1887

Abstract

Summary

In conventional waterflooding of low to intermediate net to gross reservoirs there is always some oil unswept even in the sands connected to both injection and production wells. This is oil trapped in “dangling ends”: flow units only poorly connected to the main flow path. In many cases the unswept volumes can be very large, depending on the properties of the reservoir and fluids and the well locations.

In this paper we show how percolation theory can be used to estimate the volumes of oil recovered and those left behind in these dangling ends following a conventional waterflood, without recourse to large scale simulation. Percolation theory is a general mathematical framework for connectivity and has been used previously to investigate the connectivity of flow units. The structure of these connected clusters in terms of backbones and dangling ends has not been previously studied. The results are also used to estimate the recovery of the unswept oil from dangling ends by a waterflood with a voidage replacement ratio <1.

We use a simple model of stochastically-distributed sandbodies to describe the reservoir. Many realizations for a range of net to gross ratio values and sandbody:system sizes were generated. In each realization the clusters connecting the injection and production wells were identified. These spanning clusters were subdivided into backbones and dangling ends. The volume fractions of the backbone and dangling end were then obtained. The statistical average and standard deviation of the volumes association with these clusters were obtained from the ensemble of realisations. These were used to determine the percolation scaling relationships in terms of simple algebraic formulae that cover the whole range of net to gross ratio and system sizes.

Our results show that the fraction of dangling ends can reach 20% of the clusters, and 80% among the spanning clusters, indicating a major proportion of the oil would be unswept by conventional waterflood. Recovery is improved for voidage replacement ratios less than 1 when the dangling ends are drained by oil expansion and solution gas drive.

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/content/papers/10.3997/2214-4609.20141821
2014-09-08
2024-03-28
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References

  1. King, P.R.
    , The conductivity and connectivity of overlapping sandbodies. North Sea Oil and Gas Reservoirs II, Graham and Trotman, London (1990) 21: 353–362
    [Google Scholar]
  2. Masihi, M., King, P.R., and Nurafza, P.R.
    [2005] Fast estimation of performance parameters in fractured reservoirs using percolation theory. SPE Europec/EAGE Annual Conference, 13–16 June, Madrid, Spain (SPE-94186-MS)
    [Google Scholar]
  3. Mayall, M., Jones, E., and Casey, M.
    [2006] Turbidite channel reservoirs—Key elements in facies prediction and effective development. Marine and Petroleum Geology, 23(8), 821–841
    [Google Scholar]
  4. Nurafza, P.R., King, P.R., and Masihi, M.
    [2006] Facies Connectivity Modelling: Analysis and Field Study. SPE Europec/EAGE Annual Conference and Exhibition, 12–15 June, Vienna, Austria (SPE-100333-MS)
    [Google Scholar]
  5. StaufferD., AharonyA.
    , [1994] Introduction to Percolation Theory. CRC Press
    [Google Scholar]
  6. Vittoratos, E.S. and West, C.C.
    [2010] Optimal Heavy Oil Waterflood Management May Differ From that of Light Oils. SPE EOR Conference at Oil & Gas West Asia, 11–13 April, Muscat, Oman (SPE-129545-MS)
    [Google Scholar]
  7. Vittoratos, E.S., Coates, R.M., and West, C.C.
    [2011] Optimal Voidage Replacement Ratio for Communicating Heavy Oil Waterflood Wells. SPE Heavy Oil Conference and Exhibition, 12–14 December, Kuwait City, Kuwait (SPE-150576-MS)
    [Google Scholar]
  8. West, C.C. and Vittoratos, E.S.
    [2010] VRR < 1 Is Optimal for Heavy Oil Waterfloods. SPE Offshore Europe Oil and Gas Conference and Exhibition, 3–6 September, Aberdeen, UK (SPE-166609-MS)
    [Google Scholar]
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