Abandonment of a Subsea Well
Authors: Morrill D.L. 
Published: December 2007

A completed subsea oil well was abandoned in 95 ft of water offshore Louisiana. This paper describes the abandonment procedures, drilling, completion, production operations, and the technical analysis of the recovered Christmas tree. Single-well subsea systems are available for development of shallow-water reserves, but still need improving.

Introduction
Since 1975, when the first underwater completions were made in +/- 100 ft of water in Lake Erie using conventional land equipment, subsea well completions have increased in number and complexity. Today, more than 300 sublake and 100 subsea completions have been installed worldwide. Major technological developments include Seal's Intermediate System (SIS), the Lockheed One-Atmospheric Wellhead Cellar, Exxon Corp's Submerged Production System (SPS), Transworld Drilling's Satellite Well and Central Manifold Concept, and Deep Oil Technology's Template Concept with Tension Leg Platform - all created in anticipation of deep-water Platform - all created in anticipation of deep-water production. Because of associated technological production. Because of associated technological advances, new methods, procedures, and equipment now allow industry to make shallow-water, single-well completions with "off-the-shelf" equipment at a cost competitive with platform development. These shallowwater wells have become an attractive alternative for producing shallow reserves (especially gas) that cannot producing shallow reserves (especially gas) that cannot be reached from existing platforms (Fig. 1).
This paper presents Continental Oil Co.'s experiences in abandoning the subsea well, Grand Isle 47 No. 3, while acting operator for CAGC (Continental, Atlantic Richfield Co., Getty Oil Co., and Cities Service Oil Co.)
This well was completed April 1969 in the Grand Isle Block 47 field in 95 ft of water, offshore Louisiana. The completion was primarily an experimental program, but also provided the necessary development to drill in an 8,500-ft oil zone and produced 150 to 250 BOPD. The subsea system was a remotely operated, hydraulically controlled Christmas tree designed for completion and production operations without diver assistance (Fig. 2). production operations without diver assistance (Fig. 2). Through-flowline (TFL) pumpdown tools were used down hole in the dual tubing strings. The TFL and hydraulic control manifolds were located less than 2,000 ft from the well on the Grand Isle Block 47 "A" platform. Two 2 3/8-in. flowlines and four 3/4-in. control lines connected this system to the platform equipment.
The well was abandoned in Aug. 1975 because of mechanical problems down hole and with the subsea tree, and because reserves could be recovered by offset updip wells.

Summary
Diving was the most critical and time-consuming requirement of the abandonment. More than 41 hours of diving time were spent on valve operations and wellhead re-entry. Proper coordination and control of diving by using a television monitoring system mounted on the diver's helmet was the key to operating success. With this subsea system, diver assistance cannot be eliminated completely, but it can be minimized. In fact, diverassisted backup in shallow water can be feasible economically. Initial design and planning of shallowwater, subsea systems should include diver-assisted wellhead re-entry, component repair, and production operations.
JPT
P. 435