Scale-up of miscible flood processes for heterogeneous reservoirs. Quarterly report, 1 January--31 March 1994

Abstract

The current project is a systematic research effort aimed at quantifying relationships between process mechanisms that can lead to improved recovery from gas injection processes performed in heterogeneous Class 1 and Class 2 reservoirs. It will provide a rational basis for the design of displacement processes that take advantage of crossflow due to capillary, gravity and viscous forces to offset partially the adverse effects of heterogeneity. In effect, the high permeability zones are used to deliver fluid by crossflow to zones that would otherwise be flooded only very slowly. Thus, the research effort is divided into five areas: Development of miscibility in multicomponent systems; design estimates for nearly miscible displacements; design of miscible floods for fractured reservoirs; compositional flow visualization experiments; simulation of near-miscible flow in heterogeneous systems. The status of the research effort in each area is reviewed briefly in the following section. From this work, we can make the following conclusions: (1) We demonstrated theoretically and experimentally that a linear combination of gravity and viscous forces can be used to correlate residual nonwetting phase saturations for both gravity-favorable and gravity-unfavorable displacements. (2) When gravity forces are comparable to or larger than the viscous forces) gravity unfavorable displacements have significantly higher residual nonwetting phase saturation than gravity-favorable displacements. (3) Because soils have much higher permeabilities than oil reservoirs, gravity effects on residual nonwetting phase saturations are much more significant in spilled-oil clean-up than in oil recovery processes. (4) The effective correlation length for a percolation process can be related to a linear combination of the gravity and viscous forces.