Offshore Oil and Gas Pipeline Basics
John Poullain, P.E.
This three-hour online course summarizes basic information, relevant issues and guidelines for the installation of offshore oil and gas pipelines and describes the potential impacts and mitigation measures. The advantages and limitations of the methods commonly used to lay pipelines in varying offshore water depths are discussed. Also addressed are pipeline inspection, safety issues and maintenance used to provide safe and reliable undersea pipeline transport of products in order to prevent leakage into coastal environments. The functions of various equipment, methods and procedures are described to give an understanding of typical problems encountered such as hydration and wax formation.
This course includes
a multiple-choice quiz at the end, which is designed to enhance the understanding
of the course materials.
At the conclusion of this course, the student will:
This course is intended for civil engineers, environmentalists, owners and contractors.
Benefit to Attendees
The student will gain an understanding of the methods used for laying pipeline in the offshore coastal areas of the US and the methods used to maintain the pipes. The advantages, limitations and comparisons between methods used for pipelaying are considered. Safety considerations and potential hazards to safeguard against during pipeline installation and operation as well as preventing petroleum releases are also discussed. Pipelines must be maintained to operate efficiently and to prevent leakage of petroleum products into the environment.
This course provides general guidance for the installation, impacts and measures for mitigation of offshore oil and gas pipelines. As more oil and gas reservoirs are discovered in deep water, oil and gas exploration and development have been gradually moving farther offshore and into deeper and colder water with production wells in water exceeding depths of 10,000 feet. Necessary measures to maintain the pipeline and other equipment as well as any unsound conditions or potential problem areas are considered.
After oil and gas fields are discovered the next challenge is to move the product to onshore refining or processing facilities. Determination of pipeline routes and the locations of mooring lines for pipelines and operating barges in deeper water are difficult because of uncertainties of the sea floor. Many methods such as 2-D and now 3-D seismic surveys, satellite sensors and surface-towed sonar have mapped sea bottoms with varying degrees of resolution. Sea floor maps have shown furrows, which can help locate the path of a proposed pipeline and avoid areas where the pipeline might otherwise, span over ridges. The furrows indicate sea bottom currents are present but for how long they've occurred is uncertain. Recent mapping has shown unanticipated furrows in the Gulf of Mexico further out from the continental shelf. However a challenging 65 km long pipe in a pipe pipeline was placed in the North Sea and was designed to adapt to ocean floor irregularities by snaking along the sea bottom without any restrains or anchors. Furrows however are yet another factor with possible impacts for pipe laying and drilling operations and must be considered because of abrupt changes in seafloor topography. Additional and better survey data over time will clear up those uncertainties and indicate any ongoing patterns or changes in the seafloor.
Pipe laying barges
may be outfitted with multiple welding and x-ray stalls. The pipe can be fed
from the barge and if required simultaneously burying it. Burial jetsleds operate
from bundled air and jet hoses to bury the pipe. Moored pipe laying barges may
use 8 to 12 anchors and moor lines to maintain their positions during pipelaying
operations. A barge laying pipeline on the sea bottom must be moved as certain
lengths of pipeline are installed, requiring the anchors and mooring lines to
be moved and redeployed for each reach of pipeline extension. As water depths
have become progressively deeper, conventional steel cable lines would be too
heavy and costly. A concern for using synthetic ropes stems from potential failure
from wear and tear while moored, from the repetitive redeployment while pipe
laying barges advance to new stations and from rope fatigue caused by repetitive
movements. The ropes are subjected to great stresses at the anchor and barge
points of connection. Department of the Interior, Minerals Management Service
(MMS) has funded research for mooring lines and special synthetic ropes have
been tested in such locations as the Gulf of Mexico and offshore of Brazil.
The weight saving become very large as pipe installations head farther offshore
into deeper waters. Just reducing the number of support barges required for
mooring lines can result in big cost saving.
