The Dynamic Testing Research For Oil Derrick

This paper is a part of China National Petroleum Corporation scientific research and technologicaldevelopment projects. The title of this project is the safety evaluation method of drilling rig in use. Thestudy focuses on dynamic test and evaluation methods about the bearing capacity of the derrick in use.Base on the vibration analysis theory combining finite element simulation and dynamic testing of the labderrick model, a method is presented about evaluating the safety bearing capacity of derrick with thedynamical parameter. This method can reflect the actual performance of the overall derrick structure andthen carry out the safety evaluation to derrick scientifically.Base on the structure characteristic and loading feature on the derrick, derrick structure is firstreduced a simple beam with uniformly distributed quality and constantly rigidity along the length in thispaper. Appling the analysis of vibration to the derrick structure simple model, the relationship is deducedbetween the loads on the derrick structure and dynamical parameter. And so to evaluate derrick safetybearing capacity with dynamic parameters is proved reasonable from theory.In FEM analysis, the ANSYS software is first developed. After it, the member bars are simplified thethree-dimensional beam elements base on the compositions of actual derrick structure. The computernumerical model is established and applied to analyze the dynamical characteristics of derrick structure.The vibration mode and the relationship between the loads acting on the derrick structure and dynamicalparameter are calculated. In the measure analysis, base on the DASP analysis platform, the lab derrickmodel and the derrick in use are tested by high-capacity data acquisition dynamic testing system. The datameasured reflected the relationship between the load acting on the derrick structure and dynamicalparameter really. So to evaluate derrick safety bearing capacity with dynamic parameters is provedpracticability from FEM analysis and test analysis.Finally, in view of the analysis above and the actual situation in the oilfield, a dynamical parameterevaluation method is provided applying to the derrick testing. In the derrick testing, the natural frequencyis measured without and with load on the derrick. The safety bearing capacity is calculated base on therelationship between the loads on the derrick structure and dynamical parameter. Safety evaluation iscarried on the a-shaped and K-derrick in use by this method. The evaluation result is scientific and reliable.It truly reflected the actual capacity of the derrick in use.