Effective Water Treatment in the Permian and Marcellus Shales to Mitigate Surface Equipment Failures

Abstract

Chemical and oxidative biocides are designed to sanitize water by reducing aerobic and anaerobic bacterial populations in the fresh, brackish and reclaimed source waters. These biocides are used extensively in high-rate fracture stimulations to reduce formation damage, chemical degradation, biogenic H2S and microbial induced corrosion (MIC). Oxidative biocides work by removing electrons from the cell wall of aerobic and anaerobic bacteria. The same electron transfer mechanism can be detrimental to surface equipment. This study presents the impact of several oxidative biocides on the corrosion rate and pitting of different frac iron alloys and how those biocides effect the mechanical integrity of elastomer seals. It also presents different remediation methods to mitigate their oxidative effects. The oxidative biocides tested were Chlorine, Chlorine Dioxide and a Peracidic Acid blend. The corrosion rate of the iron alloys coupons was measured by weight loss analysis. This method can measure the rate of corrosion in pounds per square foot at time and was used to compare the impact of different residual oxidizers on the corrosion rate of the ground iron. Structural changes to the elastomers were detected visually. The results of the study showed that the corrosion rate varied depending on the alloy/residual oxidative biocide combination. Usually, Peracidic Acid blend or Chlorine had the highest corrosion rates across all alloys tested; depending on the oxidative biocide/alloy combination, the corrosion rate could vary by a factor of 2X over the nine-week timeframe. Elastomer testing over 6 weeks showed variability in the types of structural changes depending on the concentration and oxidative biocide tested. The lab and field testing included onsite monitoring of the corrosion rate, oxidation reduction potential (ORP), oxygen in solution and determination of the Langelier Saturation Index (LSI). The methodology has been effective in predicting iron failures related to the composition of the water and/or presence of oxidizers. Chemical solutions implemented to mitigate the surface iron failures included use of intermittent blends of water-soluble quaternary amines and surfactants. Since these remediation attempts have started, the replacement cost of frac iron has decreased from over 550K US$ per month, per frac spread to none, over a 3-month period.