Reservoir

Doctrines vs. Realities in Reservoir Engineering

The appreciation of empirical realities permits the improvement of commercial depletion planning and enables a greater number of projects. This paper reviews the evidence for and against three doctrines in current use to develop depletion plans.

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The appreciation of empirical realities permits the improvement of commercial depletion planning and enables a greater number of projects. The concepts articulated here are applicable in almost all heavy-oil reservoirs and may be applicable also for lighter oils that possess oil chemistry typical of heavier oils (e.g., high acid content). This paper reviews the evidence for and against three doctrines in current use to develop depletion plans: (1) optimal recovery is obtained using a voidage-replacement ratio (VRR) of unity, (2) the Buckley-Leverett (BL) formulation (phase slippage) applies uniformly to heavier oils, and (3) viscous fingering dominates unstable multiphase flows.

VRR=1

  • Doctrine: Optimal Waterflood Response Occurs With VRR=1
  • Reality: Periods of VRR<1 Increase Oil Recovery

Though initially viewed with some suspicion, waterflooding has demonstrated multifold greater recovery than primary depletion for many reservoirs. It is, by far, the most important oil-recovery process. One visualization of the process is that of a leaky, deformable water piston displacing a fraction of the oil to the production wells.

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