Tertiary Oil Recovery Using Multiple Micellar Slugs
Authors: Thomas Sara , Supon Stanley B. , Ali S.M. Farouq 
Published: March 2010

Abstract
Many oil reservoirs in Canada, the United States and other countries have reached economic waterflood limit, and require the application of a tertiary method for the recovery of some of the waterflood residual oil. Micellar (or microemulsion) flooding can fulfill this objective under favourable conditions. In the present research, several micellar solutions were use for the tertiary recovery of three crude oils. The slugs were selected from equilibrium phase formed in pseudo-ternary oil-water-surfactant systems, and were oil-rich or water-rich. The respective slugs were compared for recovery efficiency when used singly, and when used in a sequence of oil-rich/water-rich slugs, driven in each case by a suitable mobility buffer. Graded slugs, starting with an oil-rich micellar solution and ending with a water-rich solution, were also successful in increasing tertiary recovery-to-slug volume ratio. It is concluded that for a given set of conditions, a composite or graded micellar slug is more efficient than a single slug.

Introduction
With many light oil reservoirs approaching the economic limit of waterflooding, it is becoming increasingly important that suitable tertiary methods be developed to recover 30% to 50% of the initial oil-in-place remaining at the end of a waterflood. Micellar flooding is one of the very few tertiary methods which have been proven in the field. Many publications, including the earlier works of Davis and Jones(l), Gogarty and Tosch(2), Farouq Ali and Stahl(3), Healy and Reed(4,5) Sayyouh, Farouq Ali and Stahl(6), Enedy, Farouq Ali and Stahl(7), and others, have discussed experimental investigations of the basic process and its many variations. It has been shown that a micellar slug, driven by a suitable mobility buffer, is capable of displacing the in-place oil and water in a miscible type displacement. Many factors influence the process efficiency, including the rock mineralogy. Preflushes may be used for "conditioning" the rock matrix. Because of the chemicals used in the micellar flooding process-preflush, surfactant and cosurfactant, and the polymer-the economics may not be favourable. The need for small well spacings is yet another factor influencing the profitability of the process. This paper is concerned with only one aspect of the micellar flooding process, viz. slug optimization. It is shown that instead of using a single micellar slug (hereinafter called "slug"), two or more slugs used in conjunction can be more effective. Several combinations are examined for three crude oils.

Experimental Details and Materials Used Fluids Used
The fluids used were three crude oils, several micellar solutions, and brine. The oils were Bonnie Glen, Provost and Bradford crude oils. Table 1 gives the viscosities and densities of these oils. The micellar solutions were prepared using a surfactant, co-surfactant, and brine. Table 2 gives the more important properties of the four surfactants used. The micellar solutions employed a particular surfactant, a given oil, and brine. The choice of the surfactant and salt has an important effect on the phase behaviour of the fluid system. This was shown by Farouq Ali and Stahl(8) for alcohol systems, Later, Healy.