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

XIE Guangyu; HE Jia; KONG Xiangwei; XU Hongxing; XU Min; TANG Yu; LI Zhenghao

doi:10.13347/j.cnki.mkaq.20250437

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 frag-mentation and bottom hole purification,and considering the influence of screw drill tools on rotational speed and torque,a mechanic-al 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 sec-tion 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 res-ults 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.