Experimental study of fluid displacement and viscous fingering in fractured porous media: effect of viscosity ratio

Abstract Viscous fingering instability has been analyzed through empirical studies using miscible flow displacement in fractured porous media. While significant research has been conducted on viscous fingering, limited information is available regarding its behavior in fractured porous structures. The experiments were conducted in rectangular porous models with fractures oriented at $${0}^\circ $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> <mml:mo>∘</mml:mo> </mml:msup> </mml:math> , $${45}^\circ $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow> <mml:mn>45</mml:mn> </mml:mrow> <mml:mo>∘</mml:mo> </mml:msup> </mml:math> , and $${90}^\circ $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow> <mml:mn>90</mml:mn> </mml:mrow> <mml:mo>∘</mml:mo> </mml:msup> </mml:math> , to investigate how fracture orientation influences fluid displacement, where both channeling and fingering mechanisms play significant roles. This paper, which is the second part of a previous study, places particular emphasis on the impact of the viscosity ratio, a crucial parameter in determining the complexity of the fingering patterns. Quantitative parameters such as sweep efficiency, tip location, and breakthrough time were evaluated and analyzed using image processing techniques. The results indicate that increasing the viscosity ratio leads to more complex finger formations. Additionally, as the injection rate increases, the size of the finger patterns slightly increases, while the channeling effect becomes less pronounced. Notably, fractures aligned at $${0}^\circ $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> <mml:mo>∘</mml:mo> </mml:msup> </mml:math> had the most significant impact on the rate of sweep efficiency and tip location, increasing the tip velocity of the fingers by up to 90%.