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Evolving the Biocide Selection Procedure for Frac

By Virginia Wornstaff, Vice President

Virginia Wornstaff, Vice President
Yes, Kill Study sounds a little morbid. I have run hundreds of these microscopic genocides in my career trying to zero in on biocide application efficiencies for production systems. Only in the last half-decade have I tried to perfect this art for hydraulic fracturing applications. We start with what we know, which in my case was controlling existing populations in production systems. The concept is transferable, but I have found some very key learnings in adapting the procedures for frac, which is about contamination prevention. It may seem like a subtle difference, but the impacts are significant. Below are five talking points that have big impact when I embark on a new path of guidance with a client. My full list has about 25 lengthy discussions with diagrams, Farside cartoons, zombie analogies, and poorly created excel charts, but I think the following points are a good place to begin the thought process.

1. Stop Using Bug Bottles!
A collective gasp is heard throughout the room! I’m serious though, this is an important statement for all microbial work in well completions. As handy, comfortable, and affordable as this technology is, it was developed for production systems, not completions work. Culture media testing indicates what can be grown, not which microbes are present. If you can’t grow it, it doesn’t mean it’s not there, accepting that bug bottles capture about 1% of the microbes in our samples. In production systems with consistent operating conditions and an existing microbe population, these bottles can be trended and correlated to microbial issues. The key concepts here are consistent operating conditions and trending. Neither of these exist when evaluating a single frac source water for viability, or when monitoring flowback from a new well. In fact, this could be a very dangerous game if one feels that zero growth means zero issues, all from a single reading. Again, you are basing the lifelong health of your well on 1% of the total available information. Same concept applies to frac kill studies. Use ATP testing. These studies are about evaluating kill, and since biocides are non-selective, they will be killing all species of microbes. Using a more accurate technology that evaluates the entire population, not just 1% of it, simply makes sense. Not to mention, it only takes 10 minutes to get a reading, not one month to wait for a bottle turn.

2. This is Prevention, Not Control.
I emphasized this above because it is a bit of a paradigm shift for those of us who have extensive experience in the production world. Controlling a microbial population means it exists already. Our objective is to keep it below levels that cause issues like fouling, corrosion, or souring. Depending on your production system, this contamination level could be as low as thousands of microbes per mL of water or as high as billions of microbes per mL of water. The environmental/operating conditions, microbial nutrients and mitigation programs all play a part in whether you’ll have microbial issues or not. In completions work, we don’t have a baseline. We are trying to prevent contamination from happening so our control levels need to be adjusted – and by adjusted, I mean lowered (real low). We don’t want to just drop it a few logs. We want to kill as much as we can. Not a 99% kill, a 99.999% kill. Yes, there is a difference when dealing with log values above 6 or 7! I recommend aiming for less than 10pg of ATP per mL when using an oxidizer, and less than 50 pg of ATP per mL when using an organic biocide. Get low my friends!

3. 48 Hour Kill Studies Are Not Enough!
I get it, these things take planning. Frac companies are on site for the duration of the frac and will run these studies for the duration of their operations (or less). The problem is that those waters are often in that reservoir for a lot longer. Consider how long it takes before your load waters are fully recovered. Is it longer than 48 hours? What about the time between frac and tying into production facilities? Sometimes this is weeks or months. Is your biocide going to maintain control for this time? When I work with clients who get random well souring in fields with consistent frac programs and treatments, I often see the difference is in the time between frac and production activities. You’ve created a little incubator full of warm, stagnant, nutrient-rich conditions. You need to make sure your treatment will disrupt this reservoir Petri dish for as long as possible! Try a three-week study or a re-inoculation procedure to measure residual biocide effects after extended periods of time. This doesn’t have to be complicated. Remember that your goal is to prevent long-term contamination of your reservoir. Testing 30 days after your well comes on production is going to give you the best indication of success; not the post-blender check box the day of.

4. Optimize -> Buffer -> Confirm on Site!
I am not going to get into the details of kill study procedures, as this is a full discussion for another day. We do need, however, to understand the purpose of the kill study exercise. The goal is to narrow in on an effective treatment based on system fluids and operating parameters, that is going to cost us as little as possible. Big kill, little price tag. Price always plays the last card and because of that, we dial down our rates to be as low as possible. That’s great, but an optimized lab study still needs to be translated to the actual field application. We run these studies based on source water that was gathered typically weeks before the frac, and prior to containment, trucking, additives, recycling, or environmental changes. Just because 50 ppm of product will control microbes in fresh river water pulled from your canoe under lab conditions, doesn’t mean it will control them on site after the water has been dumped into a dirty frac tank and nature heats it up to 30°C that week. Accept and plan for changes. Optimize the treatment program by using your kill study as a starting point, buffer your product costs with an additional 10% and test on site to confirm biocide loadings make sense for real-time ATP levels. This allows you to manage your kill and costs efficiently.

5. Help Each Other Out!
This is such a big one for me. We know that communication barriers exist in our industry and our organizations; much of it is unintentional, but it’s time to connect the dots. If a biocide application did not work in the frac, and a month later the pipeline bringing in your new infill wells fails due to microbiologically influenced corrosion, perhaps it’s a good time to chat with the completions team. Ask about optimizing frac biocide programs. It doesn’t have to cost more, and given that a good frac biocide program cost is so incredibly small when compared to a pipeline failure or a soured well, why wouldn’t you? Also, it’s not fair to assume the frac company doesn’t want to help you – this just isn’t their primary focus. Biocides don’t help place sand, they focus on the health of your well – not necessarily that of your frac. None of this is wrong or bad, but we can definitely make it better. Anytime I get to chat with production and completions teams in the same room about these issues, everyone ends up winning. Dr. Phil would approve.

From all of this, I think we are moving in the right direction. We see the challenge and are putting the pieces together to get to the best solution and are beginning to share learnings along the way. There is no shortage of good intent in our frac operations and planning, but the extended impacts also need to be discussed and understood. Less than optimal impacts don’t mean that sound decision-making is missing. We simply need more information to optimize the process. With new and accessible technologies on the market, there is an abundance of information we can apply to real applications that fuel data-driven decision making. The right data. The right decisions.

Let’s keep the conversation going! Contact Virginia.