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.