传统的地震AVO正演研究多采用参数固定的岩石物理模型,而实际地层属性参数在勘探范围内具有不确定性.本研究以目标地层岩芯样品的实验室测试数据为基础,通过样品孔隙度和干燥状态下纵、横波阻抗的高度线性关系对岩石物理模型进行了简化,并结合实验测量和测井解释建立了主要模型参数的概率密度函数.采用Monte-Carlo随机正演和Gassmann流体替换技术,对模型参数不确定性与地震AVO响应关系的研究表明,模型饱和不同流体时的AVO截距-斜率点束的分布形态和偏离饱水背景趋势线的程度受盖层泥岩速度的不确定性影响非常大,而储层砂岩孔隙度的不确定性也有明显影响.正确解释实际地震AVO异常的关键,是将岩石物理模型的参数合理地概率化,通过正演模拟来获得储层物性和流体信息的最大可能性.%Traditional seismic AVO forward study normally uses constant parameters to construct rock physics model, but these parameters in real formations have uncertainties across exploration area. Using laboratory measurements of cores from target formation, the rock physics model was simplified with relationships of reservoir sandstone porosities and P- and S-wave impedances in dry condition. To study influences of model parameter uncertainties, the probability density functions of key model parameters were introduced based on core measurement and well logging analysis. Using Monte-Carlo method and Gassmann fluid replacement technique, the AVO responses of models were obtained for saturation fluids as brine, oil and gas. The comparative analysis indicates that the velocity uncertainty of covering mud is the primary factor affecting the fluid cluster's distribution and deviation from water background trend on AVO intercept-gradient crossplots, while the porosity uncertainty of sand is also significantly affecting but less than covering mud. Thus, the correct interpretation of AVO anomalies for real seismic data requires forward simulation on probabilistic rock physics model to find out the most likely reservoir and fluid characters.
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