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With high clay content in shale gas reservoir, the hydration is easy during hydraulic fracturing, which will affect the fracture conductivity and productivity of gas wells. The illite content of the Longmaxi formation shale in Yongchuan District is high (more than 80% of clay mineral content), and gas wells have a high productivity after fracturing and shut-in. However, the hydration effect mechanism of fracturing fluid on illite rich shale is not clear. Therefore, in this paper, core hydration experiments are performed for the illite rich shale reservoir. The water imbibition characteristic of near-fracture shale is obtained, and the micro-morphology and microfracture development characteristics of hydration are studied. Moreover, the hydration mechanism of near-fracture shale is then explored from the aspects of ion diffusion and mineral interlayer spacing variation. It is deduced that the fracturing fluid is spontaneously imbibed into small pores preferentially during well shut-in after fracturing. After the near-fracture shale is touched by water, some clay minerals peel and fall off from the fracture surface after hydration, accompanied by the development of microfractures. The interlayer spacing of clay minerals expands (smectite expands by 8.8% and illite 1.5%) after water immersion, and the ion diffusion occurs. The first 15 h is the rapid diffusion stage (surface effect), while the second 15 h is the stable rising stage (internal effect). This study systematically analyzes the hydration characteristics of near-fracture illite rich shale and reveals its hydration mechanism, which are crucial for the optimization of well shut-in time and exploitation system of shale gas reservoir after fracturing.

ABSTRACTIn this study, malleable and heavy Ta particles were introduced into soft Al powders to prepare Al-Ta composite coatings through a low-pressure cold-spray process; for comparison, Al-A2O3composite coatings were also deposited. The surface and cross-sectional morphologies, deposition efficiency, microstructure, hardness and composition of the coatings were investigated. The results demonstrated that the Al-Ta coatings had roughness values that were almost twice as large as those of the Al-Al2O3coatings for the same volumetric fraction of reinforcement particles used in the feedstock. Ta particles were more effective in improving the deposition efficiency and densification than were Al2O3particles. The formation mechanism of the Al-Ta coatings was mainly attributed to the malleable and heavy nature of Ta particles, which allowed them to bond with the formed coating and impact the coating strongly through the peening effect.

In this study, malleable and heavy Ta particles were introduced into soft Al powders to prepare Al-Ta composite coatings through a low-pressure cold-spray process; for comparison, Al-A2O3composite coatings were also deposited. The surface and cross-sectional morphologies, deposition efficiency, microstructure, hardness and composition of the coatings were investigated. The results demonstrated that the Al-Ta coatings had roughness values that were almost twice as large as those of the Al-Al2O3coatings for the same volumetric fraction of reinforcement particles used in the feedstock. Ta particles were more effective in improving the deposition efficiency and densification than were Al2O3particles. The formation mechanism of the Al-Ta coatings was mainly attributed to the malleable and heavy nature of Ta particles, which allowed them to bond with the formed coating and impact the coating strongly through the peening effect.

A thick composite anodic oxide film was fabricated in an environmentally friendly malic acid electrolyte containing PolyTetraFluoroEthylene (PTFE) nanoparticles on Ti-10V-2Fe-3Al alloys. The influence of pulse frequency on the morphology, microstructure and composition of composite anodic oxide films containing PTFE nanoparticles was investigated using Field Emission Scanning Electron Microscopy (FE-SEM) equipped with Energy Dispersive Spectroscopy (EDS), Atomic Force Microscopy (AFM) and Raman spectroscopy. The tribological properties in terms of the friction coefficient, wear loss and morphology of worn surfaces were measured by ball-on-disc tests. The electrochemical property was evaluated by potentiodynamic polarization. The results indicated that the titanium dioxide of composite anodic oxide films transformed from anatase to rutile with the change of pulse frequency, which could result from the electrochemical dynamic equilibrium. The combination of PTFE nanoparticles and malic acid electrolyte molecules can influence the energy fluctuation of electrochemical equilibrium and formation of composite anodic oxide films. Moreover, composite anodic oxide films fabricated under the condition of 1.0–2.0 Hz exhibited the best wear resistance and corrosion property. The schematic diagram of the film formation and PTFE nanoparticles spreading process under different frequencies was elucidated.

