Silica-Lime Based Hydrothermal Cements for High-Temperature Geothermal Applications

Abstract

To provide a more reliable composition and help eliminate strength retrogression in Portland cements, silica-lime cements have been developed as a solution for high-temperature geothermal cementing applications. Portland cements have been used successfully in geothermal cementing; however, because of variations in their chemical composition, partly due to their complex manufacturing process, these types of cements might not be acceptable when cementing wells with bottomhole circulating temperatures (BHCT) exceeding 230°F. At these temperatures, Portland cements can demonstrate inadequate performance. In contrast, the chemical composition of silica-lime cement can demonstrate far less variability. The silica-lime cement compositions consist of a mixture of ground quartz and hydrated lime. At temperatures greater than 190°F, lime will react with quartz and water to form calcium-silicate hydrate. The temperature at which the reaction takes place will dictate the ratio of calcium-to-silica and water-to-calcium silicate. These compositions have been laboratory tested for thickening time, compressive strength, rheology, and compatibility with geothermal drilling muds. This paper presents laboratory test results as well as a discussion on the advantages of the cement compositions. Silicalime based cements are simple, but flexible systems that can offer more reliability for high-temperature cementing applications.