Impacts of Fracture Roughness and Near-wellbore Tortuous on Proppant Transport Within Hydraulic Fractures

For unconventional reservoirs hydraulic fracturing design, a greater fracture length is a prime factor to optimize. However, core observation results from Hydraulic Fracturing Test Site (HFTS) show the propped fractures are far less or shorter than expected which suggests the roughness and tortuous of hydraulic fractures are crucial to sand transport. In this study a transport model of sands is first built based on experimental measurements on the height and transport velocity of sand bank in fractures with predetermined width and roughness. The fracture roughness is quantified by using surface height integral. Then, three-dimensional simulations are conducted with this modified model to further investigate the impact of fractures tortuous on sand transport, from which an analytical model is established to estimate the propped length of hydraulic fractures at a certain pumping condition. Experiments results show that height of sand bank in roughness fracture is 20-50% higher than that in smooth. The height of sand bank decreases with the reduction of slurry velocity and increases with the sand diameters increasing. Sand sizes do little effect on the transport velocity of sand bank but the increase in slurry velocity and sand volume fraction can dramatically enhance the migration velocity of sand bank. The appearance of tortuous decreases the horizontal velocity of suspended particles and results in a higher sand bank compared with that in straight fractures. When the sand bank gets equilibrium at the tortuous position, it is easy to produce vortices. So, there is a significant height of sand bank change at the tortuous position. Moreover, sand plugging can occur at the entrance of the fractures, making it difficult for the sand to transport deep in fractures. This study explains why the propped length of fractures in HFTS is short and provides an analytical model that can be easily embedded in the fracturing simulation to fast calculate dimensions of the propped fractures network to predict length and height of propped fractures during fracturing.

An Industry First: Concept Selection, Material Testing, and Modelling Process for a Successful Managed Pressure Open Hole Gravel Pack Project

One of the major technical challenges to this project was placing horizontal open hole gravel packs (HzOHGP) within the narrow pore pressure to frac-gradient (PPFG) margin in the target reservoirs. This paper addresses the steps taken to overcome this challenge. To maximize the use of the narrow PPFG margin, the project combined a managed pressure drilling (MPD) system with low gravel placement pump rates made possible by an ultra-light-weight proppant (ULWP). Of the MPD systems available, the Controlled Mud Level (CML) system was selected over the Surface Back Pressure (SBP) system for several reasons. It enabled conventional gravel pack pumping operations and equipment and it accommodated the brine weight needed to inhibit the shales. A series of lab tests showed that the completion fluid density required to inhibit the reservoir shale reactivity was only possible using CML. An overall evaluation of CML showed that it was most suitable and offered the greatest flexibility for the gravel pack job design. The special ceramic ULWP had to be qualified and tested. The qualification testing ranged from standard API and compatibility tests to full scale flow loop testing. The flow loop tests were needed to measure the ULWP transport velocity for the target wellbore geometry. Understanding the transport velocity is critical for gravel pack design and job execution planning. Once MPD and ceramic ULWP were selected, the gravel pack placement operations were simulated to demonstrate that their features increased the likelihood of successfully gravel packing in the target reservoirs. Small PPFG margins decrease the probability of success of placing a HzOHGP. In the target formations, the pressure margin is insufficient to safely execute HzOHGP conventionally; instead, the project combined MPD and the low pump rates facilitated by using ULWP to control circulating pressures to stay inside the narrow margin and place the gravel packs. The integration of CML and ULWP into in a gravel pack operation to control circulating pressures has never been done. The concept and its successful field implementation are industry firsts.

