A Research On Load Analysis & Optimized Design Of Casing Strings In Oil & Gas Wells

In oil and gas well engineering, the problem of casing strings optimized design has a very important reality, which includes load analysis, casing strength calculation, casing strings optimized design model and its solution. In this dissertation, the collapse strength of casing with crescent-shaped wear was analyzed with finite element method as plane or spatial problem. The model was regressed from the data obtained by calculations as plane stress problem. While the diameter of casing is constant, the collapse strength loss ratio is mainly dependent on wear diameter and maximum wear depth. Thus, the method that takes the wear consideration into collapse design factor was advanced. The results show that the actual problem can be treated as plane problem, and the factors that affect the collapse strength of casing are its diameter, wall thickness, steel grade, wear diameter, and maximum wear depth. With load analysis of casing string cell, general algorithm calculating axial force in three dimension well was developed. With static water pressure theory, a comprehensive collapse load model which is suitable for combined casing strings design was advanced, The effects of casing dimensions on effective collapse load was analyzed. With the more accurate algorithm for gas column pressure calculation, the Modified Predefined Kick Size Method, Modified Prentice Method, Modified Driller's Method, Modified Wait-and-Weight Method were advanced. The research found that new method is safer. From stabilization theory of column, centralizer space equation and its analytic solution were achieved. Extended casing strings optimized design model and its solution method was advanced. Combined with the load analysis models, casing strength calculation models and database Structured Query Language (SQL), the software for casing strings load analysis and optimized design was developed. It has many advantages. The load analysis models can satisfy all formations' conditions. The temperature can be considered in pressure profile and casing strength calculations. The optimized objects can be minimum cost and/or minimum weight. In addition, there are many other options are provided. There areoptions that enable the designer to provide pressure profile directly. Arbitrary unit was supported by the software. The functions for casing strings design of common wells, deep wells, and directional wells were integrated in the software. There are casing property database and casing material property database in the software. Therefore, the software can be used more widely.