The demand for more and more oil and gas has prompted the industry to seek new areas of hydrocarbon deposits, and the development of subsea completions has kept pace. Many huge innovations have taken place since the first underwater completion was made about 70 years ago, when the first wet wellhead, basically a land Christmas tree, was deployed in shallow water. Finding hydrocarbons in deeper and deeper waters, away from existing infrastructure, has prompted the need to complete wells on the sea floor and then pipe production to floating facilities. The depth of water in which these wells were drilled made the use of platforms become technically unfeasible or not supportable by the economics of the development. The North Sea, Gulf of Mexico, Brazil, and west Africa have been the major areas of subsea development and reserves in increasing water depths have been brought into production, and more recent finds in east Africa are yet to be developed.
New technology has been deployed in a number of areas (Vernotzy 2013):
- Drilling rig and equipment design capable of operating in water depths in excess of 3000 m
- Better understanding of weather, ocean, and seabed conditions
- Flowline and pipeline design and deployment
- Design of very reliable processing and control systems
- The development of sophisticated remotely operated vehicles (ROV)
A recent study (Nelson et al. 2013) to review and understand where oil and gas has been found recently revealed the following:
- Globally, deep water has become a significant source of discoveries, accounting for more than 50% of new conventional reserves.
- The size of deepwater discoveries is an order of magnitude larger than other discoveries.
- However, less than 40% of those discoveries are in production, contributing less than 10% of conventional production.
- Deepwater production could double in the next 7 years as more fields are brought into production.
Early deepwater development required the use of proven technology, innovation, commitment, and teamwork between license holders, equipment suppliers, and service providers. Given the depth, it was essential that equipment be designed to operate at a very high level of success.
Over the years, subsea completions have become more complex, varying from single wells connected to a platform to subsea “factories” consisting of an array of wellheads, manifolds, and processing equipment. Irrespective of the complexity of seabed configurations, the fluids produced will have to be channelled to an onshore handling facility or to a fixed or floating processing unit. Given the environment under which the installed equipment has to operate for long periods of time with minimum intervention, the equipment must be robust and reliable and must ensure safety for personnel and protection of the environment.
As subsea technology has become more sophisticated over the years, collaboration between producers and suppliers of services and equipment has become more essential to ensure the delivery of first-class equipment in the areas of wellheads, manifolds, flowlines, cables, umbilicals, seabed processing facilities, and ROVs. The verification and testing of equipment prior to deployment and compliance with regulatory requirements has become critical and essential in these types of developments.
Whilst developments in deepwater technology have been focused on green fields, a new phase is emerging. Pressure depletion in some of these fields has made it necessary to seek ways to extend field life by deploying gas compressors at sea bottom. In the Norwegian sector of the North Sea, pioneering work has started (Knott 2013) in the design and deployment of compressors that will extend field life and add significantly to recovery factors. The use of these compressors will present challenges, as it is well known that attaining a high uptime even on platforms can give operators plenty of grey hairs, not to speak of operating in deep waters. The success of seabed compression will lead to application in greenfield development, thus eliminating the need for a retrofit.
A number of factors have led to the success story of deepwater drilling and seabed completions:
- Successful exploration and finding of very significant reserves that can support the huge capital investment that is required
- Collaborative work between license holders, equipment suppliers, and service providers
- Attraction of talented people to the interesting, innovative work
- Focus on safety and environmental protection
The future will present more opportunities and challenges. As the need arises to develop smaller and smaller fields, the industry will also need to seek ways to reduce the capital cost. The Industry will need to seek ways to shorten development time so that first production can be achieved faster, without compromising safety and environmental standards. Finally, talented people must be attracted and retained in this very innovative sector of our industry.
References
Vernotzy, R. 2013. Operators Move to the Next Level of Subsea Development. World Oil April Vol. 234 No. 4. http://www.worldoil.com/april_2013_OPERATORS_MOVE_TO_THE_NEXT_LEVEL_OF_SUBSEA_DEVELOPMENT.html
Nelson, K., DeJesus, M., Chakhmakhchez, A., and Manning, M. 2013. Deep-water Operators Look to New Frontiers. Offshore. http://www.offshore-mag.com/articles/print/volume-73/issue-5/international-report/deepwater-operators-look-to-new-frontiers.html
Knott, T. 2013. Subsea gas feels the pressure. Upstream April. http://www.upstreamonline.com/hardcopy/technology/article1324790.ece
