Cementless Superhot Geothermal Wells

Abstract

This study evaluates a novel cementless well construction and completion methodology for superhot geothermal in terms of thermal stress management. The objective is to extend previous work on the annular isolation barrier by specifically analyzing buckling. The scope includes assessment of sinusoidal and helical buckling risks and the optimization of metal expandable packer (MEP) placement, selective pre-tensioning, and centralization to ensure long-term well integrity under extreme thermal cycling conditions. The approach utilizes numerical modeling to simulate a very near-supercritical geothermal reservoir with a bottomhole temperature (BHT) of 700°F (371°C), completed with multiple MEP components instead of traditional cement. The study simulates transient quenching and steady-state flowback operations. Wellbore flow involves multiphase correlations to assess frictional pressure losses and wellbore/surrounding formation heat transfer. However, special focus is placed on buckling mitigation, comparing different centralization, MEP placement frequencies, and pre-tensioning loads. N2 cap is used in the pipe-in-pipe sections to manage annular pressure build-up (APB). Case studies are shown with a fully integrated well design model, allowing the wellbore flowing temperature and pressure profiles to be applied as stress loads on the tubulars. Although superhot temperatures raise concerns of buckling in cementless, selective pre-tensioning and high-frequency centralization, and extended packer systems keep the strings within their von Mises equivalent (VME) design limits. It is shown that with a proper centralization program, doglegs due to buckling can be maintained below 2-2.5°/100 ft, while the effectiveness is still limited depending on the dogleg severity (DLS) due to survey, buckling clearance, and centralizer frequency. The proposed cementless methodology offers a better alternative for managing induced wellhead growth forces than the cemented design philosophy. Furthermore, compared to the cemented strings, the proposed design may allow controlling the corrosion inhibition with feedthrough lines. Overall, with this methodology, it is possible to strategically manage temperature profiles of the cementless strings adopted during initial conditions, which can outperform the historical cemented geothermal well design where the initial conditions would always adopt the cement hydration temperature. By establishing a buckling, centralization, MEP placement, and strategic pre-stressing standardization framework for the first time, this study expands on a novel cementless geothermal well design. The approach aims to establish a baseline for global well design standardization for cementless geothermal wells.