Reverse-Circulation Method and Durable Cements Provide Effective Well Construction: A Proven Technology

Construction of geothermal wells that are effectively cemented and durable poses a significant operational challenge. Typically, lost circulation while drilling and cementing can make it seemingly impossible to place a complete column of cement behind casing strings. Incomplete cementation can lead to well failure caused by cyclic temperature loading on the casing that occurs throughout the life of a well. Because cement systems are typically heavier than mud systems, operators in the past ruled out the possibility of successfully circulating cement from the bottom of the well all the way back to the surface. However, during the last several years, the process of reverse-circulation cementing (RCC) has proven effective, even in some of the most difficult circumstances encountered in geothermal fields. The type of cement system used is critical to the long-term durability of a geothermal well. Conventional cement systems are high in strength but are often brittle. When cyclic temperature-stress loading is applied to the brittle cement systems, they typically fail. More ductile cement systems have been introduced and applied in geothermalwell applications. These systems are designed to be more ductile and can help the cement flex, rather than fail, when a well experiences temperature-induced stress loading on the casing and cement. A broad overview of the successful application of RCC operations in geothermal applications is provided as well as a discussion of chemically and mechanically enhanced cement systems.