--> Testing And Development Of Cements For High-Temperature Geothermal Wells

AAPG European Region, Geothermal Cross Over Technology Workshop, Part II

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Testing And Development Of Cements For High-Temperature Geothermal Wells

Abstract

To increase the efficiency and competitiveness of geothermal energy production recent wells target super-hot reservoirs containing supercritical fluids, such as the IDDP-1 and IDDP-2 well (Iceland Deep Drilling Project ). Envisaged reservoir temperatures and pressure reach up to above 400°C and 300 bars. Although we can build on the lessons learned from HPHT oil and gas wells (high-pressure/high-temperature), the temperatures and pressures encountered in the super-hot geothermal wells exceed the operational window experienced by the Oil&Gas Industry. Hence, there is a strong need for the development of tailored high-temperature cements to ensure plugging loss zones during drilling, anchoring and corrosion protection of casing strings, zonal isolation and well integrity at these elevated temperatures. Mineralogical changes of Portland cement that occur at these conditions and their impact on its mechanical properties have not yet been investigated sufficiently. First results of this study indicate that the material becomes more brittle . However, under these harsh conditions enhanced cement flexibility is strongly required to account for extreme mechanical loads caused by casing deformation during temperature cycles. Additionally, the residual water, required for placement, but not for hydration, in the hydrated cement or in water pockets (unstable cement slurry or drilling fluid left in place) needs to be reduced as this can result in (over)pressures that eventually trigger casing collapse during the warm-up period(s). This study aims at improving the mechanical properties of Portland cement while ensuring pumpability and proper curing behavior. In this study investigations have been performed on the current performance of Portland cements by the means of: - Cross-linking geothermal knowledge with lessons-learned from current HPHT cement applications in O&G, e.g. for SAGD (steam-assisted gravity drainage) wells, and their implementation for high-temperature geothermal applications - Investigating mineralogical and mechanical properties of cement samples obtained from the IDDP-1 well, where the top section was excavated to obtain casing and cement samples (Figure 1) which experienced temperatures up to 450°C for several months , and studying the characteristics of different cement blends under these conditions - Experimental testing and analyzing cement performance at different exposure times and temperatures Results from the above are being used to examine the effect of different crystallization effects, temperatures, pressures and exposure times on mechanical properties of the cement. This will feed into the design of cements that optimized for curing can (better) withstand the mechanical forces in a high-temperature geothermal well and will enable a reliable, sustainable geothermal energy production. This research was performed within the EC Horizon 2020 project GeoWell4 “Innovative materials and designs for long-life high- temperature geothermal wells“ under the grant agreement No. 654497.