Research On Mechanical Behavior Of The Restoration Of Expansion Casing And Coupling Thread In Casing-damage Wells

Casing acts as protecting borehole, reinforcing borehole wall, isolating oil, gas, water and restricting different kinds of complicated stratum during drilling and oil extraction. Casing is an important part of oil well, and will make great economic losses once damaged. Along with productive time lengthens unceasingly, developing plan readjusts and implements continually and different geology, project and management conditions, large amount of casing in oil wells and water wells are damaged, which has affected the stable production and high production of oil fields seriously. According to the production data statistics from oil fields, on the average, each casing-damage well will reduce oil 500 tons every year.The so-called casing damage is referred to the phenomenon that casing from the oil well and water well is damaged, and affects its production even lead to reject. There are various forms of casing damage. Generally by casing deformation, in recent years, some complicated forms of casing damage have increased year by year, such as serious leap, big curving and extensive damage. According to the statistics from the Chinese Petroleum Department, the company has more than 20,000 casing-damaged wells each year. In the initial period of oil exploitation, once have casing damage, either invest large amount of money in implementation such as lateral drilling, or reject.Mechanical model and finite element model are established through mechanical analysis in this article. The theoretical calculation formula expansive power is proposed using the non-liner theory of the expansion tube. The elastic solution and elasticplastic solution in idea condition are produced. The strained condition of expansion casing is calculated, using finite element method, increment load procedure and Newton-Raphson. At the same time, the contact problem between expanded cone and expanded casing is proposed, and the computing method of non-liner contact is put forward, including Lagrange method of multipliers, penalty function method, enhanced Lagrange method and Lagrange method of perturbation.The stress distribution rule in the process of casing expansion is studied through the fundamental research and mechanical analysis.During the optimized design of expansion casing technology, the rule of goal parameter is established as each related structural parameters changes. Then goal parameter correspondent to each structural parameter is compared, such as expanded cone, fractional coefficient of expansion casing, maximum Von Mises stress and expansion pressure etc. Finally, find the better degree of each structural parameter. Simultaneously, the reason why compressive strength reduced after casing expansion is analyzed. The coupling mode that traditional thread do not suit expansion casing is analyzed, connection mode of expansion casing with buttress thread is proposed and analyzed during the analysis of the expansion casing coupling thread. Meanwhile, the craft to the expansion casing is optimized which provide new idea, new method for optimizing expansion casing and other similar equipments.The restoration of expansion casing is a fussy project, taking hard and lengthy work in actual operation. It is a huge project to make massive qualitative and quantitative analysis on the process of casing expansion.Therefore, stress analyses on the process of casing expansion and the study on the stress situation have important guiding significance to the optimized design of casing expansion technology.