Analysis of the on stream pigging project of Bakhrabad-Chittagong (175 KM ,24'' DIA) high pressure gas transmission pipeline

Abstract

The Bakhrabad-Chittagong (BKB-CHT) high pressure gas transmission line was first commissioned in 1983. It is a 175 km long, 24" dia, 960 psig) gas pipeline which was built to supply gas from the Bakhrabad Gas field, Muradnagar, Commilla to Chittagong City Gate Station (CGS), Faujderhat, Chittagong. Gas is being supplied to the consumer of Commilla, Chandpur, Lakhsam, Feni, Maizde, Choumuhoni, Laksmipur, Chittagong as well as the huge area of the South-East part of Bangladesh by the different off-takes along the pipeline.

On stream pigging operation was first accomplished to BKB-CHT pipeline in July, 1990 and second time it was done in February, 1994. Significant amount of condensate, sludge and water were recovered from this pipeline during these operations. After thirteen years, on stream pigging operation to BKB-CHT pipeline was done during 12 -13 November, 2007 by Gas Transmission Company Ltd (GTCL). The anticipated amount of condensate, sludge etc. were not recovered from this pipeline during the latest pigging operation. It is therefore necessary to analyse the latest pigging operation to understand the effectiveness, and to find out the reasons for such large differences of the outcomes compared to the previous operations.

The investigation reveals that in the beginning years the gas processing at Bakhrabad Gas Field was inadequate. The pipeline was not being used at its full capacity. Due to these reasons, there was scope for accumulation of large amount of condensate. Therefore during the first and second pigging operations, large amounts of condensate were recovered (7,11,000 and 3,87,000 litres respectively). The third (3rd) pigging operation however did not yield the anticipated quantities. The probable reasons are: • After the second pigging operation, BKB Gas Field Process Plant are being operated in sufficient capacity. • In 1997, Ashuganj- Bakhrabad 30˝ pipeline was commissioned. So since 1997, BKB-CHT pipeline have been being operated in actual capacity range. • Since 1997, most of the gas feed to BKB-CHT pipeline was from AB pipeline and this gas was coming from other gas fields such as Titas, Habiganj, Rashidpur, Kailashtila and Jalabad Gas Field. Thus gas from these sources are already processed at origin. Moreover, some liquid is recovered at the Ashuganj Menifold Station. Therefore when the total mix of gas is fed onto BKB-CHT pipeline it is almost dry. • After the second pigging operation, BKB Gas Field, Salda Gas Field and Meghna Gas Field have been supplying dry gas. • Sufficient capacity heater are being used at ICS Feni and CGS Faujderhat after second pigging operation. • During the year 2005-2006, average 3000 gallons/month of condensate were collected at CGS Faujderhat and average 1000 gallons/month of condensate were collected at ICS feni. Therefore it is possible that whatever amount of condensate accumulated in the pipeline were removed during this period. • Since 1997, average 225-250 mmscfd gas was supplied through the BKB-CHT pipeline. So condensate and Sludge could not accumulate inside the pipeline and were collected at ICS feni and CGS Faujderhat. So almost all the condensate were collected after the second pigging operation.