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  • REVIEW ARTICLE
    Qifeng JIA, Dameng LIU, Yidong CAI, Xianglong FANG, Lijing LI
    Frontiers of Earth Science, 2021, 15(2): 202-223. https://doi.org/10.1007/s11707-020-0833-1

    Petrophysics of coals directly affects the development of coalbed methane (CBM). Based on the analysis of the representative academic works at home and abroad, the recent progress on petrophysics characteristics was reviewed from the aspects of the scale-span pore-fracture structure, permeability, reservoir heterogeneity, and its controlling factors. The results showed that the characterization of pore-fracture has gone through three stages: qualitative and semiquantitative evaluation of pore-fracture by various techniques, quantitatively refined characterization of pore-fracture by integrating multiple methods including nuclear magnetic resonance analysis, liquid nitrogen, and mercury intrusion, and advanced quantitative characterization methods of pore-fracture by high-precision experimental instruments (focused-ion beam-scanning electron microscopy, small-angle neutron scattering and computed tomography scanner) and testing methods (m-CT scanning and X-ray diffraction). The effects of acoustic field can promote the diffusion of CBM and generally increase the permeability of coal reservoirs by more than 10%. For the controlling factors of reservoir petrophysics, tectonic stress is the most crucial factor in determining permeability, while the heterogeneity of CBM reservoirs increases with the enhancement of the tectonic deformation and stress field. The study on lithology heterogeneity of deep and high-dip coal measures, the spatial storage-seepage characteristics with deep CBM reservoirs, and the optimizing production between coal measures should be the leading research directions.

  • RESEARCH ARTICLE
    Jingyu ZENG, Rongrong ZHANG, Jia TANG, Jingchen LIANG, Jinghan LI, Yue ZENG, Yefan LI, Qing ZHANG, Wei SHUI, Qianfeng WANG
    Frontiers of Earth Science, 2021, 15(1): 12-22. https://doi.org/10.1007/s11707-020-0815-3

    China’s rapid economic development has initiated the deterioration of its ecological environment, posing a threat to the sustainable development of human society. As a result, an assessment of regional sustainability is critical. This paper researches China’s most forested province, Fujian Province, as the study area. We proposed a grid-based approach to assess the regional carbon footprint in accordance with the Intergovernmental Panel on Climate Change’s (IPCC) carbon emission guidelines. Our method of assessment also introduced carbon emission indicators with our improved and published Net Primary Production (NPP) based on process simulation. The carbon footprint in Fujian Province from 2005–2017 was calculated and examined from a spatiotemporal perspective. Ecological indicators were used in the sustainability assessment. The research draws the following conclusions: 1) the carbon footprint in the eastern regions of Fujian Province was higher due to rapid economic development; 2) that of the western regions was lower; 3) an uptrend in the carbon footprint of Fujian Province was observed. All five ecological indicators based on carbon emissions and economic and social data showed an ecologically unsustainable trend over 13 years in the research area due to unsustainable economic development. Therefore, it is urgent to balance the relationship between economic development and environmental protection. Our research provides scientific references for achieving ecological civilization and sustainability in a similar region.

  • RESEARCH ARTICLE
    Jin LAI, Xiaojiao PANG, Meng BAO, Bing WANG, Jianan YIN, Guiwen WANG, Xuechun FAN
    Frontiers of Earth Science, 2022, 16(3): 587-600. https://doi.org/10.1007/s11707-021-0945-2

    Diagenesis exerts an important control on porosity evolution, and research of diagenesis and diagenetic minerals provides insights into reservoir quality evaluation and CO2 storage. Thin section, XRD (X-ray diffraction), CT (Computed Tomography), scanning electron microscopy (SEM), and NMR (Nuclear Magnetic Resonance) tests were used to investigate composition, texture, pore spaces, and diagenesis of sandstones in Paleogene Dongying Formation in Bohai Bay Basin, China, with special aims to unravel diagentic dissolution along bedding planes. The oversized pores, remnants in feldspar-hosted pores, and kaolinite within feldspar grains indicate a high degree of dissolution the framework grains experienced during burial. The CO2-rich or organic acids are responsible for the feldspar dissolution. Grain size plays the primary role in enhancing bedding dissolution process, and bedding planes in fine-medium grained sandstones with high content of feldspars are frequently enlarged by dissolution. The CT scanning image confirms dissolution pores are distributed discontinuously along the bedding planes. The dissolution pores along bedding planes have large pore size, and correspond to the right peak of the bi-modal T2 (transverse relaxation time) spectrum. The laminated sandstones and siltstones, or sandstones with cross beddings help improve framework grain dissolution. These new findings help improve the understanding of diagenetic models, and have implications in reservoir quality prediction and resource assessments in sandstones.

  • RESEARCH ARTICLE
    Songzhe LI, Biao LV, Yunping YANG, Yanhua YANG, Chenyang WANG
    Frontiers of Earth Science, 2022, 16(4): 876-889. https://doi.org/10.1007/s11707-021-0964-7

    Artificial island-type reclamation often exerts certain impacts on near-shore sandy shoreline resources and coastal ecological landscapes. The relationship between artificial islands and offshore beach evolution has attracted considerable attention in coastal protection and engineering construction. In this study, we consider Hongtang Bay in Hainan Province, China, as the research object. We adopted the Gao-Collins model to investigate the substrate transport trend in this sea area based on the analysis of the measured hydrologic and sediment data. The shore section from Nanshanjiao to Hongtangling (Taling), including the flat and straight shore sections, is dominated by the lateral transport trend of the vertical shore. The near-shore water has a strong lateral sediment transport capacity, while the outer deep-water area exhibits a sediment transport trend consistent with the tidal current movement. Using multi-year topographic data, the shoreline and seabed alterations in Hongtang Bay were analyzed, and the LITLINE beach evolution model was adopted to simulate the effects of three artificial island layouts with different island filling areas, offshore distances, and plan forms on the near-shore shoreline deformation. The results obtained indicate that the artificial island arrangement with a large offshore distance and a small area has relatively substantial advantages, such as minimizing the adverse effects of artificial island implementation on the near-shore beach.

