Numerical Simulation of Subsea Wellhead Bearing Capacity in Deepwater with Novel Expandable Surface Conductor Foundation

Subsea wellhead stability is an important technical issue in deepwater and ultra-deepwater oil and gas drilling operations. Since the soil under mudline is mainly silt and clay with weak cementation, the vertical friction force and horizontal displacement provided by the surface conductor are limited. The mechanical properties of subsea wellhead, including displacement and stress, are mainly distributed near the mud line. The novel expandable surface conductor can effectively enhance the vertical bearing capacity and horizontal mechanical properties of the subsea wellhead by adding annular absorbent expansion materials to the conductor surface. In this paper, ABAQUS software was used to establish a numerical simulation model of the novel expandable surface conductor. Annular expansion material was installed on the upper, middle, and lower part of the surface conductor, respectively, to analyze its influence on the mechanical properties of the subsea wellhead. At the same time, the mechanical properties of the subsea wellhead of the conventional conductor and the novel expandable conductor are compared and analyzed. The results show that the novel expandable surface conductor arranged near the mudline can effectively enhance the lateral mechanical properties of the subsea wellhead, but has little effect on the vertical bearing capacity of the wellhead, which is mainly due to the weak soil properties near the mudline. The annular expansion material in the middle and lower part of the conductor has little influence on the lateral mechanical properties of the subsea wellhead, but it is more obvious to improve the vertical bearing capacity of the wellhead, which is because the mechanical properties of the deep formation below the mudline are strong, and the horizontal displacement and bending moment of the conduit will not be transmitted to a greater depth under the mudline. At the same time, the lower end part of the expansion material has obvious influence on the vertical bearing capacity of subsea wellhead. An exploratory study on the improvement of the mechanical properties of the subsea wellhead with the novel expandable surface conductor and basic rule is carried out through the numerical simulation method, which provides theoretical guidance for the subsequent industrial design and application of the novel expandable surface conductor.