The use of subsea one-atmosphere chambers for early petroleum production schemes or for wells beyond the reach of platforms has been a reality for seven years. Such chambers are currently in use in the Gulf of Mexico and offshore Brazil for Shell, Union Oil, Tenneco and Petrobras.

Everyone-atmosphere chamber has two basic functions in common to isolate the equipment it contains from the subsea environment, and to allow trained oilfield technicians access to that equipment for servicing and trouble-shooting.

The type and function of the equipment installed in the chamber is unlimited. This paper deals with two applications of the one-atmosphere chamber: first, with well production chambers and equipment, and secondly with manifolding chambers and equipment. Design considerations, fabrication, installation and service techniques are discussed. Typical servicing operations are described.


The one-atmosphere early production system consists of the subsea chamber (s), the enclosed production equipment, production flow lines, connections to a production riser and a surface support system. Figure 1 (Garoupa) illustrates the early production scheme using one-atmosphere chambers in use offshore Brazil. Satellite one-atmosphere Wellhead Chambers (WHC) enclose the Xmas tree packages, a Manifold Center (MC) gathers and commingles the flow from all wells via flow-line bundles and transfers it to a floating process facility tied to a single point moor type riser. A one-atmosphere servicing system consisting of a tethered diving bell type Service Capsule (SC) and Surface Support Vessel (SSV) provide subsea servicing capability for the one-atmosphere system.

The chambers provide an encapsulated area isolated from ambient sea pressure and the corrosive effects of salt water. The environment inside the chamber is controlled to ensure that as near as possible, dry land conditions exist. Internal pressure is at one-atmosphere. Normal air is provided for breathing without masks.

Using a one-atmosphere chamber to encapsulate equipment on the ocean floor eliminates the need for production equipment specially designed to operate in ambient sea pressures and in a highly corrosive environment. Equipment, tested and proved in land applications, can be selected from regular stock and suppliers. Using a one-atmosphere chamber also eliminates the need to use divers to perform commissioning and service tasks. Instead, oilfield hands and technicians may be used for the many complex servicing and trouble-shooting activities that occur during the 20-year operating life of a subsea unit. It also allows the use of a well-proven subsea flow line connection or pull-in technique and manned intervention during the critical Xmas tree installation.

Chamber Design

The design of anyone-atmosphere chamber for use subsea is affected by the following: the working environment, both in terms of water depth and the corrosive effects of salt water; the type of production equipment to be encapsulated; life support and safety systems for periods of servicing and the installation technique to be used.

Until 1978, design criteria for subsea manned habitats permanently attached to the ocean floor were not specifically included in any regulatory codes.

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