The Impact of System Softness on Haines Jumps and Drainage in Porous Media

Abstract Haines jumps are abrupt movements of fluid interfaces accompanied by sudden changes in capillary pressure during multiphase flow in porous media. They are a fundamental pore‐scale mechanism influencing displacement patterns and efficiency. Haines jumps are controlled by the interplay of varying factors, including capillarity, pore geometry, and fluid properties. Previous studies showed that the elastic deformation of the space containing the liquid due to varying capillary pressure at pore constrictions creates a “soft” fluid system, which promotes Haines instability. Here, we use microfluidics to study the effect of system softness on Haines jumps and drainage in porous media by introducing an entrapped gas bubble with controlled volume in the liquid phase. A pore‐scale analytical model incorporating softness demonstrates that the entrapped gas bubble alters the pressure response during Haines jumps. A dimensionless number is proposed to characterize the system softness. Drainage experiments are conducted in single pore throat, pores‐in‐series, and pore network micromodels. Results show that larger elastic deformation of the entrapped gas bubble in response to the capillary pressure change causes longer jump distance and waiting time before the Haines jump event in a single pore throat. The Haines jump can fill one or multiple pores in pores‐in‐series micromodel, which is determined by the system softness. In pore networks, the final displacement pattern and saturation are barely affected, although the increase of softness results in more pronounced Haines jump events and changes the invasion process. This phenomenon may be due to the constraint of smaller pores on Haines jumps.