Numerous laboratory and field tests reveal that foam can effectively control gas mobility and improve sweep efficiency, if correctly designed. It is believed that there is a significant gap between small laboratory-scale experiments and large field-scale tests because of two main reasons: (i) typical laboratory flow tests are conducted in linear systems, while field-scale foam EOR processes are performed in radial (or spherical partly) systems; and (ii) through the complicated in-situ lamella creation/coalescence mechanisms and non-Newtonian behavior, foam rheology depends on the geometry and dimensionality. As a result, it is still an open question how to translate laboratory-measured data to field-scale treatments.
For the first time, this study investigates how foam rheological properties change depending on the dimensionality and how such dimensionality-dependent properties are affected by different flowing conditions, by using mechanistic foam fractional flow analysis. Complex foam flow characteristics such as three foam states (weak-foam, strong-foam, and intermediate states) and two steady-state strong-foam regimes (high-quality regime and low-quality regime) lie in the heart of this analysis.
The calculation results from a small radial and spherical system showed that (i) for strong foams in the low-quality regime injected, foam mobility decreased (or mobility reduction factor increased) significantly with distance which improved sweep efficiency; (ii) for strong foams in the high-quality regime, the situation became more complicated – near the well foam mobility decreased, but away from the well foam mobility increased with distance, which eventually gave lower sweep efficiency; and (iii) for weak foams injected, foam mobility increased with distance which lowered sweep efficiency. The results implied that the use of fixed value of mobility reduction factor, which is a common practice in field-scale reservoir simulations, might lead to a significant error. When the method was applied to a larger scale, it was shown that strong foams could propagate deeper into the reservoir at higher injection rate, higher injection pressure, and at lower injection foam quality. Foam propagation distance was very sensitive to these injection conditions for strong foams in the high-quality regime, but much less sensitive for strong foams in the low-quality regime.