The Study on Mechanism of Steel Pipeline Corrosion in Dagang Oilfield

Abstract

Abstract The differences of temperature and formation water characteristics among each reservoir were significant in Dagang oilfield. Although many measures have been taken in an attempt to control steel pipeline corrosion, the corrosion rate in the south block of oilfield was several times higher than that of the middle and north blocks. Further studies, therefore, were needed to clarify the case. The ion and microorganism concentrations of the water in nine central stations were analyzed by sampling of aberration-free point. Under nonsterile and aseptic conditions, the relations among corrosion rate, salinity and SRB numbers were studied by static and dynamic methods. The results showed that, the salinity of formation water in the south block was the high (35g/L), and its SO42- content ranged from 50 to 150mg/L. In the south block of oilfield, the SRB number was less than 102cell/ml, but the corrosion rate was 71 percent higher than standard value. The case in the middle and north block of oilfield was inverse: the corrosion rate was 73 percent higher than that of the aseptic condition; production water was fit for microbial growth; the change law of pH and Eh was different. In the south block of oilfield, electrochemical corrosion was the main factor due to the higher salinity. In addition, microbiologically influenced corrosion was significant. The electron microscope analysis showed that, corrosion products were mainly iron and sulfur compounds, and calcium carbonate. The influence of SRB on corrosion was obtained by experiment between SRB numbers and corrosion rates. A preliminary strategy was proposed to control and reduce SRB numbers, as well as to reduce corrosion.