Sharma Mohita, An Dongshan, Liu Tao, Pinnock Tijan, Cheng Frank, Voordouw Gerrit
Petroleum Microbiology Research Group, Department of Biological Sciences, University of Calgary, Alberta, Canada.
Department of Mechanical and Manufacturing Engineering, University of Calgary, Calgary, Alberta, Canada.
PLoS One. 2017 Jul 26;12(7):e0181934. doi: 10.1371/journal.pone.0181934. eCollection 2017.
Coiled tubing corrosion was investigated for 16 field water samples (S5 to S20) from a Canadian shale gas field. Weight loss corrosion rates of carbon steel beads incubated with these field water samples averaged 0.2 mm/yr, but injection water sample S19 had 1.25±0.07 mm/yr. S19 had a most probable number of zero acid-producing bacteria and incubation of S19 with carbon steel beads or coupons did not lead to big changes in microbial community composition. In contrast other field water samples had most probable numbers of APB of 102/mL to 107/mL and incubation of these field water samples with carbon steel beads or coupons often gave large changes in microbial community composition. HPLC analysis indicated that all field water samples had elevated concentrations of bromide (average 1.6 mM), which may be derived from bronopol, which was used as a biocide. S19 had the highest bromide concentration (4.2 mM) and was the only water sample with a high concentration of active bronopol (13.8 mM, 2760 ppm). Corrosion rates increased linearly with bronopol concentration, as determined by weight loss of carbon steel beads, for experiments with S19, with filtered S19 and with bronopol dissolved in defined medium. This indicated that the high corrosion rate found for S19 was due to its high bronopol concentration. The corrosion rate of coiled tubing coupons also increased linearly with bronopol concentration as determined by electrochemical methods. Profilometry measurements also showed formation of multiple pits on the surface of coiled tubing coupon with an average pit depth of 60 μm after 1 week of incubation with 1 mM bronopol. At the recommended dosage of 100 ppm the corrosiveness of bronopol towards carbon steel beads was modest (0.011 mm/yr). Higher concentrations, resulting if biocide is added repeatedly as commonly done in shale gas operations, are more corrosive and should be avoided. Overdosing may be avoided by assaying the presence of residual biocide by HPLC, rather than by assaying the presence of residual surviving bacteria.
对来自加拿大页岩气田的16个现场水样（S5至S20）进行了连续油管腐蚀研究。与这些现场水样一起孵育的碳钢珠的失重腐蚀速率平均为0.2毫米/年，但注入水样S19的腐蚀速率为1.25±0.07毫米/年。S19中产生酸的细菌的最可能数为零，并且将S19与碳钢珠或试片一起孵育不会导致微生物群落组成发生重大变化。相比之下，其他现场水样中产生酸的细菌的最可能数为10²/mL至10⁷/mL，并且将这些现场水样与碳钢珠或试片一起孵育通常会使微生物群落组成发生很大变化。高效液相色谱分析表明，所有现场水样中的溴化物浓度均升高（平均1.6毫摩尔），这可能源自用作杀菌剂的溴硝醇。S19的溴化物浓度最高（4.2毫摩尔），并且是唯一具有高浓度活性溴硝醇（13.8毫摩尔，2760 ppm）的水样。对于使用S19、过滤后的S19以及溶解在特定培养基中的溴硝醇进行的实验，通过碳钢珠的失重测定，腐蚀速率随溴硝醇浓度呈线性增加。这表明在S19中发现的高腐蚀速率是由于其高溴硝醇浓度所致。通过电化学方法测定，连续油管试片的腐蚀速率也随溴硝醇浓度呈线性增加。轮廓测定法测量还显示，在与1毫摩尔溴硝醇孵育1周后，连续油管试片表面形成了多个凹坑，平均凹坑深度为60微米。在推荐剂量为100 ppm时，溴硝醇对碳钢珠的腐蚀性适中（0.011毫米/年）。如果像页岩气作业中通常那样重复添加杀菌剂，导致更高的浓度，则腐蚀性更强，应避免这种情况。可以通过高效液相色谱法测定残留杀菌剂的存在，而不是通过测定残留存活细菌的存在来避免过量使用。
