Abstract

Geothermal energy is one of the most potential renewable energy resources. How to efficiently extract and utilize geothermal energy has been a worldwide hot topic. Co-axial closed-loop geothermal system is a novel method using a continuously closed wellbore without water exchange with. It is more suitable for reservoirs with medium or low temperature and permeability because many problems could be avoided such as lack of in situ groundwater or low infectivity of the reservoir. Many companies and research institutes have applied closed-loop geothermal system in building heating engineering and some fine results have been gained. However, in practical engineering construction, the area of a closed-loop geothermal system heating system is a very important parameter. It directly determines the cost accounting and initial design of the project. Accurate and reliable estimation of heating capacity becomes very important. In this study, a wellbore–reservoir coupling model is established, which is calibrated using measured data from a short-term field trial operation. We have carried out mixed convective–conductive fluid-flow modeling using a wellbore flow model for TOUGH2 called T2Well to investigate the heat extraction performance of closed-loop geothermal system. The system evolution and the effect of flow rate and injection temperature on heat production performance are discussed. The result shows that the intermittent production cycles are more beneficial for heat extraction and system maintenance, and the temperature recovery between two heating seasons is enough to maintain system heating. And we can calculate that a geothermal well can ensure heating of buildings of 10,000–20,000 m2 and the heating area of intermittent operation is 4000 m2 more than continuous operation. Besides, the sensitivity analysis of parameters is also carried out.

Highlights

  • Nowadays, energy crisis and environmental pollution are getting serious around the world

  • The results show that a discontinuous running of the co-axial closed-loop geothermal system (CLGS) can promise a higher performance than continuous running

  • The results indicate that in intermittent operation conditions, production temperature and heat extraction rate are higher than that in continuous operation conditions

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Summary

Introduction

Energy crisis and environmental pollution are getting serious around the world. It is important to develop new energy with large reserve and environmental friendliness. Geothermal energy has characteristics of clean and sustainable (Barbier, 2002; PastorMartinez et al, 2018; Sun et al, 2018c). It is widely distributed all over the world and universally acknowledged for its excellent stability and reliability of energy supply (Aali et al, 2017; Boyaghchi and Safari, 2017; Erdeweghe et al, 2017). In 2050, it will account for about 3.5% of the world’s total energy consumption (Ali and Kumar, 2017; Ghaebi et al, 2018; Li et al, 2017)

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