Laboratory Evaluation Of Foaming Agents For High-Temperature Applications — I. Measurements Of Foam Stability At Elevated Temperatures And Pressures
Authors: Maini B.B. , Ma V. 
Published: March 2010

Use of foaming agents holds considerable promise for mitigating the detrimental effects of gravity segregation and viscous fingering in steam drives. Field application of such foams requires careful selection of the foaming agent and judicious design of the injection scheme. In view of the large number of foaming agents commercially available, most of which have never been field tested, the task of selecting the most suitable chemical often requires extensive laboratory evaluations. Measurements of foam stability at steam temperature can be used as the first screening test for selecting foaming agents.

This paper presents the results of experimental evaluation of foam stability under conditions of high pressure and elevated temperatures. Foaming agents were tested at different pressures (up to 6.9 MPa) and temperatures up to 200 °C. Foams were generated by injecting nitrogen gas through a gas sparger submerged under the test solution in pressure vessels equipped with glass windows. The drainage of liquid from the foam as well as the rate of decay of the foam volume were then monitored.

Results show that the drainage of liquid from foam generally follows first-order kinetics, while the decay of foam volume can be more complex. The half-life for foam volume decay declined dramatically with increasing temperature. At the highest temperature investigated, sulphonates were found to be clearly superior. The relative performance of long-chain alpha olefin sulphonates improved with increasing temperature. This suggests that, at higher temperatures, chain lengths longer than those presently available might be advantageous.

Introduction

Gravity segregation and viscous fingering are detrimental to the efficiency of many enhanced oil recovery techniques. This is particularly true for recovery of heavy oils with steam drive due to the extremely adverse mobility ratio and the wide difference between densities of steam and reservoir fluids. It has been known for more than 25 years(1) that the efficiency of miscible and immiscible gas drives can be improved by generating a foam which is considerably less mobile compared to the gas.

In the case of steam drive, it has been postulated that, if steam is injected as part of the gas phase in a foam, it will partially plug oil-depleted zones and high-permeability channels(2,3). This would divert steam toward undepleted zones and thereby improve oil recovery.

Although the steam foam process is conceptually simple, its application on a field scale is not straightforward. It requires careful evaluation of the potential benefits in relation to the cost of the injected chemicals. For best performance, the foaming agent should possess a number of desirable characteristics. These include the capacity to generate a stable foam at steam temperature and high pressure, thermal stability, low adsorption on rock surfaces, compatibility with reservoir fluids, high apparent viscosity of produced foam in porous media, and low cost. Presently, no foaming agent is known to satisfy all these requirements. Laboratory evaluations are therefore required to select the most suitable chemical for a given application.

Most of the reported screening studies for identifying promising foams have employed some form of foam stability measurement for initial screening.