Subsea processing offers several advantages compared to traditional ways of producing, processing and transporting well fluids to onshore terminals. By removing the need for expensive, manned floaters, initial investments can be reduced significantly. A concept based on subsea processing also offers the option to provide additional energy to the well stream to reach treatment facilities (offshore or onshore). This is particularly important for exploitation of hydrocarbon reservoir in deepwater, where the needs for providing energy to the well stream is higher. This has the potential benefit of increasing the ultimate recovery and/or accelerating the production. Regardless of the chosen concept, the ability to keep wells on stream is the most important factor determining field economic performance. For subsea processing, the anticipated equipment performance and the associated operating costs are subject to uncertainty. In addition, moving into deeper water, subsea interventions become more expensive and are associated with longer waiting times for the required intervention vessels. The fundamental question is whether the reduced CAPEX of a subsea processing system is out-balanced by the higher OPEX as compared with traditional systems. Ultimately this question can be addressed using a cost/benefit approach. This paper discusses the advantages and disadvantages with subsea processing systems from a life cycle cost perspective (capital and operating expenditures), and describes how implications of component failures can be factored into business decision analyses that seek to evaluate the viability of new technology. In particular a review of the subsea processing technology provided by the industry today is given together with an overview of the new functionality that is required to make subsea processing a viable option for the exploitation of hydrocarbon reserves. The paper will identify areas of uncertainty related to subsea processing and define a rational approach to support the decision making process in the qualification of subsea processing solutions.
New oil and gas frontiers are presently looking at projects offshore of theGulf of Mexico and South Atlantic, including West African and Brazilian watersand soon after Asia Pacific. New technologies are required to performinstallation in a cost efficient and safe method; they must encompass the stateof art equipment in order to provide effective solutions. The new ships FDS2and CastorONE are Saipem's replies to the forthcoming challenges indeep/ultra-deep water field development and pipe lying. The new vessels willoperate by using new welding, NDT and field joint coating technologies, including innovative installation equipment able to generate added value forthe implemented solutions. Field development projects include complex risersystems and the new fleet is designed to offer reliable solutions for thefuture configurations, which are designed to route the oil and gas fluids tothe floating treatment units. Saipem FDS2 is described by indicating hercapabilities and her equipment, including those required for project in shallowwater and those specifically designed for deep waters installation. Furthermore, sea keeping and naval features are offered in order to demonstrateher versatility and ability to solve main installation challenges relevant tothe deep water fields. Trunk line projects will be addressed to transportationof large gas volumes over long distances across harsh environments and Saipemvessel CastorONE is presented by showing off her capabilities for the ultradeep water installation. Information on the new state of art rigid stinger isprovided together with some conceptual solutions designed to increase theefficiency of the working stations and of the method to transfer the pipes withspecific equipment. The paper concentrates on the installation requirements forthe in-field production gathering systems and on the oil and gas exportpipelines. Field development: the leading market trends Since 1998, numerous deep water field development projects, mainly in the SouthAtlantic region both in West Africa and in Brazil were carried outsuccessfully. The vision for the future leads towards two major trends: evendeeper waters and new surprising geographical regions. Moving in bothdirections, thanks to its top class technologies and assets, Saipem aim to leadthe path towards the even tougher future challenges. The scope of the work of deep water projects, within EPCI type contracts, hasnormally included all major and minor technical aspect, supplies andinstallation/operations from A to Z, with contract values typically in therange of half to one billion USD. Key of this market segment - which nowrepresents a significant portion of turnover and backlog - has been theintegrated development of original technical solutions and dedicatedfit-for-purpose installation vessels. Leveraging on its notable competence, track record and offshore constructionfleet, the two main lines of evolution for the offshore field developmentmarket were, are and will be tackled, namely ultra-deep waters and new frontierregions as follows:On one hand, the ultra-deep water developments, emerging in the traditionaloil provinces in the Gulf of Mexico and South Atlantic, will require theIndustry to make available new technologies and equipment to support the safeand effective implementation of the relevant production schemes;Simultaneously, the development of subsea oil and gas fields is taking placein new world regions bringing quite new challenges from both the technical andexecution standpoints. Exploitation of oil and gas reservoirs in water depths in excess of 2,000m (?6600') is progressively emerging as the new market. Gulf of Mexico, offshoreBrazil and West of Africa are nowadays showing the greatest concentration offield development projects. In addition, subsea developments in new areas suchas East India, Indonesia, Offshore China and Western Australia are appearing inthe offshore oil and gas theatre both for relatively moderate and for deeperwater depths. Perdido Regional Development in the Western Gulf of Mexico and the Walker Ridgearea in the Central Gulf of Mexico will be significant and challenging offshoreprojects.
