ResFrac lends itself particularly well to the optimization of hydraulically stimulated geothermal wells. ResFrac not only computes fracturing and reservoir flow simultaneously, but also calculates thermal stress changes and supercritical fluid properties. Fowler and McClure (2021) evaluate three geothermal designs: a closed-loop, a closed-loop with thermally conductive fractures, and an open-loop multi-lateral. The three designs produce between 1 and 36 MWth of energy (as shown in Figure 15 of the paper below).
However, the open-loop multi-lateral is the only design evaluated that produces economic heat for electricity production as the conversion from thermal to electrical energy results in significant losses.
Fowler and McClure (2021) discuss ways in which the open-loop multi-lateral design can by optimized, such as using a triplet well configuration instead of a doublet configuration (as shown in figure below). The triplet design takes advantage of the biwing nature of hydraulic fractures to extract extra heat from the reservoir.
Additional considerations like circulation conformance and well spacing are also important and discussed, serving as the motivation for McClure et al. (2022) to perform an economic optimization of a hydraulically fractured geothermal well. The optimization demonstrates a competition between rate acceleration (higher throughputs) and delay of thermal breakthrough. This is a delicate optimization, as higher flow rates accelerate heat extraction which in turn accelerates thermal relaxation of fractures (exacerbating conformance issues and thermal breakthrough).
Garrett Fowler, Mark McClure. 2021. A Comparison of Geothermal Closed-Loop Versus Fracture Well Doublet Systems. GRC Transactions Vol. 45.
McClure, Mark, Kang, Charles, and Garrett Fowler. Optimization and Design of Next-Generation Geothermal Systems Created by Multistage Hydraulic Fracturing. Paper presented at the SPE Hydraulic Fracturing Technology Conference and Exhibition, The Woodlands, Texas, USA, February 2022. doi: https://doi.org/10.2118/209186-MS