Subsea flowline connections in one atmosphere chambers
Authors: Woodlock D.F. 
Published: December 2007

Encapsulating oil producing equipment in subsea, dry one atmosphere chambers posed the unique problem of connecting flowlines and/or electrical cables which had been laid on the ocean bottom to piping systems within a chamber. A system was developed which provided a means of establishing a pull-in cable from the chamber to the pipe end, and providing sufficient pulling force to pull the pipe end into a port in the chamber. A unique system was also developed for scaling between the pipe end and the port and for scaling around the moving pull-in cable.

APPLICATION

The method has been successfully used by Lockheed Petroleum Services to connect flowlines to a number of Petroleum Services to connect flowlines to a number of subsea facilities in the Gulf of Mexico.

RESULTS, CONCLUSIONS AND GENERAL OBSERVATIONS

As a result of this development a simple, economical and safe method is now available to make electrical and fluid connections to one atmosphere dry subsea facilities.

SUBSEA FLOWLINE CONNECTIONS IN ONE ATMOSPHERE CHAMBERS

Introduction

This paper deals with the development of the flowline connection techniques which Lockheed Petroleum Services (LPS) use in conjunction with one atmosphere wellhead completion systems and underwater manifold centres. Pipeline riser connection techniques, where the actual pipe connection is made in a dry one atmosphere situation but the pull-in is done with the chamber flooded, is covered in the paper Subsea pipeline connections completed by welding at atmospheric pressure, written by Mr. Murray Feller of LPS for the Offshore Europe 77 Conference.

Background

Encapsulation of oil producing equipment in subsea, dry, one atmosphere chambers posed the unique problem of connecting sea bed-located flowlines, pipelines, and electrical cables to piping systems within these chambers.

Where originating or terminating at the ocean floor enclosure, these flowlines must be pulled from the surface, or along the sea bed, up into the wellhead or production equipment chamber to complete the connections. Because the buoyant LPS service capsule is mated with the wellhead cellar - LPS'S name for this enclosure - at the time of flowline pull-in, it was decided to make use of the downhaul winch and cable for the pull-in task.

The problems which remained were those of establishing the pulling cables from the wellhead to the surface, scaling around the moving pulling cable, and scaling between the pipe end and the wellhead cellar.

The method of establishing a flowline pull-in cable was designed around an adaption of the United States Navy system for establishing a rescue and locating cable from a submarine to the surface using an internally released buoy.

The oil industry had already developed high pressure line wipers and packers for scaling around multi-strand cables while doing downhole wireline work on live oil wells. It was logical to adapt one or more of these 'off-the-shelf' packer units to provide the dynamic scaling around the pull-in cable.

The remaining problem - that of scaling and locking the flowline termination into the underwater chamber was solved with the development by LPS of the flowline termination and receptacle known as the bullnose and port.

EARLY SYSTEMS

In 1972 the pull-in and connection system developed by LPS was used to pull a flowline bundle into the first LPS subsea completion installed by Shell Oil Co, in Main Pass Block 290 in the Gulf of Mexico. This bundle consisted of two flowlines of 2-3/8 in. diameter, a 1-1/4 in. annulus access line, a small diameter hydraulic supply line and an electrical cable.

The system used on this well had a bullnose port which faced upward at an angle of 45 degrees. Before being pulled in, the flowline was buoyed off on the surface and terminated by an S-shaped bend, to accommodate pumpdown tools, and a bullnose as shown in Fig. 1. The pull-in equipment shown in Fig. 2 featured a 10 in. ball valve and adaptor, a 10 in. buoy and buoy cannister, and single Bowen type wireline stripper for scaling off around the pull-in cable. An explosive guillotine cutter, or pyrocutter, was provided in the event that the cable had to be severed to close the ball valve. This system functioned satisfactorily during the Main Pass 290 operations. There were some limitations, however, prompting LPS to upgrade the system to its present form. prompting LPS to upgrade the system to its present form.