Temperature description and heat extraction optimization of enhanced geothermal system via failure volume ratio

Abstract

It is difficult to quantitatively measure the temperature characteristics to evaluate the heat extraction in Enhanced Geothermal Systems (EGS). This study aims to define a new evaluation index called failure volume ratio to describe the temperature distribution in rocks and optimize heat extraction. In the established three-dimensional thermal-hydrologic coupling model, the cumulative heat production and production temperature are interpreted and predicted by the proposed index. A set of orthogonal experiments is designed to quantitatively find the key factors affecting EGS. Results show that the failure volume ratio can provide a more rational and concise explanation for changes in the temperature and heat of production during EGS heat extraction. The ratio when the production temperature begins to decrease reflects how much heat has been extracted at the maximum production temperature. In a given model, we only need to calculate the failure volume ratio which reflects both cumulative heat production and production temperature changes, which is useful for a combined system of above-ground power generation and underground heat extraction. Based on the analysis of variance, the injection flow has the greatest impact on EGS. Its optimal value in this model is 80 kgs−1. This study provides a quantitative tool for reservoir evaluation and geothermal system optimization.