煤层气径向钻井压耗计算与井口压力预测

对煤层气径向钻井过程中钻井管柱系统压耗和高压水射流破岩机理进行分析，列出了钻井管柱系统各部分磨阻系数的计算公式和喷嘴射流动力公式。通过理论分析与室内试验，提出了煤的水力冲击破碎压力与其物理力学参数之间的关系式，以及水力冲蚀速度与无因次冲击压力之间的关系。结果表明:通过加权平均值法计算得到的临界破碎压力与实际值吻合良好；在3~8倍临界破碎压力下，冲蚀速度约为无因次冲击压力的0.4倍。根据文中压力预测步骤，对现场作业进行压力预测，得到的井口压力预测结果比实际施工压力低3~5 MPa。 

Friction loss calculation and wellhead pressure prediction in CBM radial drilling

The paper analyzed the pressure loss of drillpipe system for CBM radial drilling and high pressure water jet breaking mechanism, and listed the formula of various parts of resistance coefficient and nozzle jet power in drill pipe system, presented the relationship between hydraulic impact broken pressure and physical and mechanical parameters, and the relationship between hydraulic erosion velocity and dimensionless impact pressure by theoretical analysis and laboratory tests. The results show that the critical breaking pressure calculated by the weighted average method agrees with the measured values. At the 3~8 times critical breaking pressure, erosion rate is about 0.4 times as much as dimensionless impact pressure. According the requirements of construction, by pressure prediction step, the wellhead pressure of field operation was predicted, the predicted pressure was 3~5 MPa lower than construction pressure.