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 CO2 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–CO2 system. Second, a total of five CO2-coreflood tests are conducted under immiscible, near-miscible, and miscible conditions to thoroughly study the characteristics of the produced oils and gases during each CO2 flooding process. In the immiscible case (Pinj < MMP), the produced oil becomes heavier and heavier during CO2 injection in terms of its density, viscosity, molecular weight, and hydrocarbons (HCs). The produced gas contains up to 84–96 mol % HCs (dominantly C4–7) extracted from the light crude oil by CO2 at the beginning and 85–100 mol % CO2 at the end of CO2 injection. In the near-miscible case (Pinj ≈ MMP), the heaviest oil is produced a...