Development of New Formulation of Calcium Aluminate Cement System for Ultrahigh-Temperature Supercritical Geothermal Wells

Abstract

A national research project on the feasibility of supercritical geothermal power generation and preliminary design of supercritical geothermal exploration wells to be drilled is now in progress in Japan. One of the critical issues in drilling and completing supercritical geothermal wells is long-term integrity of well cement under ultrahigh-temperature conditions. Silica flour blend cement that consists of Portland cement and 30% to 40% BWOC silica flour has been widely used for conventional high-temperature geothermal wells. However, it is known that Portland cement should not be used if the cement will be exposed to temperatures exceeding 400 degrees C that is the upper limit of stable range of Portland cement. Therefore, calcium aluminate cement, which is a non-Portland cement system, is necessary to be considered for cementing supercritical geothermal wells. In this paper, study on development of a new calcium aluminate cement system is presented. Various compositions of aluminate cements and retarders were tested in laboratory to evaluate the rheological properties and thickening time of cement slurries, compressive strength and acid resistance of set cement. Based on the test results, optimum formulation of aluminate cement system for supercritical geothermal wells is discussed in consideration of the wellbore temperature conditions during cement placement.