Rheological and Mechanical Properties of Cement Grouts for Geothermal Well Cementation with Seashell Powder as Full Metakaolin Replacement

Abstract

ABSTRACT The different conditions associated with geothermal wells call for cement grouts that are lightweight, flexible and same time, possess good mechanical properties that can improve well integrity. This paper presents an experimental study of formulating lightweight and resilient cement grouts by a full replacement of metakaolin with crushed seashell wastes in a classical slurry formulation. Seashell powders made from Crassostrea gigas (Oyster), Pinctada maxima, Pecten maximus (scallop) and Crepidula fornicata were used to formulate the low-density slurries of approximately 1.2 specific gravities. Without using any chemical additives, the rheological behavior of the slurries, thermal properties and the mechanical properties of the set cements containing seashell powders were examined in comparison with classical samples containing metakaolin. The results showed an improved rheological behaviour in the context of geothermal well applications. The mechanical property investigations also revealed an improvement in elastic and flexural properties which may improve the global well integrity. INTRODUCTION The net-zero decarbonisation of the global energy sector will require an increase in the exploitation of renewable energy resources like geothermal energy. Geothermal energy is estimated to be capable of producing up to 8.3% of the world's electricity (WEC, 2019). Due to the high cost involved in the building and repair of geothermal wells, it is important to design them capable of producing energy for up to about 30 years. Cements used for zonal isolation in geothermal wells face conditions of high temperature and pressure (HTHP) that may affect the well integrity. A greater number of cement failures are reported to have been due to tensile loading rather than compressive (Lullo and Phil, 2000). This makes it important to optimize flexibility of the cement sheath during slurry design. Low density cements with lower Young's modulus are more flexible and are capable of providing higher expansions to accommodate the cyclic casing expansions due to temperature variations (Sugden et al., 2012). Another importance of lowering slurry density is in the avoidance of loss circulation which could occur if the hydrostatic pressure of the slurry exceeds the fracture strength of the surrounding formation (Sugama, 2007). Some methods of achieving low density slurries include foamed cement technologies (Harms and Febus, 1985; Sugama, 2007) and hollow microspheres (Abdullah et al., 2013).