Since the development of flexible pipe in the early 1970's over 2,500 km of product has been manufactured and then installed subsea. This has helped overcome many technical and commercial problems where conventional techniques were either unsuitable, unproven or not cost effective. Compared to regular linepipe the complex arrangement of plastic and steel is a premium product. Therefore it is important to have an understanding of flexible pipe performance to produce cost effective solutions to production problems. This paper looks at the principal areas where flexible pipe has been found to be the best solution and therefore producing the lowest cost solution. It also looks at future developments that should improve performance and reduce cost.
Subsea systems can be configured in many different ways to optimise the economics of each reservoir. Within the range of options available, flexible pipe is able to provide a cost effective solution to a number of problems that can be encountered. These may be aggressive production conditions, complex subsea arrangements or small one-off systems. As flexible pipe is manufactured and tested on shore, the installation is simplified as there are only flange connections to be made between each length. As the cost of flexible pipe includes assembly, testing and certification of the finished product on reels, it is difficult to compare actual material cost per kilo or meter between flexible and conventional pipe. For this reason the best comparison is the actual installed cost considering also operation and maintenance.
A typical subsea system is made up of a number of key components. They include the various production and injection wells. These wells are then attached to flowlines which transport the fluids to the production system. Then there is the associated control equipment to monitor and operate the system. This paper focuses on the flowlines used subsea and how they can effect the economics of a project. The flowlines considered are the pipes used to transport produced and Injected fluids from and into the actual well heads. With these various components, the overall cost of a system is made up of the initial capital expenditure, the operating cost and the expected life. The capital cost covers the first phase of construction which includes wells, flowlines and associated equipment. This cost is traded off against the operation cost and expected life so as to achieve an economic solution. This economic solution will then be determined by the effective costs including interest payments when compared to the performance of the system. The performance will be the production achieved during the life of the system and the residual value. With most platform based systems the residual value is negative as the abandonment costs are high when compared to any resale or scrap value. With subsea systems the abandonment cost is lower and some equipment can be re-used. This may enable a subsea project to show a positive residual value. This is especially true of flexible pipe where over 700 km, have been recovered and re-used to date.