Thermal stability tests were carried out for several types of sulfonate surfactants at 200 and 300 ºC. Most of the tested surfactants displayed half lives longer than 100 days at 200 ºC, while at 300 ºC halflives were typically less than 10 days. Alkyl benzene sulfonates were found to be superior to alpha olefin sulfonates for chemical stability at 300 ºC. while petroleum sulfonates were found to be the least stable.
The effectiveness of various foaming agents in controlling gas phase mobility was compared in terms of mobility reduction factor (MRF) which represents the ratio of pressure drop across a porous medium at given flow races of the foaming liquid and gas to the pressure drop obtained at identical flow rates with pure water and gas. MRF's were measured are 200 ºC and 6.0 MPa in 30 cm long and 5.7 cm diameter cores composed of unconsolidated sand. Tests were conducted at three different concentrations of most of the surfactants and at three different ratios of gas and liquid flow rates. The performance of the foaming agents varied considerably with their concentration in the aqueous phase. For most of the ten different foaming agents evaluated, the best performance was obtained at an optimum concentration. The values of MRF's were generally in the range of 2 to 20, however, one of the surfactants displayed values below unity. This most probably resulted from the effect of surfactant adsorption on wettability and consequently the relative permeability curves. It demons crates that careful screening of foaming agents is necessary to avoid unpleasant surprises.
Steam drive is one of the most effective methods for increasing the recovery of heavy oils beyond what can be produced by the 'huff-n-puff' technique. Unfortunately the efficiency of the steam drive process is often hampered by problems of gravity override and channelling through unproductive, high permeability streaks. These problems can reduce the pressure gradient between the injection and production wells which is one of the key forces that drive the heated oil into the production well. It is believed that, if the steam mobility is reduced by forming a foam within the steam zone, the process efficiency would improve.
Although the steam foam process is conceptually simple, its application on a field scale is not straightforward. It requires the screening of a large number of available surfactants and careful evaluation of the potential benefits in relation to the cost of the injected chemicals. A foaming agent needs to have a number of desirable properties in order co be useful for steam drive applications. These include the following:
Capacity to generate. 'stable' foam at high temperature.
Good chemical stability at high temperatures.
Capacity for large reduction in steam mobility.
Low adsorption on rock surfaces.
Compatibility with reservoir fluids.
None of the currently available foaming agents satisfy, all of these requirements to perfection. The selection process for a given application therefore involves finding the best compromise. We have been evaluating commercially available foaming agents for high temperature applications.