热弹性介质中波传播特征

Characteristics of wave propagation in thermoelastic medium

深层-超深层油气地震勘探涉及高温介质地震波传播问题,热弹介质参数对地震波传播有重要影响.含弛豫时间修正项的Lord-Shulman双曲型耦合热弹波动方程从理论上预测了热弹性介质中存在快纵波、慢纵波(一种准静态慢纵波,简称热波)和横波的传播,两个纵波为热耗散衰减波而横波不受介质热特性的影响.本文结合平面波频散分析和格林函数法数值模拟,详细研究两个热耗散衰减波的频散和衰减特征,着重分析热导率、热膨胀系数及比热的变化对波速和衰减的影响.研究表明热导率作为主要参数决定了波速与衰减的临界变化,热膨胀系数对波速和衰减的幅度有明显影响,比热则兼顾了前两个热弹系数的影响特征.最后,利用热弹性动力学频率域的二阶格林函数进行波场快照数值模拟,展示热弹性介质中纵波、横波和热波的传播行为.

Seismic exploration of deep-super deep oil and gas involves seismic wave propagation in high-temperature media.The thermoelastic parameters in this medium have an important influence on the propagation of seismic waves.The Lord-Shulman hyperbolic coupled thermoelastic equation with a relaxation time correction term predicted theoretically the propagation of a fast longitudinal wave,a slow longitudinal wave(a quasi-static slow longitudinal wave,called thermal wave for short)and a transverse wave in the thermoelastic medium.The first two longitudinal waves are thermal dissipation attenuation waves and the transverse wave is not effected by the thermal characteristics of the medium.This paper combining plane wave dispersion analysis and Green′s function numerical simulation studies the dispersion and attenuation characteristics of two thermal dissipation attenuating waves in detail,focusing on analyzing the effects of changes in thermal conductivity,thermal expansion coefficient and specific heat on wave velocity and attenuation.Studies have shown that thermal conductivity as the main parameter determines the critical changes in wave velocity and attenuation.The thermal expansion coefficient has a significant effect on the amplitude of wave velocity and attenuation.The specific heat takes into account the characteristics of the first two thermoelastic coefficients.Finally,the second-order Green′s function in the frequency domain of thermoelastic dynamics is used to simulate the wave field snapshots to show the propagation behavior of longitudinal,transverse and thermal waves in the thermoelastic medium.