Microbiologically Influenced Corrosion In Oilfield Flooding Water

With a later stage of the oil exploitation, water drive was one of the frequently-used methods for most oilfields. However, many harmful microorganisms (SRB、TGB、IB etc.) existed in the injection water would result in the water pollution and microbial influenced corrosion. The real-time monitoring and control about the equipments fouling with the MIC were essential for the oil exploitation. This paper studied the corrosion and growth characteristics of biofilm on the surface of Q235carbon steel immersed in sewage from the gathering transportation pipeline of Shenli oilfield, and the corrosion on Q235carbon steel with the coexistence of Pseudomonas and SRB in the natural sewage.Some analytical methods were applied to measure the COD、CFe2+、turbidity、MLSS and the amount of bacteria (SRB、TGB、IB) in the sewage with SRB-biofilm. The results showed the value of COD、MLSS and the amount of bacteria(TGB、SRB) increased early and then decreased. The value of CFe2+presented linear increase and somewhere decrease, and the value of turbidity increased continuous.The presence of SRB-biofilm caused the pollution in water quality. To study about growth characteristics of biofilm on the surface of Q235carbon steel, the ESEM technique and electrochemical methods were applied to the study. It was found that initially produced iron sulphides formed a compact film in the inner layer, then more and more extracellular polymeric substances (EPS) appeared in the mature biofilm on the8th day, and then films partially exfoliated after11days immersion. And the charge transfer resistance Ret decreased dramatically on the11th day was ascribed to the protective film cracked. The heterogeneous corrosion of Q235carbon steel under the SRB-biofilm in sewage was investigated using a wire beam electrode (WBE). The results showed that both potential and current maps could indicate the localised corrosion of carbon steels beneath the biofilm, and the extreme potential difference increased gradually, the extreme current difference had small changes. The value of localized corrosion factor (LF) was much high with smooth fluctuations. With the growth of SRB-biofilm, the corrosion of steels became more heterogeneous and the value of LF decreased later.It was identified that a lot of aerobes which named Pseudomonas existed in the sewage. The growth curve of SRB and Pseudomonas in mixed medium showed that SRB grew slower than Pseudomonas. The EPS of mixed bacteria could formed the EPS-Fe more effective to adhere to the surface was investigated using electrochemical methods. The research about MIC of carbon steel with coexistence of Pseudomonas and SRB in the natural sewage was carried out in static and dynamic environment seperately. The result showed that the corrosion rates accelerated as the speed increased. In the static condition, the existence of Pseudomonas could inhibited the steels corrosion by SRB, in the dynamic condition of100r/min, the inhibition slightly weakened, and the corrosion inhibition was mainly attributed to the oxygen consumption by Pseudomonas. The results also showed that the rate of diffusion for dissolved oxygen was much higher than the speed of oxygen consumption in the dynamic condition of200r/min, which made steel corrosion the most serious in the presence of mixed bacteria.