Tongqiang Xia

A fully coupling coal–gas model associated with inertia and slip effects for CBM migration

Although inertia and slip effects of gas flow that may impose significant influences on Coalbed methane (CBM) well and reservoir performance have been widely confirmed and studied, and some mathematical models have also been proposed to quantitatively evaluate these two effects, the combined inertia and slip effects on CBM migration were seldom considered in the previous models. In this study, a fully coupled finite element (FE) model of non-Darcy gas flow and coal deformation process with sorption and Klinkenberg effects in the coalbed is developed to quantify CBM migration mechanism. The FE model is validated by comparison with available analytical and numerical solutions. The results indicate that the evolution of coalbed permeability and gas transport in CBM reservoir not only relate with the sorption-induced coal deformation and the pore pressure change, but also closely depend on the coupling inertia (non-Darcy) effect and slip (Klinkenberg) effects. Based on the simulation, it is found that CBM production can be significantly enhanced due to gas slip (Klinkenberg) effect. But when slip effect is significant, the inertia effect will be ignored. The simulation results can improve the understanding of the coal–gas interactions during underground CBM migration and provide a scientific basis for evaluation of the gas-drainage efficiency, design and optimization of drainage systems, etc. However, the different pressure and permeability thresholds corresponding to prominent response of inertia or slip effect should be further determined through experiments and theoretical models in the future.

Experimental investigation on blockage boundary for pneumatic conveying of powders in narrow bifurcation slits

ABSTRACT To investigate the blockage characteristics for dense-phase pneumatic conveying in narrow bifurcation slits, a study on the blockage boundary conditions of powders was undertaken. The results show that the solid mass flow rate for blockage increases with superficial air velocity, and the variation trend can be divided into three typical stages. Besides the relationship between the solid loading ratio and superficial air velocity for blockage in the bifurcation slit displays a “S” shape with the increase of air velocity, the solid loading ratio increases, then decreases, finally increases, and in each stage above, the relationship between the two approximately meets power function, respectively. According to the “S” shape relationship, the formula used for blockage boundary [Setia, Mallick, Wypych, and Pan (2013). Validated scale-up procedure to predict blockage condition for fluidized dense-phase pneumatic conveying systems, Particuology, 11, 657–663] was modified into piecewise function for bifurcation slits. In addition, with the increase of the bifurcation angle and conveying pressure, the superficial air velocity decreases, while the solid mass flow rate and the critical solid loading ratio increase. The research work could help understand the blockage theory of the dense-phase pneumatic conveying.