Why treat clean water with a Biocide?
Microbes are everywhere; soil, ocean floors, even clouds have their own microbes. Scientist’s estimate there are over 30 trillion microbial cells in the average human body (Sender et al. 2016). Let’s face it, we live in a microbes world.
For fracturing and production applications, a common question heard when sending water downhole is why treat clean water with a biocide. The short answer: All characteristics of water need to be considered in any chemical application when determining microbial cleanliness. The cleanest looking water has the potential of harboring very high microbial counts. Fresh water may be no less contaminated than produced waters sitting in a tank.
What does clean mean?
Clean water conjures images of glacial springs that twinkle in the sunlight and look good enough to quench thirst on a hot day. However the appearance of water, the dissolved or suspended solids levels, or even the muddy or dirty look of water, are NOT an indication of microbial counts. When you consider the level of microbes in environments we consider clean such as a countertop, a bottle of drinking water or even a hospital room, you realize clean is simply a relative term that we need defined further depending on the environment we are discussing.
When it comes to oil and gas applications, we have assigned arbitrary ranges to various quantities of microbes to indicate a high, moderate or low level of contamination. These ranges vary based on test method, application, or type of treatment. Regardless, experience has shown the ranges applied bare validity and leave us with peace of mind that we are making the right decisions when implementing control methods. The results speak for themselves; no souring, microbiologically influenced corrosion identified, biomasses fouling treating facilities or build up in tanks and vessels.
What’s the contamination risk beyond the microbial level of the actual water?
The next consideration is the environment you are putting the water into – what is your risk for adverse effects? A small number of microbes in a warm, nutrient rich reservoir may flourish quickly and establish a strong community despite an original low population count on the surface. In contrast, highly contaminated water introduced to a harsh, low nutrient environment may not allow growth of any populations. This means your downhole environment needs to be considered, or any environmental conditions you are wanting to protect. Microbes are incredibly diverse, so much that we find them living in some of the most inhospitable places on Earth. Thus, predicting microbial contamination risk factors is no trivial task. However, experts can agree that the first step in preventing microbe-derived adverse effects in your system is to respect the fact that despite our perceptions of clean, microbes are everywhere, and can do almost anything!
Comic source: https://xkcd.com/1161/