Understanding of the effective fracture path bounded by a producer and an injector in complex fracture networks plays a key role in the successful geothermal heat extraction from enhanced geothermal systems (EGS). Therefore, there is a need to investigate the impact of well placement in EGS. In this paper an efficient thermal model is developed to simulate fluid and heat flow in fractured reservoirs with complex fracture networks, and the performance of horizontal wells in tapping heat energy from fractures is investigated. A general Green's function solution for fluid and heat flow in rock matrix is used, as such the need to discretize the matrix domain is eliminated. The model is first used to investigate the effect of backbone fractures, dead-end fractures, and isolated fractures on the heat extraction rate. Then, we show how the well placement in fractured reservoirs contributes to the efficiency of horizontal wells in extracting geothermal energy. The results show that the rate of geothermal energy extraction depends on the number of backbone fractures connecting the injector and producer (and this depends on the well spacing). It is suggested that more attention should be paid to well placement to maximize fracture connectivity to create more backbone fractures that allow the circulation of working fluids. The findings we present provide guidance on well placement in fractured reservoirs to maximize the efficiency of geothermal heat extraction.


Geothermal energy is considered to be a promising energy resource and a potential alternative to coal, oil, and natural gas because of its large reserve base, small carbon footprint and base load capacity. Enhanced geothermal systems (EGS) have been proposed as a method to extract heat from the subsurface by creating effective fracture networks, through which the working fluid can be circulated and heated (MIT et al., 2006; Breede et al., 2013). The occurrence of complex fracture networks have been indicated by field/microseismic data (Asanuma et al., 2007; Mukuhira et al., 2013). One of the key elements in the extraction of geothermal energy in EGS flow efficient fractures that can provide connected pathways between the injector and producer for heat extraction and fluid flow (Rinaldi et al., 2015; Rutqvist et al., 2015; Gan and Elsworth, 2016).

This content is only available via PDF.
You can access this article if you purchase or spend a download.