Multiple-Contact Phase Behavior Measurement and Application With Mixtures of CO2 and Highly Asphaltic Crude

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Abstract
Summary: This paper is an experimental study of the phase behavior relevant to CO2 flooding for multiple-contact miscible, immiscible, or huff 'n' puff applications. Unique features of this investigation are that the live reservoir oil was highly asphaltic and was modified to resemble the composition likely contacted by injected CO2. Single-contact and two types of multiple-contact PVT data are presented, and the usefulness of such data in predicting CO2 flood performance is discussed. The results show no liquid/liquid/vapor (L/L/V) three-phase region at higher temperatures and no liquid/liquid (L/L) critical point. Large CO2 concentrations were required before substantial hydrocarbon extraction occurred. A ternary diagram representation of forward multiple-contact compositional results indicates that CO2 generated miscibility with the oil by the vaporization mechanism. Precipitation of a tar-like, highly aromatic solid was associated with the development of miscibility. This solid phase represented approximately 20 wt% of the stock-tank-oil hydrocarbon. The swept-zone multiple-contact results show a cumulative liquid volume production of about 35% of the original oil in place (OOIP) after the second CO2 contact, with further contacts recovering essentially no additional oil. The residual oil was composed of heavy, aromatic hydrocarbon.