Application of Strain Transfer Model for Fracture Conductivity Modeling and Monitoring of Enhanced Geothermal Systems

Abstract

Monitoring geothermal reservoirs using fiber optics is crucial for optimizing fluid circulation and understanding fracture conductivity within the subsurface. The efficiency of optical fiber sensors in detecting strain distribution heavily depends on the quality of bonding between the formation and the fiber. Intermediate layers between the geothermal formation and the fiber core can alter strain measurements. This study aims to enhance the accuracy of strain-based measurements in enhanced geothermal systems (EGS) by applying a strain transfer model. In this research, we modify the strain transfer model developed by Bassil et al. (2020) to consider variations in the elastic properties of geothermal formations and interfacial slip within multilayer systems. We integrate Bassil’s model with a mechanical model that considers hydraulic fracture conductivity and fracture width hysteresis during fluid circulation and thermal cycling. This integrated model improves monitoring in multilayer well completions by effectively transferring strain from geothermal fractures to fiber optic sensors. Our model demonstrates that fracture width hysteresis, fracture conductivity, the strain-lag parameter, and rock mechanical properties significantly influence the strain distribution induced by geothermal fractures. The model interprets strain variations caused by changes in hydraulic conductivity, driven by pressure and temperature fluctuations during fluid circulation. The strain-lag parameter illustrates the delayed response between the induced strain and actual fracture deformation, particularly in regions with variable fracture conductivity. These insights are crucial for identifying high-conductivity fractures that control fluid movement between wells, thereby enhancing the thermal recovery of the enhanced geothermal system. This work introduces a new application of the strain transfer model to improve fiber optic-based strain measurements in EGS, contributing to the optimization of fluid circulation and better reservoir characterization. By incorporating fiber optic strain measurements, we gain a detailed understanding of fracture conductivity, which is essential for maximizing energy production in geothermal reservoirs.