Abstract
Slip boundary has an important influence on fluid flow, which is non-negligible in rock micro-fractures. In this paper, an improved pseudo-potential multi-relaxation-time (MRT) lattice Boltzmann method (LBM), which can achieve a large density ratio, is introduced to simulate the fluid flow in a micro-fracture. The model is tested to satisfy thermodynamic consistency and simulate Poiseuille flow in the case of large liquid-gas density ratio. The slip length is used as an index for evaluating the flow characteristics, and the effects of wall wettability, micro-fracture width, driving pressure and liquid-gas density ratio on the slip length are discussed. The results demonstrate that the slip length increases significantly with the increase of the wall contact angle in rock micro-fracture. And the liquid-gas density ratio has an important impact on the slip length, especially for the hydrophobic wall. Moreover, under the laminar flow regime the driving pressure and the micro-fracture width has little effect on the slip length.
Highlights
The fluid flow in rock micro-fractures is a topic of great importance for a wide range of scientific problems, such as water conservancy, oil recovery in low-permeability oilfields, nuclear waste treatment and others [1,2,3,4]
Based on the pseudo-potential model, thethe fluid flow in the rock micro-fracture, and it is verified according to two benchmark cases
The slip length increases at the wall, and the larger the contact angle, the more obvious the slip length changes
Summary
The fluid flow in rock micro-fractures is a topic of great importance for a wide range of scientific problems, such as water conservancy, oil recovery in low-permeability oilfields, nuclear waste treatment and others [1,2,3,4]. A series of experimental and numerical results indicate that the non-slip boundary notion is invalid at the micro-scale [5,6]. The slip boundaries should be taken into account during the fluid flow in these micro-fractures [8,9]. The surfaces of micro-fractures show different wettabilities due to its diverse mineral composition [10], and it has a strong influence on the wall slip. Great attention should be paid to studying the slip conditions in micro-fractures with different wettabilities
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