Experimental analysis of primary factors controlling carbonate rock dissolution capability and its impact on geothermal reservoir modification

Abstract

Carbonate geothermal reservoir is one of the main thermal reservoirs for geothermal resources development and utilization, with abundant thermal resources and good exploitation conditions. The dissolution of carbonate rocks is an important factor in the formation of geothermal reservoirs. In order to explore the control effect of lithology, temperature, and pressure on the dissolution of carbonate rocks, dolomite, limestone, marlstone, and dolomite limestone were used as rock samples. A 0.2 % acetic acid solution was employed for the simulation. A high-temperature and high-pressure solution simulation device was utilized to simulate the dissolution process from surface to deep burial conditions. The results show that: The amount of limestone dissolution follows a “V-shaped” pattern in response to temperature changes and exhibits an “up-down cycle” in response to pressure variations. Furthermore, the impact of temperature on dissolution is significantly greater than that of pressure.The karst erosion and burial depth of different lithologies exhibit a trend of "initial increase followed by decrease," existing a "peak of dissolution". The dissolution peak of dolomite occurs at approximately 4500 m, while that of limestone exceeds 6500 m. The dissolution capacity of mudstone is relatively low, reaching its maximum around 4000 m. Consequently, three potential stages for the formation of high-quality heat storage can be delineated as shallow to moderately buried limestone, moderately to deeply buried dolomite limestone, and deeply buried dolomite.Simultaneously, the “selective” mechanism of dissolution of carbonate rocks is examined, encompassing both the “composition selective” dissolution of calcite during the dissolution process and the “structure selective” dissolution occurring within fissures, particle edges, and crystal surfaces.