f Analysis of Time-Lapse TEM Data for Underground Gas Storage

Natural gas is an increasingly important energy resource in Europe. Companies are seeking new storage sites, such as depleted reservoirs or deep aquifers. Monitoring of changes in gas volume is crucial to avoid losses and to use the site at its optimum, capacity. The standard method to monitor the gas movements is to drill monitor wells, which are expensive and give information only about the near vicinity of the well. Electromagnetic (EM) methods have the potential to support the monitoring from the surface and to save drilling costs. They are sensitive to changes in electrical conductivity, and thus to movements in the gas/water contact. To demonstrate the feasibility of EM methods to monitor changes in underground gas storage sites, two transient EM surveys were conducted over a gas storage in France. The aim was to use the differences in the data from the two surveys to detect changes in the subsurface.