Investigation of Water Diversion by a Novel Polymer Gel System for Enhancing Oil Recovery

Numerical study of water diversion by gel treatment is presented in this paper, particularly investigating layered reservoirs where crossflow may be an important recovery mechanism. The transport of the new gel system which is, unlike many other systems, environmentally acceptable through porous medium and the mechanism of permeability reduction are evaluated. Permeability reduction causing the water diversion is mathematically modelled by interaction of the gelants or gel with the rock matrix in terms of equilibrium adsorption both reversibly and irreversibly. Long half-life of the gelants is applied to the gelation kinetics model to simulate the controlled release of the crosslinkers. Modelling the blockage for both aqueous and oil phases and including the inaccessible pore volume results in a more realistic situation. The location of the high permeability streak is analysed to closely investigate gravity and crossflow. Permeability reduction and crossflow are the main mechanisms involved. Results indicate that high permeability reduction in the thief zone should exist to improve the recovery. This is justified by observing the spread of residual resistance factor. Gel treatment is generally more efficient than polymer flooding in terms of increased oil recovery and reduced water cut, however, gel is not completely formed in the case of high crossflow between layers since some reactants are lost to the low permeability zone and cause damage and additional water crossflow. Investigation of individual layers shows a peak in oil saturation and production rate of the high permeability layer which is due to resaturation of this depleted layer by crossflow from the low permeability layer. The oil production rate of the low permeability layer adjacent to the thief zone increases after gel treatment reflecting the effectiveness of water diversion treatment. This effect is observed to be more significant in the case of low crossflow between layers, as discussed before. Study of the injection strategy in terms of alternating water, polymer and gel injected shows that a small slug of gel injected early after water breakthrough is more effective than injection following a polymer flood. In real cases, crossflow and permeability contrast between layers are beyond control and injection conditions should be optimized when designing a treatment. Therefore, effects of blocking properties, injection time and concentration and reaction rate are studied in details in this work.