含横向喷射流的部分饱和介质的纵波衰减和频散特性研究

当纵波在部分饱和多孔介质中传播时,孔隙内的流体会同时产生宏观、微观和中观流动,这3种尺度的流体流动共同作用,使纵波在较宽的频带范围内产生衰减和速度频散现象。目前同时考虑3种尺度流体流动的研究不多。为了研究流体的多尺度流动对纵波传播的影响,在层状双孔模型的基础上,引入了横向喷射流,建立了含横向喷射流的层状部分饱和模型。通过求解模型介质内的平均流体压力,推导了含横向喷射流的层状部分饱和模型的波动方程。利用平面波分析,得到了快纵波和两类慢纵波的相速度和品质因子,研究了3种尺度流体流动同时存在时的纵波衰减和速度频散特性,同时分析了岩石参数对纵波衰减和速度频散的影响。结果表明,在3种尺度流体流动的共同作用下,快纵波在低频和高频范围内都出现了衰减和速度频散现象,且由于喷射流的影响,快纵波在高频范围内出现了强衰减和高频散。快纵波相速度对模型的含气饱和度较为敏感,且随着模型孔隙度的减小,低频范围内的频散曲线和衰减峰向低频方向移动;随着喷射长度的增加,高频范围内的频散曲线和衰减峰向低频方向移动。
关键词：

 When P-waves propagate in partially-saturated porous media,the fluid in the pores produce macroscopic,microscopic,and mesoscopic flow simultaneously.Different scales of fluid flow together to cause the attenuation and velocity dispersion of the P wave over a wide frequency band.There were few cases to consider all these three kinds of fluid flow mechanisms.To study the influence of the multi-scale fluid flow on the P wave propagation,we introduced the transverse squirt flow and established a layered partially-saturated model,based on the layered double-porosity model.By determining the average fluid pressure in the media,the wave equations of the layered partially-saturated model with transverse squirt flow were derived.According to the plane wave analysis,the phase velocities and quality factors of the fast P-wave and two types of slow P-waves were obtained.Then we studied the characteristics of P wave attenuation and velocity dispersion under the simultaneous existence of the three scales of fluid flow,and analyzed the effect of rock property parameters on P wave attenuation and velocity dispersion.The results demonstrated that under the combined effect of the three scales of fluid flow,the attenuation and velocity dispersion of fast P-waves occur in both low-frequency and high-frequency ranges.Moreover,due to the influence of the squirt flow,the fast P wave encounters strong attenuation and high velocity dispersion over the high frequency range.The fast P-wave phase velocity was sensitive to the gas saturation of the model.The dispersive curve and attenuation peak in the low frequency range moved toward low frequencies with the decrease of the porosity of the model,while the dispersive curve and attenuation peak in the high frequency range moved toward low frequencies with the increase of the squirt-flow length.

国家自然科学基金(U1562215,U1762103)、国家油气重大专项课题(2017ZX05009001,2017ZX05036005,2017ZX05032003)和中国科协青年人才托举工程项目(2017QNRC001)共同资助。