Abstract
The gas transport in shale nanopores is always one of the major concerns in terms of the development of shale gas reservoirs. In this study, the gas flow regimes in shale nanopores were classified and analyzed according to Knudsen number. Then the gas flow model considering Darcy flow, slip flow, transition flow, molecular free flow and adsorption effect was proposed to evaluate the gas flow behavior in shale nanopores. The result shows that the contributions of Darcy flow, slip flow and transition flow in shale nanopores are reciprocal, and are mainly dominated by pore radius and pressure. The adsorption effect greatly influences the total mass flux. The total mass flux will increase as Langmuir pressure and temperature increase while it will decrease with reservoir pressure and the adsorption thickness. These results can provide insights for a better understanding of gas flow in the shale nanopores so as to optimize the production performance of shale gas reservoirs.
Highlights
In the last few years, shale gas is playing an important role among energy sources and has attracted wide attention [1,2]
Shale gas reservoirs are characterized by extremely low porosity, ultra-low permeability and high clay content [3,4]
When the shale pore radius is less than the gas molecular mean free path, the collisions between gas molecules and hole-walls are more frequent than those between gas molecules, and the Knudsen diffusion will occur
Summary
In the last few years, shale gas is playing an important role among energy sources and has attracted wide attention [1,2]. The gas transport in shale nanopores is a complex combination of all these flow mechanisms, which cannot be described by Darcy’s law [14]. Some transport models have been developed to understand and quantify gas flow in shale gas reservoirs over the past years. Javadpour [15] and Ozkan et al [16] proposed a gas transport model in shales including viscous flow and Knudsen flow. There are lots of models proposed to describe gas transport in shale nanopores, a detailed comparison and analysis of different flow patterns is lacking. It is extremely necessary to understand gas flow behavior in shale nanopores and the effects on different flow patterns so as to predict gas production and optimize the fracturing treatment for shale gas reservoirs. This work should provide insights for a better understanding of gas flow behavior in shale nanopores
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