameters and perspectives, we describe the microscopic changes in the storage and seepage spaces of fractures and vuggy cores, as well as the changing patterns of the underground condensate oil and gas production. According to the research results, the increase in effective stress leads to the contraction and closure of the fractured and vuggy spaces in the core, resulting in a decrease in their size. Under deep, high-pressure conditions, carbonate reservoirs exhibit strong stress sensitivity, and the permeability of the core drops significantly with the increase in the formation’s effective stress. The coupling effect of stress sensitivity and retrograde condensation has different impacts on the development effect of different types of cores at different pressure stages. The vuggy cores experience greater changes in storage and seepage spaces, the overall permeability damage is strong, and the condensate oil recovery rate is ultimately lower than that of fractured cores. Therefore, it is of great significance to study the impact of stress sensitivity and retrograde condensation characteristics on the gas reservoir recovery rate. The research results can provide theoretical support for the efficient development of deep, fractured-vuggy carbonate condensate gas reservoirs.