弹性阻抗在岩性与流体预测中的潜力分析

The potential analysis of elastic impedance in the lithology and fluid prediction

1. 中国石油勘探开发研究院,北京 100083;2. 中国科学院地质与地球物理研究所,北京 100029

SINOPEC Research Institute of Petroleum Exploration and Development, Beijing 100083, China

给出了弹性阻抗的概念,并根据弹性阻抗与波阻抗定义的相似性,提出了利用叠后测井约束反演方法实现弹性阻抗反演的思想。利用Gassmann方程对渤海湾地区上第三系储层进行了流体替代模拟,得出横波速度随水饱和度变化很小,纵波速度和密度随水饱和度变化较大,对流体变化较敏感的结论。用不同饱和度的纵、横波速度和密度参数,利用波动方程正演模拟得到叠前合成道集,并提取角道集剖面,然后反演得到弹性阻抗剖面。反演结果表明,利用叠后测井约束反演方法实现弹性阻抗反演是有效和可靠的。对弹性阻抗和波阻抗与水饱和度的关系进行了对比分析,结果表明,弹性阻抗可以更好地反映流体饱和度的变化,在岩性和流体的识别和预测中具有很大的潜力。对鄂尔多斯苏里格气田的实际资料进行了处理,发现入射角为16°时弹性阻抗与自然伽马有很好的相似性,因此利用16°入射角对应的弹性阻抗可以识别有效储层。此外,通过井点弹性阻抗与自然伽马的对比分析,可以确定区分有效储层的门槛值,如苏里格地区有效储层的弹性阻抗门槛值为2900。

Based on analysis of elastic impedance concept,the procedure of elastic impedance inversion was presented by use of the traditional poststack seismic inversion methodology and software package because of similarity between acoustic impedance and elastic impedance definition. Synthetic gathers generated by fluid replacement modeling and seismic verified the validity and reliability of this procedure forward modeling with elastic wave equation.The potential of elastic impedance in predicting lithology and fluid properties was analyzed. In the SLG area.due to good comparability between elastic impedance log with 16 incidence angle and gamma ray log the effective reservoir can be identified by elastic impedance inversion which provides a most efficient way of seismic reservoir description.