Arne Loeken, head of the risers and moorings section at Det Norske Veritas (DNV), Oslo, told delegates at the FPSO-TECH '97 conference in Aberdeen late last month how companies are looking to extend their technologies.
"The most important change," said Loeken, "when working in water depths of 2,000 m and beyond is to extend and further develop technology for floater, riser, and mooring systems in terms of architecture, functional loads, and exposure to environmental action.
"The industry has to focus on cost reduction through innovative design approaches, new materials, standardization, and optimized construction and operation procedures."
DNV expects floating production vessels and linked subsea developments will become the dominant technology off Norway and worldwide for deepwater field developments.
Norwegian operators are beginning to explore the Voering and Moere basins off central Norway, where water depths are 1,000-1,500 m.
Developments in water 500-2,500 m deep are taking place or planned off Brazil, in U.K.'s West of Shetland area, in the Gulf of Mexico, off West Africa, and off Southeast Asia.
"As a response to new challenges in deep water worldwide and on the Norwegian continental shelf," said Loeken, "DNV has launched several new projects in coordination with the Norwegian Research Council, oil companies, and technology partners."
Projects include deepwater anchor design; reliability-based, cost-effective methods for deepwater mooring; design procedures and acceptance criteria for deepwater risers; and deepwater analysis tools. Total budget is more than 40 million kroner ($6 million).
"For new design situations such as deepwater applications," said Loeken, "it is important to establish rational, consistent, and cost-effective design procedures.
"For this purpose, a reliability-based calibration study can be performed to develop a load and resistance-factored design equation, with calibrated safety factors to be used in the design."
Among the program's aims are improvements of existing tools for simulation of the response behavior of offshore structures "to cover in a more realistic way important effects such as ringing, vortex shedding, and slowly varying motions, as well as interaction effects between floaters, moorings, and risers."
Atlantis concept
Terje Magnussen, senior consultant with Proffshore AS, is working with Aker Maritime AS, Stavanger, to develop a concept that he reckons can sidestep many deepwater issues.Magnussen told delegates about the Atlantis E&D concept, which gets around the problem of gaining access to wells in deep water by use of an "artificial seabed" (see schematic, p. 27).
Two versions are being developed, centered on the artificial seabed: The drilling version requires only conventional well control equipment in deep water; the production version requires a conventional floater and proven subsea equipment.
"All problems related to deep water arise from the long distance between the wellhead and the surface vessel," said Magnussen. "The basic idea of Atlantis is to move the wellhead up to a more convenient water depth."
Magnussen said his invention avoids the problems and eliminates the need to spend huge resources on partial solutions that make it possible to operate in deep water but with constraints.
For drilling, a single-well version of Atlantis is being developed, comprising an artificial seabed mounted on well casing extending all the way up from the reservoir and anchored by cement at the seabed.
"The basic difference between Atlantis and other concepts using buoyant, submerged, or floating structures," said Magunussen, "is that the casings function as the only anchoring and are continuous from the reservoir to the near-sea-level-located wellhead."
The drilling version, call Atlantis-E, is intended to be deployed by a drilling rig. For both drilling and production modes, the artificial seabed would be positioned 200 m below sea level.
In the production version, known as Atlantis-P, multiple well casings would be installed and multiple wellheads would be mounted on the artificial seabed.
"Use of the Atlantis-P system gives a number of advantages," said Magnussen, "both technical and economical. It requires no central, high-cost installation like a tension leg platform.
"The cost of the artificial seabed is very low, and so are the costs of the entire installation. This gives technical and economic flexibility similar to conventional subsea field developments at moderate water depths.
"The cost of the artificial seabed is comparable to that of a subsea template, and a development could be carried out as with conventional subsea equipment and a floating production system at moderate water depths.
Proffshore is developing Atlantis in cooperation with engineering contractor and fabricator Aker and expects to complete a prototype of Atlantis-E for testing during second half 1998.
"The production version will be taken through a 2-3 year design and testing project," said Magnussen. "However, a field-specific Gulf of Mexico case study is ongoing and will be used to establish a design basis for Atlantis-P."
Norway's reserves
Norway's offshore sector seems to have yielded most of its giant finds to explorers, yet much of Norway's acreage is underexplored, and other big discoveries are possible.Eric Mathiesen, director of forecasting and resource assessment at Norwegian Petroleum Directorate (NPD) told delegates, "Exploration results on the Norwegian continental shelf were particularly good in the 1970s and first half of the '80s, when a majority of the large oil and gas fields were discovered.
"Since then, the average discovery size has dropped, although drilling activity and the number of discoveries per year have remained at the same level.
"However, this trend is challenged by a couple of large gas/condensate discoveries made recently in the Norwegian Sea and the recent gas discoveries in the deepwater Voering area."
Mathiesen said total Norwegian petroleum resources are estimated at 12.5 billion cu m of oil equivalent, split about equally between oil and gas. Only one sixth of this volume has been produced so far, and only half the total is located in the 55 fields that have been approved for development to date.
"The remainder," said Mathiesen, "is made up of a large number of small discoveries that have not yet been developed, significant undiscovered resources, and an expectation of a better utilization of the in-place resources in the existing fields."
There are now about 120 undeveloped oil and gas discoveries off Norway. Development activity is currently high, and several of these finds are due to be brought into production in the next few years.
Most of the undeveloped finds are gas discoveries and oil finds with large volumes of associated gas. Norway will be oversupplied with gas for export for several years to come. Further large gas finds have been made recently.
Development of gas finds depends on the allocation of sales contracts to individual fields, based on criteria including value creation, supply, security, and access to transport systems.
"The situation differs somewhat for oil discoveries," said Mathiesen. "A majority of the oil resources, about 60%, is expected to be developed within the next few years. For the remainder, a combination of several factors explains the lack of development plans.
"Satellite discoveries remain undeveloped because they are waiting for processing capacity on the host platforms. Others are waiting for the operator to establish a development strategy for surrounding fields and discoveries.
"Another important reason is the fact that the profitability of several of the small discoveries is sensitive to further appraisal spending. They may remain undeveloped because the partnerships are unwilling to spend more on appraisal, and at the same time unwilling to accept the higher development risk associated with these discoveries."
Copyright 1997 Oil & Gas Journal. All Rights Reserved.
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