Oilfield bacteria are present everywhere water can be found in the hydrocarbon production process. Unchecked bacteria populations can result in operational issues through the upstream and midstream production environment. Starting at the producing formation itself, bacteria introduced into the formation during drilling, completion, or flooding can result in the plugging of the formation as well as the wellbore.
Corrosion due to oilfield bacteria is thought to be responsible for as much as $420m in losses each year. Microbial induced corrosion (MIC) is a significant factor in causing this loss. Additionally, oilfield bacteria can lead to well souring, causing a decrease in the value of hydrocarbon products and introducing additional work and environmental hazards.
While there are a multitude of bacteria present in oilfield waters, there are three classes that are especially relevant due to the issues caused by their presence:
1. Sulfate Reducing Bacteria (SRBs)
SRBs are a broad class of microorganisms that use the conversion of sulfate ions (SO42-) into hydrogen sulfide (H2S) as an energy source. SRBs are anaerobic organisms, meaning that they can thrive in downhole conditions. H2S produced by SRBs can cause a variety of operational issues, including formation souring, corrosion of oilfield equipment, and creating worker hazards due to the extreme toxicity of H2S gas.
2. Iron Reducing Bacteria (IRBs)
IRBs are bacteria that utilize oxidized or ferric iron as part of their metabolic process, producing reduced, or ferrous iron. IRBs are thought to contribute to iron corrosion processes in the oilfield environment, primarily when found in the presence of biofilms and SRBs.
3. Acid Producing Bacteria (APBs)
APBs are a type of bacteria that produce acids as a byproduct of their metabolism. Acids produced by APBs can result in accelerated MIC issues, especially when APBs are attached to metallic surfaces as part of biofilms.
Oilfield bacteria populations are commonly controlled through the addition of biocides to contaminated waters at various points in the water lifecycle: during the initial drilling, during well completion activities, before water is used in flooding operations and during the treatment of produced water for recycling or disposal applications. While many chemicals can be used to disinfect oilfield waters, sodium hypochlorite produced through electrochlorination represents the optimal choice since it is the lowest cost and safest option available on the market today.
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