  • RESEARCH ARTICLE
    Huiyan XU, Dengrong ZHANG
    Frontiers of Earth Science, 2022, 16(4): 1052-1060. https://doi.org/10.1007/s11707-022-0982-5

    The three-dimensional Weather Research and Forecasting (WRF) model was used to conduct sensitivity experiments during the landfall of Typhoon Fitow (2013) to examine the impacts of cloud radiative processes on thermal balance. The vertical profiles of heat budgets, vertical velocity, and stability were analyzed to examine the physical processes responsible for cloud radiative effects on surface rainfall for Typhoon Fitow (2013). The inclusion of clouds reduced radiative cooling in ice and liquid cloud layers by reducing outgoing radiation. The suppressed radiative cooling reduced from the ice cloud layers to liquid cloud layers. This was conducive to reducing instability. The decreased instability was associated with the reduced upward motions. The reduced upward motion led to a decreased vertical mass convergence. Consequently, heat divergence was weakened to warm the atmosphere. Together with suppressed radiative cooling, these effects jointly suppressed net condensation and rainfall. Furthermore, the reduced rainfall due to the cloud radiative effects were mainly associated with the reduced convective and stratiform rainfall. The reduced convective rainfall was associated with the reduced net condensation, while the reduced stratiform rainfall was related to the constraint of hydrometeor convergence.

  • RESEARCH ARTICLE
    Zhiwen LI, Fengnian WANG, Baosheng LI, Dingding DU, Huijuan ZHANG, Yougui SONG, Shuhuan DU, Li SUN
    Frontiers of Earth Science, https://doi.org/10.1007/s11707-022-0981-6

    The coastal sediments are sensitive carriers that reveal climate change, sea-level fluctuations, and monsoon evolution. A large number of sedimentary sequences developed along the coast of the Shandong Peninsula in the Last Glacial Period. Previous studies mainly focused on material sources and climate characteristics, but seldom mention the ten-thousand-year timescale monsoon evolution and its relationship with sea level fluctuations. The Liukuang section (LKS) is adjacent to the North Yellow Sea, which is mainly composed of alternations of dune sand and paleosol of the Last Glacial. Based on the chronological framework constructed by AMS 14C and optically stimulated luminescence (OSL) dating, we measured grain size, geochemistry, and heavy minerals to reconstruct the evolution of the East Asian winter monsoon (EAWM) and climatic fluctuations during the Last Glacial Period. The variations of the climate proxy indicators show that the degree of dry-cold climate and EAWM strength are indicated by different sedimentary facies in dune sand > sandy paleosol > lacustrine > silty paleosol. On a ten-thousand-year timescale, we detected episodes of EAWM strengthened in the LKS4 (78.9-59.5 ka), LKS3b (50.5-39.6 ka) and LKS2 (29.7-13.1 ka), which correspond to Marine Isotope stage (MIS) MIS4, MIS3b and MIS2, respectively, and EAWM weakened in the LKS3c (59.5-50.5 ka) and LKS3a (39.6-29.7 ka), which correspond to MIS3c and MIS3a, respectively. These climatic events were essentially synchronous with climate changes recorded in the geological carriers such as the cave stalagmites of southern China, loess from the Chinese Loess Plateau (CLP), and sea-level fluctuations in the Yellow-Bohai Sea. It is believed that the external driving factor is from the changes of solar radiation, and the internal factor is mainly from the combined effect of monsoon changes and sea-level fluctuations.

  • RESEARCH ARTICLE
    Bingbing SHI, Xiangchun CHANG, Zhongquan LIU, Ye LIU, Tianchen GE, Pengfei ZHANG, Yongrui WANG, Yue WANG, Lixin MAO
    Frontiers of Earth Science, 2021, 15(2): 471-489. https://doi.org/10.1007/s11707-020-0851-z

    Tight sandstone reservoirs are generally characterized by complex reservoir quality, non-Darcy flow, and strong heterogeneity. Approaches utilized for evaluating physical property cutoffs of conventional reservoirs maybe inapplicable. Thus, a comprehensive investigation on physical property cutoffs of tight sandstone reservoirs is crucial for the reserve evaluation and successful exploration. In this study, a set of evaluation approaches take advantage of field operations (i.e., core drilling, oil testing, and wireline well logging data), and simulation experiments (i.e., high-pressure mercury injection-capillary pressure (MICP) experiment, oil-water relative permeability experiment, nuclear magnetic resonance (NMR) experiment, and biaxial pressure simulation experiment) were comparatively optimized to determine the physical property cutoffs of effective reservoirs in the Upper Triassic Chang 6, Chang 8 and Chang 9 oil layers of the Zhenjing Block. The results show that the porosity cutoffs of the Chang 6, Chang 8, and Chang 9 oil layers are 7.9%, 6.4%, and 8.6%, and the corresponding permeability are 0.08 mD, 0.05 mD, and 0.09 mD, respectively. Coupled with wireline well logging, mud logging, and oil testing, the cut-off of the thickness of single-layer effective reservoirs are approximately 3.0 m, 3.0 m, and 2.0 m, respectively. Depending on the cutoffs of critical properties, a superimposed map showing the planar distribution of the prospective targets can be mapped, which may delineate the effective boundary of prospective targets for petroleum exploration of tight sandstone reservoirs.

