Microfluidic Devices for Characterizing Pore-scale Event Processes in Porous Media for Oil Recovery Applications

Summary

The goal of this procedure is to easily and rapidly produce a microfluidic device with customizable geometry and resistance to swelling by organic fluids for oil recovery studies. A polydimethylsiloxane mold is first generated, and then used to cast the epoxy-based device. A representative displacement study is reported.

Abstract

Microfluidic devices are versatile tools for studying transport processes at a microscopic scale. A demand exists for microfluidic devices that are resistant to low molecular-weight oil components, unlike traditional polydimethylsiloxane (PDMS) devices. Here, we demonstrate a facile method for making a device with this property, and we use the product of this protocol for examining the pore-scale mechanisms by which foam recovers crude oil. A pattern is first designed using computer-aided design (CAD) software and printed on a transparency with a high-resolution printer. This pattern is then transferred to a photoresist via a lithography procedure. PDMS is cast on the pattern, cured in an oven, and removed to obtain a mold. A thiol-ene crosslinking polymer, commonly used as an optical adhesive (OA), is then poured onto the mold and cured under UV light. The PDMS mold is peeled away from the optical adhesive cast. A glass substrate is then prepared, and the two halves of the device are bonded together. Optical adhesive-based devices are more robust than traditional PDMS microfluidic devices. The epoxy structure is resistant to swelling by many organic solvents, which opens new possibilities for experiments involving light organic liquids. Additionally, the surface wettability behavior of these devices is more stable than that of PDMS. The construction of optical adhesive microfluidic devices is simple, yet requires incrementally more effort than the making of PDMS-based devices. Also, though optical adhesive devices are stable in organic liquids, they may exhibit reduced bond-strength after a long time. Optical adhesive microfluidic devices can be made in geometries that act as 2-D micromodels for porous media. These devices are applied in the study of oil displacement to improve our understanding of the pore-scale mechanisms involved in enhanced oil recovery and aquifer remediation.

Introduction

The purpose of this method is to visualize and analyze multi-phase, multi-component fluid interactions and complex pore-scale dynamics in porous media. Fluid flow and transport in porous media have been of interest for many years because these systems are applicable to several subsurface processes such as oil recovery, aquifer remediation, and hydraulic fracturing^1,2,3,4,5. Using micromodels to mimic these complex pore-structures, unique insights are gained by visualizing pore-level dynamic events between t....

Protocol

Caution: This protocol involves handling a high temperature oven, toxic chemicals, and UV light. Please read all the material safety data sheets carefully and follow your institution's chemical safety guidelines.

1. Device Design

1. Design a photomask in a CAD software application.
   1. Draw a rectangular channel that is 3 cm long and 0.5 cm wide (Figure 1b-top right).
   2. Create an array of enclosed shapes representing the grains of the porous media.
      NOTE: These shapes are referred to as posts because they will become three-dimensional structures during the soft lithography process....

Results

In this example experiment, aqueous foam is used to displace Middle East crude oil (with a viscosity of 5.4 cP and API gravity of 40°) in a heterogeneous porous media with layered permeability contrast. A PDMS foam generator is connected to an optical adhesive micromodel which was previously completely saturated with crude oil. Figure 1a shows the CAD design of the photomask for the PDMS foam generator, the photoresist-patterned silicon wafer, and the complet.......

Discussion

This protocol for studying oil recovery processes in optical adhesive micromodels strikes a balance between the robustness of non-polymeric micromodels – such as glass or silicon – and the facile fabrication of PDMS microfluidic devices. Unlike micromodels made of glass or optical adhesive, PDMS devices lack resistance to light organic species. PDMS micromodels are also not ideal for many experiments because the surfaces of these devices have unstable wetting properties, and the polymer matrix is permeable to.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
3 mL Leur-Lok Syringe	Fischer Scientific	14-823-435
10 mL Glass Syringe	Fischer Scientific	1482698G
Photomask	CAD/Art Services
Silicon Wafer	University Wafer	452
Propylene-Glycol-Methyl-Ether-Acetate	Sigma Aldrich	484431-4L
150 mm Glass Petri Dish	Carolina Biological Supply	#721134
60 mm Plastic Petri Dish	Carolina Biological Supply	#741246
Mask Aligner	EV Group	EVG 620
1 mm Biopsy Punch	Miltex, Plainsboro, NJ	69031-01
Industrial Dispensing Tip	CML Supply	Gauge 23
Inverted Microscope	Olympus	IX-71
Plasma System	Harrick Plasma	PDC-32G	Plasma cleaner
Polydimehtylsiloxane (PDMS)	Dow Corning, Midland, MI	SYLGARD 184
Norland Optical Adhesive 81 (NOA81) or (OA)	Norland Products Inc.	8116	Optical adhesive
Quick-Set Epoxy	Fisher Scientific	4001
Glass Slides	Globe Scientic Inc.	1321
SU-8 2015 Photoresist	MicroChem	SU-8 2015	Photo resist
Syringe Pump	Harvard Apparatus	Fusion 400
Glass Capillary Tubing	SGE Analytical Science	1154710C
High-Speed Camera	Vision Research	V 4.3
Polyethylene Tubing	Scientific Commodities Inc.	#BB31695-PE/3