基于统一强度理论的牙齿侵入井底岩石的机理分析

为了弄清深部地层复杂钻进条件下的牙轮钻头破岩机理,研究了牙轮钻头牙齿侵入井底岩石问题。在考虑井底压力的条件下,基于统一强度理论对牙齿侵入岩石的力学过程进行了分析,建立了含有统一强度参数的井底岩石侵入方程,并给出了不受轴向载荷、侵入深度和刃尖角影响的侵入系数。该方程考虑中间应力对井底岩石侵入系数的影响,在中间主剪应力的效应系数为0时,方程计算结果与Mohr-Coulomb强度理论所得结果完全相同。根据侵入方程,分析了内摩擦角、液柱压力、孔隙压力和刃尖角对侵入系数的影响。结果表明,侵入系数随中间主剪应力的效应系数的增大而增大,随内摩擦角和刃尖角的增大呈指数增大,随液柱压力的增大呈线性增大,随孔隙压力的增大呈线性减小。研究结果为牙轮钻头的现场应用提供了理论指导。 

Mechanism Analysis of Tooth Sink into Rock Based on Unified Strength Theory

In order to figure out the rock breaking mechanism in complex formation conditions,the teeth cutting into rock in bottom was studied. Considering the condition of the bottom hole pressure,based on unified strength theory,the mechanical process of teeth cutting into rock was analyzed,bottomhole rock sinking equation with unified strength parameters was established and sinking coefficient without the impact of axial load,invasion depth and bit angle have been worked out. The equation considers the impact of intermediate stress on sinking coefficient. The results of the equation and Mohr-Coulomb strength theory are identical when the effect coefficient of intermediate principal shear stress equals 0. The impact of angle of internal friction,fluid column pressure,pore pressure and bit tooth angle on sinking coefficient were analyzed based on sinking equation. The results show that the sinking coefficient increases with the increase of effect coefficient of intermediate principal shear stress,increases exponentially with the increase of angle of internal friction and bit tooth angle,increases linearly with the increase of fluid column pressure,and decreases linearly with the increase of pore pressure. The analysis of rock breaking mechanism of teeth can provide further theory guidance for cone bit onsite application.