近地表强衰减介质中的地震波传播模型

建立符合油气储层近地表复杂介质强衰减性质的数学-物理模型是油气勘探和开发的重要课题.本文针对D'Alembert黏弹性介质模型存在的量纲不统一和不能充分刻画孔隙介质结构的不足，通过引入孔隙度和渗透率等参数修改耗散项，改进了原D'Alembert模型，获得了能精细刻画具有强吸收衰减特征的近地表复杂介质模型，即改进的近地表黏弹性模型.基于这种改进的模型，推导了波频散和衰减的表达式，并研究了孔隙度、流体黏度等物理参数对波频散和衰减的影响，获得了相应的规律性认识.为了验证新模型预测近地表介质中波衰减的有效性，本文将新模型应用于胜利油田YX工区的近地表实测数据，同时与弹性Biot模型和BISQ模型以及黏弹性BISQ模型进行了比较.结果表明，与其它三个模型比较，改进的近地表黏弹性模型能够很好地刻画近地表介质的强衰减性，而且新模型所涉及到的物理参数明显少于其它几种模型，有利于新模型在油气储层近地表复杂介质地震勘探的实际应用.

Seismic wave propagation model in near-surface strong-attenuation media

Establishing a mathematical-physical model, which can conform to the attenuation properties of waves in the near-surface medium, is an important issue in oil/gas exploration. Aiming at the disadvantages of the D'Alembert viscoelastic model, which have no unified dimensions and don't describe enough the wave propagation in complex porous structures, through introducing the porosity and permeability to modify the dissipation term of the D'Alembert model, we improve the original D'Alembert model and get a new near-surface viscoelastic model with unified dimensions. This improved model can describe the strong attenuation of wave in the complex near-surface medium. On basis of the improved model, we present the dispersion and attenuation formulas of seismic wave and investigate the effects of several physical parameters (porosity, fluid viscosity) on the phase-velocity and attenuation of wave, thereby obtain some new understandings on the regularity of wave propagation in the complex near-surface medium. To verify the validity of the improved model in predicting the wave attenuation in near-surface medium, we apply the improved model to the measured data of the YX area in Shengli Oil Field and compare the theoretical results computed by the improved near-surface viscoelastic model, the elastic Biot model, the elastic BISQ model and the viscoelastic BISQ model, respectively. The comparison shows that the improved near-surface viscoelastic model with fewer physical parameters can provide more accurate predicting results compared with the other three models including more parameters. It further implies that the improved model is more useful in the practical application of seismic exploration in oil/gas reservoirs with complex near-surface medium.