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

Abstract

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 3 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.

Interpretation of above‐zone pressure influence time to characterize CO2 leakage

“…Above‐zone pressure monitoring is especially important for CO 2 leakage detection and characterization because it can monitor a large area of investigation at low cost with high resolution and accuracy. Several studies focused on analyzing above‐zone pressure data to gain information on the leakage pathways such as leaking wells and fractures and other heterogeneities in the caprock . All these studies used pressure signal passively, i.e., the pressure signal was only due to leakage.…”

“…Several studies focused on analyzing above-zone pressure data to gain information on the leakage pathways such as leaking wells and fractures and other heterogeneities in the caprock. [15][16][17][18][19][20][21][22][23][24][25][26] All these studies used pressure signal passively, i.e., the pressure signal was only due to leakage. Hosseini and Alfi 27 used pressure monitoring by performing a pressure interference test in the above zone and analyzing its response for CO 2 leakage.…”

CO2 plume and pressure monitoring through pressure sensors above the caprock

“…However, recent pressure monitoring in the Cranfield CO2 injection project indicates measurable changes of pore pressure above the caprock (~50 kPa) after two years of CO2 injection with IZ pressure change reaching a maximum of ~8.8 MPa in the absence of leaks (Kim & Hosseini, 2014;Tao et al, 2012). Analytical and numerical simulation work demonstrates that rock deformation above the injection zone can induce pressure changes in the absence of leaks through the caprock, by means of a poroelastic phenomenon known as "undrained loading" (Kim & Hosseini, 2014;Zeidouni & Vilarrasa, 2016). Despite recent advances and numerical simulations, pressure monitoring above the caprock remains largely underutilized or misinterpreted because of a lack of (1) validation schemes, (2) discrimination between fast hydraulic communication and undrained loading, (3) thorough measurement of poromechanical properties of the AIZ, (4) thorough deployment of high-resolution sensors to capture subtle pressure changes (e.g., 1 kPa), (5) coupled poroelastic simulation beyond the injection zone for all CO2 storage projects, (6) extension of existing models to two-phase fluid flow, (7) accurate prediction of absolute magnitude and transient pressure changes in the AIZ, and (8) evaluation of other leaking/sealing scenarios beyond just one leaky abandoned well (S. Hosseini et al, 2018;S.…”

“…A. Hosseini, 2019;S. Hosseini & Alfi, 2016;Kim & Hosseini, 2014;Mishra et al, 2014;Wiese et al, 2013;Zeidouni & Vilarrasa, 2016).…”

Semi-Analytical Solution to Assess CO2 Leakage in the Subsurface through Abandoned Wells

“…Furthermore, they could be used to verify and benchmark numerical methods [30][31][32]. Researchers have developed many analytical solutions and asymptotic solutions for assessing the pressure change and leakage rate [33][34][35][36][37][38][39][40][41]. The solution methods include various field scenarios corresponding to closed or constantpressure outer boundary conditions and incomplete-sealed well [42][43][44][45].…”