Multi-Scale Microfluidics for Transport in Shale Fabric

Abstract

We develop a microfluidic experimental platform to study solute transport in multi-scale fracture networks with a disparity of spatial scales ranging between two and five orders of magnitude. Using the experimental scaling relationship observed in Marcellus shales between fracture aperture and frequency, the microfluidic design of the fracture network spans all length scales from the micron (1 μ) to the dm (10 dm). This intentional `tyranny of scales’ in the design, a determining feature of shale fabric, introduces unique complexities during microchip fabrication, microfluidic flow-through experiments, imaging, data acquisition and interpretation. Here, we establish best practices to achieve a reliable experimental protocol, critical for reproducible studies involving multi-scale physical micromodels spanning from the Darcy- to the pore-scale (dm to μm). With this protocol, two fracture networks are created: a macrofracture network with fracture apertures between 5 and 500 μm and a microfracture network with fracture apertures between 1 and 500 μm. The latter includes the addition of 1 μm ‘microfractures’, at a bearing of 55°, to the backbone of the former. Comparative analysis of the breakthrough curves measured at corresponding locations along primary, secondary and tertiary fractures in both models allows one to assess the scale and the conditions at which microfractures may impact passive transport.

Fractal Characterization of Multimodal, Multiscale Images of Shale Rock Fracture Networks

“…A collection of multidimensional, multimodal, and multiscale shale core sample and rock analog images with sample sizes ranging from microns to meters and resolution ranging from nanometers to microns was sourced from published [37][38][39] and our unpublished data. A visual summary of the data included in this study, sorted according to Euclidean (vertical axis) and length (horizontal axis) dimensions is shown in Figure 1.…”

“…High-resolution photography (A series): These are images of rock analog materials at the meso-scale (lab-grade gelatin), acquired with a highresolution DSLR camera in a setup and process described in [38]. Tabular and graphic (W series): Macro-scale fracture networks were generated from tabular fracture data reported on the Wolfcamp site in the Midland, TX Formation core samples described in [20], and illustrations of microfluidics designs (M series) at the micro-scale were sourced from [39]. While a number of fractures in the G series were heat induced, fractures in the W series originate from natural and hydraulic fracturing.…”

“…M series: The data in the M series correspond to microfluidics devices created for the study presented in [39]. The objective of this study was to image solute transport within multiscale shale fracture networks.…”

“…Two fracture networks were created for that study: (i) a microfracture network (here referred to as 'M1') with fracture apertures between 1 and 500 µm, and a macrofracture network (here referred to as 'M2') with fracture apertures between 5 and 500 µm. The geometry of the network and the angles between the fracture intersections is based on an actual fractured shale sample [39]. A graphic representation of these designs is shown in Figure 1.…”

Experimental Studies of Droplet Formation Process and Length for Liquid–Liquid Two-Phase Flows in a Microchannel

“…Compared with other forms of multiphase microfluidics, liquid-liquid multiphase microfluidic droplets have an additional radial inner vortex and a larger surface area to volume ratio, both of which facilitate enhanced mixing and mass transfer [8,9]. Therefore, liquid-liquid multiphase transport in microchannels has become an important topic in many fields, such as microchemical reactions [10][11][12][13], extraction [14][15][16], oil recovery [17,18], fuel cells [19], microchannel heat transfer [20][21][22][23], carbon capture [24,25], drug transport [26,27], lab on a chip [28][29][30][31], and others.…”