The model of and predicts the extent of gravity override at steady state during gas-liquid co-injection in an enhanced oil recovery (EOR) process. The model is accurate for WAG injection if the slug sizes are sufficiently small. The model is exact for homogeneous reservoirs if the standard assumptions of fractional-flow theory apply ( ). Stone and Jenkins relate the distance to complete gravity segregation to total mobility in the mixed zone and the thickness of the override zone beyond this point to mobilities in the override and underride zones.

and have proposed extensions to Stone and Jenkins’ model for dipping reservoirs. The accuracy of these correlations were tested in this study for a wide range of conditions and angle of reservoir dip using 2D computer simulations. Both correlations are approximately correct, but deviate from observed behaviour at large dip angle. Specifically, gravity override occurs at shorter distances than predicted by Namani et al. for up-dip injection, but longer distances for down-dip injection at moderate dip angles. Jamshidnezhad’s correlation works reasonably well for down-dip injection except at large dip angles, for which segregation occurs at much shorter distances than predicted. Much of the sweep of gas occurs not at steady-state, however, but during the transient period before steady state is attained. During the period of three-phase flow, mobilities are lower; as suggested by Stone’s approach, this temporarily extends the mixed zone beyond that at steady state. In up-dip injection, the override zone is extended much deeper into the reservoir during the period when gas first enters than at steady state. The oil swept during this period can greatly exceed that represented in the mixed zone in any of these models: even though the mixed zone is reduced, overall sweep can be greatly increased by this effect. This extension of the override zone during transient flow follows the logic of Jenkins’ derivation of the thickness of the override zone based on mobilities.

Unfortunately, there is no single exact equation for gravity segregation in dipping reservoirs as for horizontal reservoirs, even at steady state. Therefore behaviour varies somewhat from case to case.


Article metrics loading...

Loading full text...

Full text loading...


  1. Jamshidnezhad, M.
    (2009). Gravity Segregation in Gas Improved Oil Recovery of Tilted Reservoirs. Society of Petroleum Engineers. doi:10.2118/119996‑MS
    https://doi.org/10.2118/119996-MS [Google Scholar]
  2. Jenkins, M. K.
    (1984). An Analytical Model for Water/Gas Miscible Displacements. Society of Petroleum Engineers. doi:10.2118/12632‑MS
    https://doi.org/10.2118/12632-MS [Google Scholar]
  3. Lake, L. W., Johns, R. T., W. R.Rossen and Pope, G. A.
    , Fundamentals of Enhanced Oil Recovery, Society of Petroleum Engineers, Richardson, TX, ISBN:978-1-61399-328-6, 2014.
    [Google Scholar]
  4. Namani, M., Hoier, L., & Kleppe, J.
    (2013). Advantages of Up-Dip Water-Miscible Gas Injection. Society of Petroleum Engineers. doi:10.2118/164836‑MS.
    https://doi.org/10.2118/164836-MS [Google Scholar]
  5. Namani, M., Kleppe, J., HØier, L., Karimaie, H., and Ole Torsæter, O.
    (2012) Analytical Model for Zones Distribution in Non-Horizontal Miscible WAG Injection. Energy and Environment Research2, 159–168.
    [Google Scholar]
  6. Rossen, W.R., and van Duijn, C.J.
    . (2004) Gravity Segregation in Steady-State Horizontal Flow in Homogeneous Reservoirs. J. Petr. Sci. Eng. 43, 99–111.
    [Google Scholar]
  7. Stone, H. L.
    (1982). Vertical Conformance In An Alternating Water-Miscible Gas Flood. Society of Petroleum Engineers. doi:10.2118/11130‑MS
    https://doi.org/10.2118/11130-MS [Google Scholar]
  8. Yu, G.
    , “Analytical and Simulation study of Sweep Efficiency in Gas-Injection EOR,” MSc thesis, Delft University of Technology, 2015. Available at http://repository.tudelft.nl/search/ir/?q=&faculty=&department=&type=dissertation&year.
    [Google Scholar]

Data & Media loading...

This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error