Numerical Simulation of Shallow Conductor-Soil Displacement Characteristics in Deep Water Drilling

Since the shallow soil is mostly composed of clay with weak cementation, the subsea wellhead is easy to be affected by external loads in the initial stage of installation, and the stability of the subsea wellhead is weak, which is prone to serious accidents such as sinking and tilting of the wellhead, resulting in significant economic losses and threatening the safety of deep-water operations. The traditional p-y curve calculation model cannot well reflect the vibration of the subsea wellhead and the detachment and displacement of shallow soil around the surface conductor. However, the Goodman contact element model in numerical simulation can simulate the discontinuity characteristics of the conductor-soil contact interface. In this paper, the numerical simulation method is used to discuss the vertical displacement characteristics of subsea wellhead under cyclic dynamic load and the displacement characteristics of shallow soil particles in different directions and depths around the surface conductor, and the factors affecting the displacement characteristics of conductor and soil are analyzed by load type, conductor installation depth, conductor diameter, and wellhead height above the mudline. It is important to explore the displacement characteristics of subsea wellheads and shallow soil for the design and stability evaluation of subsea wellheads. 1. INTRODUCTION The construction of a subsea wellhead is the key to the success of deep-water oil and gas drilling, in which the structure of a subsea wellhead mainly depends on the interaction between the surface conductor near the mudline and the surrounding soil to provide bearing capacity (Zhang et al., 2021). After the installation of the subsea wellhead, it is dynamically stable under the external load of the marine environment and the upper pipe string, which is reflected in the horizontal and reciprocating movement of the surface conductor near the mudline (Zhang et al. 2023). The surface conductor under the mudline has a repetitive action of detachment and extrusion with the surrounding soil, and the position and mechanical property parameters of the soil have changed significantly. As a result, the soil near the mudline cannot provide enough vertical friction for the surface conductor, and part of the soil separated from the surface conductor surface will enter the gap between the surface conductor and the soil, accumulate at the bottom of the gap and become compacted with the reciprocating movement of the conductor, affecting the stability of the subsea wellhead (Su et al. 2010).