CO2驱油与封存中时移地震监测AVO模型研究——以鄂尔多斯盆地低孔低渗储层为例

Study on AVO model of time-lapse seismic monitoring for CO2 flooding and storage:Taking low porosity and low permeability reservoir in Ordos basin as an example

针对鄂尔多斯盆地致密储层CO2驱替过程中时移地震监测可行性问题,以苏里格地区的致密含油砂岩储层为基础,首先利用考虑压力变化的Digby模型来进行干岩石体变模量和切变模量的计算。其次,利用Digby模型结合Gassmann方程进行横波速度和纵波速度预测,及注入CO2后随压力变化纵、横波速度的计算。然后以黄234井的含油储层测井数据为基础建立两层介质模型。最后,计算注入CO2情况下随地层压力和CO2饱和度变化情况下的AVO梯度截距。研究发现随着地层注入压力增大,梯度减小,截距增大;随着CO2饱和度增加,梯度减小,截距也减小;CO2注入前后的反射系数差异明显,致密砂岩油层注入CO2后,其AVO特性呈现第二类含气砂岩的特征,可以被二次监测地震有效地监测出来。

Aiming at the feasibility of time-lapse seismic monitoring in the CO2 flooding-EOR process of tight reservoirs in the Or. dos basin, and based on the tight oil-bearing sandstone reservoirs in the Sulige field, the volume modulus and shear modulus of dry rock were calculated by Digby model which considered the pressure changes. Then, Digby model and Gassmann equation were used to predict the primary and shear wave velocity, and to calculate their value varying with the pressure after CO2 injection. After that, a two-layer medium model was established based on the reservoir logging data of well Huang-234. Finally, the AVO gradient intercept varied with the formation pressure and CO2 saturation after the CO2 injection was calculated. It was found that with the in. crease of injection pressure, the gradient decreased and the intercept increased. As CO2 saturation increased, the gradient and inter. cept decreased. The reflection coefficients before and after CO2 injection were significantly different. As for the tight sand oil reser. voir, its AVO features were accorded with the third class of gas-bearing sandstone, which could be effectively detected by the sec. ondary seismic monitoring.