Qualitative Research On Stability Of Underwater Wellhead Based On Shallow Layer-Pipe-Soil Coupling

With the rapid development of offshore oil and gas technology worldwide,my country is also actively developing offshore drilling exploration technology and vigorously developing offshore oil drilling.Different from land drilling,marine drilling will be affected by ocean currents and monsoons during the drilling process,and the stress situation is complicated.At the same time,the soil in the deep-sea shallow strata is poorly cemented and cannot provide effective support for the wellbore.Therefore,this paper studies the force of the underwater wellhead and the shallow pipe string and the mechanical properties of the deep-sea soil.In this paper,the geological characteristics and engineering characteristics of the shallow seabed soil are learned through the investigation of the strata soil in some sea areas,and the load of the underwater wellhead and the shallow pipe string in the marine environment is calculated.In the laboratory,the shallow pipe-soil coupling model was tested,and the test results were obtained and analyzed.Through the test analysis,it can be seen that the bending moment on the test string increases with the increase of the bending moment applied to the wellhead model,and the maximum bending moment appears at the position below the mudline near the wellhead.In the range of 10m-40 m below the mud line,the bending moment of the pipe string changes significantly,indicating that in the design process of the underwater pipe string,the strength design of the pipe string in this section should be paid attention to,which is not conducive to the maintenance of the underwater pipe string and the wellhead.Stability plays an important role.A deep-water shallow pipe-soil coupling numerical model is established,including soil model,shallow pipe string model,and pipe-soil contact model.The QR decomposition method and the Newmark-β method are used to solve the static finite element and dynamic finite element equations respectively.,the numerical simulation results were compared with the experimental results to verify the accuracy of the numerical model.The effects of wellhead bending moment load,wellhead vertical load,conduit wall thickness,conduit diameter,soil internal friction angle and soil cohesion on the stability of the underwater wellhead were studied respectively.The results show that: when the bending moment load applied to the wellhead is increased,the displacement,rotation angle,shear force and bending moment of the underwater pipe string at the mudline all increase significantly,which indicates that the bending moment load on the wellhead is the main factor affecting the water flow.The key factor of the stability of the wellhead;when the vertical load of the wellhead is increased,the bending moment of the pipe string at the mudline does not change significantly,indicating that the vertical load of the wellhead has little effect on the lateral stability of the underwater wellhead;the underwater pipe string The wall thickness and diameter of the pipe have a great influence on the stability of the wellhead.Under the condition that the actual working conditions are met,the larger the wall thickness and diameter of the conduit,the more stable the wellhead;the geological properties of the soil will affect the stability of the wellhead,the soil internal friction angle and Improved cohesion also plays an important role in maintaining wellhead stability.