Capillary-Gravitational Stratification of Two-Phase Mixtures in Thick Reservoirs
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Stratification (seeds)
Capillary pressure
Experiments were performed on transparent two‐dimensional microfluidic porous systems to investigate the relationships among capillary pressure and the interfacial areas per volume between two fluid phases and one solid phase. Capillary pressures were calculated from the observed interfacial curvature of the wetting‐nonwetting interface, and these correlated closely to externally measured values of applied pressure. For each applied pressure, the system established mechanical equilibrium characterized by stationary interfaces, uniform curvatures across the model, and random surface normals. To study the relationships among capillary pressure and the interfacial areas, we compare the curvature‐based capillary pressure with the differential change in interfacial areas per volume as a function of wetting‐phase saturation. The differential pressure contributions calculated from the experimental measurements are found to be nearly independent of the measured capillary pressure. These results suggest that other contributions to the capillary pressure must be significant when imbibition and drainage processes result in saturation gradients.
Capillary pressure
Imbibition
Capillary length
Saturation (graph theory)
Capillary surface
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Capillary pressure
Hysteresis
Capillary surface
Capillary length
Pressure angle
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Capillary pressure
Multiphase flow
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The role of surface tension and wettability in the dynamics of air-liquid interfaces during immiscible fluid displacement flows in capillary tube driven by pressure has been investigated. The contact angle and capillary number drive the force wetting processes which is controlled by the balance between the capillary and the viscous lubrication forces. The dynamic wetting condition with the critical capillary number is studied analytically and validated experimentally, which demonstrates that the critical capillary number is associated with the contact angle, slip length and capillary radius.
Capillary pressure
Capillary length
Capillary surface
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Abstract High capillary pressure has a significant effect on the phase behavior of fluid mixtures. The capillary pressure is high in unconventional reservoirs due to the small pores in the rock, so including the effect of capillary pressure on phase behavior is necessary for reliable modeling of unconventional shale gas and tight oil reservoirs. We show that the tangent plane distance method cannot be used to determine phase stability and present a rigorous thermodynamic analysis to determine phase stability with capillary pressure. We then demonstrate that there is a maximum capillary pressure (Pcmax) where capillary equilibrium is possible and derive the necessary equations to obtain this maximum capillary pressure. We also discuss the implementation of the capillary equilibrium in a general purpose compositional reservoir simulator and the numerical challenges involved with its application to unconventional reservoirs. Three simulation case studies for gas condensate and tight oil reservoirs were performed to illustrate the influence of capillary pressure on production behavior. These results clarify the influence of capillary pressure on production behavior in low-permeability reservoirs. We show that the choice of the capillary pressure function and parameters significantly affects the results.
Capillary pressure
Relative permeability
Petroleum reservoir
Reservoir Simulation
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Summary High capillary pressure has a significant effect on the phase behavior of fluid mixtures. The capillary pressure is high in unconventional reservoirs because of the small pores in the rock, so understanding the effect of capillary pressure on phase behavior is necessary for reliable modeling of unconventional shale-gas and tight-oil reservoirs. As the main finding of this paper, first we show that the tangent-plane-distance method cannot be used to determine phase stability and present a rigorous thermodynamic analysis of the problem of phase stability with capillary pressure. Second, we demonstrate that there is a maximum capillary pressure (Pcmax) where calculation of capillary equilibrium using bulk-phase thermodynamics is possible and derive the necessary equations to obtain this maximum capillary pressure. We also briefly discuss the implementation of the capillary equilibrium in a general-purpose compositional reservoir simulator. Two simulation case studies for synthetic gas condensate reservoirs were performed to illustrate the influence of capillary pressure on production behavior for the fluids studied.
Capillary pressure
Petroleum reservoir
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The capillary rise technique has been used to experimentally study the “surface tension” of liquid marbles formed by encapsulating water droplets with polytetrafluoroethylene (PTFE) powder of 1, 35, and 100 μm particle size. In a typical experiment, a glass capillary tube was inserted into a water marble to measure the capillary rise of the water. The Laplace pressure exerted by the water marble was directly measured by comparing the capillary rise data from the marble and from a flat water surface in a beaker. An equation to calculate the water marble surface tension based on the Murmar’s model is then proposed. It is also justified how the capillary rise measurements the liquid marble surface tension does not require the water contact angle with any solid surface to be considered; which therefore makes a simple but efficient method for determining liquid marble surface tension. A discussion on the nature and the realistic magnitude of liquid marble surface tension is offered.
Laplace pressure
Tension (geology)
Glass tube
Capillary surface
Capillary pressure
Polytetrafluoroethylene
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Capillary pressure
Multiphase flow
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Since the pore radius is very tiny in the low permeability porous media, the capillary pressure should be taken into account. A phase equilibrium calculation model in consideration of the capillary pressure was built. The capillary pressure, dew point pressure and retrograde liquid volume of the constant compositional expansion of a practical gas condensate system were calculated by using this model. The effects of capillary pressure on the phase equilibrium of gas condensate system were discussed. The results show that the affecting mode on the phase equilibrium of gas condensate system is determined by the wettability. The capillary radius and the interfacial tension determine the affecting degree. The upper dew point pressure rises, and the retrograde liquid volume of the constant compositional expansion increases while the wetting angle changes from 0° to 90°. The variation is inversed when the wetting angle is from 90° to 180°. When the capillary radius is below 0.1 micrometers, the effect of the capillary pressure will be obvious.
Capillary pressure
Dew point
Dew
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Capillary pressure
Saturation (graph theory)
Centrifuge
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