Abstract
Western offshore, India, comprises vast network of nearly 372 numbers of sub-sea pipelines of varying sizes ranging from 4” to 42” covering approximately 3500 km. The network is essentially used for transporting well fluids, water and gas in offshore oil and gas production system. Corrosion due to H2S has serious repercussions on life of sub-sea pipelines. It even leads to premature failure of pipelines. Controlling H2S generation to the maximum possible extent is essential for reducing corrosion due to H2S. The present work pertains to analysis of H2S values measured across some of the sub-sea pipelines, located in these oil fields. The paper also describes measures initiated for reducing H2S generation. It is observed that low fluid velocities and increased water quantity in associated fluids, being transported, are responsible for sulfate reducing bacteria (SRB) to grow, thereby, enabling rise in H2S levels across these lines.
Control of process parameters before fluids being transported, pigging, biocide dosing and periodic monitoring of H2S levels are employed as measures for mitigating H2S generation in these lines. Pigging technique clears settled water inside the pipeline and prepares the surface for biocide treatment to be followed. Biocides control growth of SRBs, thereby, reducing H2S generation within pipelines. Measurement of H2S values before and after the biocide treatment has revealed that the treatment has helped to reduce H2S content in lines to a considerable extent. Monitoring of H2S values at periodic intervals is also being done to know if any rescheduling in pigging and biocide treatment frequency of sub-sea pipelines is needed. The paper concludes that implementation of these measures on larger scale has proved very effective in reducing corrosion due to H2S in sub-sea lines, located in these oil fields.
