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Fluid flow in porous rocks is commonly capillary driven and thus, dependent on the surface characteristics of rock grains and in particular the connectivity of corners and crevices in which fluids reside. Traditional microfluidic fabrication techniques do not provide a connected pathway of crevices that are essential to mimic multiphase flow in rocks.
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Here, geo-material microfluidic devices with connected pathways of corners and crevices were created by functionalising Polydimethylsiloxane (PDMS) with rock minerals. A novel fabrication process that provides attachment of rock minerals onto PDMS was demonstrated. The geo-material microfluidic devices were compared to carbonate and sandstone rocks by using energy dispersive X-ray spectroscopy, scanning electron microscopy (SEM), contact angle measurements, and a surface profilometer. Based on SEM coupled with energy-dispersive X-ray spectrometry (SEM-EDS) analyses, roughness measurements, contact angle, wettability, and roughness were comparable to real rocks.
In addition, semivariograms showed that mineral deposition across the different geo-material devices was nearly isotropic. Lastly, important multiphase flow phenomena, such as snap-off and corner flow mechanisms, equivalent to those occurring in reservoir rocks have been visualised. The presented approach can be used to visualise rock-fluid interactions that are relevant to subsurface engineering applications, such as hydrocarbon recovery and CO 2 sequestration. Multiphase flow is relevant to several industrial fields, such as geologic CO 2 sequestration, enhanced oil recovery, hydrology, and fuel cells. Wettability, which is the preference of a fluid to a solid, is a key parameter that influences multiphase flow in porous media,. Souls of mischief 93.
Wettability of surfaces is commonly quantified through contact angle (θ) measurements where θ 90° corresponds to oil-wet surfaces. In water-wet rocks, thin films of water cover the surfaces of grains and extend across adjacent grains.
These films influence immiscible displacement. For example, in enhanced oil recovery processes and during imbibition, water is known to flow in the pore space via the wetting films ahead of the advancing meniscus, bridging across the pore space containing oil, which creates the possibility for snap-off events and influences the order in which pores are saturated. Pore network models are often used to demonstrate the importance of corner flow during immiscible displacement. Other parameters such as aspect ratio, flow rate, contact angles, and dimensionless parameters (such as capillary number and viscosity ratio), have also been investigated using pore-network models. Pore network models that do not account for corner flow provide significantly different results than models that allow for the wetting phase to reside in the corners of the network. Therefore, when considering idealised geometries for experiments, it is essential to consider systems that support the natural mechanisms of porous media flow.Throughout the past few decades, microfluidic devices with porous media patterns representing porous rock have been used to study fluid flow for subsurface engineering,. Images or 3D models of actual porous rock can be generated using micro-computed tomography (micro-CT), focused ion beam-scanning electron microscope (FIB-SEM) or nuclear magnetic resonance (NMR), methods.
These images can then be transformed to a microfluidic chip using standard photolithography or soft photolithography. Karadimitriou and Hassanizadeh summarise microfabrication methods for micromodels and the history of their usage in soil science and petroleum research, particularly enhanced oil recovery (EOR),. However, microfluidic models generally do not allow for the connectivity of corners and crevices due to their 2D nature, in addition to their lack of roughness, which can limit the type of flow processes that occur during immiscible displacement experiments.Several fabrication methods for geo-material chips have been proposed to produce microfluidics devices that mimic real rock. Developed an approach to study acid injection in carbonate formation by etching microfluidics channels into a natural calcite rock, which required multiple pre-processing steps. Song and Kovscek developed a method to create a functionalised 2D silicon micromodel with pore surfaces coated mainly with kaolinite clay, which allows for the study of fluid–solid interactions.
In addition, these authors published another paper describing the use of their functionalised microfluidic platform to study the response of clay to low salinity brine injection. Other microfluidic device modifications that aid in representing real rock include altering the wettability of the porous network. Developed a novel method termed “Stop-Flow-Lithography (SFL)” to fabricate microfluidics devices with controlled wetting properties in a single lithographic step. They showed immiscible fluid displacement in single pore bodies with varying wetting properties. Porter, et al. Developed a novel fabrication method whereby fractures are etched into thin sections of different rock types (shale, sandstone, and siltstone) by a custom-built femtosecond laser direct-write (LDW) system. Similarly, Gerami, et al.
