Using TOUGH2 numerical simulation to analyse the geothermal formation in Guide basin, China
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Abstract: The Guide sedimentary basin is located in the northeastern part of Qinghai-Xizang Plateau,which is rich in geothermal resources. However,exploitation of the geothermal resources has so far been limited,because of limited understanding of the resources quantity and storage gained from scientific researches. In this study,using a typical cross section across the basin and taking into account its geothermal and geological conditions,a new water-heat coupled model was built and associated modelling was done by the software TOUGH2. During modelling process,the accuracy and applicability of the model was confirmed through the calibration of relevant parameters for modelling the heat and water transport and the formation of geothermal reservoir across the basin,with particular focus on the Neogene geothermal field. Results show that the groundwater that flows from the basin margins to the center is heated by the Neogene and Paleogene sedimentary rocks with high geothermal gradients. Since the east-west extending fault F1 is conductive,it acts as preferential flow paths which on one hand provide additional and rapid flows to the thermal reservoir; and on the other hand,cool down the thermal water to a certain extent due to the infiltration of shallower water sources in the vicinity of the fault. Furthermore,the estimated geothermal resources quantity is close to that of previous studies. In comparison with the Paleogene rock formations,the Neogene geothermal reservoir shows a better nature in terms of water content,aquifer permeability and resources exploitability,although the resource quantity of the Paleogene reservoir is considerable.
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Key words:
- Guide basin /
- TOUGH2 /
- Two-dimensional modelling /
- Numerical simulation /
- Geothermal resource evaluation
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Table 1. Geothermal reservoir of Neogene in geothermal field
Borehole No. Hole depth (m) Elevation (m) Lithology of heat reservoir Hydraulic head (m) Draw-down (m) Flow (m3/d) Water tempera-ture (℃) Salinity (g/L) ZK2 266.88 2 222.96 Medium sand, coarse sand and gravel +23.0 22.99 603.245 18.5 0.423 ZK4 272.50 2 224.98 Medium sand, coarse sand and gravel +20.33 18.13 554.342 21.5 0.568 7 ZK13 293.38 2 212.93 Medium sand, coarse sand and sandy gravel +24.75 18.90 1 074.211 25.5 0.413 3 ZK3 385.63 2 231.15 Medium sand, coarse sand and gravel +8.52 7.71 27.862 34.6 0.646 RK2 404.41 2 212.12 Medium sand and coarse sand +20.8 19.39 1 219.795 26.5 0.495 6 ZK15 470.41 2 226.94 Medium sand, coarse sand and sandy gravel +9.13 8.15 145.843 22.5 0.464 2 RK1 603.95 2 207.48 Moderate coarse sandstone +32.85 15.53 1 221.35 28.0 0.528 2 R2 1 709.5 2 206.00 Medium sandstone and medium fine sandstone +11.07 28.1 1 288.22 36.5 0.527 R3 2 701.2 2 213.00 Medium sandstone and medium fine sand +12.4 43.08 968.46 41.0 0.638 Table 2. Main parameter table
Material name No. of samples Density (kg/m3) Porosity Permeability Thermal conductivity (W/(m·c)) Specific heat capacity(J·kg·C) (X) (m2) (Y) (m2) (Z)(m2) Aquifuge (GSC) 2 2 490.0 0.18 1.0E-16 1.0E-16 1.0E-16 1.85 1 112.45 Neogene aquifer (XHS) 5 2 380.0 0.131 2.26E-12 2.256E-12 2.256E-12 1.72 920.17 Paleogene aquifer (GHS) 3 2 463.0 0.127 7.0E-15 7.0E-15 7.0E-15 1.76 924.35 Neogene fault (XDL) 2 2 380.0 0.131 5.0E-12 1.0E-16 1.0E-16 1.72 920.17 Paleogene fault (GDL) 1 2 463.0 0.127 14.0E-15 14.0E-15 14.0E-15 1.76 924.35 Thermal insulation boundary (GRBJ) 2 490 0.108 1.0E-16 1.0E-16 1.0E-16 0 1 112.45 -
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