Subsurface Technology Pivoting from Oil and Gas to Geothermal Resources: A Sensitivity Study of Well Parameters
Authors: Livescu Silviu , Dindoruk Birol 
Published: February 2022

Summary
There is enough geothermal energy several miles underneath to supply more power globally than the entire oil and gas industry. Geothermal energy is renewable, abundant, and has a minimal carbon footprint. However, the current geothermal energy use is only 1% of the global energy production. To scale it up, several technical problems need to be solved, addressing how, where, and when to harness it safely, efficiently, and cost-effectively. In this paper, the synergies and differences between the hydrocarbon and geothermal wells are reviewed and an opportunity assessment and management framework are proposed to improve the outcomes of diverse geothermal hydrocarbon projects.
Producing geothermal energy from existing hydrocarbon wells, as electricity and/or low-temperature waste heat, can yield significant advantages over traditional geothermal wells, especially in terms of reduced capital expenditure. Geothermal and hydrocarbon well studies related to geothermal hydrocarbon field development are reviewed, presenting the similarities and differences between the geothermal and hydrocarbon wells, and the challenges for economical geothermal hydrocarbon field development. To unlock the potential of geothermal hydrocarbon field development, several areas of research are identified and explored.
There are many hydrocarbon wells drilled worldwide that are either abandoned or will be abandoned in the future. This inherently brings exit options repurposing these wells in terms of extracting residual value in an environmentally friendly way. There is a great potential to extract energy in the form of low-temperature waste heat and/or work with the right power fluids, including CO2. In this study, a numerical solution and several analytical solutions are presented for closed-loop wells (i.e., concentric pipes in wells). They can be extended to enhanced geothermal systems (EGSs) (i.e., injecting and producing casedhole wells with perforations along vertical, inclined, and horizontal sections) by allowing fluid inflow into the wells. The time- and space-dependent temperature solutions for all well configurations are obtained for time- and space-dependent fluid and flow properties. A sensitivity study is then performed, showing the effects of several parameters on the flowing fluid temperature for such parameters as the fluid flow rate, well length, inner tubing and annulus diameters, geothermal temperature, and overall heat transfer coefficients.
Existing hydrocarbon fields produce larger volume of waste water over their lives, increasing their operating costs owing to greater water management expenditure. Conceptually, those operating costs could be reduced by electricity and/or heat coproduction. The proposed modeling approach is useful for the design of EGSs and closed-loop systems. It can also be used as an operational tool to monitor the well and reservoir performance over the life of a deep geothermal resource. Last but not least, it can be used to assess the conditions for economically converting abandoned oil and gas wells for sustainable geothermal energy production.