水力加压器和井下马达组合时的钻压计算

水力加压器由于能吸收钻头冲击振动,能提供一恒定的易于控制的钻压而在油田得到广泛应用。文中分析了水力加压器串联在井下马达上面和下面时两种组合钻具的钻压计算、针对水力加压器串联在井下马达上面的组合钻具,将马达压降和马达转子输出扭矩的关系简化为一直线,建立了相应的钻压计算数学模型。该模型考虑水力加压器活塞及其缸体内壁间的摩擦力、水力加压器以下钻柱重量、水力加压器以下钻柱与井壁的摩擦力和活塞下推力等参数,用迭代法计算出马达压降和钻头钻压。同时也用压力平衡法计算出钻压,现场试验表明,两模型可靠、计算结果正确。

WOB CALCULATION FOR COMBINATION OF HYDRAULIC THRUSTER AND DOWNHOLE MOTOR

The capability in absorption of bit's shock and vibration to provide a controlled constant WOB has made a wide application of hydraulic thruster in oil fields. WOB calculation has been done based on two combinations with hydraulic thruster in tandem above and beneath the downhole motor. In case of hydraulic thruster in tandem above the downhole motor,the relationship between pressure drop across the motor and the output torque of motor rotor is simplified as a straight line and a mathematic model for WOB calculation is established. Taking into account of friction between thruster's piston and the inner wall of its cylinder, drilling string weight beneath hydraulic thruster, friction between side wall and drilling string beneath hydraulic and the downward pushing force of piston,the model calculates pressure drop across the motor and WOB by iteration. Pressure balance is also applied in WOB calculation. Field test showed that both models are reliable and the calculated results are correct.