This paper describes how one-atmosphere chambers might be utilized for making deepwater pipeline connections and, as well, provide the means whereby valves, controls, etc., can be encapsulated and readily serviced subsea.
A new connector device is described. It makes use of the high seawater pressure available at depth for pulling one pipe end into close proximity with another and through a port located within a subsea one-atmosphere connector chamber Control of the entire operation and final joining of the two pipe ends by means of conventional welding is accomplished within the manned chamber.
Anticipated utilization of the connector includes deepwater pipeline construction and repair connections. Modified connector chambers can be used for line tie-ins and riser connections.
Related to growing world wide energy requirements, the search for oil and gas has expanded to deepwater areas which only a few years ago were inaccessible. In 1968, after extensive evaluation of alternative approaches for producing oil from these greater depths, Lockheed adopted the philosophy that a one-atmosphere chamber system at the seafloor provided the maximum opportunity for man to do useful work and at the same time maximize utilization of proven oilfield hardware subsea.
This work capability was first demonstrated in 1970 in up to 900 foot water depths during prototype tests of a one-atmosphere diving capsule for servicing seafloor chambers. More recently in 1972, this capability was again demonstrated in the Gulf of Mexico with an encapsulated subsea wellhead completion in 375 feet of water. A crew of three worked on bottom 11 hours out of each 12 hour shift.
At the conclusion of the 1970 tests, one of the companies supporting the test program suggested that the technology of the subsea work chamber should be extended to include deepwater pipe to pipe connection capability.
The seed having been sown, development work was undertaken. Several types of pipeline chambers were identified and were examined as to functionality, overall technical feasibility, and economic advantage. At the same time, a concept was evolved for mobilizing the ambient seawater pressure available at depth to generate a high controllable force, parallel to the seafloor, for pulling two pipe ends together.
This paper briefly describes the pipeline chamber development work conducted to this date and outlines the pipe pull concept and the experimental program conducted to establish its feasibility. The paper concludes with a discussion of situations where this subsea pipe-pull work chamber capability might be utilized as an aid to offshore pipelaying.
Fig. 1 pictorially shows the surface support vessel, the onboard support vans, launch and recovery equipment, and the Lockheed service capsule necessary for transporting men and materials to any sea floor chamber.