Self-Healing Cement - Novel Technology to Achieve Leak-Free Wells

Abstract

Abstract There is a very large number of wells worldwide that leak or have sustained casing pressure (SCP). In Central Europe and the Middle East there are hundreds of wells with reports of trapped pressure that cannot be bled off. In the US and Canada there are thousands of wells leaking to surface, which may or may not be discharged to the atmosphere. Furthermore, 25% of all wells in the Gulf of Mexico have measurable sustained casing pressure. Additionally, remedial work fixing issues relating to cement failure has been estimated to be more than $50M a year in the US alone. Throughout the lifecycle of a well, planned cycle or operational changes can contribute to unknown damage to the cement sheath integrity that is hard to identify or locate, including the generation of a microannulus. Within flow paths, hydrocarbons can either migrate to surface, or become trapped below the wellhead leading to pressure build-up. Typical events occur during cementing, while perforating or stimulating, throughout the subsequent production, and even after abandonment. These can easily create this loss of cement integrity. This paper describes a novel isolation system that is activated only when a cement integrity problem occurs. The system will automatically and rapidly form a complete hydraulic barrier by swelling in the presence of hydrocarbon flow. Once activated, it will seal the damaged zone, and will even be able to be activated again, should further damage occur again during production or abandonment. The system has properties equivalent to conventional cement systems, and requires no modifications to standard surface equipment. High pressure static and dynamic laboratory tests highlight the ability of the system to rapidly shut off gas flows within 30 minutes. Field tests have also highlighted the robustness of the system, with a number of wells currently using the system remaining leak-free. Introduction The number of wells worldwide that leak or have sustained casing pressure (SCP) is an astonishingly high percentage, and as the demand for natural gas is increasing, the situation is likely only to get worse. In the United States, for example, demand will continue to grow during the next two decades, and has been estimated to reach a level as high as 35 quadrillion Btu (quads) by the year 2020.1 Correspondingly, a high number of new wells will need to be constructed to cater for this demand. If there is no change in current well construction techniques and materials, the incidence of leaks or of SCP is likely to track the well construction rate at a similar pace. Techniques for locating and exploiting natural gas have made huge advances since the early days of 1821 when the first natural gas well in the United States was drilled. However, m any of today's wells are still at risk, despite modern advances in well construction processes and materials. Failure to isolate sources of hydrocarbon either early in the well construction process or long after production begins has resulted in abnormally pressured casing strings and leaks of gas into zones that would otherwise not be gas-bearing. Abnormal pressure at the surface may often be easy to detect, although the source or root cause may be difficult to determine. Even when attempting "industry best practices" some annular pressure problems still occur. The quality of field practices may exacerbate tubing and casing leaks. The interdependencies of various well-construction processes is critical to building successful gas and oil wells for the future.2 This paper describes a new novel concept for zonal isolation based on a new material called self-healing cement (SHC). This concept does not preclude good cementing practices, but will enhance the chance of success where perceived long term pressure risk is anticipated. The objective of SHC is to provide long-term zonal isolation with a material that has self-repairing properties within the set cement. For example, this material enables automatic repair when a microannulus, internal cement crack or other flow path is created, and thus prevents flow of formation fluids through potential leak paths along the annulus. The concept focuses on long-term durability of the cement sheath material in oil and gas wells, and thus cement sheath repair without the need for well intervention.