Foaming Behavior of CO2-Soluble, Viscoelastic Surfactant
Authors: Carpenter Chris 
Published: October 2018

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 190302, “Foaming Behavior of CO2-Soluble Viscoelastic Surfactant in Homogeneous Porous Media,” by Galang Ramadhan, The University of Texas at Austin; George Hirasaki, SPE, Rice University; and Quoc P. Nguyen, SPE, The University of Texas, prepared for the 2018 SPE Improved Oil Recovery Conference, Tulsa, 14–18 April. The paper has not been peer reviewed.

Aqueous foam has been demonstrated to have promise in conformance-control applications. This paper explores the foaming behavior of a CO2-soluble, cationic, amine-based surfactant. A distinguishing feature of this surfactant is its ability to dissolve in supercritical CO2 and to form wormlike micelles (WLMs) at elevated salinity. The presence of WLMs leads to an increase in viscosity of the aqueous surfactant solution. This paper investigates how the presence of WLM structures affects transient foam behavior in a homogeneous porous media (sandpack).

Introduction

Aqueous foam is a dispersion of a gas in an aqueous phase with a surface-active agent (surfactant) to lower the interfacial tension between the two phases. Foam functions as an effective mobility-control agent because of its high apparent viscosity in porous media.

Foam’s mobility in porous media is also influenced by the media’s relative permeability. In porous media, foam’s ability to flow from one pore to another is heavily dependent upon overcoming the capillary forces imposed by the pore-throat constrictions. Because of this yield-stress requirement, a large portion of a foam system in a porous media is not mobile. This fraction of trapped foam could occupy up to 65% of total pore volume, depending on foam-injection quality, injection velocity, and porous-media morphology. Trapped foam severely reduces the effective permeability of gas moving through a porous media by reducing the number of conduits through which the foam can flow.

Addition of Polymer and Polymer-Like Structures

The addition of polymer to a surfactant solution typically increases a foam’s apparent viscosity. From the perspective of foam generation, the addition of polymer to a surfactant solution seems to decrease the rate of foam-generation events. With the addition of liquid-phase-viscosifying polymer, a greater pressure gradient needs to be applied to reach the onset of strong foam generation. The higher pressure-gradient requirement could translate to fewer foam-generation events and potentially limit the foam generation to the near-injection-well region. From the perspective of foam stability, addition of polymer seems to reduce the occurrence of lamellae destruction. Immediately after the formation of fresh foam bubbles, the lamellae are subjected to disturbance forces that reduce the thickness of the lamellae’s liquid phase (film). The thinning process continues until the film reaches a critical thickness at which the lamella is not stable and tends to coalesce. Polymer improves the stability of thick foam film by increasing its viscosity and reducing the rate of film drainage.