Pore Scale Dynamic 3D Imaging of Water-Alternating-Gas Flooding and CO2-foam Flooding in a Double Layer Core

The geological carbon dioxide storage is usually combined with the enhanced oil recovery. The reservoir heterogeneity (such as bedding) often leads to reduced volumetric sweep efficiency in sandstone. To study the effect of layered heterogeneity on geological CO2 storage and oil recovery, we performed Water-Alternating-Gas flooding (WAG) and CO2-foam flooding on a specially constructed sandstone, and characterized the dynamic distribution of CO2 and oil by in-situ imaging. The results show that the low permeable layer contained a large amount of residual oil after water flooding. After CO2 injection, CO2 spanned over several pores in the high permeable layer and entered the low permeable layer, displaced part of the residual oil, which leaded to an enhanced oil recovery. In the second water injection, the CO2 clusters were divided into small bubbles and capillary trapped as gas in oil or gas in water in oil. Note that after second water injection, the residual oil saturation increased in both high permeable layer and low permeable layer. Obviously, WAG flooding effectively changed the spatial distribution of residual oil. However, after WAG flooding, a large amount of residual oil was still trapped in the low permeable layer until CO2-foam flooding, the foam system blocked the high permeable layer, and the oil recovery was almost 100%. In conclusion, WAG flooding changed the original spatial distribution of CO2 and oil. CO2 was capillary trapped and increasing oil recovery. CO2-foam flooding is a more effective method of enhancing oil recovery than WAG flooding.