Multiwell Deployment of a New Abandonment System
Authors: Carpenter Chris 
Published: December 2017

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 184716, “Successful Multiwell Deployment of a New Abandonment System for a Major Operator,” by Thore Andre Stokkeland and Jim McNicol, Archer Oiltools, and Gary McWilliam, Maersk Oil, prepared for the 2017 SPE/IADC Drilling Conference and Exhibition, The Hague, The Netherlands, 14–16 March. The paper has not been peer reviewed.
A new downhole-tool-based abandonment system was developed and deployed successfully on four wells for a major operator on a field in the North Sea. The operations were 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 10¾-in. casing to remove the oil-based mud (OBM) from the annulus before removing the wellheads.
Introduction
Service companies were challenged by a major operator to create a solution to set a barrier against the overburden and to circulate OBM out of the annulus between the 10¾- and 13⅜-in. casings before pulling the wellhead.
The first stage of the operation was to run a perforation gun loaded for 1 ft with 18 shots/ft (spf) of a proprietary abandonment charge (single-casing perforation gun) to immediately below the wellhead at 475 ft. Then, the 10¼-in. casing was perforated with 0.8-in.-diameter holes without damaging the 13⅜-in. casing to create a circulation path.
The second stage was to run a retrievable bridge plug (RBP) with another 1-ft-long perforation gun below. The RBP was set and perforated immediately above the 13⅜-in. shoe at 2,300 ft; then, circulation was established up to the shallow perforations above and the OBM in the 10¾- by 13⅜-in. annulus was circulated out. After the circulation parameters were established, a wash pill was pumped around the annulus to clean out the OBM.
The third step was to set the actual overburden barrier in the A and B annuli. This was achieved by displacing cement through the ball valve of the RBP into the perforations below the RBP, placing the cement plug below and into the 10¾- by 13⅜-in. annulus. The ball valve was closed, and a cement plug was pumped on top of the RBP, completing the barrier.
Background
The North Sea’s Leadon Field lies in 370 ft of water and is located in Blocks 9/14a and 9/14b of the UK Continental Shelf approximately 220 miles northeast of Aberdeen. Field development was enabled by the addition of two satellite fields, Birse and Glassel. The three fields were developed with subsea horizontal wells tied back to a floating production, storage, and offloading facility. The Lark and Horda formations produce in two well clusters, A and B. Cluster A has seven production wells and two water injectors; Cluster B consists of three production wells, two water injectors, and two aquifer wells. Both clusters have space for additional wells.
After a commercially successful period, production eventually declined, leading to a Cessation of Production Application being filed by the operator in 2004. A decommissioning program for the field was approved in March 2016.