Fractional Flow Modeling of the Foam Diversion Process in the Presence of Oil
Engineering Honours Degree, 2006
University of Adelaide
Foam has been known to lower gas mobility in porous media and for decades it has been used to divert gas in enhanced oil recovery (EOR) and to divert acid in matrix acidizing. Modeling of the foam-induced diversion process is very complex but a model based on the three-phase fractional flow theory simplifies the modeling process and provides insight into the mechanism of the foam displacement process, especially in the presence of an oil phase. Fractional flow modeling allows a quantitative description of foam diversion for the purpose of predicting sweep efficiency in foam design for field applications.
The model presented for analysis of the foam diversion process utilizes a three-phase, three-component fractional flow methodology, in the presence of oil, and examines the effect of various parameters on the efficiency of foam diversion. Results were analyzed in terms of fractional flow, front tracking, relative injectivity, pore volumes of foam injected, fluid saturation and pressure drop. A base case model was constructed to simulate the foam diversion process for an isolated, two-layer system with contrasting permeability, using a slightly modified fractional flow theory. The concept of the mobility reduction factor (MRF) was utilized to account for reduction in gas mobility in fluid flow or simply put, foam strength. One application of the model is in predicting and improving sweep efficiency of foam application for diversion purposes.
A second focus of this study was a sensitivity analysis of the foam diversion process, in which a number of parameters that were thought to affect the efficacy of foam diversion were examined. In order for diversion to take place, it appeared that both MRF and MRF ratio for the two-layer system have to be high, while a significant permeability contrast between two the layers impairs foam diversion. An upper limit also exists in terms of permeability difference for diversion to occur successfully. The results of this study also implied that there is a strong dependence of diversion success on pre-flush injection. This study lays the framework for further investigation into modeling of foam diversion using the simpler, but practical method of three-phase fractional flow.