Workover and Recompletion of Subsea Completions In the Gulf of Mexico
Authors: Brown Frank M. , Evans Charles C. 
Published: December 2007

Introduction

Atlantic Richfield Co. is now operating eight subsea wells offshore Louisiana. These wells are in the Eugene Island Block 175 field, about 70 miles southwest of Morgan City, La. Average water depth for the field is 85 ft. These wells were among the first to be installed as subsea completions in the Gulf of Mexico. The wells were drilled and completed as three-string completions between 1966 and 1968. All wells are producing from multiple pay zones and are flowing to a common production platform located 1 to 3 miles from the wells. production platform located 1 to 3 miles from the wells. Routine service work on these wells, such as pulling and inspecting storm chokes, cutting paraffin, etc., is done by the flowline pumpdown techniques from the production platform. The wells were originally completed with special platform. The wells were originally completed with special cross-over ports that allow the tubing strings to communicate in the well just above the top packer. This feature allows tools, similar to wireline tools, to be pumped down the flowline and into the tubing strings of pumped down the flowline and into the tubing strings of the wells and to be pumped back out and returned to the production platform. Three subsea wells required production platform. Three subsea wells required remedial work because of normal reservoir depletion and various mechanical problems. This paper presents basic assumptions in the planning phase and summarizes the work performed to move in the workover rig and to establish contact with the well.

Planning Phase Planning Phase In the planning phase, rig selection was of major importance. A three-leg jackup rig without a bottom barge was selected as the best rig for this job. One of the prime reasons in selection of this rig was its ability to cantilever the derrick 25 ft beyond the hull of the barge. Equally important was the ability to skid the derrick in a lateral position 16 ft. This feature allowed the barge to be positioned 15 to 20 ft from the well and eliminated the dangerous positioning of the rig with tugboats. Another problem concerned how to establish contact with the well after the Christmas tree was removed. Two alternatives were available:utilize underwater blowout preventers and bring a low-pressure riser from the blowout preventers to the rig, orconnect a highpressure riser to the wellhead and use standard blowout preventers on top of the riser.

The latter method was preventers on top of the riser. The latter method was selected, but a high-pressure riser was unavailable and one had to be built. The wells had to be in a safe condition to move the rig on location in the event of an accident. Drilling fluid was to be circulated down the wells to kill the well before moving in the rig. This was done from the production platform by circulating the fluid down the production platform by circulating the fluid down the flowlines and into the wells. Several planning meetings were held with the drilling contractor, the subsea Christmas tree manufacturer, and the diving company. These meetings were not only beneficial to company personnel but essential in teaching the divers the tools and techniques to be used to establish contact and to remove the Christmas tree from the water.

Moving Workover Rig on Location

Before moving the rig on location, divers were sent to inspect the sea bottom in the immediate vicinity of the well and in the area where the rig would be stationed. At this time, flowlines leading away from the wells were buoyed and the Christmas tree was marked with a buoy.

JPT

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