Microfluidic Strategies Use Ferrofluids for Enhanced Recovery

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 223503, “Experimental Microfluidic Strategies for Enhanced Recovery With Ferrofluid,” by Fatimah H. AlNasser, SPE, Stanford University. The paper has not been peer reviewed. _ The objective of the microfluidic investigation detailed in the complete paper is to identify and test two novel applications for magnetic fluids in porous media for subsurface oilfield applications. In particular, the study assesses the possibility of using water-based or oil-based ferrofluids as agents in enhanced oil recovery (EOR) and temporary in-situ valves to divert multiphase fluid flow. The experimental results confirmed that ferrofluid is an effective EOR agent for both wetting and nonwetting phases. Ferrofluids and Potential Applications Ferrofluid is a colloidal suspension of nanoscale magnetic particles such as iron oxide (magnetite) suspended in a carrier fluid (Fig. 1). Based on the carrier fluid, ferrofluid could be water- or oil-based. The surfactant coating on the magnetic nanoparticles ensures the ferrofluids’ stability and prevents particle agglomeration or deposition. A magnetic field exerts a magnetic body force on ferrofluid, attracting the fluid and causing it to move spontaneously toward the magnetic field source and arrange according to the magnetic field lines. Once the magnetic field is removed, the ferrofluid returns to its original state. Additionally, the presence of a magnetic field modifies the effective viscosity and shape of the fluid. Because of the unique properties of ferrofluids, the capillary number proves inadequate in effectively characterizing ferrofluid-flow dynamics and was not used as a reportable parameter in the experiments. In this study, the authors focus on two applications for ferrofluids: as EOR agents and as temporary fluid diverters or microscale in-situ valves, the latter an application that has not been examined before. Experiments were conducted on simple designs such as converging/diverging channels and pore-doublet models, then moved to more-complex designs that mimicked sandstones and fractured sandstones. The experiments encompassed two types of ferrofluids—water-based and oil-based—and three forms of external magnetic fields—a stationary magnetic field, an oscillating magnetic field, and a rotating magnetic field. The experimental results confirmed that ferrofluid is an effective EOR agent for both wetting and nonwetting phases and that ferrofluids could effectively be used as in-situ valves to divert flow to oil-rich zones or away from fractures. The experimental results also demonstrated five different mechanisms in which ferrofluids could improve recovery at the microscale. Theoretical Foundation To fully comprehend the complex behavior of magnetic fluids observed in the experiments, the underlying mathematical equations governing them must be examined. The defining characteristic of magnetic fluids is their unique attraction to magnetic fields, which sets them apart from conventional fluids. Therefore, it is essential to first quantify the magnetic body force exerted on magnetic fluids by an external magnetic field. Once this force is computed, the next step is to cover the equations modeling the magnetic fluid’s motion, deformation, and overall dynamics in response to applied magnetic fields. These equations are provided in the complete paper.