The Oooguruk offshore Arctic flowline system design, construction and operation satisfy the unique conditions presented by this shallow water Beaufort Sea location. The bundled 3-phase 12 × 16-inch pipe-in-pipe production flowline, 8-inch water injection, 6-inch gas lift/injection and 2-inch diesel fuel flowlines were installed along with power and communications cables offshore the North Slope of Alaska during 2007. The maximum water depth along the flowline route was only 7 feet but the location immediately offshore the Colville River Delta presented challenges with the flowline loading conditions, thermal interactions with the local environment and construction procedures. Key features of this flowline system include addressing flow assurance requirements for combined offshore/overland sections, strudel scour, subsea permafrost thaw consolidation, upheaval buckling, limit state design for bending, winter construction procedures and flowline leak detection systems. The subsea power cables consisted of separate cables for each conductor in order to be compatible with trucking all materials to the remote site. The dual fiber optic communications cables are being utilized with a distributed temperature sensing system to monitor the flowline burial conditions and supplement the multiple flowline leak detection systems. Introduction The Oooguruk oil field is located 6 miles offshore the North Slope of Alaska, in the Beaufort Sea. The site is partially sheltered from the more severe sea ice and wave conditions of the Arctic Ocean by its shallow water depths and a series of barrier islands offshore of eastern Harrison Bay. However, the field's shallow water location near the Colville River Delta provides its own challenges for the safe design, construction and operation of a flowline system to support the offshore field development. The flowline system transports 3-phase produced fluids, gas, water and diesel fuel and includes power and communications cables. Conventional pipeline design requirements must be integrated with the complex thermal interactions of the Arctic environment and the unique offshore arctic loading conditions. Pioneer Natural Resources Alaska, Inc. is developing the Oooguruk Unit along with partner, Eni Petroleum Co. Inc. on state leases in the Beaufort Sea, west of Oliktok Point (Hall, 2008.) Oil wells are being drilled from an artificial gravel island (Oooguruk Drill Site or ODS), located in four feet of water and tied back to new onshore facilities (Oooguruk Tie-in Pad or OTP) near drillsite 3H, within the Kuparuk River Unit (KRU.) Existing KRU facilities will process the produced fluids and transport the oil 40 miles further east to the Trans Alaska Pipeline System. KRU will also supply injection water and injection/fuel gas to Oooguruk. The Oooguruk flowline design needed to be cost effective and installed on a schedule matching Pioneer's field development plans. Flowline safety and minimizing impact to the fragile Arctic environment are fundamental project requirements for all North Slope field developments. Oooguruk follows BP's Northstar project as the second Beaufort Sea oil field to be developed using subsea pipelines (Lanan, 2001.) Additional planned Beaufort Sea field developments applying subsea pipelines include Eni Petroleum's Nikaitchuq oil field and other future projects.
The BP Northstar, Pioneer Oooguruk and Eni Nikaitchuq pipeline projects provide a significant experience base for designing, installing and operating future offshore arctic pipelines. Each pipeline is located in the nearshore zone of the Beaufort Sea, offshore the North Slope of Alaska. Maximum pipe diameters range up to 18 inches, water depths to 37 ft and lengths to 6 miles. Unique offshore arctic environmental loading conditions influenced each pipeline design differently for defining the required pipe bundle configuration, thermal insulation and trenching requirements. Similar differences affected the winter construction procedures used for each project and would be expected to impact future pipeline projects in deeper waters. A total of 13 years of pipeline operational experience has been gained and key features such as routine seabed surveys, in-line-inspection pigging and effective leak detection systems are important to the continued safe operations of these pipeline systems. Introduction Development of offshore oil and gas reserves in Arctic and sub-Arctic regions of the world have progressed relatively slowly (INTECSEA, 2011). This slow pace results largely from the remote field locations, unique arctic environmental load conditions and the lack of existing hydrocarbon export facilities. Subsea pipeline systems are often needed to connect offshore fields with onshore pipeline networks, for intrafield flowlines or for export tanker loading lines. Safe and economical design, construction and operational procedures are needed to address the unique conditions encountered for offshore arctic pipelines. Three pipeline systems have been installed in the Beaufort Sea, offshore the North Slope of Alaska for BP's Northstar, Pioneer's Oooguruk and Eni's Nikaitchuq field development projects (Figure 1). The Northstar and Oooguruk projects have been operating for a combined total of over 13 years and the Nikaitchuq project is scheduled to start operations during 2011. Each of these offshore arctic pipeline systems transports oil and gas from gravel island structures to shore. This Beaufort Sea pipeline experience can be applied on future Arctic and sub-Arctic projects having first-year sea ice, multi-year ice or iceberg load conditions. Seasonal sea ice is found at varying latitudes in both marine and inland lake locations, not just north of the Arctic Circle (or surrounding Antarctica). Other potential applications of Beaufort Sea pipeline experience include projects having complex thermal interactions with the local environment and offshore arctic projects requiring conventional marine construction procedures during the short Arctic summer season. Additionally, pipeline operations, maintenance and potential repair procedures form an integral part of an economical, safe and reliable offshore arctic pipeline system. Beaufort Sea Environmental Conditions The nearshore Alaskan Beaufort Sea ice typically breaks up or melts in place starting in June. Summer open water conditions then prevail from late July through mid-October. The summer polar pack ice edge recedes varying distances offshore based on the site location, water depth and year to year variations or long-term climate trends. Even during the open water season, however, ice floes are often present and their movement is influenced by winds and currents. Along much of the Alaskan North Slope coast, low barrier islands prevent multi-year polar pack ice from entering the nearshore lagoon areas. Ice can affect offshore marine operations outside the barrier islands at any time during the summer.