Highly oriented Mg-Al layered double hydroxide (LDHs) films were deposited on magnesium alloy AZ31 with different deformation processes by an easy in-situ growth method. The characteristics of the films were investigated by optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical, immersion and hydrogen evolution tests. The corrosion protection performance ranked the LDHs films as the increasing series: CS-LDHs (as-cast sample with LDHs) < AE-LDHs (asymmetric extrusion sample with LDHs) < SE-LDHs (symmetric extrusion sample with LDHs) < RS-LDHs (rolled sample with LDHs). A thicker and more compact LDH conversion coating was formed on the RS sample, and had the best corrosion protection performance. [ABSTRACT FROM AUTHOR]

A doublely-doped layered double hydroxide (LDH) film was produced on an anodized magnesium alloy AZ31. The Ce-doped Mg-Al LDH film was prepared by in-situ hydrothermal treatment method, and the intercalation of vanadate was realized by ion-exchange reaction. The structure, morphology and composition of as-prepared LDH film were investigated by X-ray diffractometer, field-emission scanning electronic microscope and energy dispersive spectrometry. Results indicated that a uniform and compact LDH film was formed and the intercalation of Ce3+ and vanadate would change the crystal structure of LDHs. The results of the potentiodynamic polarization, electrochemical impedance spectra, hydrogen evolution and corrosion weight loss tests showed the Ce3+ and vanadate anions significantly improve the impedance of LDH film, and the active double-doped LDH film could effectively protect the magnesium substrate from corrosion. [ABSTRACT FROM AUTHOR]

Palladium‐catalyzed cross‐dehydrogenative coupling of 3‐benzoyl substituted coumarins through C−H activation is described to synthesize indeno[2,1‐c]chromene‐6,7‐diones. A broad range of indeno[2,1‐c]chromene‐6,7‐diones using this method could be easily achieved in moderate to good yields (up to 93%). Palladium‐catalyzedintramolecular cross‐dehydrogenative coupling of 3‐benzoyl substituted coumarins through C−H activation is described to synthesize indeno[2,1‐c]chromene‐6,7‐diones. The reaction demonstrates good functional group tolerance and broad substrate scope, providing a complementary and effective approach to the synthesis of indeno[2,1‐c]chromene‐6,7‐diones from simple starting materials.

As a result of low porosity and low permeability in tight reservoirs, spontaneous imbibition plays an important role in oil recovery. While wettability has a crucial impact on the imbibition, the mechanism of the effect of wettability on imbibition is still unclear. In this study, we screened the surfactants with similar interfacial tension (IFT) at the same concentration to study the wettability properties, which will contribute to improve the oil recovery tight reservoir. Two betaine surfactants, lauramide propyl hydroxysulfonated betaine (LHSB) and cocamidopropyl betaine (CAB), were screened according to their IFT. Through spontaneous imbibition experiments, the recovery of LHSB (27.26%) was better than that of CAB (21.69%). The contact angle method and U.S. Bureau of Mines method were used to analyze the core wettability comprehensively. After LHSB treatment, the core wettability index turned to hydrophobic and the wettability index changed from −0.06 to −0.56. However, the wettability index did not change significantly after CAB treatment (−0.15). Further molecular simulations showed that, after the surface of the rock is modified by LHSB, the oil droplets spread gradually and the interface energy with the quartz was enhanced. In combination of the analysis of the ζ potential and adsorption measurement, LHSB is predicted to be adsorbed in a single-layer configuration, while CAB formed a double-layer configuration, which caused the difference in wettability. It can be speculated that, when the surfactant changes the pore surface of the tight sample toward hydrophobic, the oil-wet surface promotes the residual oil droplets to form a continuous phase and, at the same time, reduces flow resistance of the water phase, thereby increasing the spontaneous imbibition rate and the ultimate recovery. This study will help to understand the wettability impact on imbibition by the surfactant and contribute to the improvement of tight oil reservoir recovery.

Anodic oxidation is a prevalent technique to introduce superior corrosion and wear resistance upon the surface of titanium (Ti) alloys, in which the selection of appropriate electrolytes and defect-sealing strategies is a key. This study aims to address such issues through anodizing Ti-10V-2Fe-3Al alloy in malic acid, followed by a post-sealing treatment with Mg-Al layered double hydroxides (LDHs). The characteristics of the samples were investigated using scanning electron microscopy (SEM), atomic force microscopy (AFM), glow discharge optical emission spectroscopy (GDOES), X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS). SEM micrographs reveals that the anodic coating had a surface full of bulges and cracks, and was almost sealed by the following LDHs treatment. XRD pattern indicate that the anodic coating was mainly consisted of amorphous TiO 2 with a small fraction of anatase, but its crystallization degree was increased through the post-sealing. Moreover, electrochemical and tribological measurements demonstrate that corrosion current density was 2.8 × 10−6, 2.0 × 10−7, 5.9 × 10−9 A cm−2, and wear rate was 1.45 × 10−3, 1.30 × 10−4 and 6.90 × 10−5 mm3 N-1 m-1 for respective bare Ti-10V-2Fe-3Al alloy substrate, anodized specimens without and with the LDHs post treatment. Finally, a plausible wear mechanism was proposed. [ABSTRACT FROM AUTHOR]