Using acid to clean Ambethi-2 well at CB-ONN-2000/1

Vol 11, PW 2 (31 May 07) Exploration & Production

Problems continue to beset Gujarat State Petroleum at its discovery well Ambethi-2 at onland Gujarat block CB-ONN-2000/1 near Ahmedabad, the most fiercely contested block of the NELP-II licensing round.

High expectations surround Ambethi-2, which was drilled to TD of 3200 metres in April, revealing a 40-metre oil pay. But GSPC (50%) - which shares this block with GAIL (50%) - was forced to suspend testing at Ambethi-2 until the arrival of imported explosives that could withstand searing bottom hole temperatures of up to 335 degrees Fahrenheit – the highest ever seen by GSPC in an onland well.

When the explosives arrived, GSPC resumed testing of a 10-metre interval at 3100 metres depth in mid-May, with disappointing and inconclusive results. “GSPC got some oil flowâ€‌ we are told, “but it was too little.

â€‌ Not only was the oil flow too insignificant to measure, it seems the explosives clogged up the well, prompting the need for acid to clear it up. “The flow channels were clogged,â€‌ we hear.

GSPC was advised to use acid to clean the well bore and then repeat the test. Using a crew hired from ONGC, the acid job lasted around eight hours early last week before the well was shut.

This week GSPC will carry out a much longer cleaning operation when it pumps around 200 cubic metres of acid into Ambethi-2. After this the well will be shut and later opened and flowed over six days using four bean sizes ranging from 4mm-7mm.

GSPC is confident Ambethi-2 – the second of two wells committed in the Phase-III exploration period - will emerge as the biggest discovery on this block. Ambethi-1, the first well, was dry.

Oil shows at Ambethi-II were reported from 3000 metres depth down to TD at 3200 metres. First attempts to test Ambethi-2 failed because of searing heat.