Enhanced geothermal system productivity analysis of a well-group in a limited area based on the flow field split method

• Published in: Environmental earth sciences Vol. 80; no. 21
• Main Authors: Sun, Yuxue, Zhang, Xiao, Zhang, Qingsong, Li, Xianghui, Li, Zhen, Yin, Zhanchao, Li, Zhuang, Zhou, Zheng, Li, Mengtian
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.11.2021; Springer Nature B.V
• Subjects: Biogeosciences; Capacity; Design optimization; Earth and Environmental Science; Earth Sciences; Enhanced geothermal systems; Environmental Science and Engineering; Fields; Finite element method; Flow equations; Geochemistry; Geology; Geothermal fields; Geothermal resources; Groundwater; Groundwater flow; Heat; Heat exchange; Heat transfer; Hydrology/Water Resources; Hydrothermal fields; Injection; Injection wells; Mathematical models; Numerical models; Original Article; Porous media; Predictions; Production capacity; Productivity; Seepage; Splitting; Steady state models; Terrestrial Pollution; Three dimensional models; EGS; Well-group; Seepage; Hydrothermal systems; Heat generation and transport; Geothermal extraction
• DOI: 10.1007/s12665-021-10030-z
• ISSN: 1866-6280

The prediction of the production capacity of the enhanced geothermal system (EGS) is crucial for the extraction of geothermal resources. To better optimize the EGS project, it is necessary to make a reasonable prediction of the heat-production capacity of the geothermal site. This work aims to provide an accurate and simpler calculation method based on geometric split-productivity superposition of multi-well EGS productivity prediction in large geothermal fields to guide the design and optimization of EGS in large geothermal fields. First, based on a complex potential function, a steady-state seepage model of well groups is established in a limited plane. After splitting the flow field according to the flow law in the plane, the productivity control area of a single injection well is obtained. The splitting method of the small well-group is obtained, which uses the bisector of the angle between the adjacent injection wells and the production well. Then, the three-dimensional finite-element numerical models of the EGS are established for the small well-group in the limited area and the single-pore double-well after splitting. By analyzing the heat production performance of the two methods, the correctness of the splitting method of the plane small well-group is verified. These models are based on the mathematical model of flow–heat coupling composed of the Dupuit formula, groundwater-flow equation, and porous-medium heat-transfer equation, combined with the split production-capacity-control area of the single injection well and the influence of the production well eccentricity. The comparison of the heat-production performances of the two methods shows that the maximum relative error rate of the two results does not exceed 9% and that the fluctuation trend of the corresponding double-well heat exchange EGS is consistent with the whole heat exchange EGS. These results prove that the splitting method has good applicability of predicting the EGS productivity of well groups in a limited area by calculating the superposition of the double-well EGS productivity after splitting. The total capacity of the well-group EGS in a limited area is equal to the sum of the capacity of each split double-well heat exchange EGS. Furthermore, this paper also provides proof of the rationality of the split method.