Gas adsorption occurs when the dynamic adsorption equilibrium conditions of the local adsorptive sites are broken. In the overall process of unconventional natural gas generation, enrichment, storage, and production, this phenomenon plays a significant role. A double-distribution Lattice Boltzmann model for solving the coupled generalized Navier-Stokes equation and advection-diffusion equation with respect to the gas-solid dynamic adsorption process is proposed for multicomponent gas migration in the unconventional reservoir. The effective diffusion coefficient is introduced to the model of gas transport in the porous media. The Langmuir adsorption rate equation is employed to control the adsorption kinetic process of gas-solid adsorption/desorption. The model is validated in two steps through fluid flow without and with gas diffusion-adsorption between two parallel plates filled with porous media, respectively. Simulation results indicate that with other parameters being equal, the rate of gas diffusion in the porous material and the area of the dynamic adsorption equilibrium-associated region increase with the matrix porosity/permeability. Similar results will happen with a greater saturation adsorption amount or a lower Langmuir pressure. The geometric effect on adsorption is also studied, and it is found that a higher specific surface area or free flow region can enhance the gas transport and the rate of adsorption.

Citation:Liu, S., Tang Since 2006, more than 80 multilateral horizontal wells have been drilled in Panzhuang block, Southern Qinshui Basin. In this paper, 6 typical wells in a region are selected as an example. The thickness of coal, gas content, reservoir pressure, permeability, burial depth, and reservoir pressure conditions are analyzed. The practice shows that production by multilateral horizontal well declines from 43,111 m 3 /day per well in the 2 nd year to 25,126 m 3 /day per well in the 4 th year. The numerical simulation result shows that the lateral interference forms in Well QNP05 after two years of gas production, and the gas content is reduced to less than 8 m 3 /t within the controlled region after six years. The area of gas content was less than 8 m 3 /t after eight years of gas production is about 3.2 km 2 , which is about 76% of the controlled area of the six multilateral horizontal wells. The results indicate that multilateral horizontal wells contribute to high production rates at potentially profitable levels and can also serve as an effective tool for a high-rank CBM field drainage.

After the completion of fracturing operation in coalbed methane (CBM), the fracturing fluid needs to flow back to the ground in time to reduce the damage to the coal reservoir. The damage of guar-based fracturing fluid to the coal reservoir has an adverse effect on the fracturing stimulation. A series of flow experiments were carried out with the unconventional natural gas reservoir damage evaluation equipment. This paper investigates the evolution of fracture permeability in coal samples during the process of hydroxypropyl guar (HPG) fracturing fluid flow back. The experimental results show that the fracturing fluid concentration, proppant type, proppant particle size, and proppant concentration all affect fracture permeability. The high concentration of fracturing fluid caused irreversible damage to fracture permeability of coal samples. With the increase of fracturing fluid concentration, the permeability damage rate increased from 65.31% to 84.57%, and the damage degree was strong. KCL brine flushing can only decrease the damage rate of coal sample fracture permeability within a certain range. The proppant embedment and the generation of pulverized coal exacerbated the damage of fracture permeability. The research results can be beneficial for optimizing the type and performance of fracturing fluid for hydraulic fracturing in CBM reservoir.

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