Study on the Interaction Mechanisms among CO₂, the Formation Water, and Tight Sandy Conglomerate

Tight sandy conglomerate reservoirs exhibit poor physical properties, strong heterogeneity, and significant development challenges due to low permeability. Understanding the interaction of CO2 with such formations is critical for enhanced oil recovery (EOR). Experimental studies on the interaction mechanisms among CO2, formation water, and tight sandy conglomerate were conducted. The results indicate that under the reservoir conditions of 89 °C and 37.0 MPa, the solubility of CO2 in the formation water is significantly influenced by temperature, pressure, and salinity. After dissolving in formation water, CO2 forms carbonic acid, which triggers dissolution reactions of minerals such as feldspar under acidic conditions. This leads to a reduction in feldspar mineral content and a 0.31% decrease in core mass. Concurrently, the rock's microscopic surface becomes rougher with numerous dissolution pores and cavities emerging. The average pore-throat radius increases, and the displacement pressure decreases. These alterations improve the rock's pore structure by enlarging pore-throat dimensions, creating additional flow channels for oil and gas migration. Consequently, the permeability increases by 7.4-11.0%, thereby enhancing the production capacity of tight sandy conglomerate reservoirs.