Sweep Efficiency Estimates for Reservoirs with Nonuniform Layers
- A.N. Araque-Martinez (Maraven) | L.W. Lake (The University of Texas)
- Document ID
- Society of Petroleum Engineers
- SPE Latin America/Caribbean Petroleum Engineering Conference, 27-29 April, Buenos Aires, Argentina
- Publication Date
- Document Type
- Conference Paper
- 1994. Society of Petroleum Engineers
- 5.4.9 Miscible Methods, 5.4.7 Chemical Flooding Methods (e.g., Polymer, Solvent, Nitrogen, Immiscible CO2, Surfactant, Vapex), 4.3.4 Scale, 5.5 Reservoir Simulation, 5.3.1 Flow in Porous Media, 5.7.2 Recovery Factors
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We study a new vertical sweep efficiency correlation for reservoirs with non-uniform layers and compare the effect of permeability autocorrelation on these estimates. Vertical sweep efficiency correlations are important because, in spite of sophisticated numerical simulators now available, there still remains a need for rapid estimates of oil recovery. The vertical sweep efficiencies are calculated using the chemical flooding simulator UTCHEM for a two-dimensional vertical cross-section with one injector and one producer, both also vertical.
As measures of heterogeneity we use the Dykstra-Parsons coefficient (VDP) in the case of a strictly layered reservoir and the Gelhar-Axness coefficient (HI) in the case of a nonlayered reservoir. We validate a strictly layered case and predict the vertical sweep efficiency in cases with nonuniform layers. We show that for mobility ratios greater than one, the effluent concentration of the injected fluid (in this case, polymer) oscillates because of viscous instability.
For unlayered cross sections, we show that the Gelhar Axness coefficient is a better vertical sweep efficiency estimator than the Dykstra-Parsons coefficient, because it accounts for spatial correlation (autocorrelation) as well as for heterogeneity. The vertical sweep efficiency decreases as we increase HI for the same VDP.
Oil recovery calculations for miscible or immiscible displacements have been the subject of extensive research that attempts to account for the effects of mobility ratio, heterogeneity, layering and movable water saturation. These calculations frequently involve estimations of areal sweep as well as vertical sweep efficiency. Most of the works referring to areal sweep have been carried out in single-layer symmetry elements of a uniform pattern where viscous forces are the dominant fluid flow mechanism.1-3
For layered reservoirs. Dykstra and Parsons4 defined a permeability variation coefficient as a measure of heterogeneity and used it to explain their experimental work. Each experiment was controlled by different initial saturations, oil-water viscosity. flow rate, permeability and permeability variation. The vertical sweep efficiency results were correlated as a function of mobility ratio. water-oil ratio and permeability variation. The resulting method assumes a strictly layered reservoir with no gravity and no capillary effects. It also assumes a piston-like displacement and a mobility ratio that is identical in all the layers.
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