Interfacial Effects in Gas-Condensate Recovery and Gas-Injection Processes

Abstract

Summary This paper evaluates the behavior of the dimensionless numbers that gauge the gas/oil interfacial tension (IFT) with respect to the other forces (viscous and buoyancy forces) involved in two-phase flow through porous media. These numbers, referred to respectively as the capillary and Bond numbers, diverge on approach to gas/oil complete miscibility, meaning that viscous and buoyancy forces become dominant over capillary forces. The divergence behaves as a power of the distance to complete miscibility as quantified, for instance, by the difference in densities between the oil and gas phases. The exponents of these power laws are "universal," whereas the prefactors vary between gas/oil systems. This allows the classification of the most common injection gases with respect to their efficiency in reducing the gas/oil IFT. This efficiency increases with the miscibility of the injected gas in the oil: supercritical CO2 is more effective in reducing IFT than off-critical CO2 or CH4, which themselves are more effective than N2. A simple procedure is then introduced to determine the wetting (or spreading) behavior of oil on a porous substrate covered with water, as often occurs in practice. The only inputs required are the composition and densities of the three coexisting phases: water, oil, and gas. When they are not measured, these quantities can be calculated by means of an appropriate equation of state. CO2 turns out to be the most effective for promoting the spreading of the oil on water, followed by CH4 and then by N2.

Simultaneous oil recovery and residual gas storage: A pore-level analysis using in situ X-ray micro-tomography

“…It should be noted that capillary end effects (which appear in water-wet plugs and which retain water at the outlet of the plug) may be significant in our study because of the small plug size; in field operations this effect can be neglected, and the residual saturations measured in our study may therefore not be representative of the true field-scale residual saturations. In addition we would like to stress that for CO 2 -oilwater systems, a spreading coefficient close to zero (spreading situation) is expected [60], and this may change the fluid dynamics and/or thermodynamic fluid-fluid-fluidsolid pore-scale arrangement significantly.…”

The Gas–Oil Interfacial Behavior during Gas Injection into an Asphaltenic Oil Reservoir

“…30 For instance, efficient semi-miscible displacement (emulsion-like) with low residual oil saturation occurs in a very low IFT system; while at high IFT the displacement changes to a low efficiency capillary dominated flow. 31 The behavior of IFT at different pressures was first studied during the 1980s. 32 These studies proved that the existence of asphaltene in oil considerably affects the interfacial behavior resulting in higher gas−oil IFT especially at high pressures.…”

Wettability Determination of the Crude Oil−Reservoir Brine−Reservoir Rock System with Dissolution of CO 2 at High Pressures and Elevated Temperatures

“…A number of technical papers have been published to address the role of rock wettability in oil recovery, most of which suggest that compositional changes in either the oil phase or the aqueous phase can alter wettability of rock surfaces. ,,– The salinity of the connate water has been found to be a primary factor controlling the oil recovery because increased salinity can cause wettability alternation from the water-wet condition to the mixed-wet condition . In gas miscible processes, it is found from experiments that the ultimate oil recovery is the highest for the oil−wet rock−fluids system and lowest for the water−wet rock−fluids system, respectively. , In a CO 2 flooding process, the reservoir rock becomes less oil-wet after CO 2 injection. , It has also been found that the wettability alteration occurs for a CO 2 −water−coal system, a CO 2 −water−glass system and a CO 2 −synthetic brine−mica/quartz system, and a CO 2 −reservoir brine−reservoir rock system, respectively.…”

“…17,18 A number of technical papers have been published to address the role of rock wettability in oil recovery, most of which suggest that compositional changes in either the oil phase or the aqueous phase can alter wettability of rock surfaces. 15,16,[19][20][21] The salinity of the connate water has been found to be a primary factor controlling the oil recovery because increased salinity can cause wettability alternation from the water-wet condition to the mixed-wet condition. 22 In gas miscible processes, it is found from experiments that the ultimate oil recovery is the highest for the oil-wet rock-fluids system and lowest for the water-wet rock-fluids system, respectively.…”