STUDY OF THE NEOTECTONIC STRUCTURE OF THE BRATSK WATER RESERVOIR BED

Production of natural gas and crude oil in the eastern regions of Russia was accelerated in the past decade, and both the upstream and midstream segments of the oil and gas industry continue to grow at a fast pace. Innovative solutions are needed for engineering and construction surveys aimed to justify options for choosing routes and methods for laying underwater pipeline sections across large rivers and water reservoirs. In our region, positive experience has been gained by employing modern technologies to optimize routing and reduce the costs of detailed surveys. In the project of the Kovykta – Sayansk – Angarsk – Irkutsk gas pipeline construction, an optimal route across the Bratsk water reservoir was chosen based on the results of several stages of investigation, including continuous seismic profiling and side-scan sonar scanning of the reservoir bed. At the first stage, the mosaic maps of side-scan sonograms and a 3D digital model of the reservoir bed bathymetry were constructed and used to develop and propose three options for the gas pipeline design and its route across the reservoir area. At the second stage, detailed underwater and onshore geophysical and drilling operations were carried out along the proposed routes. Based on the transverse profiles, a decision was taken to lay the pipeline section across the reservoir area in a trench along the northern route, which was justified as an economically and technologically optimal solution. In the winter period when the water reservoir surface was covered with thick ice, the northern route was investigated in detail by drilling and seismic survey operations using vertical seismometer cable assemblies and the inverse travel time curve technique. With reference to the velocity law, the travel time sections were processed and converted into depth profiles. A petrophysical model of bottom sediments was constructed, and a scheme was developed to ensure proper processing and interpreting of seismic and acoustic data. Four structural-material complexes were identified: modern silts; underwater eluvial and alluvial deposits; disintegrated and low-strength bedrocks of the Upper Lena Formation; and unaltered bedrock sandstones and siltstones. The continuous seismic profiles and the data from the vertical seismometer cable assemblies were interpreted, and a neotectonic map of bottom sediments was constructed. By analyzing the fault kinematics, it was revealed that normal faults and reverse faults with low-amplitude horizontal shear dominated in the study area; the mapped faults were mainly rootless structures; and displacements along the faults occurred due to a laminar flow of the Cambrian salt layers. An increase in tectonic activity from north to south was explained by the correspondingly degraded strength properties of the bedrocks. Modern neotectonic structures detected from the survey results gave evidence that that the hydrostatic pressure increased after the reservoir had been filled with water, and the phenomenon of reservoir-related seismicity was observed in the study area. Based on the comprehensive geological and geophysical survey data, the geological and engineering conditions of the proposed construction sites were clarified, and the most appropriate route and design of the gas pipeline section across the reservoir area was approved. This study provided the pipeline designers with the qualitative and quantitative information on the phenomena and factors complicating the conditions for laying the gas pipeline in the study area.

Elastic-plastic bending of the pipeline under combined loading

Рассмотрена задача упругопластического деформирования тонкостенной трубы при комбинированном нагружении изгибающим моментом, осевой силой и внутренним давлением. Решение задачи осуществлено по разработанной методике с помощью математического пакета Matcad численным методом, основанным на деформационной теории пластичности и безмоментной теории оболочек. Для упрощения решения предложено сведение двумерной задачи к одномерной задаче о деформировании балки, материал которой имеет различные диаграммы деформирования при сжатии и растяжении в осевом направлении. Проведено сравнение с результатами численного решения двумерной задачи методом конечных элементов в упругопластической постановке. Результаты расчета по инженерной методике совпадают с точным решением с точностью, необходимой для практического применения. Полученные результаты упругопластического решения для изгибающего момента в сечении трубопровода при комбинированном нагружении позволяют уточнить известное критериальное соотношение прочности сечения трубопровода с кольцевым дефектом в сторону снижения перебраковки. Применение разработанной методики позволяет ранжировать участки трубопровода с непроектным изгибом по степени близости к предельному состоянию при комбинированном нагружении изгибающим моментом, продольным усилием и внутренним давлением. The problem of elastic plastic deformation of a thin-walled pipe under co-binned loading by bending moment, axial force and internal pressure is considered. The problem is solved by the developed method using the Matcad mathematical package by a numerical method based on the deformation theory of plasticity and the momentless theory of shells. To simplify the solution of the problem, it is proposed to reduce a twodimensional problem to a one-dimensional problem about beam deformation, the material of which has different deformation diagrams under compression and tension in the axial direction. Comparison with the results of numerical solution of the two-dimensional problem with the finite element method in the elastic plastic formulation is carried out. The obtained results of the elastic-plastic solution for the bending moment in the pipeline section under combined loading make it possible to clarify criterion ratio of the strength of the pipeline section with an annular defect in the direction of reducing the rejection. Application of the developed approach allows to rank pipeline sections with non-design bending in the steppe close to the limit state under combined loading of the pipeline with bending moment, longitudinal force and internal pressure.

Simulation modeling of non-stationary thermophysical processes when monitoring the reliability of main oil pipelines in the Arctic

The use of modern complexes for calculating the designed pipeline systems and for predicting their behavior for a period of more than ten years is necessary in modern conditions of the constantly developing hydrocarbon market and the development of new northern territories for greater oil production. It will allow avoiding accidents and environmental disasters that have become more frequent in recent years due to the deterioration of existing equipment. The article presents a method for monitoring the main reliability parameters of underground oil pipelines, taking into account changes in soil foundations, mainly in the Arctic zone of the Russian Federation. An oil pipeline section is considered as an object for monitoring of heat engineering processes and their influence on the reliability of the system. We describe the main results of calculations of the oil pipeline section and simulate changes in soil foundations. We used a multilayer pipe with polyurethane foam insulation and coating for the calculations to improve the reliability characteristics. This pipe has showed the best results of modeling in comparison with the design pipe.

