Systematic Study of Alkaline/Surfactant/Gas Injection for EOR

Abstract

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 124752, ’A Systematic Study of Alkaline/Surfactant/ Gas Injection as an EOR Technique,’ by Mayank Srivastava, SPE, Jieyuan Zhang, SPE, Quoc P. Nguyen, SPE, and Gary A. Pope, SPE, University of Texas at Austin, prepared for the 2009 SPE Annual Technical Conference and Exhibition, New Orleans, 4-7 October. The paper has not been peer reviewed. Alkaline/surfactant/polymer (ASP) flooding is a popular enhanced-oil-recovery (EOR) method. However, foam can be an alternative to polymer for improving displacement efficiency. The use of foam as a mobility-control agent by coinjection or alternating injection of gas and chemical slugs is termed here an alkaline/surfactant/gas (ASG) process. Foam reduces the relative permeability of the injected chemical slug that forms a microemulsion at ultralow oil/water interfacial tension (IFT) and generates sufficient viscous pressure gradient to drive the foamed chemical slug.  Introduction In the ASP process, polymer provides mobility control during ASP slug and polymer-drive injection. However, the use of polymer has disadvantages. High-molecular-weight polymers can plug rocks with very low permeability. Many of the commercially available EOR polymers can be unstable at high temperature. Some polymers can degrade mechanically from high shear stress through chokes or perforations at high flow rate. One potential alternative to polymer is foam, which can provide mobility control in chemical-EOR processes. Liquid saturation is reduced with increased gas saturation and trapped gas in the foam, resulting in lower liquid relative permeabilities. In foam, gas bubbles are trapped in thin films of fluid called lamellae. The surface tension on the individual lamella, as well as the drag force on it as it slides along the pore walls, causes it to resist movement out of the pore throats. This resistance to movement, when combined with relative permeability reduction of the displacing fluid, results in a favorable mobility ratio and improved displacement efficiency. In ASG flooding, as in conventional chemical flooding, the mechanism of residual-oil mobilization is IFT reduction. One of the main criteria for the success of the ASG process is the formation of stable foam with adequate mobility-reduction characteristics. The full-length paper details the results of experimental work studying the ASG process to evaluate its potential as a feasible EOR technique.