Load Analysis Of Pipe String In Deep Water Casing Running Operation And Study On Safe Casing Running Speed

With the decrease of newly discovered oil fields on land and shallow sea,deep-sea oil and gas resources have gradually become the focus of exploration and development at home and abroad.For deepwater oil and gas well drilling engineering,because the marine engineering environment and geological conditions faced by deepwater drilling operations are more complex than those of land and shallow sea,the risks and costs of deepwater drilling operations are much greater than those of land and shallow sea operations.Therefore,it is an important measure to save drilling costs to improve the safety and efficiency of drilling operations in all stages of drilling engineering.In the process of casing operation in shallow seabed and surface casing sections,due to the absence of protection of riser,the force and deformation of the casing string under the combined action of ocean environmental loads such as waves,currents and gravity of the casing string will undergo complex changes.At the same time,due to the platform's heave and offset movement,the forced vibration and accompanying motion of the pipe string will occur,which will aggravate the risk of damage to the landing string.In addition,due to the low pressure bearing capacity of shallow formation near mud line,too fast casing running speed may lead to large impact load and wellhead subsidence.It is also possible to generate greater exciting pressure,which increases effective bottom hole pressure and fracturing formation.In order to reduce the risk of casing operation in shallow formation drilling and improve the safety of operation,it is necessary to study the stress and deformation characteristics of the landing string and casing under the above operating conditions and the safe running speed.Because the action of ocean environment load and the movement of platform are the main reasons for the more complicated deformation of the landing string,this paper first studies the motion model of the platform under the action of ocean environment load and its solving algorithm,and establishes the calculation model of the action of deep-water wave load and ocean current load on the landing string,and analyses and compares the deepwater characteristics of these two main ocean loads.In order to study the stress and deformation of the landing string,the mechanical model of the landing string in deep water and its solution algorithm and strength checking method are established based on the Darumbell principle.According to the theory of axial vibration of the pipe string and the running condition of the deep water surface casing,the axial vibration model of the pipe string is established.In order to evaluate the safe pressure-bearing conditions of wellhead and wellbore when casing is running,this paper studies the calculation methods of wellhead bearing capacity and wellbore exciting pressure,and establishes a model of safe running velocity of casing considering heave movement and vibration of operating string.Based on the model and the solving algorithm in this paper,combined with the engineering application requirements of safe casing running,the software for analyzing the load and safe running velocity of surface casing string in deepwater drilling is designed and developed by using C#language.The field operation example shows that the calculation results of the model and algorithm in this paper are reasonable,and the software function is stable and reliable.Using the developed software,the effects of current velocity,gravity of lower casing string and offset of platform on the stress and deformation of the landing string are analyzed.And the casing running velocities under different casing overweight,drilling fluid parameters,wave height and formation fracture pressure are compared.The results show that the ocean current velocity has a great influence on the stress and deformation characteristics of the pipe string;the greater the gravity of the lower casing string,the smaller the deformation and bending moment;the appropriate platform offset helps to reduce the top bending moment and rotation angle;with the increase of the depth of the pipe into mud,the axial bearing capacity of the wellhead increases gradually,and with the increase of the excessive weight of the casing,the safe running speed of the casing increases accordingly.With the increase of drilling fluid density and consistency coefficient,the exciting pressure at the bottom of the well increases,and the corresponding maximum casing running velocity decreases;when the formation fracture pressure increases,the maximum casing running velocity increases;and with the increase of wave height,the maximum casing running velocity decreases.The results of this paper can provide reference and assistance for surface casing design and field operation under deep water drilling safety.