Abstract
Smart water flooding as a developing technique utilizes modified water chemistry in terms of salinity and composition to prepare the best-suited brine composition for a specific brine/oil/rock system to obtain higher oil recovery efficiency. Huge amount of unrecovered oil is expected to be remained in carbonate reservoirs; however, few research works on incremental oil recovery during smart water injection in carbonate cores at reservoir condition are reported. Several core flooding tests using one of the Iranian carbonate reservoir rock are conducted to check the effectiveness of smart water injection for more oil recovery efficiency. The results reaffirm the positive effect of sulfate ions to play a key role for better smart water performance. Moreover, it was concluded that the calcium ion concentration is not as effective as magnesium ion for the tests performed at reservoir condition. Synthetic sea water (high-salinity) flooding was considered as the base scenario which results in almost 63% oil recovery efficiency for secondary recovery scenario. Formation of micro-emulsions was found to be the main reason of additional pressure drop during low-salinity water flooding. This clearly showed that the diluted smart water injecting increases the ultimate oil recovery up to 4–12% for already water-flooded carbonate reservoirs.
Highlights
Many researchers have focused on the impact of injecting brine chemistry for more oil recovery from depleted oil reservoirs
It was observed that injecting sea water results in higher oil recovery efficiency compared to the injection of monovalents or for the solution in which the sulfate ion was removed
The experimental results showed almost 12% higher oil recovery efficiency for the diluted sea water injection case (#3) and the ultimate residual oil saturation reduced to 20%
Summary
Many researchers have focused on the impact of injecting brine chemistry for more oil recovery from depleted oil reservoirs. Positive impact of fresh water injection on oil recovery was observed in sandstone reservoirs and it was believed that emulsification and clay swelling might be the main mechanisms (Bernard 1967; Martin 1959). Impact of changing brine composition on oil recovery was studied and it was concluded that brine composition may affect the ultimate recovery (Jadhunandan and Morrow 1991). Since the oil recovery was improved for weakly water-wet conditions, modification of rock wettability was believed to be the key mechanism of oil recovery by changing the brine composition Brine composition, connate water saturation, and aging temperature were believed to be important in wettability alteration (Morrow 1987; Tang and Morrow 1996; Yildiz and Morrow 1996). Fine detachment is considered to be a mechanism of improving water-wetness of the system which can result in higher oil recovery (Yildiz and Morrow 1996)
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