Well Control; Pipe Milling Due to String Ejection
It took seven days of Engineering and Pre-Job Planning with 16 days of daylight operations to complete the project.
A vertical multi-zone gas well was drilled in the foothills region with a BHP up to 11,000 psi.. After completion of operations, the producer decided to abandon the bottom zone with a bridge plug, move uphole and land the tubing. A competitor was contracted to snub the bridge plug and completion, who chose to use a conventional unguided unit and install 10k bops. The surface pressure was 5300 psi. As they snubbed in the hole after three joints, the lower stripping rams failed, and the pipe had buckled in the stack. A decision was made to attempt to pull out of the hole, but the pipe wouldn't move, and personnel suspected a hydrate. Upon pulling, the pipe came free and launched, tagging top stripping ram and ejecting a joint from its connection. The well blew out and eventually hydrated off. A freeze job was done to secure the well further and remove the snubbing jack. A 7-10 master valve was installed on top of the stripping rams to secure the well, and the freeze plug was melted.
We were contacted after three attempts were made with coil tubing to fish the pipe unsuccessfully. We suspected the pipe was folded inside the 7" primary bop stack. The operator wanted to remove the tubing and safely secure well with 4-1/16" master valves. A 285k Unit was rigged up with a 9” ram bop stack to ensure redundancy. Due to the delicate nature of the job, the work floor height was 125', a 6-15/16" mill was run on 2-7/8' slh90 drill pipe into the stack. The pipe was milled out of 7" stack holding 7,500 psi; an E-line Unit was then mobilized to determine with a camera if the tubing was fishable. The camera showed tubing was buckled across 4-10 x 7-10 crossover and across master valves. There were concerns over milling the offset tubing and that the mill would walk-over and cut outside the gate valves. In that case, Piston designed a 4" convex mill with a 6-15/16" floating centralizer on the shank to keep the mill centred through the valve. The pipe was then milled out of valves; a skirted mill was run after the pipe was milled 6m past the master valve. Eventually, the well was secured, and the rig demobilized until further programming was completed.