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AAPG Rocky Mountain Section Meeting

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Does the salinity of injected water matter?

Abstract

In this paper we present the results of laboratory testing of carbonate and clastic reservoir rocks for wettability alteration by salinity. The relationship between salinity and wettability can be used to increase recovery for many waterfloods. Injection water salinity is usually a function of available supply. While fresher water may be preferred to minimize interactions with chemical Rocky Mountain Section – AAPG: 2019 Annual Meeting 54 additives and avoid formation damage, the potential for increased recovery is rarely considered. Knowledge of the impact of salinity on wettability provides the opportunity to steer reservoir wettability towards more oil recovery at low cost. The methodology used is an extension of the modified flotation technique and produces accurate and rapid wettability measurements at different salinities. The method can rapidly quantify the relationship between salinity and wettability using core or cuttings samples and produced oil. The laboratory methodology also offers determination of in-situ wettability as a starting point in design of engineered fluids unlike current methods. This work has identified temperature, mineralogy, oil acid, base and sulfur content and formation water chemistry (salinity and composition) as the most important variables that control wettability alteration by salinity. This approach will not work in some reservoirs and identifying the lack of response in advance of field testing is valuable. The laboratory results for several typical sandstone and carbonate reservoirs show that there is a relatively narrow range of salinity and chemical composition that can significantly alter wettability in the test rocks. Accompanying economic models show the cost is between $1.50-4 per incremental barrel for many reservoirs in the region. The optimum salinity will vary depending on the target reservoir but offers an alternative to surfactants or can be used in conjunction with surfactants to change wettability and increase recovery.