CBM reserves at Raniganj East will be clear by October

Vol 13, PW 4 (30 Jul 09) Exploration & Production

Essar Oil is also moving fast to get a better idea of CBM reserves at its Raniganj East block.

Early this month, Essar hired US-based reserves consultant Netherland, Sewell & Associates to certify block reserves. “The consultant has already begun work,â€‌ Essar tells us.

“We expect reserves numbers from them by end-September or early October, around the time when we are ready to begin drilling the (75) Phase-II wells.â€‌ Essar says the consultant will have a mass of previously unavailable data to work on and that the reserves numbers will be much higher than the original figure of 1.38-tcf in-place methane (40% recoverable) endorsed by the DGH when the block was offered by the oil ministry in the licensing round.

“We now have sub-surface data from 17 coreholes (drilled last year) and 15 test wells,â€‌ says Essar. Analysis of the cores reveals gas content to be between 6 and 7 cm/tonne of coal.

Coal seam thickness varies as there are multiple seams, but in the dozen or so seams found worthy of exploitation for methane extraction, average thickness was found to be a little more than 30 metres. Gas permeability has been found to be an average of five millidarcies.

“Permeability numbers have been obtained from analysis of the cores and confirmed from the test wells also,â€‌ says Essar, which adds that 80 acres is the average spacing between the test wells. “Eighty acres is the drainage area for the methane in this block.

â€‌ Essar takes pride in what it describes as a very successful and cost-effective Phase-I drilling campaign. “For Phase-I we used a combination of â€کwater well drilling’ and an air drilling unit,â€‌ we are told, “as a result of which our costs came down by 40%.

â€‌ The upper portion of each well – where the 9 5/8-inch casing is lowered – was drilled with a water drilling rig and the lower portion by the air-drilling unit.