  • RESEARCH ARTICLE
    Jinkai WANG, Yuxiang FU, Zhaoxun YAN, Jialin FU, Jun XIE, Kaikai LI, Yongfu ZHAO
    Frontiers of Earth Science, 2021, 15(4): 892-908. https://doi.org/10.1007/s11707-020-0836-y

    The sandstone of the third member of the Funing Formation (E1f3) in the northern slope zone of the Gaoyou Sag has the typical characteristics of high porosity and ultralow permeability, which makes it difficult for oil to flow. In this study, the lithological characteristics, sedimentary facies, diagenetic characteristics, pore structure, and seepage ability of this sandstone are characterized in detail. Correlation analysis is used to reveal the reason for the sandstone high porosity-low permeability phenomenon in the study area. The results indicate that this phenomenon is controlled mainly by the following three factors: 1) the sedimentary environment is the initial affecting factor, whereby the deposition of a large number of fine-grained materials reduces the primary pores of sandstone. 2) The Funing Formation has undergone strong compaction and cementation, which have led to the removal of most of the primary pores and a reduction in size of the throat channels. 3) Owing to fluid activity during the later stage of diagenesis, sandstone underwent intense dissolution and a large number of particles (feldspar and lithic debris) formed many dissolution pores (accounting for nearly 60% of the total pore space). Among these factors, dissolution has contributed the most to the development of high porosity-low permeability phenomenon. This is mainly attributed to the inhomogeneous dissolution process, whereby the degree of particle dissolution (e.g. feldspar) exceeds that of cementing minerals (clay and carbonate minerals). The secondary dissolution pores have increased the porosity of sandstone in the study area; however, the pore connectivity (permeability) has not been significantly improved, thus resulting in the special high porosity-low permeability characteristics of this sandstone.

  • REVIEW ARTICLE
    Haoran XU, Wei JU, Xiaobing NIU, Shengbin FENG, Yuan YOU, Hui YANG, Sijia LIU, Wenbo LUAN
    Frontiers of Earth Science, 2021, 15(3): 705-718. https://doi.org/10.1007/s11707-020-0843-z

    Investigation into natural fractures is extremely important for the exploration and development of low-permeability reservoirs. Previous studies have proven that abundant oil resources are present in the Upper Triassic Yanchang Formation Chang 7 oil-bearing layer of the Ordos Basin, which are accumulated in typical low-permeability shale reservoirs. Natural fractures are important storage spaces and flow pathways for shale oil. In this study, characteristics of natural fractures in the Chang 7 oil-bearing layer are first analyzed. The results indicate that most fractures are shear fractures in the Heshui region, which are characterized by high-angle, unfilled, and ENE-WSW-trending strike. Subsequently, natural fracture distributions in the Yanchang Formation Chang 7 oil-bearing layer of the study area are predicted based on the R/S analysis approach. Logs of AC, CAL, ILD, LL8, and DEN are selected and used for fracture prediction in this study, and the R(n)/S(n) curves of each log are calculated. The quadratic derivatives are calculated to identify the concave points in the R(n)/S(n) curve, indicating the location where natural fracture develops. Considering the difference in sensitivity of each log to natural fracture, gray prediction analysis is used to construct a new parameter, fracture prediction indicator K, to quantitatively predict fracture development. In addition, fracture development among different wells is compared. The results show that parameter K responds well to fracture development. Some minor errors may probably be caused by the heterogeneity of the reservoir, limitation of core range and fracture size, dip angle, filling minerals, etc.

  • RESEARCH ARTICLE
    Chao WANG, Zhiyuan LI, Xiong XU, Xiangsui ZENG, Jia LI, Huan XIE, Yanmin JIN, Xiaohua TONG
    Frontiers of Earth Science, 2023, 17(2): 378-390. https://doi.org/10.1007/s11707-022-1023-0

    The Large Field of View Airborne Infrared Scanner is a newly developed multi-spectral instrument that collects images from the near-infrared to long-wave infrared channels. Its data can be used for land surface temperature (LST) retrieval and environmental monitoring. Before data application, quality assessment is an essential procedure for a new instrument. In this paper, based on the data collected by the scanner near the Yellow River in Henan Province, the geometric and radiometric qualities of the images are first evaluated. The absolute geolocation accuracy of the ten bands of the scanner is approximately 5.1 m. The ground sampling distance is found to be varied with the whisk angles of the scanner and the spatial resolution of the images. The band-to-band registration accuracy between band one and the other nine bands is approximately 0.25 m. The length and angle deformations of the ten bands are approximately 0.67% and 0.3°, respectively. The signal-to-noise ratio (SNR) and relative radiometric calibration accuracy of bands 4, 9, and 10 are relatively better than those of the other bands. Secondly, the radiative transfer equation (RTE) method is used to retrieve the LST from the data of the scanner. Measurements of in situ samples are collected to evaluate the retrieved LST. Neglecting the samples with unreasonable retrieved LST, the bias and RMSE between in situ LST measured by CE312 radiometer and retrieved LST are −0.22 K and 0.94 K, and the bias and RMSE are 0.27 K and 1.59 K for the InfReC R500-D thermal imager, respectively. Overall, the images of the Large Field of View Airborne Infrared Scanner yield a relatively satisfactory accuracy for both LST retrieval and geometric and radiometric qualities.

  • RESEARCH ARTICLE
    Yapeng DUAN, Liangqing YAN, Ziling LAI, Qianting CHEN, Youying SUN, Li ZHANG
    Frontiers of Earth Science, https://doi.org/10.1007/s11707-022-0986-1

    Traditional villages are precious historical and cultural heritage. Here, we investigate Fuzhou area of Jiangxi Province, China, and consider 114 national-level and provincial-level traditional villages, applying fieldwork, historical document searches, GIS spatial analysis, spatial syntax analysis, and other methods to explore the spatial form characteristics of traditional villages in this area on a macroscopic and microscopic (individual) level, and the relationships between scales. It is found that on a macroscopic regional level, the spatial distribution of traditional villages is unevenly distributed at a low altitude and at a close proximity to water systems; while on a microscopic level, traditional villages are mainly small and medium-sized, with landscape environments mainly determined by eight different types of waterfront hills. Among the four types of village boundaries, there are more villages with finger-like characteristics, including finger-like villages with banded features and finger-like villages with cluster characteristics. The living environment patterns mostly determined by four different types of comb settlements due to the limitations of regional environments as well as the topographic and cultural factors. Our results are significant for the improved evolution, protection, and development of traditional villages such as those found in the Fuzhou area.

