科研成果 by Year: 2018

Precipitation is one of the most important factors determining the occurrence of extreme hydro-meteorological events and water resource availability. Precipitation in different grades has diverse ecological effects, and slight precipitation (SP, defined as 0.1–1.0 mm/day) is the minimal level among them. In this study, we investigated SP trends from 1961 to 2013, as well as the relationship between SP and advanced very high radiometric resolution (AVHRR) normalized difference vegetation index (NDVI) in China during growing season from 1981 to 2006. The distributions and trends of SP were analysed by calculating the daily precipitation data. The average annual slight precipitation amount (SPA) and the number of slight precipitation days (SPD), derived from 839 monitoring stations in China, show a decreasing trend over the last five decades, which is in agreement with total precipitation (TP) but in different rates. When the trend was analysed seasonally, SP in most stations decreases significantly in September–October–November (SON) and June–July–August (JJA), and the largest decrease is found in SON. About 49.5 and 68.7% of monitoring stations show a decreasing trend in SON, in both SPA and SPD, whereas the trend is less popular in March–April–May (MAM, SPA: 19.7%, SPD: 41.4%) and December–January–February (JJF, SPA: 25.6%, SPD: 43.1%). Moreover, our analysis indicates that the decrease of SP is mainly due to the decrease of SPD as the median amount of daily SP was unchanged over the past five decades (close to 0.3 mm/day). Based on 26-year (1981–2006) semi-monthly AVHRR NDVI data and the records of SP data, the relationship between AVHRR NDVI and SP was also investigated. In regions with lower (<600 mm) TP, the correlation coefficients between NDVI and SP tend to be higher. These results highlight that SP has different effects than TP on vegetation growth. We also analysed time lag effects and concluded that the sensitivity of NDVI to SP for grass vegetation (the correlation coefficient is 0.327) is more noticeable than for trees (0.211) or shrubs (−0.058). The relationship between SP and NDVI also provides us new insights on the dependence of vegetation growth on meteorological factors.

By using Derwent Innovation Patent Database and an improved DWPI manual code classification,we applied the methods of patent distribution structure,patent application trends and future patent development forecast to analyze the oil gas industry's patents. In recent years,owing to the industry's main business income decline,the number of annual patent applications shows a downward trend in oil gas exploration and mining industry,as well as in oil gas refining industry. With the rapid development of domestic storage and transportation business,the development trend of oil gas storage and transportation industry patents is promising.

In petroleum industry, creep behavior of rocks can affect the fracture conductivity, well productivity and ultimate recovery of the reservoir, in shale formations in particular. To get a better insight into this phenomenon, in this study, we applied grid nanoindentation method as a function of time to quantify creep behavior of shale rocks which is a complex material. The deconvolution results from statistical analysis of the data showed that shale samples could be distinguished by three mechanical phases where the mechanical phase with the largest hardness value exhibits the least creep deformation. Burgers models was applied to characterize the creep behavior of our shale samples. We realized as creep time increases, the creep time constant value increases, therefore, a logarithmic function can be used to quantify their correlations. This study showed that as the creep time increases, Young's modulus, hardness, and fracture toughness will decrease. Finally, we concluded, shale samples become softer and more prone to fracture growth as the creep time increases.

Pharmaceutically active compounds (PhACs) are widely detected emerging contaminants in water environments and possess high potential risks to human health and aquatic life; however, conventional water treatment processes cannot remove them sufficiently. The boom in nanoscience and nanotechnology offers opportunities to leapfrog on the back of these new technologies to develop innovative techniques in the field of water treatment. The extraordinary properties of nanomaterials, such as large surface area, quantum effect, electrochemical and magnetic properties, and other size-dependent physical and chemical properties, offer nanotechnologies great advantages over conventional technologies. To date, nanomaterials have been extensively applied or investigated in adsorption, photocatalysis, catalytic ozonation and filtration processes and have been shown to have many promising potential application prospects. Among the various nanomaterials, graphene and carbon nanotubes have shown a superior adsorption capacity for the removal of PhACs and possess great potential for modifying photocatalysts; moreover, they can also act as highly efficient catalysts for ozonation. The nano-sized photocatalysts, i.e. nano-TiO2, graphitic carbon nitride, MoS2 nanosheets, and ZnO, generally exhibit higher photocatalytic activity than bulk photocatalysts. The involvement of nanomaterials in a membrane can improve the permeability, selectivity, and anti-fouling properties of the membrane for improved filtration processes. However, some challenges, such as high cost, poor separation performance and environmental risks, are still impeding their engineering application. Aiming to provide readers with a comprehensive insight into the application of nanotechnologies for PhACs' remediation, the current review summarizes the recent advances and breakthroughs made in nanotechnology for PhACs' removal, highlights the modification methods for improving the effectiveness of treatment methods using nanomaterials, and proposes a number of possible further research directions.

In this paper, an empirical correlation is modified and applied to predict the CO2 bubble-rising velocity (BRV) in the light crude oil. On a basis of the predicted BRVs, the minimum miscibility pressures (MMPs) of three light crude oil−CO2 systems are estimated by using the BRV criterion with the rising-bubble apparatus (RBA). First, a correction term of s·2PρL0.5 is added into the BRV correlation in order to reflect the velocity of falling liquid film in velocity field by applying the Bernoulli’s theorem. The modified correlation is tuned to match the BRVs of the dead light oil–pure and impure CO2 systems from the literature and two respective numerical coefficients s of −0.00046 and −0.00028 are determined by using the non-linear least-square method. It is found that the BRV is positive proportionally increased with the bubble diameter, interfacial tension, and density difference. Second, the predicted BRVs are used to estimate the MMPs by using the BRV criterion. Two respective MMPs of the dead light oil–pure and impure CO2 systems are found to be 12.4 MPa and 23.7 MPa at Tres = 53.0 °C, which agree well with 12.4–12.9 MPa from the coreflood tests and 23.4 MPa from the RBA tests or 23.4–23.5 MPa from the vanishing interfacial tension (VIT) technique. In addition, a live light oil–pure CO2 system is added to validate the modified BRV correlation. By means of the predicted BRVs, the MMP of the live oil–pure CO2 system is estimated to be 15.5 MPa, which matches well with 15.2–15.4 MPa from the slim-tube tests. The modified empirical correlation can improve the efficiency and capability of the BRV criterion.