考虑射流−螺杆作用的深煤层钻井机械比能模型与参数优化研究

    Research on mechanical specific energy model and parameters optimization of deep coal seam drilling considering jet-screw interaction

    • 摘要: 鄂尔多斯东缘临兴区块煤层气资源丰富,但受限于埋藏深度大、地层非均质性强等因素,钻井作业面临效率低、施工难度高等挑战。现有机械比能模型对于井下复杂情况的钻压、转速、扭矩的准确计算存在困难,造成能量浪费。为此,针对临兴区块深煤层地质特征,结合水力能量对岩石破碎和井底净化的作用,考虑螺杆钻具对转速和扭矩的影响,提出了考虑射流−螺杆作用的机械比能模型。经验证,相比于Teale模型、Pessier模型、孟英峰模型,提出的模型计算的机械比能值与岩石抗压强度的相关性较好,更加接近真实的机械比能值。以临兴区块LX−55−7D井2 368~2 776 m井段为例,基于皮尔逊相关性法则,对钻井参数进行相关性分析,得到了与机械比能正相关性较强的参数,依次为转速、钻压、排量、立压、钻头压降、岩石抗压强度、大钩负载,负相关性较强的参数为机械钻速、扭矩,确定了机械比能的主要影响因素为钻压、转速、排量;通过响应面法设计了交叉试验,进行了钻井参数优选,得到了适用于该井段煤岩钻进的最佳参数:钻压50 MPa、转速55 r/min、排量35 L/s。将优化的钻井参数应用于LX−58−6D井的钻井现场设计,结果显示:优化后的钻进参数组合使机械能量转化效率提升了50.5%,钻速提高了19.1%。该方法可降低煤岩互层导致的能量耗散,为深煤层高效钻井提供了技术支撑。

       

      Abstract: The Linxing Block on the eastern margin of Ordos Basin contains abundant coalbed methane resources. However, drilling operations in this area face challenges such as low efficiency and high technical difficulty due to factors including deep burial depth and strong formation heterogeneity. Existing mechanical specific energy models have limitations in accurately calculating weight on drilling pressure, rotational speed, and torque under complex downhole conditions, resulting in energy waste. Therefore, in view of the geological characteristics of deep coal seams in the Linxing Block, combined with the effect of hydraulic energy on rock fragmentation and bottom hole purification, and considering the influence of screw drill tools on rotational speed and torque, a mechanical specific energy model considering jet and screw drill tools is proposed. Verified by the model, compared with the Teale model, the Pessier model and the MENG Yingfeng model, the mechanical specific energy value calculated by the proposed model has a better correlation with the compressive strength of the rock and is closer to the real mechanical specific energy value. Taking the well section of Well LX-55-7D in Linxing Block from 2 368 m to 2 776 m as an example, based on Pearson’s correlation law, a correlation analysis was conducted on the drilling parameters. The parameters that have a strong positive correlation with mechanical specific energy were obtained in sequence as rotational speed, drilling pressure, displacement, vertical pressure, drill bit pressure drop, rock compressive strength, and large hook load. The parameters with strong negative correlation are mechanical drilling rate and torque. It is determined that the main influencing factors of mechanical specific energy are drilling pressure, rotational speed and displacement. A cross test was designed through the response surface method, and the drilling parameters were optimized. The optimal parameters suitable for coal and rock drilling in this well section were obtained as a drilling pressure of 50 MPa, a rotational speed of 55 r/min, and a displacement of 35 L/s. The optimized drilling parameters were applied to the drilling site design of Well LX-58-6D. The results showed that the optimized combination of drilling parameters increased the mechanical energy conversion efficiency by 50.5% and the drilling rate by 19.1%. This method can reduce the energy dissipation caused by the interlayering of coal and rock, providing technical support for efficient drilling in deep coal seams.

       

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