  • RESEARCH ARTICLE
    Hongping LIU, Changmin ZHANG, Li ZHANG, Yang LUO
    Frontiers of Earth Science, 2022, 16(4): 975-988. https://doi.org/10.1007/s11707-022-0999-9

    Bedding-parallel fractures are fractures that are parallel to rock bedding structure planes and have been widely accepted as a key factor for oil and gas production in tight sandstone and shale reservoirs. However, the formation mechanisms of these parallel-bedding fractures are still under debate. In this study, bedding-parallel fractures in Yongjin Oil Field were analyzed using methods including core and microscopic observations, element geochemistry, and carbon and oxygen isotope analysis. Their origin and relations to reservoir quality, faults, and rock mechanical properties were examined. The discovery of bedding-parallel fractures in both the Upper Jurassic and Lower Cretaceous formations indicates that the BPFs are generated later than the early Cretaceous. The filling state of bedding-parallel fractures that with no bitumen and carbonate cement indicate that they formed after oil charging and carbonate cementation. The tensile fracture characteristics in core and thin section observations, and the fact that overburden stress exceeds the pore pressure indicate that the bedding-parallel fractures were neither generated from tectonic compression nor overpressure. The most likely generation mechanism is stress relief during core drilling under high in situ stress conditions. High in situ stress and low tensile strength lead to thinner fracture spacing. The existence of high bedding-parallel fracture density is an indicator of good reservoir quality and result in high oil/gas production.

  • RESEARCH ARTICLE
    Ci SONG, Qiu YIN
    Frontiers of Earth Science, 2022, 16(2): 265-276. https://doi.org/10.1007/s11707-020-0841-1

    Spatial characteristic is an important indicator of remote sensor performance, and space-borne infrared hyperspectral sounder is the frontier of atmospheric vertical sounding technology. In this paper, the formation mechanism of the vertical spatial characteristics involved in the space-borne infrared hyperspectral sounding data are analyzed in detail, which shows that the vertical spatial characteristics of sounding data depends not only on the spectral channels and their waveband coverage, but also the specific atmospheric parameter and its specific variation interested. The indicators of vertical spatial characteristics are defined and their mathematical models are established based on the mechanism analyses. These models are applied to the vertical spatial characteristic evaluation of atmospheric temperature sounding for FY-4A GIIRS, which is the first space-borne infrared hyperspectral atmospheric sounder in geostationary orbit. It is concluded that FY-4A GIIRS can sound the vertical temperature distribution in whole troposphere and lower stratosphere with height<35 km. This study can provide basic information to support the improvement of infrared hyperspectral sounder and the trace of vertical spatial characteristics of atmospheric inversion products.

  • RESEARCH ARTICLE
    Juan TENG, Zhigang WEN, Chen LI, Lingye MENG
    Frontiers of Earth Science, 2022, 16(3): 696-710. https://doi.org/10.1007/s11707-022-1020-3

    Deformation of coals under tectonic movements could cause reduction of mechanical strength and enhancement of gas adsorption, which might result in coal and gas outburst, and cause safety and environmental issues. In this study, geophysical characteristics of coals with various structures were investigated with a special emphasis on characterization of pore size distribution, rock mechanical strength, acoustic emission, resistivity and acoustic velocity of anthracites with three types of structures in the Qinshui Basin, north China. The studied No. 3 coal seam developed three types of structures, namely undeformed coal, cataclastic coal, and granular coal. Petrographic observations under scanning electron microscope and pore size distribution using N2 and CO2 adsorption of anthracites of three types show that the undeformed coal consists of primary micropores, and cataclastic coal is mainly composed of mesopores and well-connected fractures. In comparison, granular coal has the least mesopores. Rock mechanical strength, acoustic emission, resistivity and acoustic velocity of coals with three structure types were investigated under uniaxial and triaxial compression. With increasing degree of deformation of anthracites, compression strength, Young’s modulus, density, acoustic emission counting and acoustic velocity decreases, while resistivity increases. We suggest that the evolution of pore size distribution of anthracites with increasing degree of deformation contributed to variations of geophysical characteristics of coals with different structures to some extent.

  • RESEARCH ARTICLE
    Yina YU, Zhaoping MENG, Jiangjiang LI, Yixin LU, Caixia GAO
    Frontiers of Earth Science, 2022, 16(4): 963-974. https://doi.org/10.1007/s11707-022-0983-4

    The stress and temperature sensitivities of coal reservoirs are critical geological factors affecting coalbed methane (CBM) well exploitation; in particular it is important to reduce or eliminate their influence on coal reservoir permeability. To investigate coal permeability behavior at various effective stresses and temperatures, CH4 permeability tests were conducted on raw coal samples under a varying effective stress of 2.0–8.0 MPa under five different temperatures (25°C–65°C) in the laboratory. The results show that the permeability of the coal samples exponentially decreases with increasing effective stress or temperature, which indicates obvious stress and temperature sensitivity. Through a dimensionless treatment of coal permeability, effective stress, and temperature, a new stress sensitivity index S and temperature index ST are proposed to evaluate coal stress and temperature sensitivity evaluation parameters. These new parameters exhibit integrality and uniqueness, and, in combination with stress sensitivity coefficient αk, temperature sensitivity coefficient αT, and the permeability damage rate PDR, the sensitivities of coal permeability to stress and temperature are evaluated. The results indicate that coal sample stress sensitivity decreases with increasing effective stress, while it first decreases and then increases with increasing temperature. Additionally, coal sample temperature sensitivity shows a downward trend when temperature increases and fluctuates when effective stress increases. Finally, a coupled coal permeability model considering the impacts of effective stress and temperature is established, and the main factors affecting coal reservoir permeability and their control mechanism are explored. These results can provide some theoretical guidance for the further development of deep CBM.

