The short-term concerns about the environmental impact of drilling operations can be addressed through careful management of surface operations. However, of greater concern, are the long-term impacts of unplanned events during the life of the well. The number of wells that leak or show sustained casing pressure remains a high percentage of the total number of wells worldwide. Loss of zonal isolation, especially when the leaks are vented to surface, poses a clear environmental risk because of the potential emission of greenhouse gases such as methane.

A new sealant developed to improve long-term zonal isolation lessens the potential for long term environmental issues in these wells. This cement-based material has intrinsic self-healing properties and is a responsive material activated by contact with hydrocarbons whenever the integrity of the cement sheath is compromised (e.g. cracks and micro annulus). This material significantly reduces the risk of loss of hydraulic isolation, in already correctly cemented annuli, during production and after abandonment.

This new technology was applied to several gas storage wells in the south of France where the challenge is to ensure these wells can tolerate frequent cycling-injection followed by production while keeping a durable zonal isolation for the life of the well. The process that was followed includes laboratory characterization of self-healing properties in gas and field implementation. This study illustrates that designing a cement composition with self-healing properties to hydrocarbons -and more specifically to gas- requires expertise, know-how and the development of adequate experimental set-ups to assess selfhealing properties. Operational practices are reviewed, which confirms that standard field mixing and pumping processes are adequate for properly placing such cements.

None of the wells cemented during the trial phase with this self-healing cement have sustained annular casing pressure. This success, which supports other recent cases, confirms the validity and benefits of such technology in reducing the environmental footprint of oil and gas producing operations.