Casing Drilling Casing String Fatigue Life Prediction Analysis

Casing drilling system is a new drilling process technology. During tripping in, it can directly adopt casing to transmit mechanical energy and hydraulic energy to the well downhole instead of traditional drill pipe. The downhole drill group is connected with the bottom of the casing string. Tripping in the casing while drilling in, after finishing drilling, the casing used as the drill string is left in the well to use as the technology of well completion. The casing drilling merges the drilling-in and tripping-in casing into one operating process. It doesn't need conventional round trip any more. Compared with the conventional drilling technology, it can save much drilling working time and decrease downhole accident and cut down drilling cost.Compared with the conventional drill pipe during drilling, the casing string has these features:big outer diameter, thin wall thickness,small annular space, etc. Its special characters have important effect on the casing string operation and later operation. Among them, the pipe string mechanical action in the casing drilling, especially the dynamic action of rotary casing string directly ralates to the safety and reliability during drilling and in the later well completion and cementing. And it finally affects the normal production of oil/gas well. So the mechanical action analysis in casing drilling has an important sense on the development of casing drilling technology.This thesis analyzes technology with help of largy finite element software ANSYS. It uses modern experiment and analysis means to research the fatigue lifetime of casing string during casing drilling on basis of the casing string mechanics. To effeciantly raise the effeciency of casing drilling and supply theory basis of ensuring future production. This thesis mainly describes the following:(1) It finishes the casing mechanical character analysis during casing drilling, including the geometry character analysis, the mechanical analysis of drilling casing string under static load and dynamic load;(2) At the same time, it finishes the casing string fatigue lifetime analysis of casing drilling, including the fatigue problem, full lifetime analysis and the fatigue lifetime analysis about the casing string by using finite element analysis sofeware ANSYS;(3) It describes about the casing wear remaining strength analysis during casing drilling, including wear experiment research and casing wear and remaining strength analysis;(4) It describes about finite element analysis of casing thread joint. It introduces common thread bearing torque structure and establishes the finite element model of casing thread bearing torque ability.In brief, this thesis combines the drilling engineering actuality to analyze relevant mechanical property of casing string. And it provides technological support of mechanical analysis to further development of casing drilling technology. It provides new theory basis and methods to the research of casing string of casing drilling.