Presented a coal geo-material microfluidic chip that was fabricated by etching a fracture pattern into a coal surface using three-dimensional laser micromachining. Demonstrated a novel way to coat a controlled thickness of calcite (CaCO 3) nanocrystal layer onto a simple glass microfluidic channel. This process was achieved by converting the inner surface of the microfluidic silica channels to CaCO 3 through numerous chemical surface modifications to functionalise the glass surface to grow a CaCO 3 nanocrystal layer. Singh, et al. Used another approach to design a microfluidic device of a sandstone rock called “Real Rock Microfluidic Flow Cell” (RRMFC).
They mounted a thin section (500 μm) of a sandstone rock between two covers that were bonded via a plasma generator. Lastly, another approach taken by Zhu and Papadopoulos demonstrated two-phase flow in transparent miniature packed beds with rough grains and analysed the effect of roughness on flow.Traditionally, core-flooding experiments are conducted to establish the wettability, capillary pressure data, relative permeability curves, and oil recovery for a given reservoir rock sample. With different geo-material microfluidics, or rock-on-a-chip methods, oil recovery can be measured and pore-scale mechanisms (on the order of micrometres) can be captured. EOR mechanisms such as chemical or low salinity can be tested prior to core scale experiments to study a wide range of the parameter space necessary to understand pore-scale oil recovery mechanisms and/or evaluate screening criteria for particular EOR applications. This can guide the planning and assessment of core floods and/or illustrate if a given EOR mechanism could suppress oil snap-off, enhance dissolution and/or cause fines migration for a given set of flooding conditions.The aforementioned fabrication methods of geo-material microfluidics devices involve several pre-processing and complex fabrication steps, in addition to the use of expensive machines and/or packed grains that obstruct visualisation. In addition, the previous works have not provided evidence that the essential pore-scale flow mechanism of corner flow leading to snap-off actually occur in the fabricated geo-material chips.
We propose a simple process for functionalising the pore space of PDMS microfluidic chips with rock minerals and controlled wetting conditions, which allows for snap-off and corner flow mechanisms to occur. The resulting geo-material microfluidic device allows for direct visualisation and understanding of rock-fluid interactions in oil reservoirs during any type of flooding. We describe the coating of PDMS microfluidic chips with the following materials: (1) quartz and kaolinite to represent sandstone formations, and (2) calcite to represent carbonate formations. We characterise the surface composition, roughness, wettability, and uniformity of the functionalised PDMS models and compare them with reservoir rock samples.
Lastly, we conduct water flooding experiments to study the resulting pore-scale flow mechanisms and conclude that many of the well-established mechanisms important for porous media flow are captured by the microfluidic device due to the wettability and connectivity of corners and crevices added by the geo-material coating process.
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. Optimized Zoom for Your ApplicationsThe eZoom of Axio Zoom.V16 works with a motorized iris diaphragm coupled to the zoom.
Simply select the best mode for your purpose:Brightness mode: Observe fluorescence images over the complete zoom range with highest possible brightness.Eyepiece mode: This is ideal if you work mainly with ocular observation using conventional illumination. You zoom from large object fields with maximum depth of field to high magnifications with maximum resolution.Camera mode: Axio Zoom.V16 adapts to the performance of your camera. You get an optimal relation between resolution and depth of field across the whole zoom range. EpiRel produces a relief-like image contrastSlightly incline the illumination with the EpiRel slider in the Epi-Illuminator Z of your Axio Zoom.V16:Discover textures and small ridges, particularly at high magnification.
Objects will take on more contour than in conventional brightfield. Precicion: eZoom images – twice as sharpThe zoom body is the core of stereo and zoom microscopes. When zooming, lenses have to be positioned precisely. Until now, a metal component milled with great care would determine the exactness of this movement, and with it the optical quality of your microscope.eZoom replaces the mechanical curve with an electronic one. Stepping motors position the moveable lenses precisely and take the tolerances of the individual lenses into account. Each zoom body describes its own zoom curve and captures visibly more details. EZoom follows the base line for image sharpness over the magnification range with a doubled precision, compared to a mechanical zoom body.
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Programm zoom curves individually.