Polymer Injection as a Possible EOR Method for a Fractured Granite Basement Reservoir in the Cuu Long Basin, Vietnam

During the last 25 years more than 85% of Vietnam oil production have come from the fractured granite basement (FGB) reservoirs in the Cuu Long basin, located in the southern offshore of Vietnam. Among all the discovered oil fields the White Tiger is the biggest one that was discovered in 1974 and put on production in 1986. Since then, approximately more than 200 million tons of oil, has been produced from this field, whose life has started the declining phase since 2002, and because of this enhanced oil recovery (EOR) needs to be considered, including polymer injection to enhance sweep and displacement efficiency of water flooding in fractured reservoirs. In this paper, results of a comprehensive study including polymer testing, core injection and numerical simulation by ECLIPSE with different polymer injection for a model of fractured granite basement reservoir of the White Tiger field are presented. For a locally available biochemical polymer two properties, i.e., heat resistance and screen factor, were tested a high range of temperature of 130oC to 150oC typical for the deep fractured basement of the White Tiger field. The results of the polymer injection and EOR tests on the core samples in the laboratory showed that for the White Tiger basement conditions EOR using the existing biochemical polymers can reach only 4% of in-place oil reserves, whereas this number is normally 8% in the world. Reservoir simulations by ECLIPSE were done to evaluate the effect of polymer flooding into the fractured basement of the White Tiger field and the obtained results showed that polymer injection could give good sweep efficiency and a considerably more amount of oil can be expected from the injection of polymer comparing to an injection of water alone.