Heat extraction of novel underground well pattern systems for geothermal energy exploitation

•Two novel geothermal underground well pattern systems were proposed.•Heat extraction of novel geothermal well pattern systems was simulated.•Comparison between fractured reservoir and well pattern systems was conducted.•Horizontal wells had comparable production temperature with fractured reservoir.•High production pressure of well pattern systems was an advantage.

The current Enhanced Geothermal Systems (EGS) with a fractured reservoir undergoes several practical issues, such as scaling in the wellbore, the mass flow loss into the reservoir, and the challenge in designing the placement of production wells. In this paper, novel underground well pattern systems were proposed for geothermal energy exploitation. A numerical model of two kinds well pattern systems (multi-horizontal-wells system and annular-wells system) were setup taking into account the heat exchange with the surrounding formation. The numerical model was validated by the logging data from Ordos CO2 geological storage demonstration project, China. A comparison between the well pattern system and a fractured reservoir was conducted based on European EGS site at Groβ Schonebekc, Germany. Results showed that when the horizontal well length of well pattern system was about 10 times to the fractured reservoir, the production wellhead temperature and pressure of eight horizontal wells system with CO2 were respectively 38.9 °C higher and 10.9 MPa higher than that of the fractured reservoir system with CO2 after 20 years at a flow rate of 20 kg/s, an injection temperature of 20 °C and an injection pressure of 10 MPa, showing a significant application potential of the well pattern system.