Abstract
Oil recovery prediction and field pilot implements require basic understanding and estimation of displacement efficiency. Corefloods and glass micromodels are two of the commonly used experimental methods to achieve this. In this paper, waterflood recovery is investigated using layered etched glass micromodel and Berea sandstone core plugs with large permeability contrasts. This study focuses mainly on the effect of permeability (heterogeneity) in stratified porous media with no cross-flow. Three experimental setups were designed to represent uniformly stratified oil reservoir with vertical discontinuity in permeability. Waterflood recovery to residual oil saturation (Sor) is measured through glass micromodel (to aid visual observation), linear coreflood, and forced drainage-imbibition processes by ultracentrifuge. Six oil samples of low-to-medium viscosity and porous media of widely different permeability (darcy and millidarcy ranges) were chosen for the study. The results showed that waterflood displacement efficiencies are consistent in both permeability ranges, namely, glass micromodel and Berea sandstone core plugs. Interestingly, the experimental results show that the low permeability zones resulted in higher ultimate oil recovery compared to high permeability zones. At Sor microheterogeneity and fingering are attributed for this phenomenon. In light of the findings, conformance control is discussed for better sweep efficiency. This paper may be of help to field operators to gain more insight into microheterogeneity and fingering phenomena and their impact on waterflood recovery estimation.
Highlights
Waterflooding is still the most economically advantageous, secondary oil recovery method
Results include the effect of reservoir permeability on waterflood displacement efficiency using three sets of experiments, the 2D glass micromodel, the linear flow through coreflooding experiments, and displacement by centrifugal force using ultracentrifuge device, covering both steady state and unsteady state displacements
Irrespective of the differences in oil viscosities, the ultimate oil recovery is always higher for the low permeability layer followed by the medium permeability layer and the least recovery is achieved in the high permeability layer
Summary
Waterflooding is still the most economically advantageous, secondary oil recovery method. The efficiency and sustainability of a waterflood project is numerically assessed by the recovery efficiency, represented as the product of the displacement sweep efficiency by volumetric sweep efficiency of flooding water. It is defined as [1]. Where RE is the recovery efficiency; ED is the displacement sweep efficiency, which is the fraction of oil displaced from a contacted volume of reservoir. EV is the volumetric sweep efficiency, which represents the fraction of the reservoir pore volume contacted by the injected water at a given time. EI is the fraction of vertical cross-sectional area of the reservoir between injector and producer wells which is swept by water at a given time. The vertical sweep efficiency depends heavily on heterogeneity of the reservoir rock [2]
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