  • RESEARCH ARTICLE
    Melinda LAITURI
    Frontiers of Earth Science, 2020, 14(2): 256-267. https://doi.org/10.1007/s11707-020-0823-3

    Water is the essential resource of the 21st century where innovative water management strategies are needed to improve water security. This paper examines three case studies that exemplify the global water crisis, situated in rapidly urbanizing watersheds: Nairobi River Basin, Kenya; Citarum River Basin, Indonesia; and Addis Ababa River Basin, Ethiopia. Each of these watersheds are implementing large-scale water management strategies inclusive of local communities and regional governments to address water quality and waste management issues. The hydrosocial cycle (Linton, 2010) provides a framework to investigate the social, technical and physical aspects of water flows. Using the hydrosocial cycle as an organizing framework, these watersheds are examined to highlight how water security underpins water justice. The issues of gender and inequity are often overlooked in larger policy, development, and infrastructure discussions where technical requirements, restoration management, and engineering solutions obscure power inequities. Projects are compared to assess the implementation of the hydrosocial cycle through a discussion of social power and structure, technology and infrastructure, and the materiality of water in each location. This comparison reveals a dependence on large-scale technical projects with limited community engagement, and a need for science-based river restoration management. Recommendations are provided to improve and address holistic water management.

  • RESEARCH ARTICLE
    Xianfeng TAN, Long LUO, Hongjin CHEN, Jon GLUYAS, Zihu ZHANG, Chensheng JIN, Lidan LEI, Jia WANG, Qing CHEN, Meng LI
    Frontiers of Earth Science, 2023, 17(3): 713-726. https://doi.org/10.1007/s11707-022-0987-0

    The positive S-isotopic excursion of carbonate-associated sulfate (δ34SCAS) is generally in phase with the Steptoean positive carbon isotope excursion (SPICE), which may reflect widespread, global, transient increases in the burial of organic carbon and pyrite sulfate in sediments deposited under large-scale anoxic and sulphidic conditions. However, carbon-sulfur isotope cycling of the global SPICE event, which may be controlled by global and regional events, is still poorly understood, especially in south China. Therefore, the δ13CPDB, δ18OPDB,δ34SCAS, total carbon (TC), total organic carbon (TOC) and total sulfate (TS) of Cambrian carbonate of Waergang section of Hunan Province were analyzed to unravel global and regional controls on carbon-sulfur cycling during SPICE event in south China.

    The δ34SCAS values in the onset and rising limb are not obviously higher than that in the preceding SPICE, meanwhile sulfate (δ34SCAS) isotope values increase slightly with increasing δ13CPDB in rising limb and near peak of SPICE (130–160 m). The sulfate (δ34SCAS) isotope values gradually decrease from 48.6‰ to 18‰ in the peak part of SPICE and even increase from 18‰ to 38.5% in the descending limb of SPICE. The abnormal asynchronous C-S isotope excursion during SPICE event in the south China was mainly controlled by the global events including sea level change and marine sulfate reduction, and it was also influenced by regional events such as enhanced siliciclastic provenance input (sulfate), weathering of a carbonate platform and sedimentary environment. Sedimentary environment and lithology are not the main reason for global SPICE event but influence the δ13CPDB excursion-amplitude of SPICE. Sea level eustacy and carbonate platform weathering probably made a major contribution to the δ13CPDB excursion during the SPICE, in particularly, near peak of SPICE. Besides, the trilobite extinctions, anoxia, organic-matter burial and siliciclastic provenance input also play an important role in the onset, early and late stage of SPICE event.

  • RESEARCH ARTICLE
    Yixin ZHAO, Chujian HAN, Yingfeng SUN, Nima Noraei DANESH, Tong LIU, Yirui GAO
    Frontiers of Earth Science, 2021, 15(2): 189-201. https://doi.org/10.1007/s11707-021-0889-6

    Considering the complementarity of synchrotron radiation SAXS and nano-CT in the pore structure detection range, synchrotron radiation SAXS and nano-CT methods were combined to characterize the nano- to micro-pore structure of two bituminous coal samples. In mesopores, the pore size distribution curves exhibit unimodal distribution and the average pore diameters are similar due to the affinity of metamorphic grades of the two samples. In macropores, the sample with higher mineral matter content, especially clay mineral content, has a much higher number of pores. The fractal dimensions representing the pore surface irregularity and the pore structure heterogeneity were also characterized by synchrotron radiation SAXS and nano-CT. The fractal dimensions estimated by both methods for different pore sizes show consistency and the sample with smaller average pore diameters has a more complex pore structure within the full tested range.

  • TANG Xuan, JIN Zhijun, YANG Minghui, MING Haihui
    Frontiers of Earth Science, 2007, 1(2): 251-256. https://doi.org/10.1007/s11707-007-0031-4
    Many achievements have been made in experimental studies of hydrocarbon migration in the clastic reservoir. On the other hand, few migration experiments have been reported in the carbonate reservoir simulation realm. This article is a tentative experimental study on hydrocarbon migration and accumulation in the carbonate reservoir, which is a complex media that includes a pore system and fracture system. This microcosmic experiment simulates oil-water displacement using a real core model. Plentiful seepage phenomena were observed in the microcosmic experiments. Three kinds of pathways were found in the plane: parall elpathway, oblique-cross pathway and network pathway. Three types of flow were found: continuous flow, sectioning flow and their combination. Three driving fronts were found in the experiment: piston front, encircle front and impulse front. All these vary with many factors such as fluid pressure, oil saturation, fissure configuration and wettability, and these factors affect each other. The results show that the relation between the fluid pressure and volume of flow is a complex segmenting correlation, instead of a simple positive correlation like the pipe flow that follows Darcy s law. The relation between fluid pressure and the speed of flow also follows the same correlation. Speed of flow relates to the angle and width of the fissure. Speed of flow in the wide fissure that has an acute angle with the pressure gradient is faster than that in a narrow fissure with a high angle with the pressure gradient.
  • RESEARCH ARTICLE
    Chunyi XIANG, Liguang WU, Nannan QIN
    Frontiers of Earth Science, 2022, 16(1): 64-74. https://doi.org/10.1007/s11707-021-0871-3

