Multi-Scale Porosity and Pore Structure Assessment of Shale

A study of shale gas is conducted to investigate the influencing factors of the fundamental pore structure interpretations in shale gas reservoirs. The results reveal discrepancies between multi-scale techniques that are influenced by clay mineral content and organic matter. In this study, novel methods and calculation models are introduced for quantitative determination of nanopore structure parameters in shales. This study provides implications for shale formation evaluation in downhole practice

Flow-Guided Feature Aggregation for Video Object Detection

Extending state-of-the-art object detectors from image to video is challenging. The accuracy of detection suffers from degenerated object appearances in videos, e.g., motion blur, video defocus, rare poses, etc. Existing work attempts to exploit temporal information on box level, but such methods are not trained end-to-end. We present flow-guided feature aggregation, an accurate and end-to-end learning framework for video object detection. It leverages temporal coherence on feature level instead. It improves the per-frame features by aggregation of nearby features along the motion paths, and thus improves the video recognition accuracy. Our method significantly improves upon strong single-frame baselines in ImageNet VID, especially for more challenging fast moving objects. Our framework is principled, and on par with the best engineered systems winning the ImageNet VID challenges 2016, without additional bells-and-whistles. The proposed method, together with Deep Feature Flow, powered the winning entry of ImageNet VID challenges 2017. The code is available at https://github.com/msracver/Flow-Guided-Feature-Aggregation

Investigation on the adsorption kinetics and diffusion of methane in shale samples

© 2018 Elsevier B.V. Shale gas is becoming increasingly important to mitigate the energy crisis of the world. Understanding the mechanisms of gas transport in shale matrix is crucial for development strategies. In this study, methane adsorption kinetics in shale samples were measured under different pressures and temperatures. The results of methane adsorption rate were fitted by the bidisperse diffusion model. Pore structure of the shale samples were characterized by low-pressure N2 and CO2 adsorption. The results showed that pressure has a negative effect on methane adsorption rate and diffusion, while the effect of temperature is positive. Combining the total organic carbon (TOC) and pore structure, methane adsorption rate and effective diffusivity were compared between all the shale samples. The methane adsorption rate under high pressure (50bar) is positively related to the TOC content. The micropore volume showed a moderate positive relation with the methane adsorption rate at 30bar. A weak positive relation exists between the TOC and effective diffusivity at low pressure and the effective diffusivity at low pressure shows an increasing trend with micropore(<2 nm) volume. A hypothetic pore model is proposed: micropore in shales controls gas diffusion as pore throat which connects pores

Connecting packing efficiency of binary hard sphere systems to their intermediate range structure

Using computed x-ray tomography we determine the three dimensional (3d) structure of binary hard sphere mixtures as a function of composition and size ratio of the particles, q. Using a recently introduced four-point correlation function we reveal that this 3d structure has on intermediate and large length scales a surprisingly regular order, the symmetry of which depends on q. The related structural correlation length has a minimum at the composition at which the packing fraction is highest. At this composition also the number of different local particle arrangements has a maximum, indicating that efficient packing of particles is associated with a structure that is locally maximally disordered

A comprehensive review on shale studies with emphasis on nuclear magnetic resonance (NMR) technique

Multi-scale shale studies put a significant emphasis on high-resolution investigations from nanometer to decametre scales. Despite that multiple advanced techniques have been used in shale studies, they are mostly limited to the detection scopes and have restricted capacity for high-resolution characterization of shale nanopores with substantial heterogeneity. Therefore, it remains a challenge for accurate resource estimation in unconventional shales. The nuclear magnetic resonance (NMR) is an advanced technique enabling non-destructive and fast measurements, and has the advantage of high-resolution evaluation of shale formations and nanopore structure. Petrophysical studies using NMR have made breakthroughs in shale studies. However, multi-scale shale investigations with emphasis on NMR technique have not been fully reviewed. This paper thus provides an overview of the capabilities of NMR in multidisciplinary shale studies to largely improve accuracy in unconventional resource estimations. We proposed a multi-scale and quantitative NMR detection method for accurate characterization of the nanopore structure and fast relaxation fluids. The laboratory NMR core analysis and NMR well logging can be applied for the detection from nanometer to decametre scales, respectively, and precisely measure shale reservoir properties, including total/effective porosities, clay-bound water (CBW) contents, pore size distribution, surface relaxivity, absolute permeability, wettability, and fluid types. Importantly, with NMR application, new research areas such as the integrated supercritical CO2 enhanced shale gas recovery (scCO2-ESGR) and carbon geo-sequestration, and the advanced underground hydrogen storage (UHS) in shales can be developed to achieve the target of long-term energy supply and net-zero carbon emission. New techniques such as in-situ kerogen pyrolysis are also improved by using NMR dynamic monitoring

Evolution of electronic states in n-type copper oxide superconductor via electric double layer gating

Since the discovery of n-type copper oxide superconductors, the evolution of electron- and hole-bands and its relation to the superconductivity have been seen as a key factor in unveiling the mechanism of high-Tc superconductors. So far, the occurrence of electrons and holes in n-type copper oxides has been achieved by chemical doping, pressure, and/or deoxygenation. However, the observed electronic properties are blurred by the concomitant effects such as change of lattice structure, disorder, etc. Here, we report on successful tuning the electronic band structure of n-type Pr2-xCexCuO4 (x = 0.15) ultrathin films, via the electric double layer transistor technique. Abnormal transport properties, such as multiple sign reversals of Hall resistivity in normal and mixed states, have been revealed within an electrostatic field in range of -2 V to +2 V, as well as varying the temperature and magnetic field. In the mixed state, the intrinsic anomalous Hall conductivity invokes the contribution of both electron and hole-bands as well as the energy dependent density of states near the Fermi level. The two-band model can also describe the normal state transport properties well, whereas the carrier concentrations of electrons and holes are always enhanced or depressed simultaneously in electric fields. This is in contrast to the scenario of Fermi surface reconstruction by antiferromagnetism, where an anti-correlation between electrons and holes is commonly expected. Our findings paint the picture where Coulomb repulsion plays an important role in the evolution of the electronic states in n-type cuprate superconductors.Comment: 4 figures, SI not included. Comments are welcom