Abstract
A new analytical solution for the thermal-hydraulic coupling process is derived with a 1-D steady state conductive heat flow in the body of hot rock with perpendicular water flow in the single fracture and transient heat transfer from rock to water. The heat produced from the hot rock via water flow in the idealized single fracture is demonstrated by arithmetic equations. The applicability of the analytical solution is verified by numerical calculations and is limited to conditions with fast water flow rates or high water flux and long fluid pathways. The lifetime of an EGS reservoir in these reference conditions is 23.2 years and is confined by the produced water temperature of 150 °C for commercial utilization. The heat recovery factor is 12.4%. With a power plant capacity of 5 Mw installed, the total area for extracting recoverable heat within the projected lifetime of a fracture surface of 1.58 × 106 m2 was determined. The total mass flow rate of water injected into the large fracture was 57 kg/s. The discussion shows the ability of the model to estimate heat production and reservoir scale.
Highlights
The amount of geothermal energy is enormous
We propose a single fracture model based on further simplifying the concept of the independent-multiple-fracture reservoir to reveal thermal-hydraulic coupling in Enhanced Geothermal Systems (EGS) reservoirs and the resulting heat production
EGS reservoirs are usually developed in deep hot dry rocks
Summary
Using geothermal energy can contribute to reducing greenhouse gas emissions and fossil energy use. Exploiting this renewable resource, is currently limited to hydrothermal systems in which naturally present fracture networks permit fluid circulation, allowing geothermal heat to be produced by tapping these hot fluids. A body of hot rock is hydraulically fractured to become a geothermal reservoir to circulate and produce heat. The technique has been applied to extract geothermal energy from hot rocks by (1) creating permeability through hydraulic stimulation to activate existing rock fractures or creating new ones and (2) setting up and maintaining fluid circulation through these fracture networks by means of an injection system and production boreholes, allowing thermal energy to be transmitted to the land surface for human use. Sequential EGS field experiments were conducted worldwide, and ongoing work is taking place in the Hunter Valley, Coso, Desert Peak, and Cooper Basin projects
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