A Laboratory Investigation of Miscible Displacement by Carbon Dioxide

Displacements of reconstituted reservoir fluids in Boise outcrop sandstone cores of 6 to 42.5 ft in length using COD2U at various pressures were conducted. The studies indicate that a miscible displacement may be achieved by COD2U injection at pressures well below those necessary when methane is the injection fluid. Miscibility by COD2U is generated through multiple contact equilibria in which the COD2U is progressively enriched with intermediates (ethane through hexane) from the oil. The miscibility pressure for COD2U and a given reservoir fluid is difficult to determine, because COD2U exhibits highly efficient swelling and vaporization of the oil. Also it was found to be impractical to operate below the rates where differences in density between displaced and displacing fluids prevent viscous fingering in vertical cores. The miscibility pressure was defined using the anticipated increasing recovery as a function of core length in miscible displacements in combination with effluent fluid visual cell observations and chromatographic data. (23 refs.)