The mitigation of downhole, dissolved oxygen (DO) accelerated, microbiologically influenced corrosion (MIC) in hydro-fracked, oxygen contaminated, relatively high temperature, unconventional reservoirs is challenging. Additionally, little research has been published in the area. The mitigation of downhole MIC in this type of well is complicated by the reality that mechanical cleaning is not yet possible; therefore, downhole MIC mitigation is solely dependent on chemical applications. DO-accelerated, downhole corrosion is also more difficult to control in high TDS (total dissolved solids) producing wells with complex water chemistries. Furthermore, the hydrofracking process typically introduces oxygen which accelerates corrosion. In this case-study, an oilfield in Alberta, which had been experiencing severe downhole corrosion, was the subject of a comprehensive corrosion investigation, which identified MIC as the most significant corrosion mechanism. Downhole water chemistry, oxygen contamination levels, ATP determination, and 16S DNA sequencing were used to identify those specific wells which had quantifiable, carbon steel, MIC degradation issues. Several wells had high concentrations of sulfate-reducing bacteria (SRB) and methanogenic microorganisms as well as elevated dissolved sulfide concentrations. Once the problematic wells were identified, biocide and corrosion inhibitor programs were optimized in cooperation with the client and their oilfield chemical provider to effectively mitigate downhole corrosion.
MIC is a well known and firmly established threat to the integrity of oil and gas production and transmission infrastructure.1 Numerous case studies and reports have been published outlining severe corrosion rates and failures due to MIC in oil and gas production lines, separators, storage tanks and pipelines.2 Sulfate-reducing bacteria (SRB) and methanogens are typically the most prevalent microorganisms found in severely corrosive MIC scenarios in the oil and gas industry.3,4 Under mesophilic conditions, like those found in the oil and gas surface production infrastructure, mentioned above, SRB and methanogen mediated MIC is a common occurrence in conventional oil and gas production. However, many of the new wells being drilled in North America are relatively deep (1-2 km), horizontally fractured unconventional oil wells with downhole temperatures ranging from 50-80°C.
