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Description
Two-phase fluid displacement in a pore space with variable surface energies and wettability to fluids is characterised by the dynamics of the contact line (CL) between fluid-fluid and the wall surface, subject to the balance of all participating forces acting on the fluids. Understating the dynamics is critical for assessing performance of EOR and CCS projects. In a two-phase capillary system with contrasting wetting-surface sections along the capillary, when the interface between the invading and receding fluids moves cross a section interface, CL undergoes a transition of accelerating (slip) or decelerating (stick), due mainly to the transformation of surface, kinetic energy and viscous dissipation. When the stick-slip phenomena occur in one part of a pore network, it may alter the phase displacement through the whole network, as the forces must be rebalanced due to a sudden release or accumulation of kinetic or potential energy. As a result, the phase distribution across a pore network may be severely affected and parts of that network become inaccessible to one fluid when the CL is pinned in some pores. Even in a simple capillary, the slip-stick processes are still poorly understood for fluids with contrasting properties under different flow driving conditions, let alone the characteristic temporal and spatial scales of the CL behaviour transition.
Here we report a lattice Boltzmann based modelling study on CL slip-stick processes of two-phase fluid flow in 2D bi-wet channels where wetting or non-wetting fluid displaces the other. Simulations were performed at different fluid contrasts under pressure boundary conditions, for the first time, to systematically characterise CL transition behaviours. They were found to differ distinctively from those obtained from simulation under velocity boundary conditions. By design of experiment, LB simulations were performed on reservoir fluid flow through variable sized pores at low capillary numbers to develop correlations between characteristic temporal and spatial scales, termed as Transition-Stage-Time (TST) and Transition-Stage-Distance (TDS) in this work, and capillary and Laplace numbers. These correlations provide physically based parameters that can be incorporated into pore-network models to account for the impact of bi-wet pores on two-phase displacement and upscaling behaviour, bridging pore-scale contact-line physics and predictive modelling of two-phase flow in heterogeneous pore networks.
| Country | UK |
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