Causes of stuck 13-3/8″ casing and its remedial actions

Abstract

In the drilling operations under 600 m water depth by semi-submersible rig, 13-3/8″ casing had been unfortunately stuck at 1,800 mBRT which was 700 m shallower than section TD while running in hole. In our drilling program, 12-1/4″ shale section should be drilled to 3,700 mBRT with heavier mud (minimum 11.5 ppg) to avoid caving.

However, because total 300 m thickness of weak zone (limestone) had been remained as bare hole below 13-3/8″ casing shoe, we could not weigh up mud for drilling 12-1/4″ shale section.

After a challenging strengthen the weak zone had been failed, we had gave up drilling shale section while remaining the weak zone. Finally the weak zone had been covered by sacrificed 9-5/8″ liner, then shale section had been drilled by smaller hole (8-1/2″) than plan, and target formation had been drilled, unfortunately, with unplanned 6″ bit.

This paper describes its failure of operations and remedial action we performed.