On Analysis Method And Mechanical Characteristics Of S-lay For Deepwater Subsea Pipeline

With the progress of science and technology and the improvement of Human cognitive level of offshore oil resources, deepwater oil and gas exploitation has been becoming the focus of the world's petroleum industry and the forefront of technological innovation. Submarine pipeline is an important assembly part of deep sea oil and gas exploitation, which plays a key role in the offshore oil and gas field exploitation, production and transportation. Seriously impacts of many kinds of environmental and construction factors have been subject to the pipeline in pipe-laying process. Coupling effects of these factors have strong nonlinear characteristics, which resulted in the complex of pipeline configuration, movement and control during the pipe laying. Therefore, relevant researching on key mechanical problems and analysis method of pipeline S-lay is indeed necessary. In this paper, research on mechanical analysis and analytical methods on deepwater S-lay have been carried out, based on the oil and gas exploitation model in the South China Sea.Large-angle deflection beam theory was used to establish differential equations of deepwater S-lay in this paper. The feasibility was demonstrated whether simple catenary theory could be approximated to the configuration of the sagbend. In addition, nonlinear boundary conditions of the pipeline during the installation were processed using special methods. Firstly, the reaction forces of vertical, lateral and axial directions of soil foundation subject to the on-bottom were processed with special simulating method. And then, total contact model of stinger rollers and the overbend was brought up, which could simulate the real state of the pipeline of that part during the pipe laying. At the same time, Curve fitting of stinger rollers was worked out to adjust the positions of the rollers. These have laid the foundations for the researches on global nonlinear mechanical characteristics of the pipeline.The impacts of ocean current, entrance angle of the overbend, stinger size and pipe-laying vessel movements were comprehensively analyzed, using the above analysis method. Corresponding laws were obtained, and very important recommendations have been proposed for the deepwater pipe laying process and technology. The results were also verified, to ensure the accuracy of numerical simulation methods and mechanical analysis method used in this paper. These are surely going to make more effective guidance for the actual engineering projects, and provide technical support for dynamic monitoring and integrity management of the deepwater pipe-lay.