Focus: Video—Physics of Oil Recovery

Physics 10, 125
Experiments mimicking a common oil drilling technique, in which fluid is forced into an oil-filled, porous medium, have uncovered four different flow patterns.
C. Odier et al., Phys. Rev. Lett. (2017)
Forced out. Water is forced into a square array of channels from the left, displacing silicone oil. At this intermediate flow rate (regime C), the water forms a multi-branched pattern.

To increase the yield of an oil well, companies sometimes send pressurized liquid underground to flush the remaining oil out of the pores in the rock (this is different from “fracking,” which opens up new spaces in the rock). French researchers have now observed an idealized version of this process in a square array of fluid channels and found four distinct patterns of the flow, depending on the flow rate. The team explains the four regimes by analyzing the small-scale interactions between the fluids and the solid surfaces. The results will help oil engineers optimize the oil recovery process.

C. Odier et al., Phys. Rev. Lett. (2017)
In an experiment mimicking an oil extraction technique, water flows left to right, displacing oil in an array of 80-micrometer-wide channels. Depending on the water’s enforced flow rate, four different patterns appear. The color indicates the local water thickness, with yellow indicating the maximum (channel completely filled with water) and deep red indicating that water occupies only a small volume of the channel (the rest taken up by an oil residue). The flow rates are quantified with the dimensionless number Ca, the capillary number.

The French oil company Total wanted to better understand their so-called enhanced oil recovery process, so they partnered with physicist Denis Bartolo of the École Normale Supérieure in Lyon, France, and his colleagues. To study the process, the team filled a two-dimensional array of 80-micrometer-wide channels with silicone oil and then forced water, which contained a dye, through the structure. As they varied the flow rate over a range that corresponds to flow rates in real oil wells, their video recordings showed clear transitions among four different types of flow.

At the lowest flow rates (regime A), water fully fills the channels and maintains a single, compact domain. As the flow rate increases (regimes B, C, and D), the pattern takes various forms due to changes in the water/oil interface. In B, oil is not completely swept out of the channels, leaving droplets along walls and especially at channel intersections. In C, at higher flow rates, these blobs coalesce, just as the drops from a dripping faucet merge into a stream when the flow is increased. The researchers conclude that for optimal, cost-effective oil extraction, engineers face a trade-off: the highest flow rates extract the most oil, but the oil volume extracted per unit of injected water decreases with increasing flow rate.

This research is published in Physical Review Letters.

–David Ehrenstein

David Ehrenstein is the Focus Editor for Physics.

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Fluid Dynamics

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