Deep-reservoir profile modification is an effective method to force subsequently injected water to divert into low-permeability oil-rich layers and to improve the sweep efficiency. A model is built to study the effect of concentration and slug size of the treatment, heterogeneity of the reservoir, crossflow between the layers, reservoir wettability, location of the thief zones, intiation time of the treatment, brine salinity, initial reservoir temperature, and activation temperature. Finally, the obtained optimum parameters were included in a new model to verify the credibility of the results.
A 3D conceptual Cartesian grid with one injector and one producer located at opposite corners with four matrix layers and two thief zones was modeled using UTGEL simulator. Both wells were set to perforate through all layers. BrightWater® was injected into the thief zones only when the water cut in the model reached 65%. The injection process was started by flooding the reservoir with 0.06 PV pretreatment water, and then BrightWater® was injected for 120 days only (basecase scenario). Finally, 0.17 PV of post-treatment water was injected. The injection rate was 1070 barrels per day during all stages of the simulation, which ran for 20 years.
The results showed that the higher the concentration, the higher the recovery factor. The results also showed that the injection of high concentrations with short injection time (small slug) yielded better results than low concentrations with long injection time (big slug). The higher the permeability contrast, the higher the incremental oil recovered. The optimum crossflow value determined from this study was 0.1. However, low crossflow with a high permeability contrast model performed better than high crossflow with a high permeability contrast model. The obtained results showed the importance of the wettability on the performance of BrightWater®. Therefore, the permeability reduction in the thief zones was higher in the water-wet model than the oil-wet model. There was no major difference when the location of the thief zones was at the upper or at the lower part of the model, but the middle location yielded a higher recovery factor. Unfavorable mobility ratio is required to achieve better performance of the treatment. The results confirmed that the earlier the treatment, the better the results. The simulation results showed that as the initial reservoir temperature increases, the recovery factor decreases because BrightWater® was activated earlier with 250 °F than with 200 °F reservoir temperature. The results also revealed that there is no significant difference in the recovery factor when the activation temperature increased from 125 °F to 175 °F. Higher permeability reduction in the thief zone was achieved when the activation temperature was 150 °F. The "popping" and propagation of the particles were not easily displaced by the post-treatment water when the salinity of the system was 10,000 mg/L compared to 170,000 mg/L.