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In this work, the reusable high-efficiency cascade amplification of nanozymes was obtained for sensitive electrochemical analysis of target 8-hydroxy-2′-deoxyguanosine (8-OHdG) based on reversible capture/release of electronic media in a fast and green manner. [ABSTRACT FROM AUTHOR]

In this work, a "signal-off" electrochemical biosensor was established for sensitive detection of adenosine triphosphate (ATP) based on Fe 3 O 4 @covalent organic framework-immobilized gold nanoparticles (Fe 3 O 4 @COF–Au NPs) porous composite material as a nanocarrier. The proposed Fe 3 O 4 @COF–Au NPs could effectively confine Au NPs in the uniform channels of the Fe 3 O 4 @COF, which successfully avoided Au NPs aggregation to a certain extent and provided a comparatively independent and stable micro-environment via its hydrophobic porous nanochannels, thereby owning excellent electro-catalytic performance for the reduction of 4-nitrophenol. Moreover, the Fe 3 O 4 @COF–Au NPs nanomaterials were served as functional platform for immobilizing DNA substrate (S0), which was used to bind with the conversion product (S1) of the target ATP for subsequent branched hybridization chain reaction (b-HCR) to form dendritic DNA strands to hinder electron transfer between Fe 3 O 4 @COF–Au NPs and 4-nitrophenol, finally achieving sensitive detection of ATP with a wide linear range of 5 pM–50 μM and a low detection limit of 1.6 pM. Such strategy provides a multifunctional immobilized platform for the sensitive detection of ATP and a versatile strategy for monitoring other biomolecules. ● The Fe 3 O 4 @COF NPs can prevent the aggregation of Au NPs. ● The Fe 3 O 4 @COF–Au NP can provide excellent electrochemical catalytic performance for the reduction of 4-nitrophenol. ● The Fe 3 O 4 @COF–Au NP as signal probe was used to construct a "signal-off" electrochemical biosensor. [ABSTRACT FROM AUTHOR]

The degradation efficiency of photoelectrocatalytic (PEC) processes for the removal of organic pollutants is highly dependent on the performance of the photoelectroanode catalyst. The design of PEC systems with a direct Z-scheme charge transfer mechanism and visible light excitation is essential to enhance the degradation efficiency of organic compounds. Here, a α-MnO2/BiOI direct Z-scheme heterojunction photocatalyst was successfully synthesized through a convenient and feasible method. It is remarkable that the photoanode exhibited excellent PEC performance under visible light irradiation; a 95% removal rate of tetracycline (TC) pollutants was achieved within 2 h, and it had excellent stability and reusability, which was expected to degrade antibiotics efficiently and environmentally in harsh environments. The presence of oxygen vacancies (OVs) in the α-MnO2/BiOI heterojunction was confirmed by electron spin resonance technique, and the OVs acted as electron traps that contributed substantially to the separation efficiency of photogenerated carriers. ESR characterization showed that the main reactive radicals during TC degradation were •OH and •O2−. By analyzing the intermediates, the possible degradation pathways of TC were further analyzed and a suitable degradation mechanism was proposed. The toxicity changes in the degradation process were explored by evaluating the toxicity of the intermediates. This study provides a new way to enhance the performance of Bi-based semiconductor photocatalysts for the effective degradation of TC in water. [ABSTRACT FROM AUTHOR]

With the rapid development of deepwater exploration, safety issues associated with deepwater well control have been highlighted in recent years. Due to the effect of large choke line friction losses and the narrow drilling window in the deepwater scenario, the risk of well control is higher, leading to an increase in the demand for a more desirable well killing method. The Driller's Method and the Wait and Weight Method (W&W Method), both of which are the most widely used approaches in the well killing operation, have advantages and disadvantages. Therefore, the aim of this work was to present a quantitative analysis and provide a comparison between the two methods. The behavior of the drill pipe and choke pressures of the two methods was investigated by considering the influence of the choke line friction loss, gas expansion and circulation temperature. In order to evaluate their handling capacity in the deepwater well killing scenario, a mathematical model for kick tolerance and critical pit gain was developed. Moreover, a field case in the South China Sea, which has involved both the Driller's Method and the W&W Method during construction, was applied to study the differences in the two methods in the view of field application. The results recommended that the W&W Method has an advantage over the Driller's Method from the perspective of safety of the wellhead equipment and the handling capacity of the well kick, especially when the preparation ability of the killing mud is not strictly limited. [ABSTRACT FROM AUTHOR]

