A novel cyclical wellbore-fluid circulation strategy for extracting geothermal energy

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Both analytical and numerical modeling methods have helped explore power generation by producing steam with the binary organic Rankine cycle or ORC. A steady-state fluid circulation rate becomes the norm in a closed-loop system in most studies, assuming a stable geothermal gradient. In this study, we explored the suitability of those assumptions, given that the geothermal gradient is a time-variant entity at a well's proximity. Furthermore, the near-wellbore formation cooling necessitates a variable-circulation rate for the cold surface fluid to ensure a stable, wellhead-fluid temperature.This article presents a new transient analytical modeling approach for geothermal energy extraction by invoking the cyclical fluid circulation rate to ensure a stable surface fluid temperature. This analytical model entails the reverse circulation of water down the annulus and up the tubing to the surface. Specifically, we introduce a cycle (a stepwise increasing circulation rate sequence, followed by the stepwise decreasing rate sequence) to retain a stable, wellhead-fluid temperature. Of course, this cycle gets repeated to manage transient heat transfer from cold fluid circulation and the wellbore formation.Reproduction of the undisturbed formation temperature from the temperature line-source solution at each step of the cycle provided the necessary proof of the proposed approach. Model validation entailed comparing the suggested analytical model results to demonstrate that multiple transient-rate steps yielded the same initial temperature, thereby reaffirming the stepwise increasing and decreasing rate sequence strategy. We also explored the model's application in diverse settings in a probabilistic frame. As expected, the geothermal gradient, vertical-well depth, and insulation strength became the most influential on the dependent variable, wellhead fluid temperature, among the various independent variables studied.