Study of the numerical simulation of tight sandstone gas molecular diffusion based on digital core technology

Abstract

Diffusion is an important mass transfer mode of tight sandstone gas. Since nano-pores are extensively developed in the interior of tight sandstone, a considerable body of research indicates that the type of diffusion is mainly molecular diffusion based on Fick's law. However, accurate modeling and understanding the physics of gas transport phenomena in nanoporous media is still a challenge for researchers and traditional investigation (analytical and experimental methods) have many limitations in studying the generic behavior. In this paper, we used Nano-CT to observe the pore structures of samples of the tight sandstone of western of Sichuan. Combined with advanced image processing technology, threedimensional distributions of the nanometer-sized pores were reconstructed and a tight sandstone digital core model was built, as well the pore structure parameters were analyzed quantitatively. Based on the digital core model, the diffusion process of methane molecules from a higher concentration area to a lower concentration area was simulated by a finite volume method. Finally, the reservoir's concentration evolution was visualized and the intrinsic molecular diffusivity tensor which reflects the diffusion capabilities of this rock was calculated. Through comparisons, we found that our calculated result was in good agreement with other empirical results. This study provides a new research method for tight sandstone digital rock physics. It is a foundation for future tight sandstone gas percolation theory and numerical simulation research.

Mobility of Dissolved Gases in Smectites under Saturated Conditions: Effects of Pore Size, Gas Types, Temperature, and Surface Interaction

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“…During migration in shale reservoirs, oil and gas may be subjected to abnormal pressure, tectonic stress, osmotic pressure, molecular diffusion forces, capillary pressure, buoyancy, intermolecular absorption forces, and screening effects of the pore throat. − Because shale gas forms a nonbuoyant accumulation and the molecular diameter of methane is only 0.38 nm, the marine shale formation in the Sichuan Basin is in a high stage of thermal evolution, and there is almost no free water in the formation. Therefore, in the vertical direction, marine shale gas reservoirs are affected mainly by the adsorption of methane by organic matter and clay minerals (the intermolecular adsorption force) and the differential diffusion of hydrocarbon (due to molecular diffusivity and abnormal pressure) caused by the heterogeneous distribution of free gas (Figure ).…”

Diffusion and Gas Flow Dynamics in Partially Saturated Smectites

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