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文章介绍了正在研制的调制式旋转导向钻井工具MRST的组成及其工作原理；它由测控短节、偏置导向执行机构两大部分组成，是在钻柱全旋转且相对于井壁没有静止支撑点的条件下进行导向钻井的。工具偏置导向执行机构的执行是以钻井液为制导动力源，即作用在执行机构伸缩块上的内外压差而产生的液力推力，液力推力的大小与制导效果密切相关；为此，采用常规钻井水力学计算程序，对MRST在正常钻井工作条件下液力推力的大小及其影响因素进行了计算分析。结果表明，就目前国内陆上钻井设备所具有的条件，所研制的MRST是可以适应7000 m井深以内的井对导向力控制要求的；但作用在MRST伸缩块上的液力推力是随井深、排量、钻井液密度及流变性等的变化而变化的，实际应用MRST时应考虑上述因素变化对MRST工作性能产生的影响；此外，也可考虑通过微调排量的办法来调整MRST导向力的大小。

Calculation and Analysis of the Hydraulically Pushing Force in Rotary Steerable Drilling

The composition and operating principle of the modulated rotary steerable drilling tool MRST being de veloped are introduced in the paper. It is composed of two parts, i. e. the measure and control nipple joint and the bi ased steering executive unit, and the steerable drilling may be carried out under the circumstances of fully rotary drilling string and lacking of relative-to-wellface stationary support point. The drilling fluid is taken as the steering power source of the biased steering executive unit of MRST, i. e. the hy-draulically pushing force produced by the internal-external pressure difference acted upon the telescopic segment of the executive unit, and the magnitude of the hydraulically push ing force is closely related the steering efficiency. For this reason, the magnitude of the hydraulically pushing force and its influence factors of MRST at normal drilling conditions were calculated and analyzed by use of the conventional drill ing hydraulic calculation program. The results indicated that, in consideration of the existing conditions of land drill ing equipment in China, the MRST being developed might meet the need of steering force control necessary to the wells with depths of less than 7000 m; however the hydraulically pushing force acted upon the telescopic segment of MRST was various with the change in well depth, discharge capaci ty, drilling fluid density and its rheological property, so, while applying the MRST in practice, we should consider the influence of the change in the above-mentioned factors on the operating behavior of the MRST; furthermore, the magni tude of the steering force of the MRST might be controlled by slightly adjusting the discharge capacity.