The Role of One Atmosphere Chambers In In Subsea Operations
Authors: Collipp B.G. , Sellars C.A. 
Published: October 2008

Subsea chambers maintained at one atmosphere internal pressure will find numerous applications in development of underwater producing systems. They permit use of conventional oil field equipment on the sea floor and provide means for on-site maintenance. A chamber designed to contain a wellhead has been built and tested together with a diving bell for personnel access.1 Concepts have been developed for subsea manifolds and production stations in one atmosphere chambers. This could be expanded to include pipeline pump stations and instrument and control centers. During the development stage, it would be desirable to field test selected prototype designs. This would provide operating experience in current water depths and design information for extension of the concept to deep water.

Introduction

Reliable subsea wellheads and production facilities will soon be required in increasing numbers. Over 2/3 of the rigs under construction or recently introduced into service are designed for water depths beyond 300 feet. Several are provided with dynamic positioning facilities and will be capable of drilling in depths well beyond 1000 feet. The worldwide need for increased oil and gas production is obvious and drilling rigs for deep water are becoming a reality. Therefore, it is timely to proceed with development and field testing of equipment for subsea production operations.

Several concepts have been proposed and some prototype equipment built. There will be no universal solution or method for the varied environmental and producing conditions that will be encountered. However, one system that appears to offer considerable flexibility is the one atmosphere chamber. We are proceeding with design of prototype equipment for subsea facilities in chambers. These will be field tested under actual operating conditions.

The One Atmosphere Chamber System

History.

The use of one atmosphere chambers to house conventional oil field equipment on the sea floor is not a new concept. Figures 1 and 2 show a full-scale mockup of a 10-foot diameter cylindrical wellhead chamber built by Shell in 1956. This differed from the current system marketed by such companies as Lockheed Petroleum Services, Ltd., in two ways. First, personnel access was by a removable caisson supported by a drilling or workover rig. Second, the chamber was to be placed before spudding the well and used to house a conventional BOF stack. Water depth limitations of the access caisson caused this concept to be abandoned in the late 1950's in favor of a remote or wet system.

Why did the chamber concept lie dormant for 10 years? In spite of the rapid growth of the floating drilling industry during the 1960's, there was limited need for underwater completions. Platform depth capability and practice steadily increased to near 400 feet. Also few leases were available beyond this depth until the Santa Barbara lease sale. Thus, probably less than 50 underwater producing completions exist in the world today with the deepest in only 338 feet of water. A number of these have been drilled to test and evaluate concepts and equipment.