Accelerating the rate of oil recovery with lower cost and environmental footprint to match the increasing demand for fossil fuels has become more challenging. Water flooding as a common improved oil recovery (IOR) method is used in many light-to-medium density oil reservoirs to produce the remaining oil. Since three decades ago, it was observed that modifying the composition of the injected brine (compared to the formation brine) can accelerate and produce extra oil and reduce the residual oil saturation from carbonate and sandstone rocks. In Smart water flooding, the chemistry of injecting brine is modified either by changing the composition of specific ions and/or by changing the brine salinity level to disturb the existing equilibrium condition between oil-rock-formation brine. Many studies linked the consequences of this disturbance to the shift in the wettability of the rock surface towards a more water-wet condition

Carbonate fields that contain a considerable volume of the world’s oil are recognized as suitable candidates for the implementation of this technique. For instance, a remarkable improvement of oil recovery in Ekofisk reservoir to more than 50% of OOIP by seawater flooding is a well-known example of Smart Water flooding into carbonate rocks. Numerous laboratory and few field studies have shown that the oil recovery in carbonate rocks can be improved by lowering the total salinity or manipulating the ionic composition of the injecting brine. Many studies have been conducted, for example, core flooding, spontaneous imbibition, ion chromatographic tests among others to determine the underlying mechanisms and the required circumstances for the improvement of oil recovery by the injection of Smart water into the carbonate rocks. It seems that different mechanisms are acting simultaneously at different scales (i.e., from molecular up to pore scales), with wettability alteration being the most likely mechanism in carbonates based on the experimental observations. wettability modification of carbonate surface due to anhydrite dissolution, surface charge modification, double-layer expansion, and calcite dissolution, micro-emulsion formations, and viscoelasticity improvement at oil-brine interface are among the most discussed and cited processes in the literatures.

The experts in Oil and Gas Field Development Group have investigated the underlying mechanisms of smart water flooding experimentally at various scales and studied the behavior of reactive smart water transport in carbonate and sandstone porous medium using in-house codes and commercial software. The results of our study have been published in several international conferences and peer reviewed journals.