Self-Healing Cement for Long-Term Safe Exploitation of Gas Wells: A New Technology Case Study

Abstract

Abstract With today's low energy prices and with the increasing drive towards sustainability, it is essential to develop more economically efficient and ecofriendly technologies in oil and gas field development. Such a technology is self-healing cement, which was successfully applied in a large project in northern Italy in the conversion of a gas field to a gas storage field. During the construction phase of gas production and storage wells, one of the critical goals is to achieve competent hydraulic isolation between the surface and the casing to reach the reservoir. There are several cases documented in the literature where poor isolation has resulted in gas flow to surface, thereby polluting water reserves, greenbelts, and populated areas. Improper isolation can also result in interzonal communication, production of unwanted fluids, gas migration, casing corrosion, and sustained casing pressure. These can have significant health, environmental, and economic impact. Additionally, the impending need for well intervention, along with high re-entry costs, will further weaken revenue margins. Breaking through conventional cementing solutions, a global oilfield service company had established an active cement technology to improve annular isolation in gas wells. This technology is capable of self-healing when exposed to hydrocarbons of any type, unlike other self-healing systems that are limited by the level of methane (CH4) in the gas reservoir. The new system allows universal coverage for any concentration of CH4. Because the concentration of CH4 in different gas reservoirs can vary significantly, the self-healing "protection" against different levels of CH4 is tailored to suit different reservoirs. This field-proven technology, in use for more than 10 years, stemmed from the original self-healing technology commercialized more than a decade ago. Subsequently, an opportunity arose to apply this technology in a large project in the north of Italy. The project would exploit a depleted gas field by conversion to a gas storage field with the drilling of 14 wells from two clusters above the reservoir. The product testing and implementation, job execution, and results evaluation brought several benefits with positive impact to the service company and the owner/operator of the field. A higher level of isolation significantly decreases the need for future well integrity and repair, which provides medium- to long-term benefit for the operator—an added value that is sometimes omitted in well construction design. Using a zonal isolation technology, such as the self-healing cement system described here, inherently places the service company and operator in a much more secure position for the future. Furthermore, in the current industry climate, saving 30 to 40 days of rig time and the cost of remedial operations and achieving important mitigation against health and environmental impact pose a significant economic advantage.