A SIMULATION STUDY OF MISCIBLE AND IMMISCIBLE CO2 WAG INJECTION

As reservoir pressure continues to deplete leaving substantial unrecovered oil in the
reservoir after secondary recovery, various enhanced oil recovery methods need to be
evaluated to produce additional drive to increase the recovery factor of reservoir oil,
among which is the water alternating gas (WAG) injection method. Choice has to be
made whether to perform miscible or immiscible displacement, depending on
reservoir conditions, incremental recovery, and cost-benefit analysis. In this project,
several factors affecting miscible and immiscible displacement performance are
reviewed, such as volumetric sweep efficiency and unit displacement efficiency. CO2
gas is chosen to be the subject of research because of its favorable properties and
behavior for miscible flooding, and its abundance in Malaysia (Samsudin, et al.,
2005). This project focuses on studying the potential ways to achieve CO2 miscibility
with reservoir oil via increasing reservoir pressure via water flooding, or decreasing
reservoir temperature via coolant flooding, by using a compositional model simulator
with thermal option. Simulation results show that lowering reservoir temperature
allows CO2 to extract more heavy components from the oil phase, which increases
oil recovery factor. This can be done by injecting cold water and/or cold CO2 itself.
However, if CO2 temperature drops below its critical temperature, it condenses into
liquid phase with extremely high viscosity, therefore it may take a longer time to
cool down regions further away from the injector.