A Case Study on Chemical Free System for Crude Sweetening: A first in Indian Offshore; Design Challenges and Post Installation Performance Evaluation

In a producing field of western offshore, H2S content in oil was found to be in the range of 3000-5000 ppm against the desired level of 200ppm. High H2S concentration posed a serious threat to pipelines integrity and downstream equipment. Mitigation by conventional means such as chemical injection is generally avoided at offshore due to constraint like continuous pumping, storage of chemicals, frequent monitoring, logistical impediments and disposing off by-products in compliance with statutory requirements. Considering many limitations at offshore, an approach was adopted for reduction of H2S utilizing Henry's principle which states that the amount of dissolved gas in a liquid is proportional to its partial pressure. Reducing the partial pressure by utilizing sweet natural gas or some other inert gas, H2S can be removed. Same principle was applied to conceptualize a processing system wherein sour crude can be sweetened to the desired level utilizing sweet gas as stripping gas. Processing System was designed considering many downstream and upstream constraints in the existing system and without any rotating and heating requirement. Unlike conventional way of sweetening such as chemical injection which requires continuous dosing of chemical and disposing off by-products in compliance with statutory requirements and hence, found not feasible at offshore to sweet enormous amount of crude. The designed processing system, a first in Indian offshore environment, is commissioned at one of the offshore complex and has proved it efficacy wherein H2S content of around 3000 ppm in around 6000 barrel/day of crude is being reduced to less than 10 ppm level without use of any hazardous chemicals and without any need of rotating and heating equipment's and with minimum maintenance and manual intervention requirement. The system has lowest operating cost, low maintenance and without use of any rotating and heating equipment's and hence can be emerged as an ideal solution for crude oil sweetening at offshore environment or in an environment where bare manual intervention is required.