Fractional-Flow Model for High-pH Flooding

Abstract

A model based on the fractional-flow theory is developed for the enhanced recovery of acidic crude oil with caustic as the alkaline agent. The model incorporates earlier work on fluidlfluid interactions of acidic-crude-oil/caustic systems,. which provides not only the chemical reaction equilibria but also the interfacial tension (1FT) as a function of composition. The lowering of 1FT as a result of in-situ-generated surface-active agent enhances the viscous-to-capillary-force ratio, which is presumed to be the cause of the alteration in relative mobilities of oleic and aqueous phases. The complete set of species-conservation equations forms a system of three quasilinear partial-differential equations that is reducible in the generalized sense. The system is solved by the method of generalized Riemann invariants. The effect of such parameters as viscosity ratio, reference capillary number, injected fluid pH, and salinity is computed with properties of Long Beach crude. New features that arise from the influence of the optimum region when an overoptimum composition is injected are identified. On the basis of composition paths, it is shown that the optimum regions playa dominant role in the process and that the 1FT between the injected solution and the crude has no direct bearing on ultimate oil recovery. Simple graphic procedures that afford quick construction of solutions are shown to be possible.

Effect of adsorption on the optimal displacement of acidic crude oil by alkali

“…The system chemistry as presented above implies that most of species A is present either as HA, or NaA, (Ramakrishnan andWasan, 1983, 1989). Therefore species A conservation gives We now define the normalized surfactant concentration to be C2 is the injection concentration of NaCl and is equal to Ccland will be held as a parameter.…”

“…The porous medium is presumed to be nondeformable, ideal (Ramakrishnan, 1985), isothermal and water-wet. We restrict ourselves to a linear, one-dimensional problem.…”

“…44 from PNa = 0, S , = S (for details see Ramakrishnan, 1985). However, it was usually found that after a few steps of integration the discontinuity relation (Eq.…”

“…The expressions we use in this work were obtained from the relative permeability equations of Ramakrishnan and Wasan (1986). For a detailed discussion on this aspect we refer the reader to Ramakrishnan (1985). For our purpose here, it is sufficient to know that once the local capillary number is known, it is possible to obtain fractional flow of oil and vater through the relative permeability equations mentioned above.…”

“…The numerical technique for generating the discontinuity curve is to integrate Eq. 44 from PNa = 0, S , = S (for details see Ramakrishnan, 1985). However, it was usually found that after a few steps of integration the discontinuity relation (Eq.…”