Several riser system configurations have been developed to assist the recovery of hydrocarbon reserves from deepwater reservoirs. Vertical hybrid riser systems present a number of attractive features and are currently proposed for various West of Africa deepwater developments. The paper describes the Bundle Hybrid Offset Riser (BHOR) concept of a vertical hybrid riser which incorporates bundle arrangements of multiple conduits conceived to enhance the flow assurance performance of the system to allow for the delivery of the production stream to the surface treatment facilities under the production conditions which are anticipated during the field life. Gas lift capability is also incorporated in the bundle arrangement. The passive thermal insulation properties of the system are then addressed by presenting the ability of the concept to accommodate both syntactic and gel materials. Further to the above, the BHOR concept fabrication and installation scenario is discussed in relation to the specific features and constraints which characterize the West of Africa deepwater conditions. Moreover, the paper addresses both the mechanical and structural design issues associated to the proposed system configuration with specific focus on the anticipated improvements in the dynamic and fatigue behavior both under in-place conditions and during installation by tow. Finally, the paper describes the operational advantages offered by the Active Circulation System (ACS) based on hot fluid circulation from the top of the riser down to the gas lift injection point which is incorporated in the BHOR concept to provide hydrate blockage removal capability following either accidental conditions or prolonged shut-downs exceeding the cool down system capacity.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe high costs of offshore activities, particularly deepwater drilling, are currently forcing oil companies to consider new technologies and new ways of operating in an effort to reduce costs of finding oil in even deeper waters. Shell and Saipem have been working together for the last 18 months considering the idea of a Subsea Drilling rig. This work has indicated that subsea drilling is a feasible concept, which has a number of benefits over conventional drilling, although the cost to construct a fully capable rig, coupled with the technical risk associated it, means that it is unlikely to happen today. However, for rank exploration work, where success is on average very low (20-30%), it is proposed that a very small subsea rig, with the capability to gather a minimum of reservoir data through a minimum diameter hole, might be an economically attractive solution, which will enable true low cost exploration drilling.
Marginal fields, and in particular those in deep wafers, call for innovative technologies to enable economical exploitation. The subsea development is gaining acceptance as one of the most promising options and appears the only one able to offer a viable rate of return when moving into deep waters. Most of the anticipated development applications call for either a high level of complexity in case of multiwell systems or a reduced equipment set up for limited recoverables. Subsea multiphase boosting of untreated well streams is also proposed as an alternative to natural drive. The ENI Group has been devoting great attention to multiphase production and boosting for several years. Different concepts of multiphase boosting equipment have been developed and manufactured. In particular, the application of a twin screw pump has been thoroughly investigated through laboratory and onshore field endurance testing. The Offshore Industry then required long term testing to prove the suitability of a subsea prototype boosting unit to perform in real operating conditions. To this end underwater testing has been undertaken at Agip Prezioso oil field off Sicily through the design and fabrication of a subsea boosting unit housing a vertical twin screw pump, as described in the paper. First, the twin screw pump as developed and manufactured by Nuovo Pignone for underwater application is described with special focus on the pressure balancing, lubrication and seal oil systems. The overall subsea trial system configuration is then provided together with an outline of both the support facilities set up and the test conditions allowed by the site characteristics. Moreover, the key features of the subsea prototype boosting unit are presented and the basic criteria for its design and manufacturing are discussed with particular reference to the requirements for the multiphase pump monitoring and ease of retrieval for maintenance purposes. Finally, the paper outlines the underwater tests implementation program together with the operating philosophy of the system. INTRODUCTION Several alternatives are proposed by the offshore industry for the safe and economical exploitation of marginal fields. For many applications, multiphase systems as opposed to conventional technologies can represent the answer to the problems related to such developments by moving to the sea bottom the overall production plant in a configuration whose economics are much less affected by environmental parameters and are almost exclusively dependent on the magnitude and productivity of the reservoir. Multiphase boosting in particular appears to be a viable solution, [1]. Additional requirements are also posed by deep water application. In such demanding conditions all aspects of the system may become decisive for both the technical feasibility and the economics of the field development. Deep water design therefore requires an integrated approach to installation, operation and maintenance. Since 1985 Agip, Snamprogetti and Nuovo Pignone have been active in the field of multiphase production and transportation.
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