Figure 1
Schematic of the UCG process (linked vertical wells method), with water entering from the surrounding rocks [6].
Figure 2
Generated finite element mesh determining the model's geometry (non-uniform scale, aspect ratio 5:1). Geological layers: 1. sandstone, 2. clayey pebble, 3. clay, 4. lignite (UCG generator is located in the middle of this layer), 5. clay, 6. clayey sand, 7. clay, 8. silty clay.
Figure 3
Cross-section (y = 750 m) through the area of interest – position of coal gasification generator marked at the centre.
Table 1
Material parameter values of individual geological layers.
| Layer | Roof min [m] | Roof max [m] | f [−] | N [Pa] | A [Pa] | α [−] | ρs [Mg/m3] | K [m/s] | cv [J/kg/K] | λ [W/m/K] |
|---|---|---|---|---|---|---|---|---|---|---|
| Sandstone | 4.7 | 10.9 | 0.15 | 2.31E+09 | 3.46E+09 | 1.16E-05 | 2.6 | 5.00E-07 | 1100 | 3.1 |
| Clayey pebble | 25.2 | 32.7 | 0.28 | 3.90E+06 | 2.40E+07 | 6.00E-06 | 2.53 | 3.00E-06 | 639 | 2.5 |
| Clay | 50 | 50 | 0.31 | 1.32E+07 | 6.91E+07 | 5.80E-06 | 2.38 | 3.00E-08 | 566 | 2.1 |
| Coal* | 53 | 53 | 0.2 | 5.80E+08 | 8.70E+08 | 5.00E-06 | 1.21 | 5.00E-09 | 1250 | 0.5 |
| Clay | 57.2 | 69.8 | 0.4 | 1.28E+06 | 9.42E+06 | 5.90E-06 | 2.62 | 6.00E-08 | 481 | 2.9 |
| Clayey sand | 80.5 | 95 | 0.32 | 1.30E+06 | 9.00E+06 | 6.00E-06 | 2.49 | 1.20E-06 | 889 | 3.5 |
| Clay | 125.9 | 149.9 | 0.37 | 2.50E+06 | 1.85E+07 | 6.10E-06 | 2.71 | 7.00E-08 | 514 | 1.4 |
| Silty clay | 166.1 | 184 | 0.28 | 3.30E+06 | 1.50E+07 | 6.00E-06 | 2.66 | 5.00E-08 | 612 | 1.9 |
Table 2
Thermal parameters of individual pore fluids and medium.
| Thermal expansion coefficient 1) [1/K] | Initial heat transfer coefficient [W/m/K] | specific heat [J/kg/K] | |
|---|---|---|---|
| Water | 69·10−6 | 0.6 | 4150 |
| Water vapour | 1/T | 16.2·10−3 | 1970 |
| Medium | - | λ = (1 − f) λs + fλf | cν = (ρ1 cνs + ρ2 cνf) / ρ |
Figure 4
Main boundary conditions on cross-section, (non-uniform scale, aspect ratio5:1). Geological layers: 1. sandstone, 2. clayey pebble, 3. clay, 4. lignite (UCG generator is located in this layer), 5. clay, 6. clayey sand, 7. clay, 8. silty clay.
Figure 5
Evolution of temperature at selected points of the gasified area.
Figure 6
Evolution of temperature changes around the coal gasification generator over time: a) start, b) 0.5 year, c) 1 year, d) 1.5 year, e) 2 year, f) 2.5 year.
Figure 7
Water vapour presence in cross-section at times a) start, b) 0.5 year, c) 1 year, d) 1.5 year, e) 2 years f) 2.5 year.
Figure 8
Spatial situation of area of water vapour presence at time t = 1 year.
Figure 9
Distribution of displacements (m) in the cross-section at y = 750 m at times a) 1 month, b) 0.5 year, c) 1 year, d)2 years.
Figure 10
a) Charts of displacements (m) over time, b) 3D vector field of displacements near the generator at t = start, c) displacement vector field near the generator at time t = 2 years.
Figure 11
Vector field of horizontal displacements (m): a–d) on the background of the temperature in cross-section z = 51.5: a) 1 month, b) 1 year c) 2 year, d) 3 year e) horizontal displacements over time (A and B).
Figure 13
Vector field of water conduction rate (m/s) on the background of the permeability (m/s) in cross-section y = 750 m at t = 1.5 year.
Figure 14
Heat transfer coefficient (W/m/K) at t = 1 year: cross-section y = 750 m, close-up of gasification area.
Figure 15
A) temperature (°C) after 6 years when thermal parameters of water vapour were accepted in volume, where phase transition occurred, b) temperature in case, where no phase transition in the pores was modelled c) time course of temperature in both cases at point x = 71,5 m, y = 75,0 m, z = 63 m.