The submarine pipeline is the lifeline of the development of marine oil and gas fields and an important channel for transporting subsea oil and gas to shore. In the development and construction of domestic marine oil and gas fields, according to the technological requirements of the transmission medium, such as: oil, gas and water mixed transmission, oil transportation, water injection, gas transmission, etc., the structure of the submarine pipeline usually uses single-layer pipes and double-layer insulation pipes. However, no matter which structure is adopted, each submarine pipeline needs to be laid separately using a professional installation vessel. Due to the limited resources and expensive costs of the professional marine installation fleet, the construction cost of the submarine pipeline is very high, which often becomes a constraint on the beach and the marginal margin. Key factors for oilfield development. This article mainly discusses the technical and economical cluster pipeline technology that combines oil transportation and water injection pipelines together, and the feasibility of application in the development of offshore marginal small oil fields. Submarine Pipeline-Single Layer Pipe 1 Bundle Pipe Overseas Application Bundle pipe has been widely used in the development of marine oil and gas resources around the world, especially in the North Sea and the Gulf of Mexico. It is the application statistics of cluster pipelines in Norway and the North Sea area of ​​the United Kingdom as of 2000. So far, about 70 bundled pipelines have been used in the North Sea. It is the application statistics of cluster pipelines in the Gulf of Mexico. The design and construction of these cluster pipelines are mainly completed by RBrown (now part of American Technip). The application statistics of the cluster pipeline in the North Sea The application statistics of the cluster pipeline in the Gulf of Mexico Table 1 is a part of the usage statistics of the cluster pipeline in the world. 2 The cluster pipeline structure has been applied in different degrees in the North Sea, Gulf of Mexico, Australia, West Africa and other regions. Submarine cluster pipelines are usually composed of bearing pipes, sheath pipes, oil pipelines, water injection pipes, cables, spacers, bulkheads, ballast chains, etc. The main body of the cluster pipelines has a tractor structure on both sides, which is used in the Norwegian GULLFAKS project Typical cross section of the cluster pipeline. The main body of the bundle pipe has a tractor structure on both sides. Structures such as cluster pipes can provide excellent thermal insulation properties to help prevent wax formation and hydrate formation. Due to the outer sheath, it can provide excellent corrosion protection for internal oil transmission and water injection pipelines; it can be dragged to the offshore site for installation after the land construction is completed, thereby reducing the cost of offshore installation. The cross-sectional forms of bundled pipes are mainly of the following two types: open: two or more pipes are bundled together without an outer casing (see); closed: two or more pipes use one or two The outer casing is bundled together (see). Open cluster pipeline structure form Closed cluster pipeline structure form For a specific project, whether it is open or closed depends on the following factors: (1) functional requirements; (2) insulation materials used ; (3) Length of pipeline; (4) Installation method; (5) Time and cost. At present, most of the bundled pipelines installed abroad are of closed cross-section structure. 3. Compared with traditional single-layer pipes and double-layer insulation pipes, the characteristics of bundled pipes are very different in terms of design, construction and offshore installation. Mainly reflected in: it can provide good thermal insulation and corrosion protection for multiple built-in oil pipelines. Especially in the development of deep-water oil and gas resources, the risk of pipeline wax and hydrate formation caused by deep-water low temperature can be greatly reduced. Inside the oil field, multiple oil pipelines (including cables) are often required to connect the subsea chassis, oil production and external transportation facilities. The cluster pipeline system can put these oil pipelines together in a jacket tube and load pipe. These oil pipelines The track can be positioned by pads arranged at fixed intervals. The carrier pipe is used as a transport pipe during the installation process, and many oil pipelines are placed on the seabed at once. At the same time, offshore installation does not require a dedicated pipelaying vessel, and it is sufficient to use a cheap rental tug, which can not only greatly reduce the construction period and cost of offshore installation, but also minimize the width of the submarine pipeline corridor belt, avoiding unnecessary congestion . In addition, the risk of damage to the submarine pipeline due to anchorage is minimized. The prefabricated cluster pipeline is completed on the shore, which is convenient for welding quality control. Especially when the oil pipeline needs to use corrosion-resistant stainless steel or dual-phase steel, prefabrication on the shore can greatly reduce the offshore construction period and reduce costs. When leakage occurs in the built-in transmission pipelines, the sheath tube can serve as a protective barrier, thereby minimizing the risk of environmental pollution. 