document

Summary

We report results for a number of promising enhanced-oil-recovery (EOR) surfactants based upon a fast, low-cost laboratory screening process that is highly effective in selecting the best surfactants to use with different crude oils. Initial selection of surfactants is based upon desirable surfactant structure. Phase-behavior screening helps to quickly identify favorable surfactant formulations. Salinity scans are conducted to observe equilibration times, microemulsion viscosity, oil and water-solubilization ratios, and interfacial tension (IFT). Cosurfactants and cosolvents are included to minimize gels, liquid crystals, and macroemulsions and to promote rapid equilibration to low-viscosity microemulsions. Branched alcohol propoxy sulfates (APS), internal olefin sulfonates, and branched alpha olefin sulfonates (AOS) have been identified as good EOR surfactants using this screening process. These surfactants are available at a low cost and are compatible with both polymers and alkali, such as sodium carbonate and, thus, are good candidates for both surfactant-polymer and alkali-surfactant-polymer EOR processes. One of the best formulations was tested in both sandstone and dolomite cores and found to give excellent oil recovery and low surfactant retention with a west Texas (WT) crude oil.

Introduction

Recent advances, including the development of new synthetic surfactants and increased understanding of the structure/performance relationship of surfactants, have made it possible to rapidly identify promising high-performance surfactants for EOR. This process involves laboratory screening using knowledge of the molecular structure and cost of the surfactants as well as pertinent reservoir-specific information (i.e., temperature, salinity, and crude-oil properties).

This paper describes a process for identifying and evaluating potential EOR surfactants. The surfactant selection process starts with the screening of surfactants by phase-behavior experiments and progresses to corefloods with formulations that may incorporate cosurfactants, cosolvents, alkali, polymers, and electrolytes. We illustrate the application of this approach to the selection of a surfactant formulation for use in both a sandstone outcrop and a WT dolomite reservoir, but focus mostly on the dolomite application because very few studies have been reported for carbonate (Adams and Schievelbein 1987) or dolomite reservoirs. These laboratory data were used in a parallel simulation study of the same reservoir and are described by Anderson et al. (1976) in a companion paper.