Quantifying Bypassed Oil in the Vicinity of Discontinuous Shales During GravityDominated Flow

摘要

Gravity-stable, miscible gas injection is a common oilrnrecovery technique throughout the world. In homogeneousrnenvironments recovery efficiencies may be more than 90%.rnHowever the influence of heterogeneity on the sweeprnefficiency in these recovery schemes is not well understood.rnFor example most clastic reservoirs contain 'discontinuous'rnshales that cannot be correlated between wells. Severalrnnumerical studies have suggested that these may causernsignificant bypassing of oil during waterflooding or gasrninjection. However flow experiments and detailed simulationrnof viscous dominated displacements, without gravity, indicaternthat very little oil is bypassed1.rnIn this paper, we investigate flow patterns aroundrndiscontinuous shales during vertical, gravity-influencedrnmiscible gas injection in well-characterised bead-packrnexperiments at three flow-rates corresponding to unstable,rnpartly stable and completely stable flow regimes. We examinernthe volume of oil bypassed and whether viscous fingering isrnreduced by gravity or altered by the presence of arndiscontinuous shale. The results are compared to thernpredictions of detailed simulation. We find that, duringrnmiscible displacements, an isolated shale causes negligiblernbypassing. However, during adverse mobility ratiorndisplacements, the simulation program erroneously predictsrnsignificant bypassing of oil both upstream and downstream ofrnthe shale at high and intermediate flow-rates.