In this paper, a new method for converting the T2 (relaxation time) of NMR (nuclear magnetic resonance) into the pore radius is proposed. Combined with NMR and centrifugation experiments, the relationship between pore radius and T2 of the sample was established. The results show that the new method is more reasonable than the traditional method. When the sample was denser and the mercury saturation was lower, the pore distribution curve was obtained by traditional method had a worse agreement with mercury injection experiment, while pore distribution curve of the new method had a better agreement with the mercury injection curve, which reflected the greater advantage of the new method as the reservoir becomes denser. The new method can obtain all the pore information in the sample. The results show that the pores in tight sandstone are mainly consisted with mesopore and macropore, and the connectivity of macropore is better than that of mesopore. The new method can effectively characterize the full pore distribution and the seepage characteristics in different pores interval of tight reservoirs, which had a great significance to evaluate the recoverable resources of tight reservoir.
China's coalbed methane (CBM) industry is in an extremely important "climbing period" and "strategic opportunity period", which can be generally characterized by "three low and one small": low degree of exploration and development, low adaptability of main technology, low return on investment and small development scale. Under the "carbon peak and neutrality" background, the development status of CBM industry is systematically combed. The resources, technology, management problems and reasons are analyzed. Strategies and countermeasures to accelerate the industrial development are put forward according to the factors such as efficient development of resources, major technical breakthrough, talent team training, policy formulation and implementation, return on investment and so on. The existing problems are as follows: (a) The overall occurrence conditions in China are complicated and the development is difficult compared with the other countries. (b) The research precision accuracy of CBM resource conditions is not enough. (c) The adaptability of technology is poor. (d) The management mode is not suitable. In view of these problems, this paper puts forward the "two steps" development strategy and the technical and management countermeasures of "five in one". The corresponding "five in one" technology and management countermeasures are the formulation and implementation of relevant safeguard measures in accordance with the principle of collaborative innovation in five aspects: resources, technology, talents, policies and investment. Through the above measures, the dream and grand blueprint of CBM industry shall be realized.
In-situ fluid phase behavior is important in determining hydrocarbon contents and the multiphase flow through shale reservoirs. The gas-to-oil ratio (GOR) has been recognized as a critical indicator of fluid types. However, little is known about the impact of fluid phase variation across the thermal maturity on shale oil/gas production (e.g., estimated ultimate recovery, EUR). According to the specific gravity ratio of oil/gas, the producing GOR was converted and normalized into a mass fraction of gas in total hydrocarbons (MGOR) to compare North American shale oil/gas plays with Chinese shale oil and hybrid gas-condensate plays. A correlation between MGOR, the fluid phases, and production data was established to identify five phase stages of flow. MGOR varies systematically with the different production zones, which shows promise in rapidly indicating the well production performance and high production stages of shale oil/gas plays. The hybrid shale gas condensate index, Tmax, and total gas contents were integrated to present the fluid types and maturity of shale gas-condensates, which indicates fluid phase and production variation across thermal evolution. The results offer a unique perspective on the shale oil reservoir producibility based on the impact of GOR on fluid phases and EUR from the dominant global oil/gas plays.
The Wufeng-Longmaxi Formation shales with burial depths > 3 500 m in the southern Sichuan Basin are believed to have large shale gas potentials. However, the reservoir properties and gas-in-place (GIP) contents of these shales exhibit variations across different sublayers. In this study, a set of Wufeng-Longmaxi shales with burial depths of 4 000–4 200 m was derived from the Well Y101H2 in the Luzhou area, and the differences in geological and geochemical characteristics, porosity, water saturation and GIP content of various sublayer shales were investigated. The results indicate that the TOC content and effective porosity of the upper (LMX1-4) and lower (LMX1-3) sublayer shales of the first member of the Longmaxi Formation are better than those of the Wufeng Formation (WF) shales, which results in the LMX1-4 and LMX1-3 shales having higher GIP contents than the WF shales. The GIP contents of the LMX1-3 shales are higher than those of the LMX1-4 shales, and this is likely because the organic matter of the LMX1-3 shales had more aquatic organisms and was preserved in a stronger reductive environment, which leads to a stronger gas generation potential. In contrast to the middle-shallow LMX1-4 shales in the Sichuan Basin, the deep LMX1-4 shales in the Luzhou area have advantageous reservoir properties and GIP contents, and thus it is promising to synchronously exploit the deep LMX1-4 and LMX1-3 shales in some regions of the southern Sichuan Basin.