    As one of the most devastating tropical cyclones over the western North Pacific Ocean, Super Typhoon Lekima (2019) has caused a wide range of heavy rainfall in China. Based on the CMA Multi-source merged Precipitation Analysis System (CMPAS)-hourly data set, both the temporal and spatial distribution of extreme rainfall is analyzed. It is found that the heavy rainfall associated with Lekima includes three main episodes with peaks at 3, 14 and 24 h after landfall, respectively. The first two rainfall episodes are related to the symmetric outburst of the inner rainband and the persistence of outer rainband. The third rainfall episode is caused by the influence of cold, dry air from higher latitudes and the peripheral circulation of the warm moist tropical storm. The averaged rainrate of inner rainbands underwent an obvious outburst within 6 h after landfall. The asymmetric component of the inner rainbands experienced a transport from North (West) quadrant to East (South) quadrant after landfall which was related to the storm motion other than the Vertical Wind Shear (VWS). Meanwhile the outer rainband in the vicinity of three times of the Radius of Maximum Wind (RMW) was active over a 12-h period since the decay of the inner rainband. The asymmetric component of the outer rainband experienced two significant cyclonical migrations in the northern semicircle.

  • RESEARCH ARTICLE
    Seung-Woo LEE, Sung Hyun NAM, Duk-Jin KIM
    Frontiers of Earth Science, 2022, 16(1): 175-189. https://doi.org/10.1007/s11707-020-0849-6

    Estimating horizontal winds in and around typhoons is important for improved monitoring and prediction of typhoons and mitigating their damages. Here, we present a new algorithm for estimating typhoon winds using multiple satellite observations and its application to Typhoon Soulik (2018). Four kinds of satellite remote sensing data, along with their relationship to typhoon intensity, derived statistically from hundreds of historical typhoon cases, were merged into the final product of typhoon wind (MT wind): 1) geostationary-satellite-based infrared images (IR wind), 2) passive microwave sounder (MW wind), 3) feature-tracked atmospheric motion vectors, and 4) scatterometer-based sea surface winds (SSWs). The algorithm was applied to two cases (A and B) of Typhoon Soulik and validated against SSWs independently retrieved from active microwave synthetic aperture radar (SAR) and microwave radiometer (AMSR2) images, and vertical profiles of wind speed derived from reanalyzed data and dropsonde observations. For Case A (open ocean), the algorithm estimated the realistic maximum wind, radius of maximum wind, and radius of 15 m/s, which could not be estimated using the reanalysis data, demonstrating reasonable and practical estimates. However, for Case B (when the typhoon rapidly weakened just before making landfall in the Korean Peninsula), the algorithm significantly overestimated the parameters, primarily due to the overestimation of typhoon intensity. Our study highlights that realistic typhoon winds can be monitored continuously in real-time using multiple satellite observations, particularly when typhoon intensity is reasonably well predicted, providing timely analysis results and products of operational importance.

  • RESEARCH ARTICLE
    Jiang HAN, Caifang WU, Lu CHENG
    Frontiers of Earth Science, 2023, 17(1): 135-144. https://doi.org/10.1007/s11707-022-0991-4

    During the coalbed methane (CBM) exploitation, the reservoir permeability can be affected by the effective stress that varies with the reservoir fluid pressure, which is a complex, dynamic and significant engineering problem. To analyze the response characteristics of the pore-fracture system by the changing stress, this work simulated reservoir and fluid pressures during the exploitation by adjusting confining pressure and displacement pressure. Stress sensitivity experiments under different effective stresses were conducted to systematically study the stage variation characteristics of porosity and permeability of coal. The results show that the permeability decreases exponentially with the increase in effective stress, consistent with previous studies. However, the porosity shows a V-shaped trend, which is different from the traditional understanding that it would decrease continuously with rising effective stress. These variation characteristics (of porosity and permeability above) therefore result in a phased porosity sensitivity of coal permeability (PPS). Moreover, the stress sensitivity of the samples was evaluated using the permeability damage rate method (MPDR) and the stress sensitivity coefficient method (MCSS), both of which showed that it ranges from the degree of strong to extremely strong. When the effective stress is lower than 5–6 MPa, the stress sensitivity of the coal reservoir drops rapidly with effective stress rising; when it is higher than 5–6 MPa, the change in stress sensitivity tends to flatten out, and the stress sensitivity coefficient (CSS) goes down slowly with rising effective stress. Finally, suggestions are proposed for the drainage scheme of CBM wells based on the experimental results.

  • RESEARCH ARTICLE
    Shikui GAO, Quanzhong GUAN, Dazhong DONG, Fang HUANG
    Frontiers of Earth Science, 2021, 15(2): 406-422. https://doi.org/10.1007/s11707-020-0850-0

    Shale gas is a relatively clean-burning fossil fuel, produced by hydraulic fracturing. This technology may be harmful to the environment; therefore, environmentally friendly methods to extract shale gas have attracted considerable attention from researchers. Unlike previous studies, this study is a comprehensive investigation that uses systematic analyses and detailed field data. The environmental challenges associated with shale gas extraction, as well as measures to mitigate environmental impacts from the source to end point are detailed, using data and experience from China’s shale gas production sites. Environmental concerns are among the biggest challenges in practice, mainly including seasonal water shortages, requisition of primary farmland, leakage of drilling fluid and infiltration of flowback fluid, oil-based drill cuttings getting buried underground, and induced seismicity. China’s shale gas companies have attempted to improve methods, as well as invent new materials and devices to implement cleaner processes for the sake of protecting the environment. Through more than 10-year summary, China’s clean production model for shale gas focuses on source pollution prevention, process control, and end treatment, which yield significant results in terms of resource as well as environmental protection, and can have practical implications for shale gas production in other countries, that can be duplicated elsewhere.

