Copyright 2014, Brazilian Petroleum, Gas and Biofuels Institute-IBP This Technical Paper was prepared for presentation at the Rio Oi & Gas Expo and Conference 2014, held between September, 15- 18, 2014, in Rio de Janeiro. This Technical Paper was selected for presentation by the Technical Committee of the event according to the information contained in the final paper submitted by the author(s). The organizers are not supposed to translate or correct the submitted papers. The material as it is presented, does not necessarily represent Brazilian Petroleum, Gas and Biofuels Insti tute’ opinion, or that of its Members or Representatives. Authors consent to the publication of this Technical Paper in the Rio Oil & Gas Expo and Conference 2014 Proceedings. ______________________________ 1 Petroleum Engineer Post-Graduate, Electrical Engineer -UERJ 2 Ph.D., Civil Engineer – PETROBRÁS IBP1609_14 THE LOW SALINITY WATERFLOODING TO ENHANCE THE OIL RECOVERY IN SANDSTONE RESERVOIR AND APPLICABILITY IN OIL FIELDS Fabiane Q. da Silva 1 , Luis G. Rodrigues 2 Abstract In recent years, it has been observed that the injection of low salinity water in sandstone reservoirs causes an incremental recovery in original oil in place (OOIP). Various theories were proposed to explain the improvement in oil recovery, however there is no consensus on what is considered the principal mechanism behind the low salinity effect. It is a fact that the recovery is due to the chemical composition of injected water and mineralogical characteristics of formation. The interaction of these systems is still being debated in the literature. This study is based on theoretical and experimental analyzes showing the main hypotheses proposed over the recent years, the possible processing plants for treatment of offshore low salinity waterflooding, and some cases of success or failure of the tests in oil fields around the world. 1. Introduction The low salinity waterflooding (LSW) is an emerging EOR mechanism in the oil and gas industry. Several experiments with reservoir samples and SWCTTs has been proving the high potential to enhance oil recovery in some reservoirs. Low salinity waterflooding is the injection of water with a lower salinity than initial formation water and with a specially selected ionic composition. The average salinity of this EOR fluid generally varies from 1000 to 2000 ppm, but nevertheless the effects can be observed until concentrations of 5000 ppm. 2. Offshore generation of low salinity water On offshore production, the principal source of water is the sea. Seawater is widely consumed as an injection fluid in spite of presenting a great deal of erosive potential. An ordinary problem is incompatibility of injected water composition, rich in sulfate, and formation water (FW) composition, rich in barium and strontium. Only in some cases water source is a specific aquifer formation, near offshore installations, which usually contains the most suitable water composition for LSW. An alternative to offshore applications is seawater desalination as a method to produce injecting water with low salinity. Ayirala et al. (2010) developed a new scheme of desalination by Shell under the trademark of Designer Water. While British Petroleum registered LoSal brand as its technology identifier to low salinity influx. In many cases, the low salinity water may result in a more efficient oil recovery in terms of oil production profile and final hydrocarbon volume recovered resulting in an increase in recovery efficiency from 2 to 40%, depending on the reservoir and composition of both injection water and formation water. 2.1. Offshore Desalination There are various techniques for reducing the total dissolved solids in a solution. According to Ayirala et al. (2010), among the existing methods of desalination the most viable method for offshore applications is reverse osmosis membrane (ROM) due to space and weight constraints. The proposal for seawater flow treatment combines the reverse osmosis/nanofiltration technologies, prior reduction of water hardness, including the reduction of SO 4 -2 , and finally