Experimental studies on the resistance to single and multiphase flow in a capillary tube

Abstract

The resistance to the flow in pore space is of great significance because it controls how the fluids transmit the porous media over time. The fundamental of enhanced oil recovery, for example, is the displacement of two phases that occurred in the porous media, the resistance to the flow sets an obstacle for the displacement. Although many have presented their study on this subject, few considered the pore-scale study. This work focuses on the interface behavior study at pore level, presents an innovative way to measure the resistance to flows in a capillary, interprets and defines the effective pore throat and its application, defines the impact of the pore wetting, the effect of fluid property as well as the thermocapillarity on the resistance. The work presented in this thesis provides some fundamental understanding of two-phase fluids in a capillary network and will benefit research in enhanced oil recovery, fuel cell, and microfluidics, etc.

To study the resistance to fluids, the pore wetting is an effective tool to start with. In this work, we creatively designed a method to visually observe and digitally analyze the contact angle variation during the imbibition. The dynamic pore contact angle at pore level is dependent mainly on the imbibition rate and fluid specifications, such as the surface tension and the viscosity. A regression equation describing the dynamic contact angle in the capillary is proposed based on the derivation of the empirical equation.

The capillary resistances to the single-phase flow and the interface (the contact line between two immiscible phases) are measured and presented. The experimental data demonstrates a significant difference between the resistance to the single-phase and the interface. The measured resistance is compared with Washburn’s equation and Brooks-Corey’s model. Conclusively the resistance to the interface should be considered to understand the multiphase flow in the porous media.

An innovative concept of ‘effective pore throat’ is proposed in this project based on our experiment result. The effective pore throat is the critical point where the resistance to the interface rises. It is affected by pore and fluid properties and provides basic principles for applications such as capillary hysteresis or clinical science.

Thermocapillary is studied by laser-induced equipment. The temperature differential varies the surface tension along with the interface, creating unbalanced capillary pressure. In our findings, there is resistance to the system when the difference between the capillary pressure rises. The interface movement is tracked when the pressure difference is high enough. Furthermore, thermocapillary emulsification is demonstrated.