Analysis For The Dynamic Response Of Drilling Rig Derricks

Oil derricks is one of the most important rig equipment in hoist system. In oilfield drilling, people can install crown block and hang tackle, hoisting hook and special tools on it, and also complete manipulations such as making a trip, casing running and so on. Rig derrick, being main part to bear load, is always working at worse circumstances than other common steal structure. Derrick structure must undergo hook load in tripping, wind load outdoors and vibration load when drilling machine is running. At present, it can only satisfy the base requirement in stage of design to research derrick structure by static equivalent method, nothing done further when rig derrick is undergoing the dynamical load. It has drawn attention that response researches are on longitudinal impaction in special circumstance, periodic loads in work phases and wind vibration under wind load. It can effectively decrease or avoid the dynamic invalidation of derrick structure and the phenomenon of derrick collapse resulting from wind to produce accidence. So it is important and can give constructive guidance to structure design of derrick and safety production in oil field.This thesis takes the front-open type derrick as the object to build the dynamic model of drilling rig derrick by the theory of elastic body and principle of model equivalent, and classify two operating modes, especial and normal modes, by the structure character and work practice of derrick. At the same time, based on probability statistics and probability model of vertical loads, the thesis establishes the load spectrum in periodic experiment and transient course with time impact, then implements the transient analysis and dynamic response calculation. It draws some conclusions including the changes of deformation and stress of derrick structure under dynamic loads, and the vibration rules and characteristic of time responses in different orientation in the main parts such as top, racking platform and propeller strut of drilling rig derrick.This thesis completes the mode analysis of rig derrick by finite elementsoftware——ANSYS, getting the free frequencies of preceding 10 steps andvibration modes. Based all above, it completes the response spectrum analysis, getting the characteristic between frequencies and responses of the derrick system. The principle of the aerodynamics is used to study the characteristic of land wind field of the Daqing Oil Field. Then, the thesis completes the theory analysis of wind load spectrum of oil rig derrick. By gathering the meteorological data of annual maximum wind speed for 44 years from 1960 to 2003 in Daqing Oil Field, it founds the mathematics model of probability analysis, Extreme Value I, to achieve the wind probability analysis of rig derrick under design speed. According to the production reality of oilfield, 9 kinds of load situations are set up to simulate the mechanics action. After that, it calculates the wind vibration coefficients and pulsating equivalent wind-load at four parts of derrick by theory of structure random vibration. Using the energy method, it analyzes various types of pulsating wind spectrum, and puts forward the simulation method of pulsating wind based of synthetic method of triangular progression superposing harmonic. Furthermore, it gives the numerical simulation result of the wind loads by software Matlab6.5.In the thesis, the safety evaluation method of wind vibration of the oil rig derrick has been further discussed. It valuates the safety characteristic of the rig derrick under wind vibration by analysis of interaction between wind load and derrick and destroyed forms about derrick structure, using the way of safety degree and fatigue computations. Describing the leading wind direction in winter, summer and the whole year in Daqing with the wind rose picture, it builds the location orientation diagram of the well for oil field. It concludes that the top of derrick structure in case of hurricane has already exceeded the control limit of safety degree, which is likely to collapse at first wind direction, but can't been destroyed by fatigue.Respectively, the dynamic response of derrick has been researched in two different situations which are the coupling of periodic hookload and wind load and that of impact hookload and wind load. All calculations conclude that two load couplings can affect the dynamic response of rig derrick correspondingly.