A Generalized Analytical Heat Transfer Model for Enhanced Geothermal Systems: Capturing Fracture Interactions and Correcting Classical Optimistic Predictions

TL;DR

This paper introduces a generalized analytical heat transfer model for enhanced geothermal systems that accurately captures fracture interactions, correcting overoptimistic classical predictions and enabling practical, reliable geothermal reservoir analysis.

Contribution

It extends classical models by explicitly modeling fracture interactions using Green's functions, maintaining simplicity and computational efficiency for practical use.

Findings

Model closely matches numerical simulations of temperature evolution.

Corrects classical overestimations of thermal performance.

Enables practical implementation in standard spreadsheets.

Abstract

Numerical analytical heat transfer models play a critical role in geothermal design and feasibility studies. Classical solutions, such as those proposed by Gringarten et al. 1975, rely on simplified assumptions and systematically overestimate thermal performance, which can lead to unrealistic engineering decisions. This study presents a generalized analytical model for enhanced geothermal systems that explicitly captures thermal interactions between fractures while preserving analytical tractability. The formulation is based on Green\'s functions and reproduces realistic thermal behavior under conditions representative of fractured geothermal reservoirs. The resulting solution is computationally efficient and sufficiently simple to be implemented directly in standard spreadsheets, without requiring Laplace space transformations or numerical inversion algorithms. The model is validated against numerical simulations performed using CMG STARS and Volsung software, showing close agreement in temperature evolution, including the effects of interacting fractures. Compared with classical analytical approaches, the proposed model corrects optimistic bias and provides more reliable predictions of production temperature and energy recovery. These results have direct implications for geothermal feasibility studies, well design, and power forecasting, effectively bridging the gap between legacy analytical models and numerical or commercial engineering tools. Building on the analytical framework originally introduced by Gringarten et al. 1975, the proposed formulation generalizes classical heat transfer solutions to account for fracture interaction while retaining analytical simplicity and practical applicability.