Gas hydrate reservoir properties provide critical information on the controlling mechanisms of gas hydrate formation and accumulation in natural depositional environments. They also are essential to understanding and accurately predicting gas production characteristics. However, the properties of fine-grained reservoirs that host hydrates are poorly studied. Guangzhou Marine Geological Survey acquired a comprehensive set of logging-while-drilling (LWD) logs, in situ tests, and lab measurements from 2015 to 2018 in the W11-17 fine-grained, gas hydrate reservoir of the Shenhu on the South China Sea. Porosity, hydrate saturation, and gas saturation were derived from neutron porosity, nuclear magnetic resonance (NMR), and electrical resistivity logs of SH-W17 and SHSC-4J1 wells and compared with lab measurements of pressurized cores. Units A to C contain three hydrate-concentrated intervals, with a maximum thickness of 32 m and an average hydrate saturation of 0.32 ±0.05. The hydrate saturation was estimated using resistivity and NMR models. Units D and E were inferred to be approximately 20 m thick, free-gas layers containing gas hydrates. Compared to hydrate saturation, the estimations of gas saturation from resistivity and NMR models are less reliable with a range of 0.05–0.4 due to the coexistence of gas hydrates and free gas. Permeabilities estimated from the NMR log agree well with those from neuron porosity in non-hydrate bearing intervals but are slightly higher in hydrate-bearing intervals. By incorporating the lab measurements and in situ tests into the NMR pore-size analysis, the permeability of water-bearing sediments in the hydrate intervals in the SHSC-4J1 well can be constrained to the range of 0.002–0.1 md, with 0.015 md being our best estimate. The NMR pore-size geometries indicate gas hydrates appear to preferentially fill bigger pores within fine-grained reservoirs, which exhibit a similar behavior to coarse-grained reservoirs. Our resistivity and relative permeability modeling indicate that the growth of gas hydrates within pore spaces is characterized by pore-filling and cementation behaviors. • We report reservoir properties from the first hydrate production site offshore China. • Stable hydrate intervals are 32 m thick with a hydrate saturation of 0.32 ±0.05. • Unstable layers are 20 m thick and gas saturation is estimated to be 0.05–0.4. • Permeability is estimated to be in a range of 0.002–0.1 md. [ABSTRACT FROM AUTHOR]

• The gas production from hydrate dissociation accounting for about 85%. • Analysis of the radius of the hydrate dissociation area in this production test. • Five-year prediction of long-term influence radius of pressure drop. • Exploration of favorable areas for the formation of secondary hydrates. • Analysis of the response of pressure and temperature of hydrate reservoirs. The first offshore natural gas hydrate production test of China in 2017 has proved the feasibility of hydrate exploitation from clayey-silt reservoirs, which possesses the highest reservoirs than other types of hydrate resources. However, owing to the absence of monitoring wells in this production test, the hydrate dissociation behavior cannot be analyzed through pressure and temperature changes of hydrate reservoirs. This paper focuses on the simulation study on the detailed response of the temperature and pore pressure of hydrate reservoirs of Well SHSC-4 during the gas production by depressurization. Meanwhile, it highlights the analysis of favorable areas for the formation of secondary hydrates and the influence of the secondary hydrates on pressure and temperature field of hydrate reservoirs. The simulation results indicate that in the first 60 days, the hydrate reservoirs feature a dissociation radius of about 5 m, and the gas production from hydrate dissociation accounts for about 85%. After 1 year, 2 years and 5 years of hydrate exploitation, the influence radius of low-pressure area (<10 MPa) is 15 m, 16 m and 17 m, respectively, suggesting that the hydrate reservoirs have higher gas production efficiency in the first year. Furthermore, the temperature and pressure of hydrate reservoirs are not favorable to the formation of secondary hydrates in the first 60 days. In long-term production, secondary hydrates are mainly formed at hydrate dissociation front. This can increase the pore pressure and further decrease the effective stress in the local areas of hydrate reservoirs, thus affecting mechanical stability of the local hydrate reservoirs. [ABSTRACT FROM AUTHOR]