Waterflooding is the most popular secondary oil recovery method. Attempts were made to increase the sweep efficiency of waterflooding by focusing on various physical and chemical aspects of this process. Low salinity waterflooding was an important research topic in recent years, with a focus on the possible effect of various compositions of injected fluid on oil recovery. In this study, the effect of the salinity level on oil recovery in a limestone reservoir was investigated. The methodology utilized multiple limestone core samples. After x-ray analysis, four samples with high calcite content (more than 98% calcite) were used in flooding experiments and the impact of the salinity level on oil recovery was measured.
This study is a continuation of a project at The University of Tulsa (Al Shaikh, 2012). The design of the coreflooding study was constructed base on the contact angle measurement results of the wettability study. The Tagochi method was used to design wettability measurement experiments that span varieties of salinity combinations. The current study showed that coreflooding recovery has a clear relationship with the contact angle measurement of calcite plate. We showed that contact angle values are better indicators for choosing optimum injected water composition in compare to the salinity level. Sequential injection of water with the lower measured contact angles led to the highest recovery. This relationship is not necessarily valid for the salinity level because our wettability experiments show that there is no direct relationship between the measured contact angle and the salinity level of water.
During this experiment, incremental oil recovery from 12 to 18 percentages was reported. This shows the high potential of success for this method. We showed that Tagochi method is an effective way to design an experiment for measuring the contact angle and finding the optimum level of salinity. Similar experiments are required before applying this method to the field. In practice, there is an optimum salinity beyond which purifying the brine water further will not lead to incremental oil recovery. Finding the optimum salinity scenario is essential for increasing recovery with minimum cost.