Requirements for New Technology In Offshore Pipeline Construction
Authors: Corley C.B. , Warner D.G. 
Published: October 2008

Most offshore pipelines have been installed in relatively calm, shallow waters. Maximum water depths for existing lines are about 340 ft for 12- to 24-in. lines and 140ft for a 48 in. line; these are about the present depth capability limits for construction in calm water, particularly :for 24-in. and larger diameter lines. Experience in rough weather-has shown that construction is limited to periods when seas are less than about 6 to 8 ft and that weather downtimes may account for 40 to 60 percent of the total time on the job.

Offshore exploration is now being conducted and discoveries have been made in-water much deeper and/or environments more severe than previously experienced. Furthermore, pipelines may represent one of the largest investment elements in developing some remote fields. The capability to install pipelines may also be the lead time critical path for initiation of production from reservoirs underlying deep, rough waters.

To satisfy anticipated requirements, laybarge construction techniques may need to incorporate improved pipe-joining methods, barges with better motion characteristic, improved barge-mooring or positioning systems, shortened [or eliminated] stingers, greater tensioning ability, inclined ramps, more efficient pipe transfer and handling methods, and faster weather disruption procedures. Other pipe-laying methods may provide alternatives for rough and deep water, but further developments are required to satisfactorily prove their capability.

Heretofore, producing companies have successfully looked primarily to the offshore construction industry to provide the equipment needed for pipeline, construction. However, the operator now finds himself needing capability not apparently available. Thus, operators and contractors face the mutual challenge of developing the technology needed to overcome existing problems and high costs and to progress to deeper water and more hostile environments.

INTRODUCTION

Although most offshore pipelines have been laid in relatively calm, shallow water, some experience in more hostile environments indicates that the technological limits of presents pipeline construction capability are being reached. Exploration for offshore oil and gas is now being extended to areas with water deeper and weather more severe than previously encountered. Discoveries in these areas will require improved pipeline construction technology.

This paper will review existing offshore pipeline construction capabilities, project deep and rough water requirements, and define needs for extension of technology.

OFFSKORE PIPELINE CONSTRUCTION CAPABILITY

Calm Environment

Fig. 1 presents water depth experience for construction of existing offshore pipelines [data points show some of the more significant individual lines]. Maximum depths may be characterized as)20 to 340 ft of water for 12- to 24-in. diameter lines, 160 ft for a 30-in. line and 140 ft for a 48-in. line. Most construction has been in relatively calm water in the Gulf of Mexico, the Persian Gulf and Lake. Maracaibo which are, of course, the areas with the largest offshore production. While both reel barge and line-pulling construction, method have been used, the conventional stringer laybarge method has been most prevalent.