Assessment of Geothermal and Hydrocarbon Wells Using Supercritical Fluids for Heat Production

Subsurface geothermal resources are estimated to hold several orders of magnitude more energy than hydrocarbon resources. It is renewable, abundant, and has a small carbon footprint, however, its commercial-scale development faces several critical problems from reservoir to the final delivery point. To resolve these issues, it is essential to understand and analyze the transport and thermodynamics aspects in the geothermal well, which is the main objective of this work. Here, we extend the previously proposed mathematical model for closed-loop wells in enhanced geothermal systems by including (i) time- and space-dependent fluid/flow properties and temperature, (ii) heat-inflow from formation undergoing transient cooling, and (iii) local-property dependent heat transfer coefficients for the two-phase flow. A detailed sensitivity studies were performed to show the effects of several transport and geometric parameters (such as flow rate, well length, inner tubing and annulus diameters, geothermal temperature, overall heat transfer coefficients) on the thermal output. The result of this work contains two folds. In the first part, we show that the fluid properties and transfer coefficients are local-property dependent and must be included in the model. The second part was focused on sensitivity of thermal output of the well, where we observe significant difference in the power generation when local-property dependent fluid properties and transfer coefficients were included. Depending on the assumed boundary conditions and other simplifying assumptions, numerical simulations of coupled heat transport and fluid flow in well and reservoir may help predict more accurately the thermal output and the long-term economics, only when essential physics are included in the models. The novelty of this work lies in non-isothermal fluid flow modeling of coupled well and reservoir with local property-dependent transfer coefficients and fluid (PVT) properties for enhanced geothermal systems. The work is crucial for accurately evaluating the thermal output and economics of geothermal or hydrocarbon wells for power generation, especially with supercritical fluids.