Comparing Compositional and Black Oil Models in Simulating Miscible C O2 Injection

The miscible displacement in CO2 injection is a process where the oil in the reservoir
completely mixes with the injected CO2. To see and understand the process of the
CO2 miscible injection, the simulator is the essential tool for engineering design.
Normally, a compositional simulator is used for a detailed simulation by solving the
equation of states for fluids and calculating the partitioning fluid between phases.
However, the method is time consuming that the Black Oil Model would take a
greater advantage as a simpler method for simulation.
In this study, the simulation of Black Oil Model for CO2 Miscible Injection using the
Water Alternating Gas Injection Technique, was carried out to investigate its ability
and accuracy compared with the compositional simulator with the range of models
and scenarios. All reservoir characteristics were kept constant in order to pay an
attention on the PVT Properties of the fluids in the Black Oil and Peng-Robinson
fluid characterization in Compositional Simulator. Schlumberger ECLIPSE 100 and
ECLIPSE 300 were the main tools used for comparing the two simulations.
It is found that the Black Oil simulator is capable to predict the similar trends of Oil
Recovery Factor, Total Oil Production and Reservoir Pressure to the Compositional
Simulator in certain cases, however, there are the obvious differences in values
between two simulators depending on the reservoir models and WAG scenarios
examined. The gas injection rate is found to be an important parameter in
determining the accuracy of Black Oil comparing to Compositional simulators.
In agreement with other studies, Black Oil simulator is found to have 6.45 speed up
factor comparing to the Compositional simulator.
Keywords: Miscible CO2 WAG Injection, Black Oil Model, Compositional Model