Stanford Geothermal WorkshopFebruary 9-11, 2026

The three most important factors controlling the performance of enhanced geothermal systems are, (i) the hydraulic conductivity of the fractures, (ii) the connectivity between the injection and production wells, and (iii) the fluid conformance in the injection well. Data obtained at the Forge EGS site and numerical simulations clearly show the importance of these three factors. Good connectivity between the injector and the producer through fractures is essential to EGS success. This inter-well connectivity was measured with both fiber optic data in the producing well and through tracers. DSS (strain) measurements made in the producing well while the frac stages were being pumped in the injection well clearly showed the location and timing of the frac hits in the producing well. Over 48 different frac hits were recorded. To ensure good inter-well connectivity, the producing well was perforated at the location of the major frac-hits. To further improve inter-well connectivity hydraulic fractures were initiated through these perforation clusters in the producing well. Subsequent fluid circulation tests showed excellent connectivity between the injector and producer. Fluid inflow distribution along the producer was monitored by both DTS fiber measurements and tracer data. Both data sets were consistent and showed good inter-well connectivity. Good fluid conformance is essential to avoid thief-fractures from causing early temperature breakthrough and a rapid decline in energy production rate over time. Large sections of the geothermal reservoir can remain undrained when this occurs. Fluid conformance in the producer was measured by DTS and by tracer tests. The results from the tracer test clearly show some preferred corridors of fractures indicating poor conformance in some parts of the wellbore. Ways to minimize this in the future are discussed. Simulations were run to show how this can be achieved in future EGS fracture designs. Good fracture conductivity can be achieved by pumping proppant during the fracture treatment. In the first 3 stages of the fracture treatment of the 16A well at the Forge site, no proppant was pumped. This resulted in very large injection pressures being needed to inject fluid from the injector to the producer. All stages in which proppant was used were able to inject fluid at much lower pressures. The use of proppant results in better conductivity and is essential for maintaining injectivity and minimizing the parasitic energy needed to circulate fluid between the wells. Simulations results clearly show the impact of poor fracture conductivity and conformance on the energy recovery rate. Measuring good connectivity, conductivity and conformance in enhanced geothermal systems is shown to be critical for ensuring high and stable energy production rates.

Topic: Enhanced Geothermal Systems