Fall-Off Test Analysis and Transient Pressure Behavior 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 leads 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. In the field scale foam can reduce the gas mobility, fight against gravity by inducing excess viscous forces and reduce the gas-oil ratio in the producer. 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 response; once foam is generated in the reservoir the pressure increases. Foam frequently exhibits non-Newtonian (shear-thinning) behaviour, as it is propagated through the porous medium, which can influence the pressure transient test behaviour. This paper studies different well testing interpretation and pressure behaviour of foam flow in a homogenous reservoir. Local-equilibrium or implicit-texture foam model (that of STARS) are used to model the foam behaviour in porous media. Pressure fall-off test behaviour presented in this paper is new for foam injection. The flow regimes including inclined radial flow, radial flow, transient section, and reservoir boundary are discussed. A method which uses a pressure and a pressure derivative plot is developed for foam injection so that the mobility changes, flow behaviour index, location of foam front, reservoir parameters and reservoir boundary can be estimated. The results of this study can be used to analyse data from injection well, where monitoring of the generation, stability and distribution of foam is a key factor in the success of a foam field project. This paper discuss the dependency of the results on foam-model parameters, which indicates that by using pressure transient data one can obtain the foam model parameter.