| When the semi-submersible drilling rig is operating, periodic heave motion will be produced under the action of waves, which will lead the hook to up and down periodically and repeatedly. this will induce drilling pressure fluctuations in down hole, and cause the drill bit out of the bottom or shocking rock, which may impact drill efficiency, as well as the safety hazards in operation. Crane heave compensation system can provide effective heave compensation for platform to meet the needs of offshore drilling, with its advantage of effective compensation, strong compensation capability and huge loads withstand, etc.This article takes the Offshore Oil 981 as the research object, and analyzes the frequency and time domain response. Transient response under the operation conditions allowable of the platform has been obtained, thus the maximum heave amplitude and speed of compensation system can be acquired. According to drilling manual and related drilling design specifications, column, of the drill string, the weight, equivalent stiffness coefficient and the maximum allowable heave of the drill string in different well depth are obtained, with the composite pipe string design method for marine drill string design. The dynamic response analysis of semi-submersible platform and marine drilling string design provide an important basis for subsequent heave compensation system design.Firstly, this article studies the passive compensation system and designs its main structure, on the basis of which, the passive compensation hydraulic is designed with the principle of gas/liquid spring. Through the theoretical derivation and appropriately simplification, a mathematic model of the system static analysis is established, through which, the curve of hydraulic cylinder force versus the crown in the slide rail is obtained; with the separation method, stress analysis is carried out on the various objects, and dynamic equations are listed, then the crown motion equation is established after conversion and assembly. According to the passive compensation hydraulic design and theoretical derivation, the hydraulic simulation models of upright double-cylinders and inclined double-cylinders are set up respectively, so as the hydraulic simulation. It is concluded that compensation effect of inclined double-cylinders is better than that of upright one. Based on the inclined hydraulic simulation model, the analysis of system parameters is carried out, thus the air tank volume, depth-drilled, platform heave amplitude, platform heave period and the influence law of the hydraulic cylinder angle to the effect of crown heave compensation are obtained.On the basis of passive heave compensation structure design, the double upright active compensation cylinder structure is introduced, which constitutes the crown active heave compensation system structure. The hydraulic system is designed according to the system structure design, and it adopts the method of collectively controlling by variable pump together with the throttle, meaning that the variable pump controls the outlet pressure, while the throttle controls the outlet flow, and the two complements each other to complete compensation function energy-saving and efficiently. For the air tank, a pressure control system is designed. By adjusting the air tank pressure, force from hydraulic cylinder to crown can be dynamically changed, and then the condition of compensation system can be adjusted dynamically.On the basis of active compensation structure design and hydraulic design, dynamic equation of crown is established with the method of dynamics, which provides the theoretical basis for the active compensation system. Active compensation hydraulic model is constructed, and the curve of crown displacement versus time is obtained, also the compensation effect of crown is analyzed. In view of the simulation software failing to consider the hydraulic lag effect, a lag angle is added deliberately and the simulation is carried out in this article, so the relation between the lag angle and crown compensation effect is obtained. Based on hydraulic simulation model, the energy calculation module is added to analyze energy consumption of the system, and the parameters impact on energy consumption is analyzed, also the influence law of various parameters on the energy consumption is concluded, which provides important basis for system energy saving.To crown active compensation system, a detailed design of the key components such as active compensation cylinder, passive compensation cylinder, air storage tanks, tubing and so on is carried out, including design of size and performance parameters, as well as the corresponding checking, to make sure that it meets the use requirement. |
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