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Numerical simulation of heat production potential from hot dry rock by water circulating at Desert Peak geothermal field
Enhanced geothermal system (EGS) is an engineered system which adopts artificial circulating water through underground fractured hot dry rock (HDR) to economically extract the geothermal energy; generally, the mined heat is used for electricity generation or district heating. Recently the heat production potentials from hot dry rock by water circulating were numerically investigated based on the geological data of well DP23-1 under the EGS project at Desert Peak geothermal field using 20 years production by the scientists from Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences.
Firstly through two horizontal wells the heat production potential from deep HDR by water circulating was numerically investigated. The results indicate that the desirable electricity production power and energy efficiency can be obtained under suitable reservoir permeability, water production rate and injection temperature; meanwhile water flow impedance remains at a relative lower level. The sensitivity analysis indicates that the electricity production power mainly depends on the water production rate and the injection temperature; the water flow impedance mainly depends on the reservoir permeability, water production rate and injection temperature; the energy efficiency mainly depends on the reservoir permeability and the water production rate. The heat production performance will be improved when the reservoir permeability, the water production rate and the injection temperature are under reasonable conditions. However, this study is based on that the fractured reservoir is equivalent to a homogeneous porous medium and there is no water loss in the reservoir, so the practical energy output and efficiency of water circulating through two horizontal wells at Desert Peak geothermal field needs further study in the future.
Secondly through a novel single vertical fracture the heat production potential from deep HDR by water circulating was numerically investigated. A technically feasible fracture aperture of 2 mm is assumed. The injected water is assumed to sweep the fracture along the diagonal and the effect of high pressure and temperature on water density is taken into considerations. The results indicate that desirable heat production efficiency can be attained under suitable fracture permeability and water production rate, however the heat and electricity production power remains a relative low situation and the water flow impedance retains a relative high level during production process. The sensitivity analysis indicates that the electricity production power mainly depends on rock thermal conductivity, water production rate and injection temperature; water flow impedance mainly depends on the fracture permeability, the rock thermal conductivity, the water production rate and the injection temperature; and energy efficiency mainly depends on the fracture permeability, the water production rate and the rock thermal conductivity. When the fracture permeability and water production rate are under reasonable conditions, the energy output and production efficiency will be optimized. However, rock contraction due to temperature reduction and water-rock interaction are not taken into considerations in this study, so the practical heat output and efficiency through one single vertical fracture needs further study in the future.
These results are respectively published on the high JCR ranking Journal Energy 56(2013):92-107 and Energy 63(2013):268-282.