Analysis Of Mechanical Properties And Fatigue Life Of Coiled Tubing

This dissertation is finished under the support from the project "Coiled Tubing Operation Optimization Decision-Research on Mathematical Model and Computation Module", which is major project of CNPC Chuanqing Drilling Engineering Co., LTD. The dissertation's content is part of the project.With the development of coiled tubing (CT) technology and drilling technology in recent years,coiled tubing has become a hot spot of foreign drilling technology.Research, development and promotion of coiled tubing technology has great significance for petroleum exploration and exploitation.This dissertation focuses on the analysis on buckling phenomenon,axial load transmission,mechanical strength and fatigue life of coiled tubing.The main research contents and results of this dissertation are as follows:(1) The deformation differential equations deduced from energy law and hydrostatic balance method obtain the same results,which proves the rationality of the deformation of differential equations.The critical buckling load of coiled tubing is obtained through analyzing the critical buckling loads at inclined section and vertical section of the well.(2) The mathematical models of buckling mechanical properties,strength,elongation and sticking point calculation are established,and a coiled tubing strength database is also established.Based on the stress of danger point,equivalent stress and fatigue failure criterion,a coiled tubing fatigue life prediction model is established to provide the mathematical model and database for coiled tubing mechanical strength analysis software.(3) The solution and algorithm of coiled tubing mechanics model is established.Analysis on buckling and axial load of coiled tubing is carried out.The force distribution and axial force at key point of coiled tubing during tripping operation are analyzed.The burst strength and collapse strength are calculated,and decision model for helical locking is studied.A prediction model for fatigue life of coiled tubing is established.(4) Based on the mechanical model and fatigue life prediction mathematical model established in this dissertation,a coiled tubing mechanical analysis software with independent intellectual property rights is developed.The software can visually determine the buckling of coiled tubing in of different well sections,calculate coiled tubing collapse buckling load and predict and analyze the fatigue life of coiled tubing.(5) In this dissertation,the developed software is applied,tested and perfected.Software testing calculations in 14 actual wells including Weiyuan H3-1 and Baiqian 203-H1 are completed.The coincidence rate of calculated result and actual construction result is more than 92%.The software has been verified to be able to guide the field operation of coiled tubing.