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Numerical simulation of electricity generation potential from fractured granite reservoir through a single horizontal well at Yangbajing geothermal field


Hot Dry Rock geothermal energy is heat energy stored in subsurface hot and low permeable crystalline rocks, which normally locates at depth within 3-10 km. However, the purely waterless hot dry rock system, the hot wet rock system and the hydrothermal system constitute a spectrum of geothermal resource type.

The Yangbajing geothermal field located 94 km northwest of Lhasa, the capital of the Tibet Autonomous Region, China is the first high-temperature hydrothermal convective geothermal field in China. Generalized definition of hot dry rock system mainly emphasizes the reservoir is comprised of hot fractured rocks, and whether there is pre-existing water is not the key point, so the naturally hot fractured granite reservoir at Yangbajing geothermal field might be taken the consideration into the hot dry rock resource type. Development of deep high-temperature heat reservoir at Yangbajing geothermal field has very important significance for capacity expanding and sustaining of the ground power plant. The geological exploration found that there is a fractured granite heat reservoir with an average temperature of 248ºC at depth of 950-1350 m at well ZK4001 in the north of the geothermal field. A simplified conceptual model of the 950-1350 m reservoir is established based on all the existing geological data, and the electricity generation potential from this fractured granite reservoir by geothermal water mining through a single horizontal well is numerically simulated by the scientists from Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences.

The results indicate that the single horizontal well system attains an electric power of 3.23-3.48 MW and an energy efficiency of about 50.00-17.16 during 20 years under reference conditions. The main parameters that affect the heat extraction and electricity generation are reservoir porosity, permeability and water production rate. Higher porosity or higher permeability or higher water production rate will be favorable for improving the electricity generation performance, under the precondition of not arousing vaporization and precipitation in the liquid water saturated reservoir.

These results are published on the high JCR ranking Journal Energy 65(2014):472-487.