The C-Series marginal gas field in Tapti is located approx. 60 KM West of Daman. Under Phase-I implementation, four unmanned well platforms namely C-22P, C-24P, C-39-P1 & C-39-PA have been installed. C-39-PA is the farthest platform and connected to C-24P via 60 kms of 22" and C-24P to NQG process platform via 115 kms of 28" sub-sea pipelines. Gas from NQG is transported to Uran after processing.

Pipeline is very long sub-sea pipeline bearing a very typical profile with un-favorable contour having multiple sources, having a reverse profile with C-series platforms at a shallow depth of 19-23m and the receiving process platform NQG at a depth of about 64 m. The gas, condensate and liquid production profile makes this pipeline more critical during regular production and having severe surging problems.

Dewatering and commissioning of the pipeline with a conventional approach to launch the pig train from the launcher at C-24 well platform and receiving the pig train at NQG receiver was considered initially. The pipeline filled with 60 thousand cubic meters of treated water. If pigging is done conventionally huge surges are anticipated at NQG, may cause process upset and may lead to shutdown of the process complex. Because of this a different way of launching the pig from receiver end i.e., (NQG), deeper pipeline profile and receiving the pig at C-24 platform, a shallower pipeline to ensure safe and practicable operation. The pigging was done successfully with nitrogen in between the 4 pig train followed by gas. After pigging of NQO-C-24 section, gas from C-24 platform was used to propel the pigs in 22" pipeline segment. Finally, dewatering of both segments was carried out successfully and this is first time in ONGC, the operations carried out in a large scale

You can access this article if you purchase or spend a download.