Microfluidic Fabrication Techniques for High-Pressure Testing of Microscale Supercritical CO2 Foam Transport in Fractured Unconventional Reservoirs

Summary

This paper describes a protocol along with a comparative study of two microfluidic fabrication techniques, namely photolithography/wet-etching/thermal-bonding and Selective Laser-induced Etching (SLE), that are suitable for high-pressure conditions. These techniques constitute enabling platforms for direct observation of fluid flow in surrogate permeable media and fractured systems under reservoir conditions.

Abstract

Pressure limitations of many microfluidic platforms have been a significant challenge in microfluidic experimental studies of fractured media. As a result, these platforms have not been fully exploited for direct observation of high-pressure transport in fractures. This work introduces microfluidic platforms that enable direct observation of multiphase flow in devices featuring surrogate permeable media and fractured systems. Such platforms provide a pathway to address important and timely questions such as those related to CO₂ capture, utilization and storage. This work provides a detailed description of the fabrication techniques and an experimental setup that may serve to analyze the behavior of supercritical CO₂ (scCO₂) foam, its structure and stability. Such studies provide important insights regarding enhanced oil recovery processes and the role of hydraulic fractures in resource recovery from unconventional reservoirs. This work presents a comparative study of microfluidic devices developed using two different techniques: photolithography/wet-etching/thermal-bonding versus Selective Laser-induced Etching. Both techniques result in devices that are chemically and physically resistant and tolerant of high pressure and temperature conditions that correspond to subsurface systems of interest. Both techniques provide pathways to high-precision etched microchannels and capable lab-on-chip devices. Photolithography/wet-etching, however, enables fabrication of complex channel networks with complex geometries, which would be a challenging task for laser etching techniques. This work summarizes a step-by-step photolithography, wet-etching and glass thermal-bonding protocol and, presents representative observations of foam transport with relevance to oil recovery from unconventional tight and shale formations. Finally, this work describes the use of a high-resolution monochromatic sensor to observe scCO₂ foam behavior where the entirety of the permeable medium is observed simultaneously while preserving the resolution needed to resolve features as small as 10 µm.

Introduction

Hydraulic fracturing has been used for quite some time as a means to stimulate flow especially in tight formations¹. Large amounts of water needed in hydraulic fracturing are compounded with environmental factors, water-availability issues², formation damage³, cost⁴ and seismic effects⁵. As a result, interest in alternate fracturing methods such as waterless fracturing and the use of foams is on the rise. Alternative methods may provide important benefits such as reduction in water use⁶, compatibility with water sensitive form....

Protocol

CAUTION: This protocol involves handling a high-pressure setup, a high-temperature furnace, hazardous chemicals, and UV light. Please read all relevant material safety data sheets carefully and follow chemical safety guidelines. Review pressure testing (hydrostatic and pneumatic) safety guidelines including required training, safe operation of all equipment, associated hazards, emergency contacts, etc. before starting the injection process.

1. Design geometrical patterns

1. Design a photomask comprising geometrical features and flow pathways of interest (Figure 1, Supplementary File 1: Figure S....

Results

This section presents examples of physical observations from scCO₂ foam flow through a main fracture connected to array of micro-cracks. A glass microfluidic device made via photolithography or SLE is placed inside a holder and in the field of view of a camera featuring a 60 megapixel, monochromatic, full-frame sensor. Figure 11 illustrates the process of fabrication microfluidic devices and their placement in the experimental setup. Figure 12 is illu.......

Discussion

This work presents a protocol related to a fabrication platform to create robust, high-pressure glass microfluidic devices. The protocol presented in this work alleviates the need for a cleanroom by performing several of the final fabrication steps inside a glovebox. The use of a cleanroom, if available, is recommended to minimize the potential for contamination. Additionally, the choice of the etchant should be based on the desired surface roughness. The use of a mixture of HF and HCl as the etchant tends to reduce surf.......

