Abstract

Deep saline aquifer is deemed as an effective and promising site for carbon sequestration. A geological storage site must be operated safely; however, CO2 may leak through several pathways, such as fractures, faults and/or improperly plugged wells.

This study presents a new analytical model predicting the pressure change in the monitoring well and the leakage rate, caused by an inclined fracture in the caprock, to detect and evaluate the leakage. Distinct with previous analytical method, herein we propose a new case of the leakage through the inclined fracture in a closed aquifer system, which expands on earlier work to a wider application. The solutions for the injection at a constant rate and the time-dependent leakage through an inclined fracture of caprock are derived with Laplace transform, Fourier cosine transform and Duhamel's principle. Then, by means of the superposition method, the pressure change and the leakage rate with both of the two processes are determined in succession. Based on the above solutions, we discuss the effect of the leakage path and the boundary of the aquifer on the system.

At the early stage, the leakage rate increases more rapidly with the smaller radius of the aquifer. Moreover, in the smaller aquifer, the rapid pressure transient results in that the system quickly reach the stable stage. The effect of the inclined fracture on the system is embodied in its permeability, location and angle. With higher permeability the leakage rate increases more quickly at early stage and reaches the constant value more quickly at late‐time stable stage. The fracture has slight impact on the leakage in the long term. Location of fracture does not affect the leakage rate at rapid increase stage. Leakage rate is larger and increases with smaller distance at transitional stage. With the increase of angle, leakage rate increases at all three stages. At the late‐time stage, the larger the angle is, the larger the leakage rate is.

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