ABSTRACT

Subsea pipeline is an important part of offshore oil and gas engineering, which undertakes the important task of transporting materials between offshore oil and gas fields and land terminals. If the drag anchor squeezes or collides with subsea pipeline buried in seabed during installation, subsea pipeline will be exposed to potential damage risks. Although the current research on installation trajectory of towed anchor in seabed tends to be mature, there is still a lack of research on impact response of subsea pipeline in the process of drag anchor installation. In this paper, the installation process of drag anchor and the impact response of pipeline in the coupled system of anchor-seabed-pipeline are simulated based on CEL method, and the overall displacement and local deformation of pipeline under impact of drag anchor are analyzed. The numerical simulation results can provide reference for the design, installation and safety protection of subsea pipeline.

INTRODUCTION

Subsea pipeline is the main component of offshore oil and gas field development and production system. It is known as the "lifeline" of offshore oil and gas production system. Subsea pipeline not only have to bear the effects of waves, tides, earthquakes and corrosion, but also face third-party risks such as anchoring and dragging anchors. In the process of drag anchor installation, if there is a collision or hook interaction with the subsea pipeline buried in seabed, it will threaten the normal operation of subsea pipeline, and even cause damage accidents such as fracture and leakage of subsea pipeline. With the development of marine navigation and offshore oil and gas industry, more and more attention has been paid to the research on installation trajectory of drag anchor in seabed and the damage of subsea pipeline.

In the theoretical analysis of drag anchor installation trajectory, Stewart (1994) first applied the limit equilibrium method to calculation of drag anchor trajectory. Neubecker and Randolph (1996) used this method to establish the differential equation of drag anchor motion in two-dimensional plane, and obtained the analytical solution of drag anchor installation trajectory. Thorne (1998) used the limit equilibrium method to analyze stress state of each part of the drag anchor during installation, and extended the drag anchor limit equilibrium method to three-dimensional space. The plasticity limit method was first proposed by Bransby and O'Neil (1999), and the soil resistance of wedge-shaped anchor plate and rectangular anchor plate installed in the seabed was analyzed by this method. In the numerical simulation and experimental study, Aubeny (2010) calculated the installation trajectory of drag anchor based on plasticity limit method, and analyzed the influence of anchor claw length, anchor shank angle and anchor plate thickness on the installation trajectory. Grabe (2015) used CEL method to study the installation process of AC-14 high grip anchor in clayey soil and sandy soil. Zhao and Liu (2016) analyzed the tension and deformation of anchor chain in the installation process of drag anchor by constructing the CEL analysis model of drag anchor installation. Taking Hall anchor as research objects, Ren (2022) carried out the installation test of drag anchor in the seabed flume model, and established the numerical calculation model of drag anchor installation trajectory with reference to the model flume test data.

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