Echinocandins accelerate the particle transport velocity in the murine tracheal epithelium: dependency on intracellular Ca 2+ stores

The mucociliary clearance of lower airways is modulated by different physiologic stimuli and also by pathophysiologic agents like polluting substances or pharmaceutical molecules. In the present investigation, we measured the particle transport velocity (the PTV) of mouse tracheae as a surrogate for mucociliary clearance. In mouse tracheal preparations, we detected a sustained increase in the PTV under the application of the echinocandins caspofungin, anidulafungin, and micafungin. In further experiments we observed the effects of echinocandins on the PTV were dependent on intracellular Ca 2+ homeostasis. In Ca 2+ -free buffer solutions, the amplitude of the echinocandin-evoked rise in the PTV was significantly reduced relative to in the experiments in Ca 2+ -containing solutions. Depletion of intracellular Ca 2+ stores of the endoplasmic reticulum (ER) by caffeine completely prevented an increase in the PTV with subsequent caspofungin applications. Mitochondrial Ca 2+ stores seemed to be unaffected by echinocandin treatment. We also observed no altered generation of reactive oxygen species under the application of echinocandins as probable mediators of the PTV. Consequently, the observed echinocandin effects on the PTV depend upon the Ca 2+ influx and Ca 2+ contents of the ER. We assume that all three echinocandins may act intracellularly on ER Ca 2+ stores to activate Ca 2+ -dependent signal-transduction cascades, enhancing the PTV.

Ultra slow acoustic energy transport in dense fish aggregates

A dramatic slowing down of acoustic wave transport in dense fish shoals is observed in open-sea fish cages. By employing a multi-beam ultrasonic antenna, we observe the coherent backscattering phenomenon. We extract key parameters of wave transport such as the transport mean free path and the energy transport velocity of diffusive waves from diffusion theory fits to the experimental data. The energy transport velocity is found to be about 10 times smaller than the speed of sound in water, a value that is exceptionally low compared with most observations in acoustics. By studying different models of the fish body, we explain the basic mechanism responsible for the observed very slow transport of ultrasonic waves in dense fish shoals. Our results show that, while the fish swim bladder plays an important role in wave scattering, other organs have to be considered to explain ultra-low energy transport velocities.

Ultrafast and long-range self-transport of droplets on multi-bioinspired surface with periodic gradient structure

Droplet self-transport is crucial in various fields ranging from physics to biochemistry. Despite extensive progress, existing systems for droplet self-transport still perform at low transport velocity or limited transport range. Here, a multi-bioinspired surface comprising two-dimensional gradient structures is proposed innovatively, which integrates the heterogeneous wettability with the shape gradient morphology. Droplet transport behaviors are systematically investigated from experiment, theory, and simulation. The fabricated structure achieves the ultrafast (over ~ 450 mm/s) and long-range (over ~ 200 mm) self-transport of droplets. Moreover, the fantastic scalability of this structure enables it to pump numerous multi-scale droplets from one site to the preset region with ultralow loss. Drawing inspirations, two systems have been designed to complete complex tasks on open surface. This work provides a reliable droplet manipulation strategy for various applications, such as water collection, microfluidics, and biomedicine, etc.

Effects of BNO 1016 on ciliary transport velocity and cell culture surface liquid height of sinonasal epithelial cultures

Background BNO 1016 is an ethanolic extract of a mixture of five herbs that has been sold in different formulations for decades in the European market and more recently, in the United States market as an over-the-counter treatment for rhinosinusitis. Previous studies indicated activation of chloride secretion and increase in ciliary beat frequency by BNO 1016 but the functional consequences on mucociliary transport velocity and airway surface liquid homeostasis are unknown. This study intends to examine the effects of BNO 1016 on these properties in vitro. Results Human sinonasal epithelial cells were grown at an air-liquid interface, with addition of BNO 1016 basolaterally in each experiment. Polystyrene fluorescent microspheres were added to the apical surface of the culture, and distance traveled across the surface of the culture over a fixed time period was measured using live imaging. BNO 1016 concentrations of 50 μg/ml and 500 μg/ml were tested. Basolateral application of compound resulted in a non-dose-dependent increase in culture surface liquid height compared to controls at 30 min, and this effect persisted through the one-hour duration of the experiment (p < 0.01). Basolateral application of BNO 1016 also resulted in a non-dose-dependent increase in microsphere transport velocity at 45 and 60 min following compound application (p < 0.01). Conclusions Basolateral application of BNO 1016 at a concentration mimicking post-ingestion serum levels appears to elicit increases in cell culture surface liquid height and mucociliary clearance, as assessed by microsphere transport velocity. These properties can potentially be leveraged for therapeutic efficacy in diseases affecting mucus production and mucociliary transport.