Laboratory Study Of The Use Of Foam Cyclic Steam Injection (1991)

Abstract Most of the work on steam-surfactant oil recovery carried out in this and other laboratories has focused on steam drive processes. However, field pilots and commercial operations in Alberta's heavy oil resources are almost invariably cyclic Steam operations. This work was carried out to develop a methodology for cyclic steam laboratory studies and provide some understanding of the performance of surfactant foams in a cyclic process applied to oil sand formation. Runs were carried out by cycling the production pressure between 700 kPa and 1750 kPa at one end of the core while injecting steam at a constant rate into the other end. The formation of foam within the flow path during the drawdown and low pressure periods war inferred from the higher ΔPs observed when surfactant was used. Foam formation occurred most readily during the low pressure phase. The presence of a relatively high concentration of surfactant was required to cause foaming during the drawdown. Non-condensible gas coinjected with surfactant showed little or no effect on pressure drop behavior. The influence of drawdown rate was also investigated. The results showed that foam formation occurs over a large range of rates; faster drawdown rates resulted in higher oil recovery. Performance of the foaming surfactant was unaffected by permeability of sand in the flow path over the range (10 to 80 darcy) studied. Pressure drops increased in successive cycles as more oil was removed from the core, in agreement with other studies which have shown that high residual oil saturations are detrimental to foam formation. Introduction Foam injection for improving conformance and increasing oil recovery has been successfully employed in a number of steamflooding operations(1–3). Field applications have been supported by several laboratory studies(4–8). These beneficial effects of foam can be attributed to diversion of steam from high permeability zones of low oil saturation into the oil-rich zones of the reservoir (or core). On a pore scale the mechanisms of foam formation and propagation are now well understood(9,10). The diverting effect of foam within an experimental core containing a high permeability flow path is schematically depicted in Figure 1, showing flow paths of steam in the presence and absence of surfactant. The majority of steamflood operations in Alberta involve cyclic steam injection. Successful application of foaming surfactants to control injection profiles in cyclic steam processes has been reported(11,12), and their use to limit steam flow through depleted zones of the reservoir during cyclic steam stimulation has been proposed(13). However, relatively little experimental work to evaluate the performance of foam forming surfactants in cyclic processes has been reported, and little is known about how the foam operates in various parts of the cycle. Cyclic processes may either be single well, in which steam is alternately injected into and produced from a single well or multiwall, in which steam is continuously injected into a well and the production pressure at other wells is cycled. In either case maximum oil production occurs during the drawdown phase, when production pressure is dropped.