Time‐lapse application of pressure transient analysis for monitoring compressible fluid leakage

Detecting early leakage of gaseous fluids from deep formations into shallower formations has financial and environmental implications and could potentially save commercial projects from expensive remediation. Detection of CO 2 leakage in the context of CO 2 geological storage and methane leakage at hydraulic‐fracturing sites is a possible scenario in which the approach described herein could be used. Any vertical leakage from a deep formation will most likely start with brine leakage, followed by arrival of the gaseous phase at the leakage pathway (faults, plugged and abandoned wells, fractures, etc.). We apply well‐known pressure transient analysis (PTA) techniques to solving challenges related to leakage monitoring, including distinguishing between brine and gaseous‐phase leakage and detecting leaks that may occur over a long period of time. The latter development is important because small leaks may not be detected by simple monitoring of absolute change in pressure. The proposed analysis is based on time‐lapse measurement of monitoring‐zone storativity (or total compressibility), and without loss of generality, we apply our analysis to CO 2 leakage scenarios. Our numerical results suggest that if well‐known PTA techniques are used, CO 2 leaks can be detected, allowing the volume of leaked CO 2 into the monitoring zone to be estimated. © 2015 Society of Chemical Industry and John Wiley & Sons, Ltd