Study On Capacity Of Subsea Wellhead And Conductor In Deepwater

Even though the increasing exploration and development of petroleum improves the level of drilling and completion in deep water, our country falls far behind foreign companies, like BP, Exxon Mobile, etc. Especially in terms of subsea wellhead equipment, this is the bottleneck of energy engineering. Specific to the environment in South China Sea, this dissertation presents a method of analyzing the bearing capacity of wellhead and conductor, including strength, stability and fatigue caused by wave, current and offset of drilling vessel. It also shows the influence of various factors on the strength, stability and fatigue life of wellhead and conductor, and presents a method of pre-drilling design of conductor. The research findings will provide technical supports for the operation technology development of deep water drilling and completion subsea wellhead and conductor. It is supported by the National Major Science and Technology Project “Research on Deepwater Drilling Riser Operation Management and Safety Evaluation Technology”(2011ZX05026-001-05) and the fundamental research funds for central universities of the study “Research on Capacity and Durability of Subsea Wellhead System in Deepwater ”(13CX06086A). 1 Study on the pre-drilling design of conductorInitially, this part describes the structure of subsea wellhead and application of jetting technology in South China Sea. Aiming at increasing the bearing capacity of wellhead and conductor, this part also presents subsea wellhead and conductor predrilling design method, soil data method, and the design method of conductor length when there is little soil data. 2 Strength analyses of wellhead and conductorSpecific to the environment in South China Sea, the load analysis of subsea wellhead in various behaviors is carried. This part establishes the whole static analysis model, from risers to conductor, and emphasizes on certain factors’ influence on the strength and stability of wellhead, including the offset of drilling vessel, top tension of rises, dimension of conductor and well structure. Besides, sensitivity analysis of deep water drilling conductor mechanical characteristics is studied. The test results are disposed to determine influencing priority by means of range analysis and variance analysis. Based on sensitivity analysis of drilling conductor mechanical characteristics, the measures are proposed to the strength and stability of subsea wellhead and conductor. 3 Fatigue analyses of wellhead and conductorReferring to civil engineering, this part calculates the ultimate axial load at the head of conductor, and develops the distribution of axial force and fictional resistant along conductor shaft. Moreover, the horizontal capacity of wellhead is studied. It presents a method with which the minimum length of analytical model can ensured. With the analytical model, it can analyze the cementing operation’s influence on the bearing capacity of wellhead and conductor. Meanwhile, the influence which reciprocations of conductor have on the surround soil is studied. 4 Fatigue analyses of wellhead and conductorFatigue is the progressive and localized structural damage that occurs when wellhead is subjected to cyclic loading caused by wave and current. To solve the fatigue failure problem, this part studies on the fatigue property of subsea wellhead and conductor. It presents a fatigue damage analysis method of subsea wellhead and conductor, and the fatigue life is also calculated. Moreover, the local analysis model is established in this part to calculate the stress concentration factor and local fatigue life. 5 Pre-drilling software and evaluation of pre-drilling design methodIn Chapter 2, it presents a pre-drilling design of conductor in deep water. This part will evaluate the result of the pre-drilling design and soil data, and check whether the method can satisfy application. Moreover, it uses MATLAB GUI to develop pre-drilling software which can realize the pre-drilling of conductor in deep water. The software includes design database and design module. The database includes all parameters which are needed in the pre-drilling design, and the data could be edited, modified and saved in the database. The design module is used to calculated the set depth of conductor in deep water, including the max depth and minimum depth of conductor.