Investigating clay swelling and permeability impairment in sandstone formations during steam flooding

Abstract In heavy oil fields hosted in sandstone, steam flooding is a crucial technique for enhancing oil recovery. The swelling of clay minerals in these reservoirs, particularly those with high clay content, presents a significant challenge by causing permeability damage and hindering oil production. The objective of the present study was to investigate clay swelling phenomena in a sandstone oil reservoir where smectite-illite clays make up 40% of the reservoir rock. Through comprehensive static and dynamic tests, clay swelling behavior and its impact on permeability degradation were examined under varying temperature and salinity conditions typical of thermally enhanced oil recovery (EOR) processes. Results indicated that clay swelling is exacerbated under low salinity and high temperature, leading to severe permeability impairment. At high salinities (2000–4920 mg L –1 ), the swellability was relatively low, but it increased significantly as salinity decreased to a range of 0–2000 mg L –1 . Static swelling tests revealed that the maximum clay expansion, with a 2.25-fold increase in volume, occurred in distilled water at 200°C. Additionally, the critical salt concentration (CSC) was found to increase with temperature, causing a more pronounced and earlier swelling effect. This increase in temperature coupled with a decrease in salinity impaired permeability significantly, with the most severe reduction, of 73.3%, observed at 150°C during distilled water flooding. Comparisons between static and dynamic tests showed consistent degrees of clay swelling across both methods. The findings of this study advance the understanding of clay swelling under thermal EOR conditions, particularly regarding the effects of salinity and temperature on permeability impairment in sandstone formations.