Sweep Efficiency

Part 11, Chapter 11: Wells, Recovery, and Displacement

Displacement Efficiency and Sweep Efficiency

Why can we never recover all the oil? Total recovery is the product of efficiencies. Displacement (microscopic) efficiency is how much oil the water removes from the pores it actually contacts; it is capped because some oil is trapped as immobile residual oil SorS_{or} behind the front. Sweep (macroscopic) efficiency is the fraction of the reservoir the water actually contacts, split into areal sweep in plan view and vertical sweep in cross-section. The recovery factor is their product, areal times vertical times displacement, so the weakest of the three caps the result.

Sweep efficiencyoriginal oil in place100%x areal sweep 70%70%x vertical sweep 60%42%x displacement 56%24%Recovery factor = 70% x 60% x 56% = 24%. The efficiencies multiply, so the result is smaller than any one of them and the weakest link caps it.

Why Patterns Matter

This is why patterns matter. Injectors and producers are laid out in repeating patterns, the five-spot (a producer ringed by four injectors) being the classic, to push the swept area as high as possible. The one dimensional picture in the simulator captures the displacement physics; a real flood layers areal and vertical sweep on top of it, which later chapters model on the full three dimensional grid.

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