The Displacement of Oil by Polymer Slugs Considering Adsorption Effects

Abstract

Oil displacement by injection of chemical solutions is a widespread Enhanced Oil Recovery method. Analytical models for one-dimensional displacement of oil by water with chemical components have been developed since the 1960´s. This problem involves complex physical-chemical processes of interphase mass transfer, phase transitions and transport properties changes. The continuous injection of this kind of fluid would be very expensive, so, the injection of chemical slugs is an attractive alternative to improve the recovery of mature oil fields. The continuous injection of chemical solutions is a Riemann problem, easily solved by the introduction of a self-similar variable. Nevertheless, the slug injection is not self-similar, and the problem becomes much more complex from the mathematical point of view. This paper presents the analytical solution of chemical slug injection in an oil reservoir. A flow potential associated with the conservation of the aqueous phase is introduced as a new independent variable instead of time. This change of variables allows the system splitting into one equation (lifting equation) and a thermodynamic system (auxiliary system). The number of auxiliary equations is less than the number of equations in the compositional model by one. In this paper different adsorption isotherms were analyzed. The transport equation solution, or lifting problem solution involves interaction between waves of different families and allows the design of slug sizes in order to obtain the maximum efficiency of this process. Another important application of these solutions is the prediction of chemical flooding regardless of the transport properties (relative permeabilities and viscosities). If the mobility ratio is close to one, this model may be applied in the development of streamlines simulators.

Application of Fractional Flow Theory for Analytical Modeling of Surfactant Flooding, Polymer Flooding, and Surfactant/Polymer Flooding for Chemical Enhanced Oil Recovery

“…Generally, if there is a step change in the boundary condition, the new set of waves will be set up and may overtake slower waves from the original boundary conditions and cause interference. However, in this case, the surfactant front has a velocity larger than unity, i.e., the velocity of the miscible front [51]. Therefore, the water drive will not catch up with the surfactant front in the surfactant slug.…”

Analytical solution of polymer slug injection with viscous fingering

“…This analytical solution is complicated by the fact that there is a third discontinuity that occurs between the chase water and the trailing edge of the polymer slug, in addition to the two shocks described in the previous section. As noted in the introduction, analytical solutions to this problem have been presented by Bedrikovetsky [3], Ribeiro et al [22], de Paula and Pires [20], Borazjani et al [8], and Vicente et al [26]. However, these solutions are more mathematically complex than those presented here; moreover, they focused on assessing the effects of adsorption and did not consider the effect of viscous instability.…”

“…2). A number of authors have presented analytical solutions that can be used to estimate the impact of adsorption on a polymer slug including [3,20,22,24], and [8], but to date no-one has derived a solution to describe the impact of viscous fingering.…”

Water slug injection containingnpolymers in porous media

“…In the last case, it was only considered continuous injection of aqueous solutions containing chemicals, leading to self‐similar solutions. Ribeiro and Pires developed an analytical solution using the same model for the case of water slug injection containing one polymer, considering linear (Henry), convex (Langmuir) and concave isotherms for an “S” shape fractional flow function. For convex fractional flow function, it was also presented a solution for the injection of slugs containing two polymers that adsorb according to Henry's isotherm; a solution for the injection of a slug containing a polymer and a surfactant which does not adsorb but changes residual oil saturation; and the solution for the injection of a water slug containing one polymer in the presence of salt that changes the polymer adsorption.…”