CO2 Trapping in Layered Porous Media by Effective Viscosification

Abstract

Safe and efficient storage of CO₂ in saline aquifers requires mobility control to prevent CO₂ from accumulation and rapid spreading at the formation top below the caprock. In the past, we have demonstrated the effectiveness of two engineered olefinic-based oligomers for viscosification of sc-CO₂ and the significant improvements in residual trapping of sc-CO₂ in brine-saturated homogeneous sandstone cores (Ding et al., 2024, https://doi.org/10.2118/214842-pa). The objective of this work is to examine the sweep efficiency and residual brine saturation in the layered cores by effective viscosification with two engineered molecules, providing the implications for CO₂ trapping in layered porous media by effective viscosification. In neat CO₂ injection, the CO₂ channels through the high permeability layer, causing rapid breakthrough and high residual brine saturation. This results in an inefficient process for CO₂ storage in saline aquifers. In viscosified CO₂ injection, we observe significant improvements in crossflow at the interface between the two-permeability layer, partly due to the mobility control and residual brine saturation reduction. In comparison to the neat CO₂ injection, the synergistic effect of the mobility control and increases in interfacial elasticity by injection of vis-CO₂ results in delay in breakthrough by a factor of 2 and about 95% higher brine production. Compared to our previous work on displacement experiments in homogeneous sandstone core, there is a more significant reduction of residual brine saturation in layered cores by viscosified CO₂ injection. Increases in injection rate is also demonstrated to improve the CO₂ storage in layered cores. Both the CO₂ viscosification and increases in injection rate may promote the injection pressure to overcome the capillary entry pressure, leading to CO₂ displacement of brine in the low-permeability layer. CT-imaging data advances understanding of boundary conditions, brine production, and local residual brine saturation in layered cores.