A Comparative Study of the Impact of the CO2 Properties on the Thermal Output of a Geothermal Well

Abstract

The problem of growing carbon footprint calls for the exploitation of cleaner and sustainable energy resources. Geothermal energy is clean, renewable, and in abundant supply underneath the surface of the earth, which makes it one of the most optimum solutions to this problem. With the depletion of hydrocarbon resources, geothermal energy also helps to close the gap between demand and supply of cleaner energy resources reliably, although several problems need to be solved before producing geothermal energy globally. In this study, an effort is made to understand and improve the reservoir heat extraction through a geothermal well. There are approximately 3 million abandoned wells within the U.S. and this number will only increase in the future. Producing electricity from these abandoned hydrocarbon wells, as the source of geothermal energy, have intrinsic importance in the context of extending the life of the well in the context of energy production and as well as generation of future options for new wells. Whether the costs are sunken or not (for the existing wells), incremental costs for the new potential wells can be minimum to redesign them to fit for future geothermal energy production. Not only the design/retrofitting the wells, but also the selection of right power fluid is crucial to effectively produce the geothermal energy. Using CO2 as the power fluid to generate electricity from low temperature abandoned hydrocarbon wells while sequestering it will help in reducing the well costs to a minimum as well as optimizing the energy production to lower temperature thresholds. In this paper, a previously developed coupled well-reservoir model (Livescu and Dindoruk, 2022a, for fixed reservoir delivery as successions of steady state) is extended to study the effects of the fluid properties on the thermal output. Specifically, the previous model considered fluids with constant properties. Several correlations and look-up tables are used in this study for pressure- and temperature-dependent fluid properties (i.e., density and viscosity) to explicitly quantify their effect on the thermal balance of the geothermal system. These results are important for understanding the effects of the fluid PVT properties on the physics and economics of the entire geothermal project. This study is important for the design of closed-loop systems and can be extended to enhanced geothermal systems. For a given reservoir intake conditions, it can also be used to perform economic evaluation for abandoned oil and gas wells to assess their feasibility for geothermal energy production while reducing the overall CO2 footprint. In particular, the novelty and importance lie in Impact of choice of fluid/fluid PVT properties on the physics and economics of the entire geothermal project. Parametric study of using CO2 as the power fluid to generate electricity from relatively lower temperature abandoned hydrocarbon wells and variants in terms of P&T ranges.

A Possible Explicit Equation Fitting Method for the Gaseous Heat Capacity Near the Critical Point Based on Density and Temperature

“…In environmental, cost, and safety terms, CO 2 is regarded as an ideal natural heat transfer medium [21][22][23][24][25][26][27][28]. The SC-CO 2 -based Brayton cycle has been seen as a good alternative to conventional power cycles because of high cycle efficiency, compact turbo machinery, and compact heat exchangers [29][30][31][32][33]. The big change in SC-CO 2 heat capacity near the critical point makes it efficient to store and release energy.…”