Coalbed methane is a kind of highly efficient and clean energy source. The permeability of coal seam affects the application of gas extraction. There are so many factors affecting gas permeability, such as gas pressure, temperature, moisture content, confining pressure, and coal rank. We experimentally investigated gas permeability of three different coals at four different temperatures (23°C, 34°C, 45°C, and 60°C) and three different moisture contents (dry, medium moisture and moisture-saturated coals). Injection gas pressure varied from 1 MPa to 6 MPa (up to 8 MPa for N2) at constant axial confining pressure of 9 MPa. The results show that under constant axial and confining pressure conditions, with the increase of gas injection pressure, the permeability of N2 and CH4 shows a "V"-shaped change trend, that is, "inflection point"; CO2 permeability decreases with the increase of gas injection pressure. The permeability of coal core samples decreases with increasing temperature, caused by thermal expansion, decrease of gas absorption and increase of porosity. As the temperature rises, the decline gradually flattens. The permeability of coal core samples decreases with the increase of moisture content, related to moisture and gas competitive adsorption, coal porosity reduction. The permeability of high rank coal is lower than the medium rank coal under the same experimental conditions, caused by the pore structure of coal sample.
The significant feature of coalbed in China is the low permeability. A new unsteady seepage flow model is developed for the low permeability coalbed by considering the startup pressure gradient and methane desorption effect. Since the complexity of the problem, a new method which we call it "L‐FVM" is developed, based on comparing the normal numerical calculation methods and comprehension research on FVM. The results show that L‐FVM has the same precission but higher calculating velocity than normal FVM. This result is very important for monitoring the area pressure drawdown in coalbed methane engineering
In this work, we have explored the use of a third species during chemical vapor deposition (CVD) to direct thin-film growth to occur exclusively on one surface in the presence of another. Using a combination of density functional theory (DFT) calculations and experiments, including in situ surface analysis, we have examined the use of 4-octyne as a coadsorbate in the CVD of ZrO2 thin films on SiO2 and Cu surfaces. At sufficiently high partial pressures of the coadsorbate and sufficiently low substrate temperatures, we find that 4-octyne can effectively compete for adsorption sites, blocking chemisorption of the thin-film precursor, Zr[N(CH3C2H5)]4, and preventing growth on Cu, while leaving growth unimpeded on SiO2. The selective dielectric-on-dielectric (DoD) process developed herein is fast, totally vapor phase, and does not negatively alter the composition or morphology of the deposited thin film. We argue that this approach to area-selective deposition (ASD) should be widely applicable, provided that suitable candidates for preferential binding can be identified.
Heating coal seams or injecting heat flow into coal seams is a potential enhanced coalbed methane recovery technique. However, methane desorption characteristics of coal seams under combined effect of confining pressure, methane pressure, and applied heat is complex. In the present work, we investigated the combined effect on methane adsorption on different types of coal. Through comparing the desorption capacity and its influencing factors of two samples (bituminous coal and anthracite coal) at different combination of methane equilibrium pressure (1 MPa, 3 MPa, and 5 MPa) and confining pressure (8 MPa, 10 MPa, and 12 MPa) under heating, we found that the cumulative desorption capacity of methane is positively correlated with gas pressure and negatively correlated with confining pressure. Under the same conditions, the cumulative desorption capacity of anthracite is significantly larger than that of bituminous coal. Methane desorption amount under heating is higher than that without heating, while methane desorption amount of large core sample is smaller than that of coal powder. These results indicate that raising the coal seam temperature while capturing methane is a promising method for obtaining higher coalbed methane recovery rates, reducing greenhouse gas emissions, and improving mining safety.
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)
