An explicit integral solution for pressure build‐up during CO 2 injection into infinite saline aquifers

The increase of fluid injection projects with large burial depths, such as CO 2 geological storage, poses a new challenge for the change law of pressure in reservoirs. To obtain the pressure of anywhere at anytime conveniently and then evaluate the injectivity and safety of reservoirs, a Darcy formulation suited for two‐phase flow of displacement is put forward in this paper. A convenient and practical explicit integral (analytical) solution of pressure build‐up for two‐phase flow under a constant injection rate of CO 2 , based on an infinite reservoir with a constant pressure boundary whose location is a function of time is then derived. Subsequently, this work compared the results of the explicit integral solution with the results of Nordbotten's approximate solution and the simulated results of TOUGH2/ECO2N for an analysis case of CO 2 injection, which demonstrated a good consistency, verifying the correctness and the reliability of the explicit integral solution. Furthermore, the sensitivity analysis of S lc (the saturation of brine in the CO 2 domain) and S lw1 (the saturation of brine in the brine domain 1) showed that they both have a great impact on the pressure profiles in reservoirs, and the pressure is more sensitive to S lw1 than S lc . Therefore, the determination of S lc and S lw1 should be careful and based on the actual project in applications. Generally speaking, the explicit integral solution is simple, convenient, and practical compared with numerical simulators and other analytical solutions with similar assumptions. © 2016 Society of Chemical Industry and John Wiley & Sons, Ltd