Operational Parameters Governing Tethered Capsule Diving Activities On One-Atmosphere Subsea Chambers
Authors: Stewart J.P. 
Published: December 2007

THIS PAPER WAS PREPARED FOR THE OFFSHORE EUROPE 77 CONFERENCE IN CONJUNCTION WITH THE ABERDEEN PETROLEUM SECTION OF THE SOCIETY OF PETROLEUM ENGINEERS OF AIME, HELD IN ABERDEEN, SCOTLAND, 14–15 SEPTEMBER 1977. PERMISSION TO COPY IS RESTRICTED TO AN ABSTRACT OF NOT MORE THAN 300 WORDS. ILLUSTRATIONS MAY NOT BE COPIED. THE ABSTRACT SHOULD CONTAIN CONSPICUOUS ACKNOWLEDGMENT OF WHERE AND BY WHOM THE PAPER IS PRESENTED. PUBLICATION ELSEWHERE AFTER PUBLICATION IN THE JOURNAL OF PETROLEUM TECHNOLOGY OR THE SOCIETY OF PETROLEUM ENGINEERS JOURNAL IS USUALLY GRANTED UPON REQUEST TO THE EDITOR OF THE APPROPRIATE JOURNAL PROVIDED AGREEMENT TO GIVE PROPER CREDIT IS MADE.

Servicing subsea petroleum equipment and connecting subsea pipelines using the dry, one-atmosphere approach, is a unique pipelines using the dry, one-atmosphere approach, is a unique concept which has been developed and proved by Lockheed Petroleum Services Ltd., of New Westminster, B.C. By encapsulating subsea equipment in dry, sealed chambers which are readily accessible to a service crew, work can be carried out by non-diving technicians in a shirtsleeve environment.

The key to the establishment and maintenance of these subsea systems is the LPS service system, which is able to transport men and materials between the surface vessel and the subsea chamber in a tethered service capsule.

This paper takes a close look at the three LPS service systems and their equipment, and discusses the problems, the solutions, and the experience gained since the installation of the first LPS subsea chamber in 1972.

LPS' successful operation in completing the welded pipeline connections at the base of the Thistle "A" platform is discussed in detail.

Conducting diving operations close to a platform presented LPS with a number of new problems concerning mooring patterns and diving techniques, not the least being those additional hazards generated by the rapidly changing and often unpredictable weather conditions in the North Sea.

Introduction

The connection of subsea pipelines and the servicing of subsea petroleum installations in a dry, one-atmosphere environment is a consept which has been developed and proved by Lockheed Petroleum Services Ltd. (LPS) of New Westminster, British Columbia. Petroleum Services Ltd. (LPS) of New Westminster, British Columbia. The encapsulation of wellhead valves and controls, petroleum manifold centers, and pipeline connections, in readily accessible, sealed chambers permits a considerable range of subsea operations to be conducted by nondiving technicians working in a "shirtsleeve" environment. Such a concept obviates the necessity for complex hyperbaric facilities, long periods of decompression, and the attendant hazards of saturation diving. Of even greater importance is the fact that the shirtsleeved technician has available to him a variety of replacement parts, tools, manuals, blue prints, and the ready assistance of other shirtsleeved technicians.

The key to successful operation of the LPS subsea service is the ability to transport technicians to the job site when needed by the customer, to supply them with the necessary life-support and power requirements while performing their tasks, and to return them power requirements while performing their tasks, and to return them safely to the surface support vessel at the completion of their work.

The subject of this paper primarily concerns the LPS service systems and the operational parameters imposed upon them by environmental conditions. In addition, it presents an historical overview of LPS' field experience with emphasis on the Thistle 'A' Program - which, together with design criteria, formulated these parameters.

The Thistle 'A' Program was LPS' first experience in the North Sea, and its first involvement in capsule operation adjacent to a platform jacket. When work at the job site began many unknown factors remained to be faced in spite of considerable planning and years of experience in the Gulf of Mexico. But, although the North Sea was not a gentle and understanding teacher, a great deal was learned in a very short time.

THE LPS SERVICE SYSTEMS

An LPS service system comprises a surface support vessel (SSV), a service capsule (SC), and surface support equipment (SSE).

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