Abstract: In the exploration and development of deep tight oil and gas reservoirs, drilling operations face significant challenges due to high confining pressures and high hydrostatic pressure, which result in frequent engineering problems such as bit wear and cutter breakage. To better understand the rock-breaking mechanism of bits in deep tight formations, this study investigates the mechanical properties and cutting behavior of sandstone, granite, and shale with different porosities under dry, saturated, and hydrostatic conditions. A comprehensive analysis is conducted to explore the variations in rock-breaking across different cutting conditions. The results show that water saturation reduces the mechanical strength of rocks, with the greatest impact on shale and the least influence on sandstone. Under hydrostatic pressures, the compressive strength of rocks initially increases with pressure, then decreases, and subsequently increases again. Saturated rocks exhibit lower cutting forces, smaller cutting sizes, smoother cut marks, and higher rock-breaking efficiency. Under hydrostatic pressures, rock failure predominantly occurs through plastic deformation, characterized by increased cutting forces and mechanical specific energy (MSE)for rock breaking, enhanced energy dissipation, and a tendency for cuttings to accumulate and adhere, accompanied by muddling phenomena. Under the influence of pore pressure and pressure differential balance, the cutting force for low-porosity granite and shale increases with the rising hydrostatic pressure, while the cutting force of sandstone decreases due to excessively high hydraulic pressure. At atmospheric pressure, rocks typically undergo brittle fracture, whereas confining pressure reduces the extent of brittle fracture, and the hydraulic environment facilitates the transition of rock failure from brittle to ductile fracture.

Key words: tight oil and gas, hydrostatic pressure, rock failure behavior, cutting condition, rock-breaking mechanism

摘要： 在深层致密油气勘探开发中,钻井面临高围压、高液柱压力等挑战,导致钻头磨损和断齿等工程问题频发。为理解深部致密地层钻齿破岩机理,研究了孔隙度不同的砂岩、花岗岩及页岩在干燥、饱和及液压状态下的力学特性和切削行为,综合分析了不同切削环境下的岩石破碎差异。研究结果表明:水浸泡会降低岩石力学强度,页岩受影响最大,砂岩最小;液压下岩石抗压强度随液压增加呈现先增大后减小再增大的趋势。饱和岩石切削力更低,岩屑尺寸更小,切痕更光滑,破碎效率更高。液压下,岩石以塑性失效为主,切削力和破岩比功增加,能量耗散更大,岩屑易堆积黏附,并伴随泥化现象。在孔压及压差平衡影响下,孔隙率低的花岗岩和页岩切削力随液压增加而增大,砂岩切削力则因过高液压而降低。常压下岩石多为脆性破碎,围压使脆性破碎减弱,液压环境使岩石从脆性破碎转变为塑性破碎。

关键词: 致密油气, 液柱压力, 岩石失效行为, 切削环境, 破岩机理