OIL INDIA LTD operates a number of oil and gas pipelines in the fields of Upper Assam. The total volume of oil handled annually is around 4 MMT. The crude oil produced is generally of waxy nature with a specific gravity of 0.87, having a high pour point of 25 deg.C and viscosity from 3.5cp till 6cp.
Over the period of years a number of methods have been developed with field and laboratory data to design, construct and maintain the pipelines including the flow lines from the well pads to the oil collection centers. At present an effective method to handle the highly paraffinic crude is the use of water bath type heaters with a heating range till 80 degree centigrade. Indirect heaters together or at times alone are used with pour point depressants, commercial name being Maxdip 1500 which is a vinyl acetate co-polymer.
During our design of new pipelines over and above to the codes of API 31.4/31.8 for pipeline design we have incorporated certain additions and deletions’ as per our requirement of handling the Assam oil. Certain redesign has also been done in certain pipelines to handle very high paraffinic crude. The 8" Duliajan Digboi refinery crude oil delivery line is an example. Design modifications were done on the existing pipeline without effecting the refinery operations. For the Salmari field heavy oil, in-house design and maintenance efforts with combination of Merus rings and heating through bath type indirect heaters has enabled a trouble free operation. To overcome the problem of congealing in well flow lines a number of methods like steam injection, heating of the crude oil and gas and use of high pressure hot oil pumps have been developed to redesign, re-modify the existing flow lines. Recently we had undertaken a pilot project to introduce a scrapper tool inside the closed circuit loop of the well flow line.
With the above endeavors developed in-house we have been able to maintain modify design and construct (lay) pipelines in our operational area with almost 100% flow assurance