Design Of Drill String Heave Compensation System Applied In The Marine Drilling

The ocean is rich in resources. With our gradually speeding up the pace of marching to the sea, the related marine engineering equipments should be urgently researched and developed. Drill string heave compensator is an important equipment for offshore drilling, it minimizes the effect of heave motion to the wight of bit(WOB) and provide reliable protection for normal drilling operations, thereby prolonging the time of operations at sea and bringing huge economic benefits.With the development of hydraulic drive and control technology, drill string heave compensator has gone through several stages:first, using a large gas-liquid spring to form the passive heave compensation devices, PHC doesn’t need additional energy, but its compensation accuracy is low, the volume of high-pressure gas is too big, taking up a large deck area;second, with the foundament of the PHC, increasing an electro-hydraulic proportional or servo control loop to form active heave compensators (AHC, known as semi-active heave compensators in domestic), AHCs need additional energy, but its compensation accuracy is higher than PHC, also the high-pressure gas volume is reduced; third, a variety of improvements to reduce the high-pressure gas volume are developed, except joining the active compensation circuit, there are Junik converter, variable radius curve pulley mechanism; fourth, breaking the traditional design concept, active winch-type drill string heave compensator and hydraulic lifting rig are emerging.As a large marine engineering equipment, there are several key questions for developing drill string heave compensation devices:First, how to determine the design specifications and the main structural parameters, sea conditions are continuously changing, and the rigs operating locations also change, which led to difficultly balance the relationship between the ability to compensate for compensation and the actual working conditions requirements, in this dissertation, mature products’ parameters are discribed to facilitate the designers to choose; drill string heave compensator is a high-pressure equipment, the need to ensure its safe and effective work,which must have a fault detection system and protection measures; third, the control system design, the need for multiple operating modes, each mode has a different compensation objectives, switching between different modes and the designing of controller is difficult.The first chapter, introduced the working principle of the drill string heave compensation equipment in the drilling work and rope work, and then introduced drill string compensator according to different classification methods in detail, pointed out the question of big volume of high-pressure gas and related improvements-the Junik converter; introduced foreign drill string heave compensator development, made a comparative analysis for a variety of different structures compensator, summarized the trends-modularization, universalization, serialization. At last, some reasonable suggestions are put forward for drill string heave compensation device development in our country.The second chapter first introduced the main design parameters of the heave compensation device:load, compensation displacement and period, gas-liquid spring stiffness; described the mature design parameters to facilitate designers in the design of drill string heave compensator for oil drilling at sea; then provided an overview of the modeling methods of the drill string to explain its complex stress state, and finally summed up two structures of drill string heave compensator called the "parallel" and "series" according to the mechanical structure of drill string heave compensation system, with different compensation strategy, drawn the expression of the required active compensating force, which provides a reference for the design of semi-active the drill string heave compensation devices.The chapter three, depended on the specific design requirements, calculated the primary parameters for a "series’" semi-active drilling. First, calculated the parameters of passive portion. Second.validated compensation effect after estimating the amount of relative change in its volume, proved that a passive part can be able to significantly reduce the ship heave influence to the drill string. Third, calculated the parameters of active portion. With comparison the consuming power of active and semi-active, results showed that the semi-active heave compensation system needs only about5.85%and7.31%power of the pure active compensating systems. Finally, according to calculated data, suggested that controlling the heave compensation system pressure constant as a control target, because the required power consumption for active portion is smallest under the circumstances.The chapter four designed two experimental test systems about drill string heave compensation devices, from simple to complex. First, using proportional directional valve to constitude compensation loop and using ordinary solenoid valve circuit to simulate the ups and downs of the ship, the ship heave approximate constantly speed. Second, using servo valve to form compensation loop and using servo motor through the ball screw driving compensation cylinder movement to simulate the ups and downs of the ship, controlling the movement of the "ship" in accordance with the laws of sinusoidal, gradually increasing the frequency of the ship heave movement. Using Simulink xPC Target module to build host-target real-time control system, designing a PID control loop and achieve a good compensation effect.