Since discovery of oil in deep Eocene formation of Oil India Limited's (OIL) Assam field in 1998, OIL identified the deep Eocene target as strategically important for the future. Kopili shales are potentially serious problem in Eocene wells. These are non reactive, pressured shales. While drilling these shale sections OIL faced lot of problems such as excessive cavings leading to well washouts, frequent held up and reaming during drilling and round trips, stuck pipes, high torque, drag and hole fill up in almost all round trips. These problems led to poor hole condition, logging problem, bad cementation job, time overrun and more importantly formation damage arising out of long exposure time. OIL adopted many measures in steps and lessons learned from previous wells are implemented on the next well to overcome and improve upon the previous problems. OIL so far has introduced change in casing policy, mud system and mud weight to overcome few of its drilling problem.

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