CO_2地质封存四维地震监测和属性分析

Attribute analysis and 4D seismic monitoring for the geological storage of CO_2

CO2地质封存四维地震监测的主要目标是监测地质封存的安全性和CO2驱油效果。注入CO2过程中,储层中流体饱和度和储层压力变化导致储层弹性参数及地震响应发生相应变化。从理论上讲,储层开发的基本地质条件是不变的,所以两次四维地震属性相减得到的成像显示,消去了油气藏静态性质(如构造、岩性等),得到的是油气藏的流体动态成像(如压力、饱和度等)。本文采用的加拿大Weyburn油田CO2地质封存项目四维地震数据进行分析和研究,两次三维勘探数据采集时间分别是1999年(Baseline)和2002年(Monitor),CO2封存量为280×104t。首先,以测井资料为基础,通过Gassmann方程和人工合成地震记录,计算替换前后其速度和振幅等属性的变化,以此约束实际地震属性的筛选;然后,在对两次观测的四维地震数据进行四维地震匹配处理的基础上,进行两次观测地震数据的地震属性筛选与对比分析,利用两次地震属性的差异,识别注入CO2后储层内流体的分布特征;最后,以盖层重复性为指标,标定储层,提取储层的不同属性,同时结合人工合成地震记录的结果,得到一个能更好表现其流体变化的属性。

The targets of 4D seismic monitoring are the security of the geological storage of CO2 and the oil displacement efficiency of CO2. The changes of the reservoir fluid saturation and the reservoir pressure could result to relevant changes of the elastic parameter and the seismic response in the process of the CO2 injection. The static properties(geotectonics, lithological properties) of the reservoir are eliminated from the image generated by subtraction of two 4D surveys to get the dynamic properties of reservoir fluid(pressure, temperature, saturation,etc.) as the basic geology conditions of reservoir development is unchanged theoretically. This case study is 4D seismic data acquired in Weyburn field, Canada in 1999(Baseline) and 2002(Monitoring), the quantity of the storage of the CO2 is 280 × 104 t. First, the changes of the attributes(velocity, amplitude, etc.) before and after the replacement are calculated to constrain the selection of the actual seismic attribute by the Guassmann equation and synthetic seismogram based on the logging information. Second, the seismic attributes of the data acquired in 1999 and 2002 are selected, compared and analyzed based on the 4D seismic data matching, and the distribution characteristics of the reservoir fluid are identified by the differences of the seismic attribute between the first and the second acquired data after the CO2 injected. Last, the repeatability of the cap layer is taken as indicator to calibrate the reservoir and the different attributes of the reservoir are extracted, and combine them with the synthetic seismogram to get a better attribute which indicates the changes of the fluid.