Produced Water Reuse for Sustainable SmartWater Flooding in Carbonates

SmartWater flooding through tailoring of injection water salinity and ionic composition has gained significant attention for improved oil recovery in carbonates. In this paper, we experimentally evaluate the potential of reusing produced water to achieve sustainable SmartWater flooding in carbonates. For this purpose, we utilized the treated low salinity waters obtained from the desalination of hypersaline produced water and unconventional frac flow-back produced water using zero liquid discharge (ZLD) technology to generate desired SmartWater chemistries. Three types of tailored SmartWater recipes were formulated using high salinity water and two treated low salinity produced waters. First SmartWater (conventional) represents the diluted high salinity water version with deionized water, while the other two SmartWater formulations are obtained by blending of high salinity water with treated low salinity produced water streams. Both zeta potential and core flooding experiments were conducted using carbonate rocks and crude oil. Zeta potentials were measured in calcite /brine, carbonate rock /brine, and crude oil in brine suspensions at both ambient and elevated temperatures (25 °C and 70 °C). Core flooding experiments were carried out at reservoir conditions (70 °C and 2000 psi) by first injecting high salinity water then followed by the injection of different SmartWater chemistries in tertiary mode. The calcite/brine and carbonate rock/brine zeta potentials showed negative surface charges with all SmartWater chemistries. Interestingly SmartWater formulations obtained with treated produced water showed increasingly negative surface charges at calcite/brine and rock/brine interfaces when compared to conventional SmartWater. The measured zeta potentials at crude oil/brine interfaces also showed slightly higher negative surface charges for both the treated produced water based SmartWater chemistries. The same zeta potential trends were observed with SmartWaters at elevated temperature across calcite/brine, rock/brine and oil/brine interfaces even though the magnitude of negative surface charges were found to be relatively higher over those obtained at ambient temperature. These zeta potential results demonstrate that SmartWaters prepared with treated produced water have enhanced wettability alteration capability over conventional SmartWater formulated using high salinity water. The core flood performed with conventional SmartWater showed about 7% incremental oil recovery beyond high salinity water injection, while the core flood incremental oil recoveries were about 16% and 13% with the injection of SmartWaters formulated using the two treated produced waters, respectively. The core flood results corroborated very well with zeta potential data to confirm the potential of reusing treated produced water to formulate SmartWater and increase oil recovery in carbonates. This experimental study for the first-time demonstrates the potential of reusing treated produced water as effective "wettability modifier" to achieve sustainable SmartWater flooding in carbonates. The recycling of produced water as ‘SmartWater" can become a game changer to avoid costly produced water disposal and promote circular water economy/environmental sustainability in SmartWater flooding field projects.