Diagnose of Corrosion Acceleration in Water Injection System Due to Influence of Dissolved Oxygen and Sulphate Reducing Bactria: A Case Study

Abstract

Abstract Corrosion acts a major risk to water injection systems in oilfields. Dissolved Oxygen (DO) is one of the most significant causes of internal corrosion problems of carbon steel pipes worldwide. Consequently, the existing of both DO and Sulphate Reducing Bacteria (SRB) in injection water with reasonably high concentrations are greatly influencing on accelerating corrosion process in water injection system, that can severely impact costs of operations, and their control can introduce a vital challenge for the system operator. An Iraq oilfield (Z), in which water injection for pressure support started in 2012 by five wells, then the wells number and the total injection rate are gradually increased in the following years by using both fresh rivers water and produced water. After 30 months, corrosion indications in water injection system are progressively increased. Many costly solutions are used to ensure continues water injection in this field. In this paper, corrosion acceleration signs are observed during 5 years, to identify the corrosion status in different locations of water injection system. Corrosion indications are the leakage accidents in surface flow lines, workover operations to replace damaged tubing inside injectors, and increasing stimulation jobs as a result of the corrosion scaling accumulation inside injection wells and sand face. Many lab tests result of DO and SRB contents in water injected are collected, analyzed and in-depth studied to correlate the impact of different DO and SRB concentrations on the acceleration of corrosion problems in the water injection system. The work results presented that the increasing of DO in water, leads to hugely acceleration of corrosion in all parts of injection system in the field under study. SRB as an anaerobic bacterium is playing a very complicated role in the corrosion of water injection system. SRB accelerates corrosion process by many ways, some of them are enhancing by DO concentration. The worst influence of SRB is expected to be grown with time when SRB go to the reservoir with injected water. SRB activity in reservoirs is reflecting by continuous upward of H2S concentration in reservoir fluids. This work introduced a reputable field experiences of diagnose corrosion process acceleration in a good case study in an Iraq oilfield, and how can reducing this corrosion speeding up by proper control of DO and SRB contents in water injected.