Why We Use Ozone

I'm often asked why we use ozone instead of other oxidizers and really the answer is simple. Ozone is a stronger oxidizer, can be generated onsite for lower cost and lower carbon footprint and has improved compatibility over other oxidizers. I'll briefly go into each of these key areas.

Oxidizer Strength and Residual

Ozone as you can see is a stronger oxidizer than some of the common oxidizers used in the oilfield, including Hydrogen Peroxide, Chlorine Dioxide and Sodium Hypochlorite, but the difference is you have no more liquid chemical storage, no more trucking chemical tote after chemical tote to location and as a result a much smaller carbon footprint.

Then there's the issue of residual. I keep hearing this and scratching my head. In a frac reuse environment you are taking your treated water and adding proppant and friction reducer (FR). Most FRs have organic based chemistries and as a result get oxidized. The idea of having residual oxidation in this environment is synonymous with compatibility problem. If you have too much residual oxidizer you will degrade your FR. Weaker oxidizers like Sodium Hypochlorite are less likely to degrade FR, but stronger oxidizers like Hydrogen Peroxide and Chlorine Dioxide will. Why didn't I mention Ozone ? Well it has to do with half life, Ozone degrades quickly into Oxygen and Hydroxyl Radicals, another strong oxidizer. In other applications ozone is criticized because it degrades so quickly and doesn't have long residual, but in the frac recycling this is exactly the opposite of what you need.

When people were using Chlorine Dioxide a few years ago the issue of compatibility was a concern and as a result the concept of reducing Chlorine Dioxide concentration with the addition of a non-oxidizing biocide, typically DDAC because it is compatible with oxidizers, was introduced. This process was presented as Chlorine Dioxide with a preservative to preserve the disinfection, but in reality it was a way of reducing the incompatibility.

Oxygen is generated as part of the Ozone process and Ozone degrades back into Oxygen. So when the issue of residual oxidation is raised, Oxygen is Ozone's residual and a strong oxidizer on it's own, stronger than Sodium Hypochlorite. So back to why Ozone ? It degrades quickly, is a strong oxidizer and has improved compatibility.

Friction Reduction and Compatibility

Ozone is injected as a gas in smaller microbubbles. It is also injected as a 10% gas with the balance being Oxygen. These gas microbubbles cause friction reduction.

We have observed this in the field and measured it with a 3rd party friction loop. We have seen anywhere from 10% to as high as 30%. On the opposite side when testing with other oxidizers we see a decrease in friction reduction as a result of the oxidizer degrading the FR. This gives Ozone a significant advantage over other oxidizers, but as mentioned earlier weaker oxidizers like Oxygen or Sodium Hypochlorite don't have the same effect and we don't see an increase in friction or degradation of the FR.

When you combine the degradation from stronger oxidizers like Chlorine Dioxide or Hydrogen Peroxide to the friction reduction of the microbubbles generated through the Ozone process we see an improved compatibility with frac fluids.

Corrosion Concerns

One of the common concerns people have with Ozone or oxidizers in general are corrosion concerns. And yes an oxidizer in the right concentration will cause some corrosion. The difference is Ozone as a gas needs water flow to create a vacuum through a venturi to inject Ozone. So you cannot introduce ozone using a venturi without water flow. Why is this important, the Ozone is diluted to about 10ppm in water and at that concentration we get great oxidation with no corrosion and we have performed many coupon tests to validate this. This is true of all oxidizers being injected at the proper dose into water, but what if the water flow turns off. In most gathering systems water flow does stop from time to time and if your oxidizer is being continuously dosed it will be pumped into an empty pipe and begin corroding it. Simple automation with flowmeters can prevent this, but we still see many continuous dose systems in the field. Ozone is not just automated to not allow this, but operational cannot happen because you need water flow to initiate the injection of ozone.

What about oxygen, doesn't it cause corrosion? If you've ever seen rust accumulate on steel laying outside you've witnessed oxygen at work. Oxygen is a rather slow acting oxidizer and although it can lead to some corrosion, water has a limit in the amount of oxygen it can hold, also referred to as solubility. Where water can only hold a few ppm air has 20% oxygen or 200,000 ppm. In a frac environment pumping and moving water will increase the amount of dissolved oxygen. Adding ozone spikes it but because of solubility limits the excess oxygen is released in the working tanks. So by the time you leave working tanks your dissolved oxygen is back to within 20% of where it started, but no you head to the blender. The mixing action sucks air into the blender and fluid. We have measured oxygen levels post blender and found that the largest spike in oxygen actually comes after the blender. So whether you use ozone or not you will be introducing oxygen from pumping and moving water, but more so from the frac blender, but in all these case coupon testing does not show an increase in corrosion rate.

Conclusions

So why do we use Ozone ? It is a strong oxidizer that is more effective as a result of being stronger in killing bacteria, oxidizing iron and sulfides, but degrades quick enough not to cause a compatibility problem. In fact the opposite the gas microbubbles improve friction reduction so you have improved compatibility.

Ozone does not cause chlorinated disinfection byproducts and only uses surrounding air as it's raw material. No more trucking chemicals or salt, no more chemicals spills and you're lowering your carbon footprint. But more important today is it can be more cost effective than other oxidizers as well. We have applications in the Permian basin today that have costs below $0.01/bbl. So this is why we use Ozone.