Abstract
An experimental investigation is presented of immiscible, high-mobility ratio forced imbibition in a representative linear homogeneous sandstone. Water floods with mobility ratios (from 1 to 155) at various water injection rates were conducted. Fine-scale (order mm3) in situ water saturation history was collected via X-ray computed tomography (CT). Three-dimensional images were constructed of stable displacement and the initiation and growth of unstable water fingers. Interestingly, viscous fingers do not lead the displacement front by significant distances, counter to experience in miscible systems. In this homogeneous porous medium, both water (displacing phase) injection rate and oil (displaced phase) viscosity have an obvious effect on the stability of the water front. As the oil viscosity and displacement rate increase, the water front becomes less stable. In addition, the so-called shock mobility ratio, as computed from steady-state relative permeability, is found to be predictive regarding displacement front stability. When the shock mobility ratio is greater than 1, the displacement is always unstable. Steady-state relative permeability, however, is found to be a function of viscosity ratio for unstable displacements.
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Abbreviations
- A :
-
Cross-sectional area
- CT:
-
CT number, a measure of X-ray attenuation
- f :
-
Fractional flow of a phase
- k :
-
Absolute permeability
- k r :
-
Relative permeability
- L :
-
Length of core, characteristic length
- M :
-
Mobility ratio
- N RL :
-
Rappoport and Leas number
- OOIP:
-
Original oil in place
- PVI:
-
Dimensionless time, pore volumes injected
- S :
-
Phase saturation, fraction of void space filled by a phase
- t :
-
Time
- u :
-
Superficial, Darcy, velocity
- \({\phi}\) :
-
Void fraction or porosity
- λ :
-
Phase mobility
- μ :
-
Phase viscosity
- σ ow :
-
Oil–water interfacial tension
- θ :
-
Contact angle on a flat surface
- a:
-
Air
- ar:
-
CT image of air-filled rock
- w:
-
Wetting phase (water)
- wr:
-
CT image of water-filled rock
- o:
-
Nonwetting phase (oil)
- o:
-
Denotes endpoint
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Tang, GQ., Kovscek, A.R. High Resolution Imaging of Unstable, Forced Imbibition in Berea Sandstone. Transp Porous Med 86, 617–634 (2011). https://doi.org/10.1007/s11242-010-9643-3
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DOI: https://doi.org/10.1007/s11242-010-9643-3