Physical Properties of High-Rank Coal Reservoirs and the Impact on Coalbed Methane Production
Abstract
:1. Introduction
2. Geological Setting
3. Experimental and Methods
3.1. Samples
3.2. Experiments
3.3. Evaluation of Fractal Dimension
- Vm, the volume of mercury input;
- D, the fractal dimension;
- R, the aperture;
- C, a constant.
3.4. Structural Curvature
- K, the curvature value;
- Z, elevation of coal seam floor, Z = f(x,y).
3.5. The Gray Correlation Analysis Method
3.5.1. Determine the Comparison Sequence and Reference Sequence
3.5.2. Dataization of Variables
3.5.3. Calculate Correlation Coefficient
3.5.4. Calculate Correlation Degree
4. Results and Discussion
4.1. Physical Characteristics of Coal Reservoirs in the Research Area
4.1.1. Reservoir Pore Characteristics
4.1.2. Reservoir Fracture Characteristics
4.1.3. Permeability Characteristics
4.1.4. Reservoir Pressure Characteristics
4.1.5. Reservoir Adsorption Characteristics
4.2. Characteristics of Coalbed Methane Production Capacity in the Research Area
4.3. The Influence of Reservoir Physical Properties on Coalbed Methane Production
4.3.1. The Impact of Pore and Fracture Structures on Productivity
4.3.2. The Impact of Gas-Bearing Characteristics of Reservoirs on Productivity
4.3.3. The Impact of Permeability Characteristics on Production Capacity
4.3.4. The Ratio of Critical Desorption Pressure to Reservoir Pressure
4.4. Other Factors Affecting Production Capacity
4.4.1. Construction Conditions
4.4.2. Production Strategy
4.5. Gray Correlation Analysis
4.6. Comprehensive Evaluation of CBM Development Effect
5. Conclusions
- (1)
- The micropores in high-rank coal seams are well-developed, while the macropores and mesopores (exogenous fractures) are underdeveloped. The coal seam has obvious reservoir characteristics of high gas adsorption and low permeability. The 3# coal seam is mostly located in the stress-sensitive permeability zone, and its permeability is significantly affected by the burial depth of the coal seam.
- (2)
- The fractal characteristics of coal seam pores and fractures can reflect the permeability characteristics of the reservoir. The fractal dimension of the micropores is relatively high, while the fractal dimension of the macropores and mesopores (exogenous fractures) is relatively small. The permeability is positively correlated with macropores (exogenous fractures) and mesopores, and negatively correlated with micropores.
- (3)
- Gas content, burial depth, and porosity are the main factors affecting productivity under the physical properties of high-rank coal reservoirs. Based on gray relational analysis, the coalbed methane production capacity in the study area was evaluated, dividing the research area mainly into a high-yield area, a medium-yield area, and a low-yield area.
Author Contributions
Funding
Data Availability Statement
Conflicts of Interest
References
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Coal Seam | Ash Content (%) | Moisture Content (%) | Fixed Carbon (%) | Volatile (%) | ||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
Min | Max | Ave | Min | Max | Ave | Min | Max | Ave | Min | Max | Ave | |
3# | 1.12 | 48.53 | 11.19 | 0.63 | 13.78 | 1.38 | 47.61 | 90.30 | 80.79 | 3.23 | 16.94 | 6.58 |
Porosity (%) | Minimum Value | Maximum Value | Average Value | ||
---|---|---|---|---|---|
1.3 | 6.3 | 3.8 | |||
Types | Extra large hole | Macropore | Mesopore | Transition pores | Micropore |
Aperture (nm) | >10,000 | 10,000–1000 | 1000–100 | 100–10 | 10–3 |
Volume (ml/g) | 0.0041 | 0.0013 | 0.0015 | 0.0107 | 0.0244 |
Proportion (%) | 9.7619 | 3.0952 | 3.5714 | 25.4762 | 58.0952 |
Specific surface area (m2/g) | 0.0000 | 0.0020 | 0.0280 | 2.2780 | 18.8410 |
Proportion(%) | 0.0000 | 0.0095 | 0.1324 | 10.7712 | 89.0870 |
Parameter | Numerical Value | Unit |
---|---|---|
drainage speed | 8 | q/(m3/d) |
coal seam thickness | 6 | h/m |
initial permeability | 0.03 | k/mD |
system compressibility | 0.0013 | C1/MPa−1 |
initial porosity | 0.04 | φ |
fluid viscosity | 1.1 | μ/(mPa·s) |
critical desorption pressure | 4 | Pc/MPa |
Capacity Classification | Average Daily Gas Production (m3/d) | Average Daily Water Production (m3/d) | d1000 | d1000/dt |
---|---|---|---|---|
High-yield well | ≥1000 | <1.5 | >100 | >0.5 |
Medium-yield well | 500~1000 | <5 | >50 | — |
Low-yield well | 100~500 | — | <50 | — |
Water-production well | <100 | >1 | 0 | 0 |
Parameter | Value | |
---|---|---|
Reservoir pressure/MPa | 3.36 | |
Critical desorption pressure/MPa | 2.53 | |
Langmuir pressure/MPa | 3.17 | |
Langmuir volume/m3·t−1 | 44.27 | |
Porosity/f | 0.02 | |
Absolute penetration/×10−3 μm2 | kx | 3.4 |
ky | 1.7 | |
kz | 0 | |
Compression coefficient/MPa−1 | 0.062 | |
Skin factor | −3.2 | |
Coal density/t·m−3 | 1.375 |
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Liu, G.; Tang, R.; Mu, C.; Liu, X.; Zhang, J. Physical Properties of High-Rank Coal Reservoirs and the Impact on Coalbed Methane Production. Processes 2024, 12, 1754. https://doi.org/10.3390/pr12081754
Liu G, Tang R, Mu C, Liu X, Zhang J. Physical Properties of High-Rank Coal Reservoirs and the Impact on Coalbed Methane Production. Processes. 2024; 12(8):1754. https://doi.org/10.3390/pr12081754
Chicago/Turabian StyleLiu, Gang, Runchi Tang, Chi Mu, Xing Liu, and Junjian Zhang. 2024. "Physical Properties of High-Rank Coal Reservoirs and the Impact on Coalbed Methane Production" Processes 12, no. 8: 1754. https://doi.org/10.3390/pr12081754