International Journal of Engineering, Science and Mathematics Vol. 6Issue 7, Month 2017, ISSN: 2320-0294 Impact Factor: 6.765 Journal Homepage: http://www.ijesm.co.in, Email: ijesmj@gmail.com Double-Blind Peer Reviewed Refereed Open Access International Journal - Included in the International Serial Directories Indexed & Listed at: Ulrich's Periodicals Directory ©, U.S.A., Open J-Gage as well as in Caďell’s DireĐtories of Puďlishing Opportunities, U.S.A 533 International Journal of Engineering, Science and Mathematics http://www.ijesm.co.in, Email: ijesmj@gmail.com Phase Behavior Study for Chemically Enhanced Waterflooding Chinmoy Dutta  Bidisha Borah  Suraiya Rahman  Ranjan Phukan  Bhaskarjyoti Saikia  Abstract During chemical based enhanced oil recovery (EOR) process, ultralow oil- water interfacial tension (IFT) (less than 10 -2 mN/m) should be achieved to mobilize the residual oil left behind after conventional recovery methods. This research work studied the phase behaviour of surfactant systems with a view to screen formulations for chemically enhanced waterflooding with ultralow IFT. The phase behaviour tests help to determine the optimum salinity, which is one of the most important parameter in the surfactant flooding because it is at this salinity at which maximum oil recovery can be obtained. The phase behaviour studies of (surfactant + brine + crude oil) systems were performed with various combinations of chemicals with crude oil (31 0 API) of an Upper Assam oilfield at reservoir temperature (70 0 C). The surfactants considered for the experimental works were Sodium Dodecyl Sulphate (SDS, anionic), TritonX-100 (TX-100, non-ionic) and Black Liquor (BL, natural). Five core flood experiments were done to determine the EOR potential of the surfactants used and to validate the chemical formulations that performed well in phase behavior experiments. Mixed surfactant systems were found to perform better in the phase behavior tests and recovered higher residual oil during core flooding due to synergistic effect. Keywords: Enhanced Oil Recovery; Microemulsion; Phase behaviour; Black Liquor; Core Flooding. Copyright © 2017 International Journals of Multidisciplinary Research Academy. All rights reserved. Author correspondence: Chinmoy Dutta M.Tech. Program, Department of Petroleum Technology Dibrugarh University, Assam, India Email: chinmoydutta.petro@gmail.com 1. Introduction The major part of the world’s crude oil production currently comes from aging oil fields. With the discovery of new reserves steadily declining over the years, it is pertinent to strive for increasing the recovery factors of the producing oilfields to meet the ever increasing energy demand. On an average, the worldwide recovery factor from hydrocarbon reservoirs is about a third of what was originally present in the reservoir. The remaining 2/3 of the original resource being substantial is an attractive target for enhanced oil recovery (EOR) technologies. Technically, the EOR processes can mobilize or recover the oil left behind or that cannot be produced economically from mature and depleted oil reservoirs. Although more expensive in implementation, EOR methods are implemented successfully in many parts of the world. Among the EOR techniques, chemical flooding is one of the widely used methods capable of recovering an additional 35% of the original oil in place (OOIP) after conventional waterflooding [1]. These methods are based on the injection of water containing chemical additives like surfactants, polymers, alkalis, salts, nanoparticles etc. depending upon the specific application. Currently, alkaline-surfactant-polymer (ASP) is considered as the most promising chemical method in EOR because it integrates the advantages of alkali, surfactant and polymer.  Department of Petroleum Technology, Dibrugarh University, Assam, India.  Department of Petroleum Engineering, DUIET, Dibrugarh University, Assam, India.