Construction and installation of offshore pipelines have special challenges to maintain the pipes and to provide efficient and long-term performance, especially when compared to onshore pipelines. Pipe installations from lay barges and reel barges tests the mechanical durability of the corrosion coatings and welds as the pipes are passed over the barge stingers and rollers or when towed along the sea floor. Offshore pipes must withstand varying operating temperatures, large temperature differences between the inside and outside of the pipe walls and high hydrostatic pressures.
Just as pipe laying has many challenges, recovery and/or removal of damaged pipelines may be required. The integrity of older existing pipelines has been a concern due to the corrosion susceptibility, data from repair histories and knowing the actual existing conditions. MMS has made studies and published papers regarding the assessment of existing pipelines with attention to corrosion monitoring, leak detection and other related issues.
Pipelines are also used to load liquefied natural gas (LNG) tankers. In cases where the offshore coastal area has a relatively gentle slope, long stone jetties or else channels are dredged to gain sufficient draft for tankers to load or unload the LNG for processing plants. Subsea pipelines can be a feasible and cost saving alternative. Avoiding the construction of long stone jetties means less oceanbed will is disturbed. Avoiding channel dredging also reduces the impacts to biologically sensitive areas and less disruption to navigation during the construction and future maintenance dredging.
Many advances have been made in mechanical equipment such as remote spillage or leakage detectors, monitoring systems and alarms that safeguard against the threat of petroleum releases. Periodic inspections, knowing when a component of a system is defective or improperly maintained and understanding what is necessary to correct observed problems are important to continue proper operations of a pipeline. The course covers the basic feature of good maintenance, value of inspections and factors that adversely effect pipeline operations.
Recently developed alternatives to offshore pipelines are floating production, storage, and offloading vessels (FPSO) which look like oil tankers but are used to store oil and load tankers out at sea. They can hold up to 2 million barrels and replace pumping the crude through pipelines from wellheads. The vessels can be advantageous where extremely long pipeline are needed and/or where political instability with acts of sabotage would cause costly repairs and setbacks in oil production. Long offshore pipelines are very expensive and take years of construction time.
FPSO have been
used along the coast of Brazil, W. Africa and Southeast Asia but not in the
GOM which has an existing and extensive system of pipelines. An advantage for
FPSO in GOM would be the ability of disconnecting from undersea wells before
hurricanes and towing them out of severe storms until the storm have passed.
Many GOM pipelines, wellheads and risers were severely damaged by the 2005 hurricanes.
These floating production vessels are very expensive and whether they are cost
effective would have to be based on case by case economical analysis.
This course is based primarily on the US Department of the Interior
OCS Report MMS 2001-067, "Brief Overview of Gulf of Mexico OCS Oil and
Gas Pipelines", 2001 Edition, 19 pages), PDF file. The course is also based
on an article reprint from the Underwater Magazine, "Subsea Pipelines:
From Survey to Start-Up New Technologies Conquer the Ocean Deep", (2002
publication, 5 pages), HTM file.
The links to the course materials are:
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This course serves
as a guide for the methods used for offshore pipeline placement. The operation,
inspection and proper maintenance necessary to prevent or warn of any leakage
of the products into the environment are explained. Also described are the main
equipment and devises used for pipelaying operations and the problems that are
commonly encountered during installation and operation. Problem areas and what
to look for in deciding undersea pipeline routes are discussed. The environmental
and other sensitive areas that may be impacted by pipelines and pipelaying operations
are addressed. Possible mitigation measures are also considered.
technical information related to this subject, please refer to:
The US Department of the Interior, Minerals Management Service (MMS) has publications and data sheets on pipeline installation and regulation in Outer Continental Shelf (OCS) areas of the Unite States. The Technical Assessment & Research (TAR) program of MMS assesses the design and installation of future pipelines as well as mitigation for the existing ones.
Onshore technical data and offshore pipeline oil and gas projects are discussed. The site also offers guidance on systems and methods of exploration.