Microfluidic Investigation of Magnetic Fluids in Porous Media
Creators: name: AlNasser, Fatimah H.
Publisher: name: Stanford Digital Repository
Year: 2024
Subjects: subject: Microfluidics
subject: Petroleum engineering
subject: Magnetism

description: This thesis presents a comprehensive microfluidic investigation of magnetic fluids and their applications in porous media, tailored for petroleum engineering context. The study explores various aspects of magnetic fluids’ behavior and their potential uses in applications such as enhanced oil recovery (EOR) and reservoir management. The experimental platform utilized advanced microfluidic techniques that were developed through the integration of silicon-based micromodels as analogues for porous media, and magnetic fluids, such as ferrofluids and paramagnetic brines. The micromodel fabrication involved the design and construction of custom microfluidic devices using photolithography to create precise pore network geometries. Microfluidic devices were selected for the experiments because of their ability to produce representative pore geometry and length scales, which are essential to delineate the fundamental mechanisms dictating the pore-scale fluid behavior of multiphase flow in porous media.

A key focus of this investigation is the utilization of magnetic fluids as EOR agents. The experiments explored various magnetic field configurations, including static, oscillating, and rotating fields. Through the application of an external magnetic field, the distribution and flow of the magnetic fluids can be optimized to improve oil displacement and recovery. The effectiveness of magnetic fluids as EOR agents has been demonstrated through both micro-scale examinations of the residual oil post-flooding and macro-scale observations of the displacement front. 

An innovative application is presented in the form of magnetically actuated in-situ valves within the micromodel. The research demonstrates how strategically applied magnetic fields can induce localized changes in the magnetic fluid’s viscosity, effectively creating dynamic flow control and diversion. Flow diversion improved the overall recovery in the micromodel by directing flow into oil-rich target zones and away from fractures, preventing early breakthrough. This application is explored through microfluidic experiments that simulate both simple and complex reservoir geometries, from pore doublets to fractured sandstones.

The third application of magnetic fluids is heavy oil recovery, which was explored through a series of micro-scale studies and macro-scale displacement experiments. The research investigates how magnetically induced viscosity alteration can improve mobility ratios and enhance the overall recovery of high-viscosity oils. Additionally, the study demonstrated how magnetically assisted floods mitigate the development of viscous fingering, a phenomenon that frequently undermines the effectiveness of standard flooding techniques in heavy oil. Accordingly, magnetic fluids proved their versatility in enhancing recovery across a range of oil viscosities, from light to heavy. 

In an effort to investigate more accurate representations of the subsurface, we shift from homogeneous to heterogeneous micromodels that capture the permeability extremes found in real geological formations. The study addresses the challenge of high-permeability thief zones by investigating the use of magnetic fluids as selective blocking agents. Unlike the previous application where magnetic fluids were used as in-situ valves and flow diverters, this application demonstrates how magnetic fluids can strategically reduce permeability contrast and improve sweep efficiency in high-permeability regions through the application of targeted magnetic fields. After thoroughly examining the high-permeability zones, our focus shifted to the other end of the spectrum, where we investigated low-permeability, heterogeneous pore space as found in shale. Unconventional resources are examined through the lens of magnetic fluid invasion into low-permeability shale zones. The experiments investigate how magnetic forces can overcome capillary barriers and enhance fluid invasion into tight formations, that are otherwise not accessible to the injected fluid.

Finally, the impact of magnetic fluids on solids mobilization is investigated in applications where both high injection rates and backflushing prove ineffective in dislodging the deposited solids. The study examines how magnetic fields can be used to control the transport and prevent the deposition of fine particles within porous media, offering insights into preventing formation damage and maintaining good productivity in petroleum field operations.

The theoretical framework of the research is further expanded upon through a comprehensive analysis of the mathematical forces and magnetic pressures governing magnetic fluids’ behavior in porous media. This involves revising and amending commonly used flow equations, such as the Navier-Stokes equations, to better accommodate the behavior of magnetic fluids. Based on the properties of magnetic fluids and the experimental observations, it is possible to identify five recovery mechanisms that worked in conjunction to improve the overall recovery, that are (i) direct displacement by the magnetic body force (ii) pore-scale agitation (iii) mobility ratio reduction by viscosity alteration (iv) interfacial tension reduction, and (v) magnetic nanoparticle chaining. Furthermore, this study explores the optimal configuration for magnetic fields, as determined through experimental research. This detailed analysis aims to identify the most efficient magnetic field setup, enhancing the recovery process and offering valuable insights for future implementations of this recovery technique.

This thesis contributes to the growing body of knowledge on magnetic fluids’ applications in the oil and gas industry, offering insights into their potential for improving recovery rates, enhancing reservoir management, and addressing common production challenges. By demonstrating the utility of magnetic fluids in representative micromodels, this research opens new avenues for the integration of smart magnetic fluids in advanced petroleum engineering operations.