  • RESEARCH ARTICLE
    Murugesan BAGYARAJ, Thirunavukkarasu RAMKUMAR, Senapathi VENKATRAMANAN, Balasubramanian GURUGNANAM
    Frontiers of Earth Science, 0: 65-75. https://doi.org/10.1007/s11707-012-0347-6

    Groundwater potential zones were demarcated with the help of remote sensing and Geographic Information System (GIS) techniques. The study area is composed rocks of Archaean age and charnockite dominated over others. The parameters considered for identifying the groundwater potential zone of geology slope, drainage density, geomorphic units and lineament density were generated using the resource sat (IRS P6 LISS IV MX) data and survey of India (SOI) toposheets of scale 1:50000 and integrated them with an inverse distance weighted (IDW) model based on GIS data to identify the groundwater potential of the study area. Suitable weightage factors were assigned for each category of these parameters. For the various geomorphic units, weightage factors were assigned based on their capability to store ground-water. This procedure was repeated for all the other layers and resultant layers were reclassified. The reclassified layers were then combined to demarcate zones as very good, good, moderate, low, and poor. This groundwater potentiality information could be used for effective identification of suitable locations for extraction of potable water for rural populations.

  • RESEARCH ARTICLE
    Amin MOHEBBI, Fan YU, Shiqing CAI, Simin AKBARIYEH, Edward J. SMAGLIK
    Frontiers of Earth Science, 2021, 15(1): 133-150. https://doi.org/10.1007/s11707-020-0814-4

    Arizona residents have been dealing with the suspended particulate matter caused health issues for a long time due to Arizona’s arid climate. The state of Arizona is vulnerable to dust storms, especially in the monsoon season because of the anomalies in wind direction and magnitude. In this study, a high-resolution Weather Research and Forecasting (WRF) model coupled with a chemistry module (WRF-Chem) was simulated to compute the particulate matter spatiotemporal distribution as well as the climatic parameters for the state of Arizona. Subsequently, Ordinary Least Square (OLS), spatial lag, spatial error, and Geographically Weighted Regression (GWR) techniques were utilized to develop predictive models based on the climatic indicators that impacted the formation and dispersion of the particulate matter during dust storms. Census tracts were adopted to create local spatial averages for the chosen variables. Terrain height, temperature, wind speed, and vegetation fraction were designated as the most significant variables, whereas base state and perturbation pressures, planetary boundary layer height and soil moisture were adopted as supplementary variables. The determination coefficient for OLS, spatial lag, spatial error, and GWR models peaked at 0.92, 0.93, 0.96, and 0.97, respectively. These models provide a better understanding of the current distribution of the particulate matter and can be used to forecast future trends.

  • RESEARCH ARTICLE
    Jiashan ZHU, Ming WEI, Sinan GAO, Hanfeng HU, Lei MA
    Frontiers of Earth Science, 2022, 16(2): 221-235. https://doi.org/10.1007/s11707-020-0863-8

    Squall line is a kind of common mesoscale disaster weather. At present, there are few studies on the elaborate detection of squall line by dual polarization radar. With the dual polarization upgrade of weather radar network, we need to study the relationship between squall line echoes of base data and polarization data to reveal new echo phenomena and formation mechanisms. The relationship between radar parameters and atmospheric physical processes also need to be examined. Based on the NUIST CDP radar, a squall line in the Yangtze and Huaihe River basin that occurred from July 30 to 31, 2014 is analyzed. The results show that polarization parameters have obvious advantages in the characteristics analysis of size, phase state, shape and orientation of the water condensate particles. The phase states of water condensate particles in convection cell can be distinguished through comparative discussion. Several phase states exist in the squall line, including small, medium and large raindrops, melting hails, dry hails and ice crystal particles and the ZDR column can be used to identify the location of the main updraft. In addition, the polarization parameters are more sensitive to the melting layer. The gust front is presented as a narrow linear echo in Z affected by strong turbulence. It is an obvious velocity convergence line in V and approximately 0.70 in rHV. The ZDR can be used as a criterion to distinguish the horizontal and vertical scale of turbulence. The deforming turbulence, which is affected by environmental airflow, will cause an abnormally high ZDR in the gust front and a negative ZDR before and after the gust front. The variation of ZDR depends on the turbulence arrangement, orientation and relative position between turbulence and radar. These dual polarization parameter characteristics offer insights into understanding the structure and evolution of the squall line.

  • RESEARCH ARTICLE
    Fangyan ZHU, Heng WANG, Mingshi LI, Jiaojiao DIAO, Wenjuan SHEN, Yali ZHANG, Hongji WU
    Frontiers of Earth Science, 2020, 14(4): 816-827. https://doi.org/10.1007/s11707-020-0820-6

    Climate change, a recognized critical environmental issue, plays an important role in regulating the structure and function of forest ecosystems by altering forest disturbance and recovery regimes. This research focused on exploring the statistical relationships between meteorological and topographic variables and the recovery characteristics following disturbance of plantation forests in southern China. We used long-term Landsat images and the vegetation change tracker algorithm to map forest disturbance and recovery events in the study area from 1988 to 2016. Stepwise multiple linear regression (MLR), random forest (RF) regression, and support vector machine (SVM) regression were used in conjunction with climate variables and topographic factors to model short-term forest recovery using the normalized difference vegetation index (NDVI). The results demonstrated that the regene-rating forests were sensitive to the variation in temperature. The fitted results suggested that the relationship between the NDVI values of the forest areas and the post-disturbance climatic and topographic factors differed in regression algorithms. The RF regression yielded the best performance with an R2 value of 0.7348 for the validation accuracy. This indicated that slope and temperature, especially high temperatures, had substantial effects on post-disturbance vegetation recovery in southern China. For other mid-subtropical monsoon regions with intense light and heat and abundant rainfall, the information will also contribute to appropriate decisions for forest managers on forest recovery measures. Additionally, it is essential to explore the relationships between forest recovery and climate change of different vegetation types or species for more accurate and targeted forest recovery strategies.

