Displacement of oil by Solvent at High Water Saturation

Abstract

Displacements oj laboratory oils by propane in long, consolidated sandstone cores in the presence of high water saturations have shown that oil recoveries approaching 100 percent may be realized by continuous water.propane injection, even for oil saturations close to residual oil. However, it was o/ten necessary to inject many pore volumes of solvent to attain this high a recovery Initial oil saturations were established by injecting water and oil at a constant ratio intc the porous medium containing residual oil to a waterflood until a steady state was obtained. Propane and water were then injected in the same fixed ratio to displace the oil. These and other experiments indicate that in the presence of a high water saturation only part of the oil is /lowabIe. Part resides in locations that are blocked by water, and the oil in these stagnant locations is not f!owabIe. This nonflowable oi[, it is believed, can be recovered by molecular diffusion into tbe flowing propane of a water-propane displacement. Values for the saturation of hydrocarbon that is contained in the stagnant locations and values /or the ratio of the longitudinal hydrodynamic-dispersion coefficient to displacement velocity were determined at various water saturations in the test sandstones. The data suggest that rock wettabiiity may inf Iuence the stagnant saturation and that stagnant oil saturations may not be as large in reservoir rocks as they are observed to be in laboratory sandstones. Mass transfer between the fIowing solvent and hydrocarbon components in tbe stagnant saturation was expressed by a first-order rate expression. Rough values for tb~mass transfer coefficients /or the propane-trimetbylhexane hydrocarlw~pair were estimated from exp erir.zents. Computations using these values for mass trans~er coefficients indicate that exp era"ments in laboratory-size cores may show much poorer displac~ment efficiency than that which might actually occur in the field.

An Investigation of Phase-Behavior/Macroscopic-Bypassing Interaction in CO2 Flooding

“…1, neither the previous nor the present study addresses effects of mobile water. 2,3,4 This was examined in a separate study conducted as part of the overall program. Gravity being neglected has already been implied by the term "viscous-dominated."…”

Simulation of Residual oil Saturation in Near-miscible gas Flooding Through Saturation-dependent Tuning of the Equilibrium Constants

“…Sub-Darcean bypassing is of course also present in immiscible and near-miscible displacements, as visualized for example by Sohrabi and coauthors in two-dimensional experiments (Sohrabi, Tehrani, Danesh, & Henderson, 2004;Sohrabi & Danesh, 2008). It is generally observed that oil trapping by water films is more severe in water-wet conditions than mixed-wet or oil-wet conditions (Stalkup, 1970;Campbell & Orr, 1985;Stern, 1991;Sohrabi, Tehrani, Danesh, & Henderson, 2004).…”

“…The question of whether the residual oil saturation measured in laboratory experiments applies at the field scale is of course to be discussed, but the problem is similar regardless of which method is chosen to enforce it. In particular, as we move from laboratory to field scale, the relative importance of sub-Darcean bypassing with respect to Darcean bypassing might decrease (Stalkup, 1970). A further point to keep in mind is that the SDTEC method considers time-independent values of -parameters and S orv (although they could possibly be rock-type-dependent).…”

A Review of CO2-Enhanced Oil Recovery with a Simulated Sensitivity Analysis

“…According to Jackson et al [65], oil recovery efficiency clearly reduces with increasing WAG flood ratio, and Ghedan [58] has clearly shown the importance of carefully selecting the CO 2 -WAG flood ratio, as an unnecessarily high WAG flood ratio may cause the oil production to be delayed with the injection of a greater proportion of water that acts as a barrier for CO 2 to reach the oil, reducing the displacement efficiency of the CO 2 . Many laboratory studies have also found similar effects of WAG flood ratio on sweep efficiency [67,68]. The effect of initial reservoir pressure on oil production was then investigated by changing the initial reservoir pressure from 7 MPa to 24 MPa while maintaining all other parameters constant (temperature at reservoir temperature, CO 2 injection rate of 5 mmscf/day, water injection rate of 2000 bbl/day).…”