4 Comparison of bundled pipelines and conventional pipelines According to the characteristics of bundled pipelines, Table 2 gives a comparison of the design, construction, installation and cost of bundled pipelines and conventional pipelines. Table 2 Comparison and comparison between cluster pipeline and conventional pipeline Content cluster pipeline conventional pipeline Description Cross-section layout of multiple oil and gas pipelines, service pipelines, umbilical cables, etc. Can be closed or open cross-section design. For a single pipe, double-layer insulation pipe structure is needed if insulation is needed. In addition to the conventional pipeline design technology, the design method also includes other designs, such as: structural design, bulkhead design, fast interval design, umbilical cable design, tractor design, towing design, etc. Conventional piping design. Insulation design can use cheap insulation materials, in a dry environment; can use hot water circulation insulation; can use conventional wet insulation. Use double-layer insulation tube. The thermal insulation performance of cluster pipes is much better than conventional pipes. Construction methods: Onshore construction and integration; onshore hydrostatic pressure test; no construction is required at sea. If the reel is used for installation, it can be partially constructed onshore; matching and S-type installation methods; most of the construction including site nodes must be completed at sea. The onshore construction method of the cluster pipeline can be carried out in a parallel or vertical manner. The installation method uses a conventional towing barge, generally 24 ships, depending on the length and size of the pipeline; prefabricated on the shore and launched after the test; the weight of the pipeline is adjusted; from the construction site towed to the offshore installation site, a professional pipelaying vessel is used; Adopt S type, type, or reel type pipe laying; after laying, hydrostatic pressure test shall be carried out; pigging and drying shall be carried out. The cost of towing barges is relatively low; and the cost of professional pipelaying ships is high. The scope of application is only suitable for short-distance transportation within the oil field; it is more suitable for multiple pipelines; and it is suitable for the situation where the thermal insulation requirements are high. Suitable for all situations. The project time generally requires 1-2 months of onshore prefabrication; prefabrication, assembly, and testing do not exceed three months; due to the onshore construction, the construction period can be flexibly arranged and not affected by the time of offshore installation. The time available for offshore installation is relatively short; there are many uncontrollable factors; and the time risk is relatively large. Overall costs For the same conventional pipelines, the use of bundled pipelines can save 20%. Mainly save the cost from offshore operation time and professional pipelaying vessels. The offshore installation costs of professional pipelaying vessels are very high; the daily rent of shallow water pipelaying vessels in the international market It is about 200,000 to 300,000 US dollars; the daily rent of deep-water pipelaying ships in the international market is about 500,000 to 800,000 US dollars. 5 Application prospects of cluster pipelines in China Oil and gas fields developed offshore China, some are located in beach waters, relatively close to the shore, and some pipelines have relatively short distances between platforms. Especially in the Bohai Bay, the crude oil produced has the characteristics of high viscosity, high condensation, and high waxiness, and due to the low reservoir pressure, water injection is sometimes required. In this way, for the development of an oil and gas field, it may be necessary to build insulation pipelines and water injection pipelines at the same time, and submarine cables need to be built for the power supply of the facilities on the platform. If the traditional single-layer pipeline or double-layer insulation pipeline is used, each pipeline requires a special pipe laying ship and a large floating crane for offshore laying, pigging, pressure test, drying, etc. The offshore construction operation period is long and special pipe laying Boats and large floating cranes are expensive. If oil pipelines, water injection pipelines and cables are bundled together, it not only solves the problem of thermal insulation, does not require the use of professional pipe laying fleets, but also can achieve the overall prefabrication of the land, improve the construction quality, greatly reduce the offshore welding inspection construction cycle and reduce Offshore installation costs, thereby promoting the development of marginal small oil and gas fields. 6 Conclusion This article discusses the possibility of the application of cluster pipelines in the development and construction of domestic marginal oil and gas fields through a comparative analysis of the status quo, structural forms and characteristics, technology and economy of foreign cluster pipeline applications. Because the cluster pipeline can gather multiple pipelines together on the land prefabricated without using a professional pipe laying fleet, it can be considered that the cluster pipeline has good application prospects in the development and construction of China's marginal oil and gas fields. Advanced Vacuum Dough Kneading Technology
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