Development of High-temperature Well Cement for Supercritical Geothermal Drilling with Consideration of Set Cement Strength

Abstract

Supercritical geothermal system has attracted attention in recent years as next generation of geothermal resource. These systems are located at the depth of 3-6 km with the formation temperature and pressure higher than 400℃ and 30-60 MPa respectively. Therefore, the heat resistance of the cement materials used for cementing can be considered as a problem during the drilling for the supercritical geothermal wells. The objective of this paper is to evaluate the properties of conventional high-temperature cement and cement under development to improve their thermal resistance through high-pressure and high-temperature (HPHT) curing tests using Autoclaves. Moreover, based on the results of these analyses, the applicability of cement materials to supercritical geothermal wells is discussed. The conventional cement for high-temperature (GWC) used in this study is Portland cement mixed with silica flour, while the cement under development is a modified version of alumina cement. In this experiment, All have been cured at the temperature of 250℃ and for 72 hours as a normal curing. In addition, we cured each sample from 300℃ to 450℃ by 50℃ for 24 hours. After the curing, we confirmed the changes in diameter and length of the samples were checked and measured the uniaxial compression strength and Young's modulus. Moreover, the water permeability of the cement was measured using the PoroPerm. As a result, the GWC showed sufficient performance. However, the cement under development had problems such as volume reduction in above 400℃ tests.