Numerical Simulation And Model Test Study On The Interaction Between Subsea Wellhead And Conductor System And Soil

In the process of deep water drilling and completion,the wellhead and conductor system is an important part to ensure the safe operation of oil and gas Wells.It is faced with some problems,such as low bearing capacity of shallow formation,large heavy load of blowout preventer set,large lateral offset of conductor and severe wind,wave and current load transfer,which seriously threaten the operation safety.However,when dealing with the pipe-soil interaction,the conventional p-y curve model of API does not consider the overloading effect of BOP.For the urgent needs of the deep water oil and gas resources development of the south China sea,this paper relies on the national natural science fund project "Rigid-flexible coupling dynamics mechanism and damage mitigation of subsea wellhead system in deepwater".This paper studys numerical simulation and model test of pipe-soil interaction for subsea wellhead and conductor system in deepwater,and verifies the applicability of the new p-y curve model to the deepwater wellhead pipe system by establishing the numerical model of conductor-soil.A scale model test of pipe-soil interaction considering vertical heavy load of BOP is studied for verifying the correctness of the numerical model of conductor-soil.And In this paper,the dynamic stability of wellhead and conductor system based on a new p-y curve model is studied.The study will provide reference for the safe oil and gas exploitation in the deepwater in the South China Sea,and it has good academic value and innovation.The main research contents and results are summarized as follows:(1)Study on bearing capacity analysis of wellhead and conductor system and comparison of p-y model.Based on the theory of pile foundation and soil mechanics,two analysis models of the vertical bearing capacity and lateral bearing capacity of the wellhead and conductor system are established,and the calculation method of the bearing capacity under different soil types is analyzed.And the difference between the new p-y curve model of sand considering the vertical load and the API standard p-y curve model is explored;It shows that the API standard p-y curve model is insufficient to determine the ultimate soil resistance of shallow soils,and it has a higher estimate of the ultimate soil resistance of deep soils.(2)Study on numerical simulation of the interaction between wellhead and conductor system and soil.Establishing the finite element model of the interaction between the wellhead and conductor and soil based on the ABAQUS software,and analyze the response characteristics of the conductor and soil.Investigating the applicability of different sand p-y curve models in the analysis of lateral bearing capacity of wellhead and conductor system,and it is proved that the new p-y curve model of sand has better applicability.And analyze the influence of related factors on the lateral bearing capacity of conductor to reveal the law of interaction between conductor and soil.(3)Study on scale model test of pipe-soil interaction.Designing scale test equipment and data acquisition system,and carry out scale model test on the interaction between wellhead and conductor system and soil under heavy BOP were carried out,and verify the accuracy of the numerical simulation of conductor-soil.Analyzing the load bearing characteristics of the model pipe under combined loads and the distribution law of p-y curve of the test based on experimental data.And a set of p-y curve test method considering the vertical load is formed.(4)Study on stability of wellhead and conductor system based on a new p-y curve model.Based on the new p-y curve model and the conventional p-y curve model of API,the riser and wellhead system models were established to explore the dynamic response differences of the wellhead and conductor system,and it shows that the system under the new p-y curve model is more stable.Based on the new p-y curve model,the influence of key factors on the stability of the wellhead and conductor system is studied.And analyze new strategies for improving wellhead and conductor system stability.