МурманшельфИнфо. 2009, N 5.

Рисунок 3. Результаты расчетов для случая укладки газопровода с рабочим давлением 15 МПа на глубине 400 метров. а) Список литературы 1. Международная научно-техническая конферен- ция. Безопасность морских объектов (SOF 2007). 30-31 октября 2007 года. Тезисы докладов / Москва, ВНИИГАЗ, 2007. 2. Теория турбулентных струй // под ред. Г. Н. Абрамо- вича. - М.: Наука, 1984. 3. Friedl M. J. Bubble Plumes and Their Interactions with the Water Surface. – Dissertation. Swiss Federal Institute of Technology, Zurich 1998. 4. А. В. Иванников. Экспериментальное исследова- ние истечения газожидкостной струи через слой жид- кости. 5. Диссертация на соискание ученой степени кандидата технических наук. – М: РГУ Нефти и Газа им. И. М. Губкина, 2007. 6. Шеберстов Е. В. Применение модели затоплен- ной струи к оценке последствий подводных выбро- сов из скважин и трубопроводов. Математическое моделирование и информатика в научных исследо- ваниях и научном проектировании газовой отрасли. М.: ВНИИГАЗ, 2000. С. 182-191. б) в) 52 ÿíâàðü 2009 № 5 ÌóðìàíøåëüôÈíôî The issue of operation safety is a special emphasis for Giprospetsgaz engineers in the studies being implemented for the Shtokman project. The assessment presented below is devoted to one of the aspects of safety improvement. Inevitable decrease in national onshore gas production resulted in the shift of petroleum industry development towards exploration of hydrocarbon reserves located at the world ocean bottom. The first-priority region in this regard is northeastern shelf of the Barents Sea with Shtokman gas condensate field situated there. Construction of underwater pipeline for natural gas transportation from the Barents Sea shelf onshore to the Teriberka settlement is part of the field development project. DesignoptionsofferedforthefirstphaseoftheShtokmanfielddevelopment provide high level of security from emergencies. However, some factors, both natural (corrosion, stress corrosion) and human, may cause incidents, accidents and emergencies at the offshore facilities. Gas transportation design foresees high pressure (up to 20 MPa) in the pipeline. So, one of the major damage factors in case of a pipeline break accident is gas plume generated as a result of intensive gas release into liquid. Picture 1 demonstrates the plume coming to surface. When gas gets into the water at rest it causes emergence of a vertical upstream flow. The most probable jet regime in case of a pipeline break will be continuous gas efflux where the flow is decomposed into bubbles being quickly formed close to the nozzle. In this case an upstream vertical two-phase gas-liquid jet is being formed, the movement source for which is bubble plume having buoyancy force. In the initial section of plume formation zone gas jet energy is dampened not far from the source. Its lower part is occupied by gas cavern area. The cavern’s surface is unstable; gas bubbles and fluid drops get formed there. Gas bubbles going upstream from the cavern’s surface get into the ‘boiling bed’ involving fluid and gradually increasing its velocity. The fluid going upstream in this bed is being replaced due to ejection through the side surface. The second section of the gas-liquid jet is the bubble plume itself, where the flow obeys the turbulent streams law. The special feature of a turbulent stream is infinitesimality of the velocity’s transverse component in any jet cross sections compared to longitudinal velocity. Pressure in the jet according to the tests is practically invariable and equal to the environment pressure. In our case the pressure will be determined by depth of the jet cross section location. Onthewatersurfacegas-fluidjetcausesswellingwithmaximalheightover the general level in the point of total liquid velocity slow down. The vertical component of velocity is zero (liquid is spreading horizontally) there. Thus, the radius of the potentially dangerous spot with reduced water density in the area of jet emersion on the surface is practically invariable. Spreading of the plume is accompanied by significant alteration inthemedium’sdensity.Whenvesselsorfloating structuresgetintothebubble medium zone their buoyancy force significantly reduce causing alteration in their floatage and stability. In order to provide navigation safety and to keep vessel buoyancy, a certain strength margin is foreseen when designing vessels. This safety factor enables vessels’ operation even when it is overloaded or when buoyancy forces are reduced. Reserve buoyancy is calculated as a percentage of the general displacement. In order to calculate risk for the vessel three characteristics are important: class, dimensions of the vessel and value of gas content parameter. The danger of buoyancy damage occurs when gas content on the surface is under critical value and vessel’s length is comparable to the plume emersion spot diameter. Based on correlation of concentration parameters and reserve buoyancy data we can conclude that an underwater pipeline break accident at the Shtokman field when occurred at depths over 100-150 m will not constitute any danger to navigation in terms of buoyancy loss. However, taking into account that the main pipeline route from Shtokman field to Teriberka will go at depths of 200 – 300 m, the risk of buoyancy loss exists only for a relatively short distance. This circumstance is to be taken into account when designing and operating underwater pipeline to limit where possible long presence of vessels directly over the pipeline. Assessment of the subsea pipeline break impact onto vessels and marine structures S. PIOTROVSKIY, Engineer, Giprospetsgaz JSC Глубина, м Глубина, м Глубина, м Радиус сечения шлейфа, м. Скорость на оси струи, м/с. Параметр концентрации газа на оси струи. 42 дюйма 46 дюймов 42 дюйма 46 дюймов 42 дюйма 46 дюймов Диаметр газопровода Диаметр газопровода Диаметр газопровода