The most difficult practical operation in the oil industry is to displace oil in the low permeability zones in heterogeneous reservoir. This situation becomes worse when the permeability contrast is high and in the presence of oil and acid.
In this study. experiments were conducted to investigate what type of foam is stable to temporurily plug the high permeable cones
Different permeability contrasts of Berea sandstone were used for the experiments. These experiments were conducted in the absence and presence of oil followed by acid injection, while foam quality and velocity were controlled.
Results show that most of the surfactants were interacting with oil and acid under certain shear rate. Only some specific surfactants (not used in the oil industy) resulted in more stable foam and best acid diverting jobs When water was followed by the acid job, most of the oil in the low permeability zones was removed and flowed out of the rock. Certain foam slug sizes were needed in different permeability contrasts. As a result of the experiments, a simple way was to predict foam rate was observed. Laboratory experiments were performed before the application of the acid job in the field. As a result, less acid might be needed to perform the stimulation job.
The presence of foam in a heterogeneous porous media helps to reduce the liquid mobility in the high permeability layers. This reduction in mobility causes the diversion of most of the liquid to the lower permeability layers.
It is generally accepted that foam, in the presence of oil, does not have a reduction in mobility. In laboratory experiments with oil, the foam propagation was usually retarded because of the presence of oil and in some cases there was no mobility reduction until the oil saturation became low enough.
Minssieux(1) proposed to use stabilizing agents capable of increasing the viscosity of their aqueous phase (such as a polyvinyl alcohol) to stabilize foams in the presence of oil. In the field application, as Maini (2) reported, the injected foam inevitably contacted some residual oil. This contact between oil and foam had a major effect on foam properties. However, the mixing of the injected foam agent with surfactants already present in the oil led to enhancement of foam properties when the two surfactants behaved synergistically. He also found that the fonnation of oil in water emulsion could be a factor in overall mobility reduction behavior. Nikolov et al(3) reported that during the process of three phase foam thinning, three distinct films occurred: foam films (water film between oil bubbles), emulsion films (water between oil droplets), and pseudoemulsion films (water film between air and oil droplets). Their micromodel experiments showed that after a certain thickness a pseudoemulsion film formed between the oil lens and the air bubble surface ruptures causing the oil to spread on the surface. This oil spread disturbed the mechanical equilibrium between the foam lamellae and their borders causing the entire frame to break.