Journal article

Identification of above-zone pressure perturbations caused by leakage from those induced by deformation

Pressure changes in the above zone, i.e., the overlying aquifer of an injection zone separated by a sealing caprock, are usually attributed to leakage through wells. However, pressure changes can be induced geomechanically due to rock deformation without any hydraulic connection between the injection zone and the above zone where the pressure change is observed. To account for these two causes of pressure change in the above zone, we develop an analytical solution to evaluate the deformation-induced pressure changes and we derive an asymptotic analytical solution for pressure perturbations caused by leaking wells. The analytical models compare well with available numerical/analytical solutions. Using the analytical solutions for the deformation-and leakage-induced pressure changes, we propose a graphical diagnostic plot to determine the cause of pressure change. Considering that the pressure change is caused by leakage, we then use the asymptotic solution to develop an easy-to-use fully graphical methodology to characterize leaking wells. This methodology improves a previous analysis methodology that was based on an inverse modeling algorithm that can be highly instable and computationally expensive. Based on the graphical method presented here, the slopes and intercepts of the proposed line-fitted graphs are used to determine the leak location and transmissibility. We apply the graphical method to an example problem to illustrate its application procedure and effectiveness in differentiating deformation-induced pressure changes from leaking wells. Overall, the diagnostic plot proposed here proves to be useful to determine the cause of the above-zone pressure change.


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