Reservoir Engineering: Coal Seam
1. Since, gas is primarily stored by adsorption into the coal as a function of pressure @ which the gas gets adsorbed, can we replicate the scenario, whereby ‘the amount of gas adsorbed per unit increase in pressure remain decreasing with increasing sorption pressure’ @ laboratory-scale using experimental investigations?
2. Feasible to achieve ‘equivalent sorption pressure’ @ laboratory-scale, where the water pressure of the water-saturated coal seam remain exceeding the pressure @ which all gas becomes adsorbed into coal-solids or into solution gas?
3. With a relatively low bulk permeability of coal (around 1 md); and, with a ready desorption from solid; what should be the closest spacing of cleats (10 mm or 100 mm), whereby, the dominant mode of fluid transport in a coal seam could be treated as to be Darcy flow (as against with a relatively less fractured structure; and, with slower desorption from solid, where the rate is controlled by diffusive movement)?
If not, how exactly to deduce an average cleat spacing and permeability into which the solid blocks could be considered to diffuse?
4. With Darcian flow being the prime importance in the movement of gas within the coal, can we reproduce the scenario, where the permeability could be strongly directional-controlled by predominant cleat sets @ lab-scale?
5. What is the physical basis by which we decide the permeability of a given cleat structure within coal remains to be dictated either by
(a) phase relative permeability effects, whereby the degree of saturation would affect the gas and water relative permeabilities of the reservoir? or by
(b) changes in the effective stress (total stress minus the seam fluid pressure) within the seams?
Feasible to capture the way the effective stress tends to close the cleats; and the way, it tends to reduce the permeability within coal @ lab-scale?
Under what circumstances, the permeability would remain related to effective normal stress across the cleats?
Any idea about how exactly the gas gets traveled through the core specimen?
6. Feasible to capture all the required 3 factors that influence the effective stress @ lab-scale?
(a) initial-stress (given the weak and jointed nature of coal, while it also remains to be directional); (b) fluid pressure changes; & (c) shrinkage/expansion characteristics of coal matrix (which remains related to the equivalent sorption pressure in the seam).
Feasible to secure stress patterns by ML/AI - from stress measurements in the rock surrounding the seam – deduced as a function of (a) stress caused by gravitational effects, where the overburden stress and the associated lateral stress getting developed under conditions of no lateral strain; and (b) horizontal stresses, which gets induced by tectonic forces (and, which should remain proportional to the moduli of the rocks, while the respective horizontal strains remain approximately equal)?
Achieving "equivalent sorption pressure" at laboratory scale during coal seam experiments is a challenging task but can be feasible with careful experimental design and appropriate equipment. Sorption pressure refers to the pressure at which a gas or fluid is adsorbed onto the surface of a solid material, such as coal.
Laboratory-scale coal seam experiments aim to simulate the conditions found in actual coal seams to study various aspects of coal behavior, including gas adsorption and desorption. While it may be difficult to precisely replicate the conditions of a coal seam in the laboratory, it is possible to create similar pressures and temperatures that allow for meaningful research.
To achieve equivalent sorption pressure, the following considerations are important:
While achieving "equivalent sorption pressure" may not be possible to the exact degree observed in an actual coal seam, laboratory-scale experiments can provide valuable insights into the behavior of coal under controlled conditions. Researchers can study the sorption characteristics, measure adsorption isotherms, and evaluate the effect of different parameters on sorption processes.
It is worth noting that coal seam conditions are complex and can vary depending on the geological formation and coal composition. Laboratory-scale experiments serve as a valuable tool for studying fundamental aspects of coal sorption but may not capture the full complexity of in-situ coal seam behavior. (ChatGPT)
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