Mechanics Analysis And Application Of The Casing String Indeep Well Cementing

In cementing process, casing string bears different loads in different time, it is very important to prevent or reduce casing failure by studying the impact of complex well conditions on the force statement of casing string.According to casing string actual structure and force statement, Select the whole casing string as research object. Build the casing string mechanical model with considering the variable of structure with casing string, force and displacement boundary change during solidification, and the force calculation formula for casing string during solidification and other external load formula and strength checking method are given.The gap element is adopted to simulate the contact condition between casing string and wellbore, nonlinear statics analysis of finite element method for casing string is set up. The software of"Mechanics analysis for casing strings in deep well cementing"is developed by delphi language, which can compute the force statement in different working conditions. Obtain the relationship between different factors and mechanics analysis: The axial force of the wellhead and cement surface presents nonlinear increase with the increasing of cementing length; The axial force of the free section of casing strings presents linear increase with the testing pressure of wellhead , the average value is 4.7t/10MPa; The axial force of the wellhead and cement surface present linear reduces with the increasing of the retraction, and the value gradually increases with the increase of cementing length.The retraction value calculated in this article is larger than what is got from the classic formulas, so it has guiding significance to determine the retraction. Application shows: three Wells meet the strength requirement in different working conditions, and the axial force respectively has increased 10t, 5t, 11t during solidification. The fore coincidence rate compared with field test is 98%, 100%, 98%. It verifies the correctness of the theoretical methods and the software.In order to sovle the instability phenomenon about casing in cementing, select the casing string that below zero axial as object in well, considering the contact about the casing with wellbore and the variable cross-section of structure, the casing post-buckling and contact with wellbore are sloved by using nonlinear method of large displacement and contact, the initial displacement of casing is obtained from the structure stability analysis, this method can be used in the post-buckling of casing string.