The Mechanical Behavior Analysis And Load Capacity Research For Downhole Derricks

In oilfield, downhole derricks are the main part that bears the loads in the downhole operation hoist system. Load capacity of the downhole derricks directly affects the downhole operation work At present, most mechanical behavior analysis for derricks are in the domain of elasticity, using finite element method to establish the computer analysis model, by analyzing get the stress, displacements and other mechanical parameters. The studies for derricks in the domain of plasticity are very few. The downhole derricks sometimes are over loading and most derricks are already worked for many years. They inevitably have varieties of damages and distortions, which made the derricks in-use have different mechanical characteristics as contrasted with their ideal status.This thesis presents a method of double nonlinear analysis to study the mechanical behavior of derricks steel structures. Large analytical software ANSYS was used. The large deformation of structures is considered by geometric nonlinearities analysis. The mechanical characteristics of derricks in the domain of plasticity are considered by material nonlinerities analysis. Contrasted with the results that come from linearity and nonlinearity analysis, it is concluded that to analyze derricks steel structures is feasible with linearity theory in the condition of light load and small deformation.Derrick guy wire as the special supporting member of downhole derricks, its performance has much impact on the mechanical behavior of derricks. Its nonlinear effect has been dealt with equivalently in this thesis. The equivalent elastic module has been used instead of derrick guy wire's effective elastic module in the study of the nonlinear behavior that caused by derrick guy wire. The effect of derrick guy wires nonlinear behavior to structure's deformation has been analyzed. According to the analysis, the nonlinear effects are mainly on the stiffness of downhole derricks steel structure.The ultimate load of the structure has been studied in this thesis and arrived by using nonlinear buckling analysis, which technique employs a nonlinear static analysis with gradually increasing loads to seek the load level at which the structure becomes unstable. The author presented a simulating method for bending deformation of derricks by using the mode, which is consistent with the buckling mode of derricks. The relation between the bending degrees and structural ultimate load capacity has been researched by using the simulation method.