The second critical capillary number for chemical flooding in low permeability reservoirs: Experimental and numerical investigations

Abstract

High capillary numbers are often adopted for chemical flooding in reservoirs to achieve the highest oil recovery. A high capillary number may be disadvantageous for high and medium permeability formations, while no experimental or field data are available for low permeability formations. In this work, through the use of a newly designed experimental apparatus for the measurement of the dynamic capillary pressure in low permeability formations, chemical flooding experiments on sandstone core samples (1–10 mD) were conducted to investigate the effects of high capillary numbers (0.001–2). In addition, these effects were examined through numerical production simulations on a real low permeability reservoir. The dynamic capillary pressure and relative permeability were measured to reveal the dynamic fluid flow characteristics. The dynamic contact angle was investigated to explore the dynamic interface properties. The results show that there is a second critical capillary number (higher than 0.02) that can be used to optimize the chemical flooding performance in low permeability reservoirs. Moreover, the oil relative permeability reaches its highest value at the second critical capillary number, while the water relative permeability always increases with the increase in the capillary number. The dynamic contact angle will reach approximately 180° at a high capillary number, causing an oil film to remain. An optimized capillary number range is proposed for chemical flooding in low permeability reservoirs.