Experimental Study of Proppant Bridging in a Model of a Hydraulic Fracture

Summary In this article, we investigate formation of the local clogging (bridging) of proppant in a channel with gradually narrowing walls. The experimental facility allows us to simulate the process of the proppant transport in a hydraulic fracture by reproduction of the characteristic channel width, velocity of slurry, rheology of fracturing fluids, and typical concentrations of proppant. The goal of the study is to give qualitative description of the dynamics of the congestion of the proppant up to the complete blockage of the flow. In contrast to common practice of imposing bridging criteria by postulating certain threshold value of the width to proppant size ratio, we demonstrate that the bridging process involves several stages: clogging of two to three particles, growth of stable “islands,” connection of the islands by arches, and, finally, the total sandout of the cell by the bridged proppant. The observations of the paper gives better understanding of the bridging process giving the directions for more precise numerical simulations.

Supplemental Material: Minerals Matter: Science, Technology, and Society

Animation flies through the mineral structure of analcime, a mineral with ionic to superionic conductivity. Structure is represented by a ball (showing atoms) and stick (showing bonds) model. The beginning view is a “surface cell” perpendicular to the channel axis looking down <111> to view the pseudo-trigonal representation. Channel axes is 273 Angstroms wide. First image is about 23 times the channel width or 1288 unit cells. Courtesy of David Palmer, CrystalMaker.

Supplemental Material: Minerals Matter: Science, Technology, and Society

Animation flies through the mineral structure of analcime, a mineral with ionic to superionic conductivity. Structure is represented by a ball (showing atoms) and stick (showing bonds) model. The beginning view is a “surface cell” perpendicular to the channel axis looking down <111> to view the pseudo-trigonal representation. Channel axes is 273 Angstroms wide. First image is about 23 times the channel width or 1288 unit cells. Courtesy of David Palmer, CrystalMaker.

The investigation of the efficiency of oil displacing from the pore in the rock formation depending on the width and height of the pore using nanosuspension as a displacing agent

The numerical investigation of the two-phase fluid flow in a microchannel was carried out. The effect of the pore width and height on the oil displacing efficiency by nanofluids for various Reynolds numbers was studied. The computational domain was a T-shaped microchannel with a horizontal main flow channel and a vertical channel that imitated the pore in the rock formation, called a pore channel. The main channel width and height were 200 µm, and the pore channel width and height were varied in the range from 100 µm to 800 µm. The Reynolds number was varied from 0.1 to 100. The main studied characteristic was the oil recovery coefficient, defined as the ratio of the volume of oil remaining in the pore to the volume of the pore. That characteristic, obtained for a case, when the nanofluid was used as a displacing agent, was compared to the similar one obtained for a case, when pure water was used as a displacing agent. A single-phase fluid with properties, determined experimentally, was considered the nanofluid. The mass concentrations of SiO2 nanoparticles were 0.25% and 0.5%. The average diameter of nanoparticles was equal to 5 nm. It was found, that the oil recovery coefficient increased with an increase in width of the pore channel and a decrease in its height. It was obtained that the nanofluid can enhance the oil recovery in several times as compared to pure water. It was also found that the main factor affecting the efficiency of oil recovery is the contact angle of wetting.

Mixing in the NETmix Reactor

NETmix is a static mixing reactor composed of a network of mixing chambers interconnected by channels. The repetitive mixing pattern inside the reactor enables the use of reduced geometries to represent the NETmix network, such as the ExtendedNUB model, used in this work. Mixing in NETmix is based on the impingement of jets, issuing from channels. Inside the chambers, the jets are engulfed by dynamic vortices which can be quantified using Lagrangian techniques. Batch Lagrangian Mixing Simulation (BLMS) is based on successive injections of particles to measure the fraction of the fluids at the outlet of the mixing chambers. The distribution of the outlet fraction of particles indicates that it is possible to have nearly perfect mixing inside the NETmix chambers, depending on the dimensions of the channels and chambers. The NETmix design is here optimized in relation to the chamber diameter to channel width ratio, D/d. Results from BLMS show that best performance in NETmix occurs for 6.65≤D/d≤6.85.

A Double-Bridge Channel Shape of a Membraneless Microfluidic Fuel Cell

A double-bridge shape is proposed as a novel flow channel cross-sectional shape of a membraneless microfluidic fuel cell, and its electrochemical performance was analyzed with a numerical model. A membraneless microfluidic fuel cell (MMFC) is a micro/nano-scale fuel cell with better economic and commercial viability with the elimination of the polymer electrolyte membrane. The numerical model involves the Navier–Stokes, Butler–Volmer, and mass transport equations. The results from the numerical model were validated with the experimental results for a single-bridge channel. The proposed MMFC with double-bridge flow channel shape performed better in comparison to the single-bridge channel shape. A parametric study for the double-bridge channel was performed using three sub-channel widths with the fixed total channel width and the bridge height. The performance of the MMFC varied most significantly with the variation in the width of the inner channel among the sub-channel widths, and the power density increased with this channel width because of the reduced width of the mixing layer in the inner channel. The bridge height significantly affected the performance, and at a bridge height at 90% of the channel height, a higher peak power density of 171%was achieved compared to the reference channel.