  • RESEARCH ARTICLE
    Ramesh SIVANPILLAI, Kevin M. JACOBS, Chloe M. MATTILIO, Ela V. PISKORSKI
    Frontiers of Earth Science, 2021, 15(1): 1-11. https://doi.org/10.1007/s11707-020-0818-0

    Following flooding disasters, satellite images provide valuable information required for generating flood inundation maps. Multispectral or optical imagery can be used for generating flood maps when the inundated areas are not covered by clouds. We propose a rapid mapping method for identifying inundated areas based on the increase in the water index value between the pre- and post-flood satellite images. Values of the Normalized Difference Water Index (NDWI) and Modified NDWI (MNDWI) will be higher in the post-flood image for flooded areas compared to the pre-flood image. Based on a threshold value, pixels corresponding to the flooded areas can be separated from non-flooded areas. Inundation maps derived from differencing MNDWI values accurately captured the flooded areas. However the output image will be influenced by the choice of the pre-flood image, hence analysts have to avoid selecting pre-flood images acquired in drought or earlier flood years. Also the inundation maps generated using this method have to be overlaid on the post-flood satellite image in order to orient personnel to landscape features. Advantages of the proposed technique are that flood impacted areas can be identified rapidly, and that the pre-existing water bodies can be excluded from the inundation maps. Using pairs of other satellite data, several maps can be generated within a single flood which would enable emergency response agencies to focus on newly flooded areas.

  • RESEARCH ARTICLE
    Junhua ZHU, Jianwei QIAO, Feiyong WANG, Quanzhong LU, Yuyun XIA, Ransheng CHEN, Haiyuan ZHAO, Jingliang DONG
    Frontiers of Earth Science, 2020, 14(4): 758-769. https://doi.org/10.1007/s11707-020-0840-2

    Liangjia Village earth fissure, one of the 79 earth fissures along the Kouzhen–Guanshan fault located in the northern Weihe Basin, causes severe damage to buildings and farmlands. Since the late 1950s, 40 earth fissures have occurred in a similar east–west (EW) direction parallel to the Kouzhen–Guanshan fault, and a further 39 earth fissures have occurred with north-west, east-north, or north-east orientations intersecting the fault. In this study, a case study of Liangjia Village earth fissure was conducted to investigate the mechanisms of fissure generation in detail. Geotechnical and geophysical methods including measurements, trenching, drilling, and seismic exploration were used to reveal the basic characteristics, geological background, and origin model of the Liangjia Village earth fissure. This earth fissure, with a total length of 800 m in 2014, runs EW parallel to the Kouzhen–Guanshan fault, and it has damaged buildings and farmlands by forming sinkholes, gullies, subsidence, and a scarp. The trenching results indicated that this fissure underwent multi-phase activity. Analysis of geological drilling and shallow seismic profiling results showed that the fissure also possessed characteristics of a syn-sedimentary fault. Regarding its genesis, the fissure was formed through the combined actions of three factors: an earthquake created the fissure, the Kouzhen–Guanshan fault controlled its development, and loess erosion and groundwater runoff subsequently enlarged the fissure. Regional extension first generated many buried faults along the hanging wall of the Kouzhen–Guanshan fault before seismic activity caused the buried faults to propagate to the surface, where loess erosion and groundwater runoff promoted the formation of the current earth fissure.

  • RESEARCH ARTICLE
    He FANG, William PERRIE, Gaofeng FAN, Zhengquan LI, Juzhen CAI, Yue HE, Jingsong YANG, Tao XIE, Xuesong ZHU
    Frontiers of Earth Science, 2022, 16(1): 90-98. https://doi.org/10.1007/s11707-021-0887-8

    Gaofen-3 (GF-3) is the first Chinese spaceborne multi-polarization synthetic aperture radar (SAR) instrument at C-band (5.43 GHz). In this paper, we use data collected from GF-3 to observe Super Typhoon Lekima (2019) in the East China Sea. Using a VH-polarized wide ScanSAR (WSC) image, ocean surface wind speeds at 100m horizontal resolution are obtained at 21:56:59 UTC on 8 August 2019, with the maximum wind speed, 38.9 m·s−1. Validating the SAR-retrieved winds with buoy-measured wind speeds, we find that the root mean square error (RMSE) is 1.86 m·s−1, and correlation coefficient, 0.92. This suggests that wind speeds retrieved from GF-3 SAR are reliable. Both the European Centre for Medium-Range Weather Forecasts (ECMWF) fine grid operational forecast products with spatial resolution, and China Global/Regional Assimilation and Prediction Enhance System (GRAPES) have good performances on surface wind prediction under weak wind speed condition (<24 m·s−1), but underestimate the maximum wind speed when the storm is intensified as a severe tropical storm (>24 m·s−1). With respect to SAR-retrieved wind speeds, the RMSEs are 5.24 m·s−1 for ECMWF and 5.17 m·s−1 for GRAPES, with biases of 4.16 m·s−1 for ECMWF and 3.84 m·s−1 for GRAPES during Super Typhoon Lekima (2019).