Mostafa Takband - Enhanced Oil Recovery (EOR) Research Centre, School of Chemical and Petroleum Engineering, Shiraz University, Shiraz, Iran
Masoud Riazi - Enhanced Oil Recovery (EOR) Research Centre, School of Chemical and Petroleum Engineering, Shiraz University, Shiraz, Iran
Seyyed Shahaboddin Ayatollahi - School of Petroleum and Chemical Engineering Sharif University of Technology, Tehran, Iran

Carbon dioxide (CO2) injection has been widely used to increase oil recovery efficiency from oil reservoirs, however, poor sweep efficiency has been reported in many CO2 injection projects. Various injections scenarios including water alternating gas and simultaneous water and gas injection have been suggested and, to some extent applied in the field to reduce this problem. One of the most recent alternative for more oil recovery efficiency is carbonated water injection (CWI).This paper describes the comparison between two different techniques for tertiary CO2 injection. The First set of tests includes injection of brine followed by CO2 flooding. The second group of experiments is focused on injection of brine, carbonated water (CW) and CO2. The tests were carried out using core flood apparatus and at pressure of 13.8 MMPa (2000 psi).The results show that tertiary CO2 injection after CWI has a higher recovery efficiency than ordinary tertiary CO2 injection. This event could be due to relief of problems of direct contact between water and CO2. Besides,.Injection of CW prior to CO2 makes the spreading coefficient to be positive. Therefore, oil spreads on water surface in contact with CO2, which leads to more CO2 diffusion into oil that results in higher oil recovery.

Enhanced oil recovery, Iranian carbonate reservoir, carbonated water, core flood, Modified CO2I, Spreading coefficient