For safe and cost-efficient operations of new and existing offshore Arctic pipelines, monitoring of pipeline structural integrity is imperative. A well-founded pipeline integrity management program can optimize production output, extend the life of the pipeline, and serve as a tool for providing preventative maintenance information. Without the implementation of a routine integrity monitoring campaign, pipeline integrity degradation may go undetected until the point of failure. Arctic-specific offshore pipeline design and operational challenges, such as strudel scour, seabed ice gouge, pipeline upheaval buckling, permafrost thaw settlement, and remote location increase the risk and severity of a loss of pipeline integrity. These design cases can create abnormal conditions and ground deformations along sections of the pipeline which can be difficult to immediately detect through standard integrity monitoring systems and schedules. Many of the existing offshore pipelines in the Arctic are buried in remote locations under seasonal ice cover and the failure to detect pipeline damage in a timely manner could have severe safety, environmental, and economic consequences. An Arctic pipeline integrity monitoring philosophy can be implemented to provide further mitigation against loss of pipeline structural integrity by means of regular bathymetry surveys, In-Line Inspection (ILI) campaigns and Fiber Optic Cable (FOC) monitoring. This paper provides a guideline for buried offshore Arctic pipeline integrity monitoring. The guideline covers pipeline integrity assurance incorporated into the pipeline design, the surveys to be completed during installation, as-built assessment of the pipeline profile, the warm-up assessment/implementation needed before start-up, and the integrity inspections to be completed during operations.
In the nearshore zone of the Alaskan Beaufort Sea, three subsea pipeline bundles have been successfully installed by using conventional onshore construction equipment in the winter season operating from a thickened sea ice platform. Differences in water depth, route length and corresponding pipeline design for BP Northstar, Pioneer Oooguruk and Eni Nikaitchuq impacted the winter construction procedures used for each project. Each of these projects used the winter construction season to its maximum advantage, allowing the use of conventional and adapted onshore construction equipment and techniques. Comparatively, ice based winter pipeline construction in subarctic conditions has been generally less successful. On-ice pipeline fabrication and installation into a subsea trench has a track record for shallow water pipeline installation with reduced permitting issues compared to summer installation. Based on the experiences of these projects, this paper reviews the limitations of on-ice construction, the typical construction activities; the main equipment used and will highlight the main lessons learned.
Offshore pipelines in an Arctic or ice-covered environment face unique challenges different from traditional subsea pipeline design. In 2018, Intecsea as lead consultancy delivered a report to the US Bureau of Safety and Environmental Enforcement (BSEE) Alaska Region which provided a comprehensive review and gap analysis of the Status of Arctic Pipeline Standards and Technology. The objective of this study was to provide BSEE with a comprehensive review and gap analysis of current offshore Arctic pipeline design standards, codes and regulations pertaining to design and development of offshore pipelines in the Arctic, and to report on the state-of-the-art and emerging technologies for offshore pipelines in Arctic applications. Project development information from nine existing offshore Arctic pipelines in the U.S., Canada, and Russia was summarized, as well as guidelines and industry best-practice for monitoring and leak detection. This paper provides an overview of the results of this study; what offshore Arctic-specific pipeline design and construction challenges may entail, how they have been overcome in past projects, perceived gaps in regulations, and technology advancements that may help with future developments. This paper also summarizes the results of a comprehensive review and gap analysis of Arctic pipeline standards, assessment of the suitability of a single-walled versus pipe-in-pipe system for Arctic applications and presents information on some of the advancements in pipeline design, installation, operations and repair solutions that may be applicable to an Arctic environment.
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