Abstract
Geothermal energy is clean and independent to the weather and seasonal changes. In China, the huge demanding of clean energy requires the geothermal energy exploitation in the reservoir with depth larger than 1000 m. Before the exploitation, it is necessary to estimate the potential geothermal energy production from deep reservoirs by numerical modeling, which provides an efficient tool for testing alternative scenarios of exploitation. We here numerically assess the energy production in a liquid-dominated middle-temperature geothermal reservoir in the city of Tianjin, China, where the heat and fluid transport in the heterogeneous reservoir and deep wellbores are calculated. It is concluded that the optimal injection/production rate of the typical geothermal doublet well system is 450 m3/h, with the distance between geothermal doublet wells of 850 m. The outflow temperature and heat extraction rate can reach 112°C and 43.5 MW, respectively. Through decreasing injection/production rate lower than 450 m3/h and optimizing layout of the injection well and production well (avoiding the high permeability zone at the interwell sector), the risk of heat breakthrough can be reduced. If the low permeability zone in the reservoir is around injection well, it usually leads to abnormal high wellhead pressure, which may be solved by stimulation technique to realize stable operation. The methodology employed in this paper can be a reference for a double-well exploitation project with similar conditions.
Highlights
In China, coal burning contributes 70% of CO2 emissions, 80% of SO2 emissions, and 70% of soot emissions [1], which caused serious environmental pollution
In order to describe the spatial distribution of reservoir permeability and porosity more realistically, we introduced the variation function, a geostatistics concept, to determine and limit the spatial distribution of permeability and porosity by assigning variance and correlation length which strongly depends on the variation function type and the model scale [43]
It is concluded that the optimal injection/production rate for typical geothermal doublet well system studied here with a reservoir thickness of 700 m and a well distance of 850 m is 450 m3/h
Summary
In China, coal burning contributes 70% of CO2 emissions, 80% of SO2 emissions, and 70% of soot emissions [1], which caused serious environmental pollution. It is estimated that in northern China, there are 42.3 days on average every year suffering from smog from 1999 to 2013 [2] with mean PM2.5 concentration reaching 93 μg/m3 [3]. As one of the most important renewable and clean energy, geothermal energy is expected to occupy 3% of total energy utilization in China by 2030, which will be mainly used for heat supply in winter and electrical power generation as well [4]. Most of the geothermal resources in China are of middle and low temperature. To obtain the high-temperature geothermal resource, it is desirable to explore and exploit the geothermal energy in the reservoir with the depth more than 1000 m. In Tianjin, located in Northern China Plain, the target geothermal reservoir in the five years moves to Wumishan
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