井底岩石的共振响应分析及数值模拟研究

Analysis and numerical simulation for resonant response of bottom hole rock

共振钻井是一种新型的钻井提速技术,在钻井过程中,为了达到最优的破岩效果,需要使振动频率与不同状态下岩石的共振频率相匹配,因此研究岩石在井底围压及约束状态下的共振响应特性十分必要。考虑到井底岩石的内部孔隙结构,以及岩石受到的井底围压作用,通过理论分析和数值模拟,获得不同约束下、不同孔隙分布下,岩石的位移响应振幅与冲击力频率的关系,进而得到岩石的共振频率。在模拟条件下,岩石的共振频率不随围压变化,但围压下的共振频率略高于自由状态下的共振频率;当岩石受到径向位移约束时,共振频率变大,且共振频率随岩石泊松比的增大而增大;当岩石内部孔隙沿冲击方向分布均匀时,其共振频率与孔隙度无关;当岩石内部孔隙沿冲击方向分布不均匀时,其共振频率与孔隙分布的不均匀程度相关,不均匀程度越高,共振频率越低。为分析岩石在井底状态下的共振响应特性提供了初步的理论基础,也为共振钻井技术的参数选择提供了依据。

Resonance drilling is a new drilling speed raising technology.It is crucial to make impact frequency match rock’s resonant frequencies under different conditions to achieve the best rock-breaking efficiency in drilling process.Therefore,it is necessary to study resonant response of bottom hole rock under confining pressure and constraint conditions.Here,considering bottom hole rock internal pore structure and rock subjected to bottom hole confining pressure,through theoretical analysis and numerical simulation,relations between rock displacement response amplitude and impact frequency were obtained under different constraints and different pore distributions,and then rock’s resonant frequencies were acquired.It was shown that under simulation conditions here,rock’s resonant frequencies don’t change with variation of confining pressure,but they are slightly higher than those under the free condition;when bottom hole rock is constrained along radial displacement,its resonant frequencies become higher,and they increase with increase in rock’s Poisson’s ratio;when pore in rock distributes uniformly along impact direction,rock’s resonant frequencies are not related to porosity;when pore in rock distributes unevenly along impact direction,rock’s resonant frequencies are related to uneven degree of pore distribution,the higher the uneven degree,the lower the rock’s resonant frequencies.The study results provided a preliminary theoretical basis for analyzing rock’s resonance response characteristics under the condition of bottom hole,and provided a basis for choosing parameters of the resonance drilling technology.