Materials

Name	Company	Catalog Number	Comments
1/4” bolts and nuts			For fabrication of the metallic plates to sandwich the glass chip between them for thermal bonding
3.45 x 3.45 mm UV LED	Kingbright		To emitt LED light
3D measuring Laser microscope	OLYMPUS	LEXT OLS4000	To measure channel depths
40 mm x 40 mm x 10 mm 12V DC Cooling Fan	Uxcell		To cool the UV LED lights
120 mm x 38 mm 24V DC Cooling Fan	Uxcell		To cool the UV LED lights
5 ml (6 ml) NORM-JECT Syringe	HENKE SASS WOLF	Lot #16M14CB	To rinse the chip before each experiment
Acetone (Certified ACS)	Fisher Chemical	Lot #177121	For cleaning
Acid/ corossion resistive tweezer	TED PELLA		To handle the glass piece in corosive solutions
Acid/solvent resistance tweezers	TED PELLA, INC	#53009 and #53010	To handle the glass in corrosive solutions
Alloy X	AMERICAN SPECIAL METALS	Heat Number: ZZ7571XG11
Ammonium hydroxide (ACS reagent)	Sigma Aldrich	Lot #SHBG9007V	To clean the chip at the end of process
AutoCAD	Autodesk, San Rafael, CA		To design 2D patterns and 3D chips
BD Etchant for PSG-SiO2 systems	TRANSENE	Lot #028934	An improved buffered etch formulation for delineation of phosphosilica glass – SiO2 (PSG), and borosilica glass – SiO2 (BSG) systems
Blank Borofloat substrate	TELIC	CG-HF	Upper substrate for UV etching
Borofloat substrate with metalizations	TELIC	PG-HF-LRC-Az1500	Lower substrate for UV etching
Capture One photo editing software	Phase One		To Capture/Edit/Convert the pictures taken by Phase One Camera
Capture station	DT Scientific	DT Versa	To place of the chip in the field of view of the camera
Carbon dioxide gas (Grade E)	PRAXAIR	UN 1013, CAS Number 124-38-9	non-aqeous portion of foam
Chromium etchant 1020	TRANSENE	Lot #025433	High-purity ceric ammonium nitrate systems for precise, clean etching of chromium and chromium oxide films.
Circulating baths with digital temperature controller	PolyScience		To control the brine and CO2 temperatures
CO2	Airgas	100% pure - 001013 - CAS: 124-38-9	For CO2/scCO2 injection
Computer		NVIDIA Tesla K20 Graphic Card - 706 MHz Core - 5 GB GDDR5 SDRAM - PCI Express 2.0 x16	To process and visualize the images obtained via the Phase One camera
Custom made high pressure glass chip holder			To tightly hold the chip and its connections for high pressure testing
Cutrain (Custom)			To protect against UV/IR Radiations
Deionized water (DI)			For cleaning
Digital camera with monochromatic 60 MP sensor	Phase One	IQ260	Visualization system
Ethanol, Anhydrous, USP Specs	DECON LABORATORIES, INC.	Lot #A12291505J, CAS# 64-17-5	For cleaning
Facepiece reusable respirator	3M	6502QL, Gases, Vapors, Dust, Medium	To protect against volatile solution inhalation
Fused Silica (UV Grade) wafer	SIEGERT WAFER	UV grade	Glass precursor for SLE printing
GIMP	Open-source image processing software		To characterize image texture and properties
Glovebox (vinyl anaerobic chamber)	Coy		To provide a clean, dust-free environment
Heated ultrasonic cleaning bath	Fisher Scientific		To accelerate the etching process
Hexamethyldisilazane (HMDS) Cleanroom® MB	KMG	62115	Primer for photoresist coating
Hose (PEEK tubing)	IDEX HEALTH & SCIENCE	Natural 1/16" OD x .010" ID x 5ft, Part # 1531	Flow connections
Hydrochloric acid, certified ACS plus	Fisher Chemical	Lot # 187244	Solvent in RCA semiconductor cleaning protocol
Hydrogen Peroxide	Fisher Chemical	H325-500	Solvent in RCA semiconductor cleaning protocol
ImageJ	NIH		To characterize image texture and properties
ISCO syringe pump	TELEDYNE ISCO	D-SERIES (100DM, 500D)	To pump the fluids
Kaiser LED light box	Kaiser		To illuminate the chip
Laser printing machine	LightFab GmbH, Germany.	FILL	Glass-SLE chip fabrication
Laser safety glasses	FreeMascot	B07PPZHNX4	To protect against UV/IR Radiations
LED Engin 5W UV Lens	LEDiL		To emitt LED light
Light Fab 3D Printer (femtosecond laser)	Light Fab		To selectively laser Etch of fused silica
LightFab 3D printer	LightFab GmbH, Germany		To SLE print the fused silica chips
MATLAB	MathWorks, Inc., Natick, MA		To characterize image texture and properties
Metallic plates
Micro abrasive sand blasters (Problast 2)	VANIMAN	Problast 2 – 80007	To craete holes in cover plates
MICROPOSIT 351 developer	Dow	10016652	Photoresist developer solution
Muffle furnace	Thermo Scientific	Thermolyne Type 1500	Thermal bonding
N2 pure research grade	Airgas	Research Plus - NI RP300	For drying the chips in each step
NMP semiconductor grade - 0.1μm Filtered	Ultra Pure Solutions, Inc	Lot #02191502T	Organic solvent
Oven	Gravity Convection Oven	18EG
Phase One IQ260 with an achromatic sensor	Phase One	IQ260	To visulize transport in microfluidic devices using an ISO 200 setting and an aperture at f/8.
Photomask	Fine Line Imaging	20,320 DPI FILM	Pattern of channels
Photoresist (SU-8)	MICRO CHEM	Product item: Y0201004000L1PE, Lot Number: 18110975	Photoresist
Polarized light microscope	OLYMPUS	BX51	Visual examination of micro channels
Ports (NanoPort Assembly)	IDEX HEALTH & SCIENCE	NanoPort Assembly Headless, 10-32 Coned, for 1/16" OD, Part # N-333	Connections to the chip
Python	Python Software Foundation		To characterize image texture and properties
Safety face shield	Sellstrom	S32251	To protect against UV/IR Radiations
Sealing film (Parafilm)	Bemis Company, Inc		Isolation of containers
Shutter Control Software	Schneider-Kreuznach		To adjust shutter settings
Smooth ceramic plates
Stirring hot plate	Corning®	PC-620D	To heat the solutions
Sulfuric acid, ACS reagent 95.0-98.0%	Sigma Aldrich	Lot # SHBK0108	Solvent in RCA semiconductor cleaning protocol
Syringe pump (Standard Infuse/Withdraw PHD ULTRA)	Harvard Apparatus	70-3006	To saturate the chip before each experiment
Torque wrench	Snap-on	TE25A-34190	To tighten the screws
UV power meter	Optical Associates, Incorporated	Model 308	To measure the intesity of UV light
UV power meter	Optical Associates, Incorporated	Model 308	To quantify the strength of UV light
UV radiation stand (LED lights)			To transfer the pattern to glass (photoresist layer)
Vaccum pump	WELCH VACCUM TECHNOLOGY, INC	1380	To dry the chip
Variable DC power supplies	Eventek	KPS305D	To power the UV LED lights