Possibility of improving oil recovery by a polymer gelation method using CAG (CO_2-Water alternating gelant injection process)

摘要

Experimental studies were carried out forinvestigating the applicability of the CO_2-Water Alternating Gelant Injection Process (CAG) which was proposed by the author to improve oil recovery. First flood experiments were conducted with linear glass-bead-packed cores. The oil-saturated cores were firstly flooded by water, and later flooded by alternating slug injection of CO_2 water and gelant (CAG). The oil recovery increased after waterflood by 12.1% for the high permeability core and by 24.2% for the low permeability one. The increase in in-situ fluid viscosity with gelation during CAG has improved oil displacement efficiency through mobility-control effect and led to these incremental oil recoveries. Second flood experiments were conducted with two linear glass-bead-packed cores of different permeabilities mounted in parallel. The oil-saturated cores were simultaneously flooded by 3.0PV of water, 1.4PV of CAG and 1.6PV of water in sequence. Experimental results showed that 29.1% of incremental oil recovery was obtained by CAG and succeeding waterflood, and its effect of iimproving oil recovery was much larger than polymer flood. The increase in oil recovery by CAG was caused by following mechanisms: (1) The increase in in-situ fluid viscosity with gelation improved oil displacement efficiency in the high permeability core. (2) Water effectively swept the oil in the low permeability core after the gel plugged the high permeability core. Especially the second effect of improving sweep efficiency by permeability profile modification was found to be large.