Quantitative investigation of multi-fracture morphology during TPDF through true tri-axial fracturing experiments and CT scanning

Due to the reservoir heterogeneity and the stress shadow effect, multiple hydraulic fractures within one fracturing segment cannot be initiated simultaneously and propagate evenly, which will cause a low effectiveness of reservoir stimulation. Temporary plugging and diverting fracturing(TPDF) is considered to be a potential uniform-stimulation method for creating multiple fractures simultaneously in the oilfield. However, the multi-fracture propagation morphology during TPDF is not clear now. The purpose of this study is to quantitatively investigate the multi-fracture propagation morphology during TPDF through true tri-axial fracturing experiments and CT scanning. Critical parameters such as fracture spacing, number of perforation clusters, the viscosity of fracturing fluid, and the in-situ stress have been investigated. The fracture geometry before and after diversion have been quantitively analyzed based on the two-dimensional CT slices and three-dimensional reconstruction method. The main conclusions are as follows:(1) When injecting the high viscosity fluid or perforating at the location with low in-situ stress, multiple hydraulic fractures would simultaneously propagate. Otherwise, only one hydraulic fracture was created during the initial fracturing stage(IFS) for most tests.(2) The perforation cluster effectiveness(PCE) has increased from 26.62% during the IFS to 88.86% after using diverters.(3) The diverted fracture volume has no apparent correlation with the pressure peak and peak frequency during the diversion fracturing stage(DFS) but is positively correlated with water-work.(4) Four types of plugging behavior in shale could be controlled by adjusting the diverter recipe and diverter injection time, and the plugging behavior includes plugging the natural fracture in the wellbore, plugging the previous hydraulic fractures, plugging the fracture tip and plugging the bedding.

Influence of High-Pressure Nitrogenation on the Structure,Magnetism and Microwave Absorption Properties of SmFe_(10)Mo_2

Nitrogenation of SmFelolVIo2 powders was performed in a self-made furnace under a high-purity N2 atmo- sphere up to 40 MPa at 500 ℃. Upon nitrogenation at atmospheric pressure, the lattice parameters a and c increase by 0.5% and 2.7%, respectively, whereas the Curie temperature Tc increases from 519 to 633 K. With further increasing the nitrogenation pressure to 20 and 40 MPa, the 1：12 main phase starts to decompose and a large amount of Mo and a-Fe precipitates. This leads to variation of Mo concentration in the 1：12 phase and causes a sharp decrease in Tc and in the coercivity. The relative complex permittivity and permeability of paraffin-SmFeloMO2 composites show multi-resonant behavior. After nitrogenation, the magnetic loss of the powders decreases, which may originate from the influence of eddy currents due to the increase in the particle size.

In Situ Transmission Electron Microscopy Observations of the Growth Process of Fe3O4–Ag Nanoparticles

The properties of nanocrystals are highly dependent on their morphology, composition and structure. To obtain full control over their properties, the behavior of nanocrystals under external stimuli, such as heat treatment, needs to be understood. Herein, to in situ observe their microstructure and morphology changes, Fe3O4–Ag heterodimers were selected as a model system. Their structural changes after heat treatment were investigated by in situ transmission electron microscopy. A combination of real-time imaging with elemental analysis enabled observation of the transformation of Fe3O4–Ag heterodimers having a loose interface configuration to those with a Janus structure at the atomic scale after heating from room temperature to 600 °C. After incubation at 600 °C for 32 min, two kinds of Janus structures could be seen, including a clear linear interface in the Fe3O4–Ag heterodimers and a semi-crescent-shaped interface between the Ag and Fe3O4 nanoparticles(NPs). These dynamic observations provide unique insights into NP growth mechanisms, which are essential for understanding and controlling the structure and morphology of nanoparticles.