随钻四极子声波测井是目前随钻环境下测量地层横波速度的有效技术手段,地应力的存在会极大地影响地层横波速度的测量.为分析地应力对随钻四极子频散曲线的影响,通过微扰法建立随钻环境下地应力与频散曲线相速度改变量之间的关系,在此基础之上,研究了地应力作用下随钻四极子频散曲线的特征.数值模拟结果表明:与均匀地层相比,施加应力后随钻四极子频散曲线截止频率处的相速度明显增大;与裸眼井相比,由于钻挺的存在,随钻测井井孔附近的应力集中效应更为明显,但不会影响原状地层横波速度的测量.值得注意的是,地应力条件下随钻四极子频散曲线和以原状地层横波速度计算的均匀地层的频散曲线两者有较大差异,这可以作为判断地应力存在的一个依据.地应力条件下随钻四极子频散曲线的特征为随钻环境下地应力识别及反演提供了理论基础.%The logging-while-drilling (LWD) quadrupole acoustic logging is an effective technique to measure the formation shear wave velocity at present, and the existence of formation stress will greatly affect the measurement of formation shear velocity. In order to analyze the influence of the formation stress on the LWD quadrupole dispersion curve, the relationship between the stress in the LWD environment and the change of the phase velocity of the dispersion curve is established by the perturbation method, on the basis of which the characteristics of the LWD quadrupole dispersive curve are studied. The numerical simulation results show that the phase velocity corresponding to the cut-off frequency of the quadrupole dispersion curve is increased obviously compared with the homogeneous formation, and the stress concentration effect of the borehole is more obvious than that of the open hole, but it will not affect the measurement of the shear velocity of undisturbed strata. It is worth noting that in the LWD environment, the frequency dispersion curve and the frequency dispersion curve of the uniform stratum are very different under formation stress, which can be used as a basis for judging the existence of formation stress. The characteristic of the LWD quadrupole dispersive curve under the condition of formation stress provides a theoretical basis for the recognition and inversion of the stress in the LWD environment.
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