Method for oil balance control under quasi-stationary modes of operation of an oil pipeline section with free flow

Автоматизированные системы управления используются в нефтепроводном транспорте с целью автоматизации технологических процессов транспортировки нефти и нефтепродуктов, при этом основной задачей является обеспечение надежности и безопасности перекачки, что невозможно без контроля целостности трубопровода. В связи с этим актуальной остается тема обнаружения утечек, требуют продолжения исследования в области повышения надежности автоматизированных систем обнаружения утечек (СОУ). При эксплуатации СОУ особую важность представляет описание процессов заполнения и опорожнения участков трубопровода с безнапорным течением. Скорость установления стационарного режима работы таких участков и участков с полным сечением существенно отличается. Слабые возмущения давления могут приводить к значительному дебалансу расхода нефти и, как следствие, вызывать ложные срабатывания СОУ. Авторами представлен алгоритм вычисления скорости изменения запаса нефти на участке трубопровода при медленном изменении размера самотечной полости, на основании которого предложен способ корректировки уравнения баланса вещества. Показано использование разработанного алгоритма для повышения чувствительности СОУ и уменьшения количества ложных срабатываний. During the operation of leak detection systems (LDS), it is of great importance to describe the processes of filling and emptying pipeline free flow sections. The speed of establishing a stationary operation mode of such sections and full sections is significantly different. Weak pressure perturbations can lead to significant imbalance in the oil flow rate and, as a consequence, cause false LDS positives. The authors present an algorithm for calculating rate of change in oil reserve in the pipeline section with a slow change in the size of gravity cavity, on the basis of which a method for adjusting the substance balance equation is proposed. The use of a developed algorithm is shown to increase the sensitivity of LDS and reduce the number of false alarms.

Development of the mathematical model for assessing the optimal measurement step when surveying the depth of the underground pipeline from the ground

Existing methods for estimating the bending stresses of buried pipeline section based on the survey data for the depth of the axis of the pipeline from the ground surface are characterized by a large error between the real values of the bending stress and the values of the bending stress obtained from the calculation results based on the survey data. The purpose of this study is to improve the methodology for calculating the bending stresses of buried pipeline section based on the results of determining the depth of the axis of the pipeline from the ground surface, taking into account the design features of the pipeline and the used search equipment. Mathematical models are proposed that allow for the set value of the maximum error in determining bending stresses for a particular pipeline to choose the optimal measurement step before the survey, which will allow to reduce the error. Explanations are given on the choice of the maximum step of the study based on the strength characteristics of the pipeline. A calculation is provided that confirms the adequacy of the developed mathematical models and the possibility of their application in practice.

Forced oscillations of the main gas pipeline open section during the cleaning piston passage

The problem of forced oscillations of an open section of a gas pipeline during the cleaning piston passage belongs to the type of problems of forced oscillations of one-dimensional elastic objects under the influence of a moving inertial load on them. Currently, there are two ways to solve such problems. The first way is related to the integration of the partial differential equation and the solution of such problems is a superposition of eigen-oscillations and accompanying oscillations. The second way does not involve the integration of the partial dif-ferential equation. Methods of generalized coordinates, generalized displacements and various numerical methods belong to the second type of solving. None of the mentioned methods is simple. Therefore, the authors suggest the method, in which the first mathematical model provides the determination of forced oscillations of the gas pipeline section during the passage of the cleaning piston without taking into account its inertial load on the gas pipeline. In future, on the basis of the first model it is planned to develop the second mathematical model which will provide an approximate determination of the deflections of the pipeline axis, taking into account the inertial load of the piston on the pipeline. The purpose of this article is to obtain a solution to the problem of forced oscillations of the pipeline section during the passage of the cleaning piston without taking into account the inertial forces on the pipeline. The problem is solved by partial differential equation, Fourier method is applied. The right side of the non-homogeneous differential equation is decomposed into an infinite series, which is the sum of the produc-tions of the eigenfunctions of the pipeline section free oscillations and the unknown function of time. After finding out this function, the authors determine the unknown time function in the Fourier method and hence the solution of the problem in the form of an infinite series, the summands of which lessen rapidly. The authors calculate the deflections of the pipeline axis along the entire section of the gas pipeline for different points of time, as well as deflections of individual sections changing in time and moments of deflection.

ESTIMATION OF PARAMETERS OF STRENGTH AND RELIABILITY OF A SECTION OF A STEEL GAS PIPELINE TAKING INTO ACCOUNT VERTICAL SECTIONS ON THE NOVODEVICHY DUKER PROJECT WITH APPLICATION OF NUMERICAL METHODS

Article considered main stages of strength calculation of the steel gas pipeline under the Novodevichy Duker project. Specialists of the Moscow city Center used the basis of the finite element for calculation. The list of tasks consists of: 1. Strength calculation of the underground laying gas pipeline section. 2. The calculation of the stability of the two vertical sections. According to the results of strength calculation, specialists made the conclusion about ensuring the strength and stability of the considered section of the gas pipeline.