| Ensign Rig #161 spud the Marble 1HN well on 4/24. After reaching TD of 2,742' at 6 AM on 4/25/22, the crew began circulating drilling mud to prepare for cementing the surface casing. Additional fresh water was called for to increase mud volumes, however a rig crew member accidentally added 130 bbls of D822 base oil to the mud pit instead of fresh water. This represents about 15% of the total drilling mud volume. The oil-contaminated mud was circulated in the hole, and discovered after circulating through the hole and returning to the pit. Operations were shut-down, the contaminated mud was transferred to the tank farm, and the pits were filled with fresh water. New water-based mud was circulated in the hole to flush out the oil-contaminated mud and 99% of the oil-contaminated mud was recovered. Planned operations resumed around 17:30 on 4/25/22. It is likely that the original water-based mud provided a seal against the aquifers. |