Experimental study of gas injection in a surfactant-alternating-gas foam process

Fractional-flow methods have been shown to be accurate and successful in modeling surfactant-alternating-gas (SAG) foam processes. Fractional-flow theory indicates that the success of gas diversion in a SAG process depends on steady-state foam behavior at very low water fractional flow f(w) (very high foam quality). Previous simulation studies of these processes have relied on extrapolating steady-state data taken at much higher values of f(w). Radically different results are predicted depending on how these extrapolations are made. Data are needed at very low f(w) to predict SAG performance in the field. Laboratory coreflood experiments were conducted to obtain the needed fractional-flow curves. For each value of f(w) constant water- and gas-injection rates were imposed and maintained until the system reached steady state. The corresponding average water saturation in the core was determined by weighing the core continuously during the experiment. Experimental fractional-flow curves are presented for two surfactant formulations in Berea sandstone core, with no oil present, at extremely high foam quality. Results are then scaled up using fractional-flow theory to a hypothetical field-scale application. In both cases, the data scale up to successful mobility control on the field scale. In one case, foam suffered an abrupt decline from stronger foam to coarser foam with increasing foam quality, with a multivalued fractional-flow function, in agreement with some earlier experimental and theoretical results.