Investigation of pressure transient behaviour during Injection Fall-Off (IFO) test in foam flooding

Gas injection projects often suffer from poor volumetric sweep because under reservoir conditions the density and viscosity differences between the gas and the in-situ oil lead to override and bypassing of much of the oil in place. Foam has been suggested as a potential solution to this shortcoming and has shown success in some of the field applications. On the field scale foam can reduce the gas mobility, fight against gravity by inducing increased viscous forces and consequently reduce the gas-oil ratio in the producers. Nevertheless, foam propagation in the reservoir, with low fluid velocities and survival of foam in the path from injector to producer, are among major uncertainties in foam projects. This necessitates the design of surveillance plans to monitor foam rheology and its propagation in porous media. Usually foam generation inside a porous medium is indirectly inferred from the pressure increase in the injection well. However, foam often exhibits a non-Newtonian (shear-thinning) behaviour as it propagates through the porous medium, which can influence the pressure transient behaviour. This paper studies application of pressure fall-off test, as a relatively inexpensive and simple surveillance technique, for interpretation of pressure behaviour of foam flow in the reservoir. A local-equilibrium implicit-texture foam model is used to model the foam behaviour. We investigate the dependency of the pressure behaviour on the foam-model parameters. We show that different foam flow regimes (inclined radial flow, radial flow, a transient section), and reservoir boundaries can be inferred from the pressure fall-off tests. The results also indicate that pressure fall-off data can be used to obtain foam-model parameters to predict the in-situ foam strength. The results of this study can be used to analyse data from injection wells, where monitoring or surveying of the generation, stability and distribution of foam is a key factor in the success of a foam field project.