Recently offshore pipelines are under active construction in the Russian Federation. The main advantages are their operating reliability, cost effectiveness, high efficiency and simplicity of operation. Offshore pipelines require differentiated approach to adopted technical and technological decisions depending on the natural and climatic characteristics of the region. Stability plays an important role for reliable and safe operation of offshore pipelines. One of the main conditions for stability is the strict adherence to standards and rules of calculation and design. But the standards cannot include all factors and force impacts to be taken into account. There are only general requirements to calculation and design of pipeline systems. Whereas the technical feasibility of all basic parameters necessary for reliability of offshore pipelines must be chosen and substantiated on early stages of design. Stability of a pipeline depends on environmental loads and the trench (seabed) profile [1]. When calculating stability it is assumed that pipeline must preserve stable position on the seabed even in maximum possible seabed deformations in places where no soil layer is designed above the pipeline. Where there is no current influencing the trench of pipeline filled with the transported product buoyant force equal to the float displacement will be acting. Float displacement depends on the water-mass density: increase of density results in increase of buoyant force and reduction of pipeline stability on the bottom of the watered trench. Works for development of hydrocarbon offshore fields (offshore pipeline lay, dumping) lead to concentration of suspended matter that manifold exceeds the natural level (figure 1). Time of existence and extent of suspended matter cloud can be determined by factors, the most significant of which are as follows: method of dredging (implementation of machines -dredging machines, sand suckers, hydraulic monitors, etc.); method and scope of disposal; current speed and depth at the disposal point; granulometric composition of suspended matter.
The creation of an effective system of rescue support (the abbreviation ASO is adopted on the territory of the Russian Federation) in the implementation of the processes of oil and gas production and transportation in the Arctic seas of Russia is an urgent and difficult task. The feasibility of creating such a system for offshore oil and gas production facilities is due to the statistics of accidents and incidents at such facilities, as well as the fact that the Merchant Shipping Code of the Russian Federation, in essence, does not consider the applicability of the existing system of rescue operations on platforms that are exploring and developing mineral and other non-living resources the seabed and its bowels. The successful solution of numerous problems of rescue support, including the requirements for the quality of the system, indicators and criteria for the effectiveness of the operations carried out, can be significantly increased by using mathematical models that make it possible to identify patterns in the processes of performing urgent work, improve the quality of planning, and, consequently, the efficiency of management of various organizational systems. Applied in many areas of activity, the scientific direction "research of operations" is advisable to use when system generation of rescue support within the framework of improving the system of technical regulation of oil and gas enterprises. Determining the effectiveness of a purposeful process quantitatively will allow, on a scientific basis, with the involvement of modern mathematical methods, to solve the problem of increasing the effectiveness of the use of forces and means of the marine rescue support, including the functioning of the emergency support system in the mode of daily and emergency activities, as well as the preparation of the necessary forces and means. The novelty of the presented work lies in the application of the provisions of the theory and the apparatus of operations research to assessing the effectiveness of the system of the marine rescue support, which will further serve as a methodological basis for the development of a number of documents and provisions that are of practical importance: methods, requirements for the system of rescue support, documents in the field of control over the rescue system, etc.
Development of offshore hydrocarbon (HC) fields is today"s oil and gas industry priority in the Russian Federation. Water areas of the Arctic shelf are considered to be potential offshore HC production regions. When designing pipelines for such fields it is necessary to take into account the impact of specific Arctic conditions including hazardous ice impact (ice gouging), possible presence of permafrost on the seabed, lithological and geomorphological distinctive features of bottom soils. All main parameters ensuring safety of offshore pipelines must be determined and validated at the early design stage.The paper reviews one of the main conditions that influences reliable operation of underwater pipeline systems, namely, stable position of the underwater pipeline at design reference marks.Calculations of offshore pipeline stability on the seabed use the following main conditions: environmental conditions; geotechnical conditions of the seabed; bathymetrical conditions (water depth); pipeline parameters (diameter, wall thickness).Criteria of pipeline stability on the seabed include:
Development of offshore hydrocarbon (HC) fields is today’s oil and gas industry priority in the Russian Federation. Water areas of the Arctic shelf are considered to be potential offshore HC production regions. When designing pipelines for such fields it is necessary to take into account the impact of specific Arctic conditions including hazardous ice impact (ice gouging), possible presence of permafrost on the seabed, lithological and geomorphological distinctive features of bottom soils. All main parameters ensuring safety of offshore pipelines must be determined and validated at the early design stage. The paper reviews one of the main conditions that influences reliable operation of underwater pipeline systems, namely, stable position of the underwater pipeline at design reference marks. Calculations of offshore pipeline stability on the seabed use the following main conditions: –environmental conditions;–geotechnical conditions of the seabed;–bathymetrical conditions (water depth);–pipeline parameters (diameter, wall thickness). Criteria of pipeline stability on the seabed include: floating up or submerging of pipeline;transversal stability;longitudinal stability. Soils with weak strength properties, especially when they are used for backfilling, may be potentially dangerous due to liquefaction under hydrodynamic forces. It is especially dangerous in the first years of operation when the soil is not consolidated enough. Relief in a local zone of diluted soil causes longitudinal stresses in pipeline, which may result in offshore pipeline stability loss. Liquefied soil potential depends also on backfilling process technology. This operation is performed by special ships – dredgers. Such ship has two pipes, one for soil suction, and the other equipped with water injection nozzles - for washing out and backfilling. When a trench is backfilled with controlled soil flow, "front" of backfill material is formed under pipe working head and a layer of fluidized material appears in the upper part of this "front". Therefore, if weak soil is used as backfill material, a size of liquefied soil layer will be considerable, as well as its impact on the pipeline. This process may lead either to floating up or submerging of pipeline into the soil. To stabilize offshore pipelines position the following measures can be taken: backfilling with soil not subject to liquefaction; pipeline laying below the layer of liquefied soil to eliminate risks related to soil liquefaction; using different methods of ballasting.
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