Service companies were challenged by a major operator to come up with a solution to set a barrier against the overburden and to circulate oil based mud out of the annulus between the 10-3/4 in. and 13-3/8 in. casings before pulling the wellhead. The most common industry solution to this challenge is to cut the 10-3/4 in. casing by the 13-3/8 in. shoe and pull the casing to surface. An innovative new downhole tool based abandonment system was developed and successfully deployed to meet this objective.
The first stage of the operation was to run a perforation gun loaded with one foot of 18 shots per foot of a proprietary abandonment charge (single casing perforation gun) to just below the wellhead at 475 ft. Then perforate the 10-3/4 in. casing with 0.8 inch diameter holes without damaging the 13-3/8 in. casing behind, to create a circulation path.
The second stage was to run a V0 rated Retrievable Bridge Plug, RBP, with another one foot long perforation gun below. Set the V0 rated RBP and perforate just above the 13-3/8 in. shoe at 2,300 ft. then establish circulation up to the shallow perforations above and circulate out the oil based mud in the 10-3/4 in. by 13-3/8 in. annulus above. After the circulation parameters were established, a wash pill was pumped around the annulus to clean out all the oil based mud.
The third step was to set the actual overburden barrier in both the A and B annulus. This was done by displacing cement through the ball valve of the V0 rated RBP into the perforations below the RBP; placing the cement plug below and into the 10-3/4 in. × 13-3/8 in. annulus. The ball valve was closed and a cement plug was pumped on top of the RBP completing the barrier. The barrier was verified by pressure testing through the shallow perforations to 1,000 psi above the seawater gradient. A barrier was in place in both A and B annuli.
This procedure was deployed on four wells for a major operator on the Leadon South Field in the North Sea with great success. The operations were flawlessly executed with each well taking less than 18.5 hours to secure. The successful operation saved the major operator considerable time and expense by eliminating the need for cutting and pulling the 10-3/4 in. casing to get the oil based mud out of the annulus before removing the wellheads.
This paper provides an overview of the innovative new abandonment system elements and describes the successful deployment operation in detail.