Status of Caustic and Emulsion Methods
Authors: Johnson C.E. 
Published: December 2007

Proposals for caustic injection to improve waterflood oil recovery, have a Proposals for caustic injection to improve waterflood oil recovery, have a long history. Early work and a recent resurgence of research interest now present four fundamentally different mechanisms by which caustic can present four fundamentally different mechanisms by which caustic can operate, along with many process variations.

Introduction
The first patent on caustic for improved oil recovery was issued in the United States in 1927. Since then, an extensive published record of research and field testing has accumulated. There are now several proposed mechanisms by which caustic waterflooding may improve oil recovery. These include (1) emulsification and entrainment, (2) wettability reversal (oil-wet to waterwet), (3) wettability reversal (water-wet to oil-wet), and (4) emulsification and entrapment. Each mechanism requires somewhat different initial conditions with respect to reservoir oil, rock, and injection water properties, and each process is designed to improve oil recovery in a somewhat different manner.
Oil-in-water emulsion injection as a means for improving waterflood efficiency is related to caustic flooding, but its development and field application is less advanced.
The proposed mechanisms by which these oil recovery processes operate, the conditions required for successful application, recommended laboratory screening methods, and the published results of field testing are reviewed.

Background
Even before the issuance of Atkinson's patent on flooding oil-bearing sands with water containing caustic alkali, the benefits of alkaline flood water were well known. In 1917, Squires disclosed that "The displacement of oil may be made more complete by introducing an alkali into the water...." In 1925, Nutting described the use of alkaline salts such as sodium carbonate and sodium silicate for improving waterflood performance. Nutting dismissed stronger bases, such performance. Nutting dismissed stronger bases, such as sodium hydroxide, for field use because they were too reactive with crude oil and would be used up before they could be effective. Nevertheless, Atkinson's patent described the benefits of just such solutions of patent described the benefits of just such solutions of strong bases, including both sodium and potassium hydroxides. In 1927 Beckstrom and Van Tuyl also reported improvements in oil recovery using solutions of alkaline compounds. Although they preferred sodium carbonate, dilute solutions of sodium and potassium hydroxides also were shown to increase the yield of oil. In 1942, Subkow patented the injection of aqueous emulsifying agents for recovering heavy oil or bitumen. Sodium hydroxide was among the suitable emulsifying agents.

Mechanisms
The early workers were often vague about the mechanism by which caustic acted to increase waterflood oil recovery. Squires gave no reason for his statement that alkaline solutions were beneficial. Nutting believed that alkaline solutions released residual oil from adherence to sand surfaces. essentially a wettability change. He also noted that alkali prevented formation of semisolid, crude oil-water interfacial films, but he discounted the importance of this property in improving recovery.
JPT
P. 85