Peng Hou

The surface layer of coal influences its physicochemical, mechanical, and gas-storage properties, but its characteristic thickness has not been systematically determined for coals of different rank within a single basin. This study quantifies the surface-layer thickness of coals from the Karaganda Basin (Kazakhstan) using a physi-co-mathematical surface-layer model combined with previously obtained laboratory, geophysical, and production data. After substitution of the surface-energy relation-ship, the temperature cancels out, giving d ≈ 0.17 × υ (nm), where υ = M100/ρ is the mo-lar volume of the organic matter of coal. The calculated thickness decreases from 198.7 ± 19.1 nm (long-flame coals) to 151.5 ± 17.0 nm (anthracites), and the number of mon-olayers from ≈550 to ≈420; all values (146.0–214.2 nm) are consistent between adjacent ranks within ±10–11%, whereas the end members differ significantly. The theoretical shear strength of the surface layer, τt = 2σ/d, increases from 4.4 to 9.0 MPa, comparable to the strength of the basin coals estimated from the Protodyakonov coefficient. The calculated thickness covaries with gas content, permeability, and propensity for spon-taneous combustion; these relationships are mediated by depth and rank and are for-mulated as testable hypotheses. The results can serve as an additional structural indi-cator for ranking seams in degassing and hazard prediction, but not as a stand-alone hazard index. Future work will focus on experimental validation (nanoindentation, low-temperature N₂/CO₂ adsorption, surface-energy measurements) and model cali-bration.

The migration‐clogging‐sealing process of microparticle suspensions in constricted channels is highly relevant to geotechnical, hydraulic, and environmental engineering. In this study, a coupled lattice Boltzmann‐discrete element method is employed, incorporating dense‐particle corrections into the classical partially saturated method and integrating DLVO (Derjaguin‐Landau‐Verwey‐Overbeek) interactions into the contact model. This approach enables high‐precision simulation of suspended microparticle motion in electrolyte solutions. A systematic analysis of particle properties, flow field characteristics, and channel geometry shows that the sealing mechanism is jointly controlled by the Archimedes and Stokes numbers and can be classified as either deposition‐dominated or collision‐dominated. Under high‐velocity conditions, clogging is more likely triggered by mechanical bridging resulting from particle collisions. Switching the injection method from volume (constant discharge) control to pressure (hydraulic head gradient) control reduces the continuous erosion of particles after sealing. With respect to geometry, the constriction angle and the width of the narrow section are the key parameters affecting clogging, while channel height also plays a significant role when it is less than roughly 10 times the particle diameter. Based on these factors, a dimensionless index J is proposed to evaluate the ease of suspended particle transport. The results indicate that as J increases, the particle transport state sequentially transitions from continuous flow (particles can pass through the channel freely) to continuous erosion (particle deposition is in equilibrium with deposited particle mobilization), to intermittent flow (particles alternately accumulate and remobilize at the constriction), and finally to sealing (clogging prevents subsequent particle migration).