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Enhanced Oil Recovery: What You Need to Know


This week, the crude oil market is continuing to dip, dive, bounce and then dip and dive again. I thought it would be a good time to look into some of the technologies that we expect drillers to focus on while the volatility levels out.

Enhanced Oil Recovery (EOR) is one such technique that a few players have been using to great advantage in recent years, and that we expect will become more common in the near-term future.

What is Enhanced Oil Recovery?

In a conventional reservoir drilled with conventional methods, the expected initial extraction rate of available hydrocarbons maybe as much as 15% – leaving 85+% of hydrocarbons in the reservoir. Pump jacks and initial gas injection or thermal recovery can increase that capture to the 25-30% range. By applying EOR techniques you can extract another 10-15% of the initially available hydrocarbons.

Enhanced Oil Recovery Theory

How do we encourage these additional hydrocarbons to flow through to the well head? There are two major ways:

Increase Pressure

EOR is sometimes referred to as “water-flooding” in a nod to this technique, where large quantities of liquid (or gas) are pumped into the formation in order to encourage the release and migration of hydrocarbons towards the producing well.

Increase Permeability

To increase permeability we treat the reservoir in such a way as to widen the pathways, so that the hydrocarbons will have an easier time flowing through the reservoir and into the target producing well. Hydraulic Fracturing is an example of a technique that increases permeability, although for EOR there are a number of other methods including adding heat, solvents, and other chemical treatments.
EOR figure 1 enhanced oil recovery
Of course as with most oil field innovation, nowadays we do a little of both in most cases, and in fact almost always add something to decrease viscosity as well – by adding heat or surfactants into the equation.

Wait what? Producing well?

The typical method for EOR is to send your liquid or gas or stimulant through some designated wells – injection wells, or “flooders” – and use that pressure to drive hydrocarbons to designated wells for production. The image to the right shows an injection well and a recovery well. In practice there is likely to be an array of injection wells.
Image Source: Wikipedia

Ok so Flooding…

I am not an engineer by training, although I find reservoir engineering to be very interesting. This discussion of techniques is very high-level, and is not designed to take into account the reality of heterogenous rock structures and the myriad of considerations like hydrocarbon gravity, temperature, and pressure that exist underground. For further exploration of those details, is a great resource.

When the “five-spot” waterfloods (so named because the layout of four injection wells around 1 recovery well resembled the 5 spot side of a gaming die) were originally practiced in the 1920s, excess saline water or brine produced from the drilling operation was used for injection, but over time a variety of other substances have been introduced.

  • Water floods – H2O is generally available in quantity and inexpensive, but most effective if treated to be compatible with the existing reservoir’s “connate” water, and can damage the existing rock. Waterflooding has been practiced since the 1920s.
  • Steam floods – Thermal injection can provide even more recovery boost as well as make the hydrocarbons less viscous (eg; makes them flow more easily).
  • Miscible floods – One of the most common types of EOR is Miscible Flooding, where you use water to balance out the voided pressure within the reservoir and then flood gas, normally CO2 or Nitrogen, into the reservoir. The solvent properties of the gas encourage more oil recovery. As a side benefit, injecting CO2 into these reservoirs effectively helps remove it from the atmosphere.

EOR figure 2 enhanced oil recovery
Image Source:

  • Flooding with hydrocarbons – Some reservoirs have been flooded with hydrocarbons – methane or diesel for example – with strong results.
  • Additional solvents and surfactants – Very rarely is one technique used to the exclusion of all others, and in many cases additional chemicals are incorporated into the flood to aid in recovery, notably by reducing viscosity or surface tension and further easing the flow of the hydrocarbons.

Other techniques

Operators aren’t restricting their Enhanced Oil Recovery strategies to these methods, of course.

  • Stacked fracking– operators in areas with lots of different hydrocarbon bearing formations – like the Permian Basin – have experimented with fracking vertical wells. This allows them to get additional recovery from the tight “source” rock zones while still focusing their primary effort (and economies) on the reservoir rock within the play area.
  • Acid – Using Hydrochloric (HCl) or hydrofluoric (HF) acid is an effective means of increasing the permeability in certain rock structures.

But you don’t have to take my word for it

Occidental has been a leader in CO2 flooding in the Permian Basin for a number of years, and a number of other big names are involved in Permian EOR.

EOR Picture 3 enhanced oil recovery

In conclusion

Enhanced Oil Recovery is a toolbox for getting more producibility from reservoirs that you are already invested in, and as such provides an efficient lower-cost method of E&P that we expect to be hearing a lot more about in the coming months.

Your Turn

What do you think? Have you seen additional EOR practices in the field? What other oilfield techniques are likely to become more prominent in a lower-priced crude oil market? Leave a comment below.

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Eric Roach

Eric Roach is the editor of Drillinginfo's blog, which was selected as the Top Oil & Gas Industry Blog based on visibility, engagement and relevance. He also prepares a weekly newsletter of top industry news for blog subscribers, and would be grateful if you would subscribe and tell your friends. (There's a box on the upper right of the page where you can subscribe).