Research And Design Of Hydraulic Heave Compensation System For Drill String

Drill string heave compensation system is vital device of offshore drilling operation. Themovement of drill ships or semi-submersible drilling rigs with the waves of the sea presents aunique problem in drilling with these types of rigs. Heave, however, removes weight from thedrill bit as the ship or rig rides to the crest of a wave, and puts weight back on the drill bit as theship or rig rides down into the trough between waves. This fluctuation in the force applied on thedrill bit severely hinders an operator's ability to drill the well bore. To account for the problemsassociated with heave, floating drilling rigs are equipped with a heave compensation system. Theheave compensation system is typically in the form of an active heave drawworks system or asystem that is an integral part of the drilling derrick or mounted directly on an extension of thetraveling block. When functioning properly, these primary heave compensation systems arecapable of protecting against the effects of heave.The object of the article is to introduce and compare drill string compensation systemgenerally used in the terms of structure, operating principle, hook displacement and energyconsumption, and to disclose a new type drill string compensation system on this basis, designand system performance investigation including with a view to improve compensation results andreduce energy consumption.First, structure and operating principle of several kinds of drill string compensators arecompared, including compensator mounted between travelling block and hook, crown mounteddrill string compensator and that mounted on the dead line. By the advantage of easy-made rig,crown block, and standard traveling block and hook, compensator mounted between travellingblock and hook with reverse cylinder is chosen to develop new type of drill string compensationsystem.Then in accordance with classification method of the passive, active and semi-active system,the performance of compensator mounted between travelling block and hook is studied deeply.Mathematical mode, simulation model are set up. The models are simulated and calculated by themeans of AMESim. The three kinds of system based on different way of energy providing areanalyzed and compared in the terms of hook displacement and energy consumption according to the simulation results. Because of good performance of semi-active system, new method toimprove performance of compensator can be developed on the basis of it.On the base of previous work, new drill string compensation system is proposed. Thecompensation cylinders of new system have their rod end controlled and piston end worked inthe passive way to simplify the system. The rod ends of cylinders are controlled with both pumpand valve in order to save energy. Function principle is studied, the structure and hydraulicsystem are designed and calculated, and at last mathematical model is set up. The model issimulated with AMESim. The performance of the system is analyzed from the simulation resultsand compared with systems currently being used. Then the feasibility of new drill stringcompensation system is confirmed.In order to verify the actual performance of the system, experimental system is needed. Newtype of drill string heave compensation system is designed at the end of the paper, including thestructural design and hydraulic system design. Through experiments, basis for the new drill stringheave compensation system to improve will be provided.