A Novel Experimental Investigation of Cement Mechanical Properties with Application to Geothermal Wells

Abstract

Geothermal well integrity has proven to be of high importance, especially because the geothermal life span is expected to be longer than that of conventional oil and gas wells. Recent studies have demonstrated that cement-casing interfacial bonding is a classical well failure in such wells, but field measurements do not correlate with the simulations. We believe that this discrepancy is due to limitations of the simulation itself, which in most cases assumes a free movement of the casing after the interfacial bonding has been exceeded. Since the casing is cemented using a complex hardware package such as centralizer and other cementing components, the free movement of the casing is only possible when no-cement exists behind the casing. This paper proposes a novel experimental method to understand cement strength properties other than the standardized unconfined cement strength (UCS). The novel setup allows the measurement of interfacial bonding strength between cement and casing and the pure cement shear strength. The later becomes an important parameter as the interaction between casing couplings and cement will show. In the past, standard cement bending tests were designed to measure cement shear, but the value obtained from such tests is not relevant for the geothermal in situ casing-cement interaction, and thus the need for a new testing method arose. The new method is capable to mimic the interaction between the casing connection edges and the cement. We believe that the results presented within this paper will help engineers to validate their numerical simulations and to optimize the geothermal well design which will result in the increase of the well integrity for the life of the geothermal well.