Salt Dissolution–Induced Permeability Enhancement and Its Implications for Improved Oil Recovery During Waterflooding in Saline Lacustrine Carbonate Reservoirs

Waterflooding in saline lacustrine carbonate reservoirs frequently induces dissolution of soluble salt minerals, a process that substantially alters pore architecture and transport properties. However, the quantitative relationship between salt dissolution, permeability evolution, and ultimate oil recovery remains incompletely characterized. In this study, high-temperature, high-pressure core-flooding experiments were combined with numerical simulation to investigate the salt dissolution–induced permeability enhancement (SDPE) effect. Core samples from the Qianjiang Formation, containing 8–15% soluble salts, were tested under reservoir conditions (temperatures up to 100 °C, confining pressure up to 25 MPa). The results show that dissolution of halite and anhydrite cements preferentially enlarges pore throats in the 0.01–1 μm range, as confirmed by NMR T2 spectra. Based on these observations, a time-dependent permeability model was developed using cumulative water throughput per grid as the key leading to a permeability increase of up to 170%, and was implemented as a user-defined module in the commercial reservoir simulator Comparative simulations between the conventional constant-permeability model and the time-dependent model reveal that accounting for the SDPE effect increases predicted cumulative water injection by 25%, expands sweep volume by 18 percentage points, and improves ultimate oil recovery by 4.5 percentage points over 15 years of production. These findings demonstrate that the SDPE effect is a practically exploitable mechanism for improving waterflood performance in salt-bearing carbonate reservoirs, and provide a quantitative framework for optimizing waterflooding design.