Physicochemical Characterization of Produced Oils and Gases in Immiscible and Miscible CO2 Flooding Processes

In this paper, the oil and gas samples produced from tight sandstone reservoir core plugs in immiscible, near-miscible, and miscible CO 2 flooding processes at the reservoir temperature are experimentally characterized. First, the vanishing interfacial tension (VIT) technique is applied to determine the minimum miscibility pressure (MMP) of the light crude oil–CO 2 system. Second, a total of five CO 2 -coreflood tests are conducted under immiscible, near-miscible, and miscible conditions to thoroughly study the characteristics of the produced oils and gases during each CO 2 flooding process. In the immiscible case ( P inj < MMP), the produced oil becomes heavier and heavier during CO 2 injection in terms of its density, viscosity, molecular weight, and hydrocarbons (HCs). The produced gas contains up to 84–96 mol % HCs (dominantly C 4–7 ) extracted from the light crude oil by CO 2 at the beginning and 85–100 mol % CO 2 at the end of CO 2 injection. In the near-miscible case ( P inj ≈ MMP), the heaviest oil is produced at 0.4 pore volume (PV) of the injected CO 2, which is followed by a relatively lighter produced oil from CO 2 breakthrough (BT) at 0.6 PV to the end of CO 2 injection. The produced gas has 40–60 mol % HCs (dominantly C 5–8 ) at the beginning and then consists of almost 100% CO 2 after CO 2 BT. In the miscible case ( P inj > MMP), the produced oil becomes much lighter and lighter with the injected PV. The produced gas contains 20–75 mol % HCs (mainly C 5–8 ) at the very beginning and quickly becomes almost 100% CO 2 after CO 2 BT. In summary, this laboratory study provides the comprehensive characterization of the produced fluids in three distinct CO 2 flooding processes. These new experimental data will help to better evaluate the field-scale CO 2 -enhanced oil recovery (EOR) processes and design the future CO 2 -EOR projects as well.