Effect of Cement Behaviour on Casing Integrity in Superhot Geothermal Wells: A Numerical Study

Abstract

ABSTRACT: This paper presents the results of numerical studies aiming to assess the effects of cement hydration on the casing integrity in superhot well conditions. Casing integrity challenges for high and super-high temperature geothermal wells were first discussed. A simplified well cement material model was implemented in the stand-alone code, Casinteg, to simulate cement behaviour in field conditions. Numerical simulations were performed, based on the IDDP-2 well scenarios, to investigate the effect of cement retarders, cement hydration heat and cement shrinkage on the casing stresses. The obtained results have shown that by engineering proper cement solutions, the risks of casing failure in geothermal wells can be minimized to sustainably harvesting green power from superhot geothermal reservoirs. 1. INTRODUCTION To answer the growing need for energy and at the same time fighting against the global climate change, development of renewable energy sources is indispensable. Geothermal energy is today recognized as one of the potential renewable sources, contributing to the "green shift" from fossil fuels toward more sustainable energy. Currently, most commercial geothermal power plants operate at the temperature range of 150° – 300° C. However, exploring the huge potential from/of? super-high temperature reservoirs (up to 400° – 500 °C) may be needed to increase the power production output, thereby lowering levelized cost of electricity (LCOE) of geothermal projects (Reinsch et al., 2017). For sustainable exploitation of geothermal energy, robust and cost-efficient casing systems are an absolute demand. However, the harsh operation conditions encountered in the high-temperature (HT) geothermal reservoirs are very challenging and are detrimental for the well integrity. Improper material selection and design principles may lead to serious failure events, and loss of the production well, as reported in many HT geothermal well projects (Ford et al., 2017). Recent examples are experiences from the Iceland Deep Drilling Project (IDDP). The two first IDDP wells are themselves pilot experiments and great learning sources for both researchers and industry. However, they could not be used for power production due to well integrity problems. Both wells experienced severe casing damage/failure (casing collapse and corrosion), which were the main technical obstacle to tap geothermal power from these ultra-high temperature production wells (Kruszewski and Wittig, 2018).