Work

Permeability decline due to fines migration during CO2 injection in sandstones

Year: 2025

Type: article

Abstract: One of the key risks for CO 2 storage is injectivity decline. During CO 2 injection, evaporation of the connate brine in the near-wellbore region results in drying-up the rock yielding the influx/backflow of the reservoir brine into the dried-up zone that leads to the accumulation of precipitated salts. Drying the rock also yields the mobilisation, migration, and straining of clay particles. Those phenomena lead to rock permeability decline. We present the results of eight corefloods. The corefloods exhibit intensive fines production at the beginning of injection, followed by a lower rate of fines production rate during the main evaporation period and a gradual decline in fines production during the later stages of evaporation. We also observe an abrupt increase in gas permeability in the middle of the evaporation period and evidence of changing gas pathways after each rock re-saturation and new gas injection. The explanation of these observations stems from the three sequential regimes of fines detachment during two-phase displacement, identified in this work: (i) movement of gas-water menisci; (ii) pendular rings of residual water; (iii) dry flux. It was found that, for the conditions of these corefloods, fines detachment is possible in regime (i) only. Fines production during overall injection period is explained by continuous brine evaporation and subsequent transversal menisci advancement during unstable CO 2 -water displacement in micro-heterogeneous rocks. Rock permeability for gas declines up to 5 times, while for brine it decreases up to 2.7 times. Typical full evaporation time is up to million pore volumes injected (PVIs). The observed phenomena will lead to significant modification of the mathematical model for CO 2 storage. • Eight corefloods on brine displacement by CO 2 exhibit unstable gas viscous fingering. • Permeability decline is attributed to fines migration and some salt precipitation. • Water is produced during 10 3 PVIs, while full evaporation occurs during 10 6 PVIs. • Fines detach by moving CO 2 -water menisci while pendular water rings secure the fines. • Abrupt permeability increase occurs by reaching the saturation percolation threshold.

Source: Gas Science and Engineering

DOI: 10.1016/j.jgsce.2025.205613