Structure Optimization And Mechanical Analysis Of Composite Coiled Tubing

Coiled tubing operation has great advantages in improving the oil recovery rate andreducing production cost. It has been used in U.S.A and Canada, etc. CT plays a key role inCT operation, whose quality and lifetime determine the operation results. CT made ofcomposite material is in its initial stage. These are a lot of problems to be solved. In order tolay a foundation for the development of composite material CT of our country, aiming at thecharacteristics of composite material and operation condition of coiled tubing, a multilayeredstructure has been designed and analyzed to obtain proper structure. Fatigue life has beenpredicted and methods for enhancing its life time have been given.The tensile tests of several types of lay-patterns glass fiber composite material wereperformed for studying the performance parameter of glass-fiber woven reinforcement epoxy.The comparison of the experimental data and theoretical calculation results demonstrated thevalidity of directional dependence of the elastic properties of composite material.On the basis of the seniors’ research, constitutive equation of composite material beingdifferent from the isotropic material was substituted into dynamic characteristics of thedrilling string. Dynamic gap element models for the drilling string based on the operationcondition and mechanics were established. It is possible to simulate the contact and impactstate between the drilling string and the wall by modifying the elastic modulus of dynamicgap element.A type of three-layer composite coiled tubing was designed according to the defect ofmetal coiled tubing. The main functions of the inner liner include corrosion resistance,abrasion resistance and leakage prevention. The external protection lay can resist abrasion andcorrosion. The structural layer can bear the axial pull, pressure and the vibration loads of thetubing body. Lay-patterns of glass fiber of structural layer were designed, and the elementmodels were been established and analyzed. The stress states were analyzed in terms ofdifferent lay-patterns and ply angle, and the composite material CT structure were obtained that can be suitable for drilling conditions. The feasibility and the advantage of compositematerial CT were validated.Based on the research methods for fatigue property and theoretical analysis for fatiguefailure of coiled tubing, the decay laws of performance parameters and nonlinear damagecumulating theory of composite materials in the process of loading were introduced intofatigue life analysis of composite material coiled tubing. Fatigue life prediction modelsuitable for the composite material coiled tubing were established and the fatigue life timecalculated. According to analysis of impact of different parameters on fatigue life ofcomposite coiled tubing, methods of improving the fatigue life were presented. Thecomparative analysis of fatigue life between composite material and metal coiled tubingshows that fatigue life of composite material coiled tubing is higher.In order to avoid the mechanical damage to the coiled tubing caused by clamping device,the structure and clamping capacity of the clamping block were studied. The contact modelsof clamping block and CT were established taking as the object of study the three structuresof champing block. Comparative analysis of the contact stress and compressive stressbetween clamping block and coiled tubing were performed, and the change law of the contactstress and compressive stress with circumferential wrap angle. The ideal circumferential wrapangles for different structures were obtained.