Summary
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: (1) Typical laboratory flow tests are conducted in linear systems, whereas field-scale foam enhanced-oil-recovery (EOR) processes are performed in radial (or spherical partly) systems and (2) 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 as to how to translate laboratory-measured data to field-scale treatments.
Motivated by earlier studies of Kovscek et al. (1994, 1997), this study investigates how such dimensionality-dependent foam rheological properties are affected by different injection conditions on small and large scales, with a mechanistic foam-modeling technique. 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 small radial and spherical systems showed that (1) for strong foams in the low-quality regime injected, foam mobility decreased [or mobility reduction factor (MRF) increased] significantly with distance showing a good sweep efficiency; (2) 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 a relatively low sweep efficiency; and (3) for weak foams injected, foam mobility increased with distance showing a poor sweep efficiency. The results implied that the use of a fixed value of MRF, 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.
Quantitative Modeling of the Effect of Oil on Foam for Enhanced Oil Recovery
