Foam Propagation in Snorre Reservoir Core - Effects of Oil Saturation and Ageing

Abstract

A s eries of foam floods was conduct ed in Snorre re s e rvoir core at 90°C and 300 bar, at different o il saturations . The rate of foam propagation and the time requir ed to reach the maximum attainable apparent foam viscosi ty depended strongly on oil saturation. Apparent foam viscosity decreased steeply at a "critical " oil saturation of 13 to 15%. Extremely high apparent foam viscosities , up to 1000 cP, veere generated at miscible gas flood residual oil saturat i on (13%) . Above the critical oil saturation, strong foam with apparent vi scosities of about 200 cP vee re sti11 formeel, compared to apparent gas viscosities in the absence of surfactant of 0 .5 to 0 . 7 cP . The effect of gas composition (Snorre field gas , methane , nitrogen) on foam pe rform ance was minor . Significant re sidual gas mobility reduction was observed during gas injection into the foam-filled corgi . . INTRODUCTIO NFoams have b e en considered for mobili ty or profile control in gas injection IOR processes, for blockéng and d ive rting using either conventional or gell ed foams , and for controlling GOR at production Wells . In a mobili ty control application, goud foam stability to oil and love surfactant adsorption are essenbal , but mode rate mobili ty re duction is sufficient. If foam is to be placed into swept (love oil saturation) zones to dive rt gas flow into unswept zone s , a faam witti intermediate or love stabil ity to oil may be adequate , but high resistance to flow under an applied pressure gradient is required . A foam treatment to reduce GOR at production W ells require s a foam witti high flow resistance an d goud stabili ty to oi l ; moderate or high adsorption le vels may b e acceptable for a near-wellbore treatment . Whatever the application , the foam has to propagate away from the wellbore in order to be effective .Studies of foam propagation r e po rt varied results, but agree in concluding that foazn propagation d epends c ri tical ly on injection strategy (1-4) . Irani and Solomon (1) found that faam does not propagate du ring altemating injection of small surfactant slugs and C02 or during surfactant/C02 co-inj ection in an oil-free slim tube . The relativel y smalt volume of injected surfactant soluti on did not propagate past the inlet section of the corgi, resulting in a high pressure gradient near the corgi inlet only . The au thors conclude that gas and liquid do not move through the slim tube simultaneously du ring co-injection, bit that faam forens where gas and suifactant contact each e ther. B y contrast, a dual stug injection method consisting of a large stug of dilute surfactant solution followed by C0 2 resulted in effective foam propagation in the absence and presence of residual oil . Hudgins and Chung (3) found th at faam gen eration and propagation depends on WAG ratio and injection sequence in an oi1-free slim tube . At a residual oil saturation of 23%, faam was formeel only when the surfactant stug was large enough to fill the slim tub e, and foam was g enerated only in the t...

Foam Dynamics in Limestone Carbonate Cores

“…It is reasonable to believe that foam generates and propagates, according to the established tracer profile in dispersion measurement, which represents areas of lower flow resistance, as this coincided with the start of the foam plateau level in most experiments. Compared to experiments in homogeneous sandstone cores, it is often observed that the foam propagation follows the injection rate. , Thus, it seems like foam propagation in oil-free carbonates is faster than in sandstones, which could be reflecting the heterogeneous nature or the complexity of the pore structure of carbonates.…”

“…Compared to experiments in homogeneous sandstone cores, it is often observed that the foam propagation follows the injection rate. 26,27 Thus, it seems like foam propagation in oil-free carbonates is faster than in sandstones, which could be reflecting the heterogeneous nature 33 or the complexity of the pore structure of carbonates.…”

“…The focus of foam research in carbonates has been on studies of foams in fractures (see the study by Dong et al). In general, when generating foam, the presence of remaining oil saturation (ROS) reduces the efficiency of foams. − In carbonate core material, aging of the core with crude oil may result in a more oil-wet state. Foam generation combined with wettability alteration in oil-wet low-permeability carbonates has been discussed by Ghosh and Mohanty .…”

Foam Generation, Propagation and Stability in Porous Medium

“…The wettability may, in addition to the residual oil saturation, reduce foam propagation rate as foam nucleation sites may be unavailable for foam generation. Mannhardt and Svorstøl (1997) studied foam generation and foam propagation at Snorre reservoir conditions and reported a strong dependence of foam propagation on oil saturation. Higher oil saturation reduced foam propagation and foam propagation in the absence of oil followed the injection rate.…”