Abstract

Micellar flooding is a promising oil recovery method for light oils, where the target is the residual oil left after a waterflood. Laboratory experiments continue to play an important role in the design of micellar floods in the field, owing to the intricacies of the process, which often preclude satisfactory numerical simulation. This paper discusses the design of micellar flooding experiments, using scaling rules derived in this study. The derivation is based on three-phase flow (oleic, aqueous and emulsion phases), with six components (oil water, surfactant, polymer, monovalent ions and divalent ions), using the inspectional and dimensional analysis approaches.

Introduction

Micellar flooding (more accurately, microemulsion flooding) is an important oil recovery method for light oil reservoirs that have been waterflooded to the economic limit.

It is a complex chemical method, relying on the use of a micellar solution, driven by a polymer buffer, in turn driven by water. The micellar solution contains a hydrocarbon, water, a surfactant, and possibly a cosurfactant and an electrolyte. It interacts with the driving polymer solution so that polymer may also be present There are also reactions with the monovalent and divalent ions in the rock matrix. All these interactions are difficult to describe in mathematical form, but approximations can be made. The fluid phase behaviour can be described by a pseudoternary diagram, such as the one shown in Figure 1. Here the electrolyte is considered together with water, and the surfactant is a petroleum sulfonate mixed with a small amount of the cosurfactant (n-amyl alcohol). Of course the crude oil is a multicomponent hydrocarbon also. The number of phases on such a diagram may vary from one to three (or more), depending on the composition, temperature, pressure and other variables. In the diagram shown there is a single phase (miscible) region and a two-phase region.

The concentrations of a given component in the various phases are given by the tie lines. Additionally, K-values can be used to relate some of the concentrations, such as those of the electrolyte. In scaled experiments, usually the same fluid system is used as that of the prototype. Proper scaling of the above variables would be difficult.

The purpose of this paper is to present dimensionless groups for scaling micellar flooding experiments. The groups are derived by inspectional analysis and dimensional analysis, for a six-component, three-phase fluid system, as well as for a three-component, two-phase system.

Previous work

Only a few of the over 500 papers published on micellar flooding have dealt with the question of scaling of laboratory studies. This is partly due to the complexity of the process. Nevertheless, considering that the vast majority of micellar flooding studies have been experimental laboratory studies, it is important to have scaling criteria for the process.

Offeringa and van der Poel1 authored the first paper on miscible displacement scaling. The concepts developed in that work have relevance to micellar flooding. Geertsma, Crees and Schwarz2 discussed the general aspects of derivation of scaling criteria for waterflooding and miscible displacement.

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