The Triassic and Jurassic tight sandstone gas in the western Sichuan depression, Sichuan Basin has attracted much attention in recent years, and the Upper Triassic coal-bearing Xujiahe Formation is believed to be the major source rock. However, there are relatively few studies on the carbon isotopic heterogeneity of methane generated from coal-measure source rocks and the origin of the natural gases in Xinchang Gas Field is still controversial. In this study, one coal-measure mudstone sample and one coal sample of the Xujiahe Formation in western Sichuan Basin were selected for gold tube pyrolysis experiment to determine their gas generation characteristics. Geological extrapolation of gas generation and methane carbon isotope fractionation parameters reveals that the main gas generation stage of Xujiahe Formation ranges from Late Jurassic to Cretaceous in the Xinchang Gas Field. The natural gas in the 5th member of Xujiahe Formation in Xinchang Gas Field is mainly derived from the 5th member of Xujiahe Formation itself, i.e., self-generation and self-reservoir, however, the gas in the Jurassic gas pools is mainly derived from the source rocks of the 3rd member of Xujiahe Formation rather than the 5th member of Xujiahe Formation.
Shales in the Carboniferous–Permian Fengcheng (FC) and Lucaogou (LCG) formations in Junggar Basin are important organic rich rocks containing significant oil resources. To evaluate the difference in sedimentary environment conditions and hydrocarbon-generating potential between the FC and LCG formations. Total organic carbon (TOC), Rock-Eval pyrolysis, solvent extraction, column fractionation, stable carbon isotope, gas chromatography-mass spectrometry (GC-MS) of saturated hydrocarbons and organic petrology from the source rocks of FC and LCG formations. were analyzed. The biomarker composition indicates that during the deposition of FC, LCG-1 to LCG-2, the sedimentary environment for the source rock formations changed with gradual decrease of salinity, from anoxic to dyoxic/suboxic in redox conditions, and from strong stratification to weakened stratification of water. The FC Formation source rock, with main telalginite (planktonic green algae), archaebacteria and minor terrestrial organic matter, deposited in the environment characterized by high salinity and strongly reducing condition. Its TOC content is relatively low with a high original hydrocarbon-generating potential of unit organic material. The LCG Formation source rock deposited in the environment with low salinity and large variations, the organic matter is mainly sourced from telalginite (planktonic green algae), lamalginite, bacteria and higher plants, resulting in strong heterogeneity of the source rock. The abundance of TOC is high, but the original hydrocarbon generation potential of unit organic matter is lower than that of FC Formation. The results provide a geochemical basis for further study of saline-brackish water sedimentary environment shales in the Junggar Basin.
Most production methods of heavy oil involve thermal production. However, it is challenging to delineate the thermal-affected zone due to complex reservoir conditions. With steam injected, the heavy oil viscosity drops; the reservoir density and velocity decrease accordingly, causing changes to seismic impedance. Moreover, the oil-and-water viscosity ratio and permeability show the difference with changing temperature, indicating that the reservoir's ability to transmit seismic waves would also be temperature-dependent. Therefore, the seismic responses and attenuation characteristics of the steam chamber can be helpful to monitor the steam-affected zone. We introduce an improved viscoelastic model to approximate the heavy oil reservoir during thermal production, and use the frequency-space domain finite difference algorithm to simulate the seismic wave-fields. Numerical results demonstrate that this model is applicable to a wide temperature range, and can effectively reveal the seismic characteristics of the steam chamber. Through analyzing the propagation differences of seismic waves under different temperatures, it is concluded that the attenuation coefficient, root-mean-square amplitude difference and amplitude ratio of PP-wave and PS-wave under different conditions can reveal the temperature variation in the steam chamber, with which it is possible to detect the steam chamber spatial distribution.
The Early Cambrian Niutitang Formation is characterized by wide distribution of black shales on Yangtze Block, South China. Here we have reported the pyrite concretions in the bottom of the Niutitang Formation deposited in the slope-basin environment of Yangtze Block. The pyrite concretion was mainly composed of pyrite associated with hydrothermal minerals (barite, hyalophane, tetrahedrite), followed by quartz and organic matter. Trace elements Mo and U displayed significant enrichment (enrichment factors > 10), indicating the euxinic bottom water condition. Cu, Ni, and excess Ba concentrations were relatively high, denoting high primary productivity. In-situ sulfur isotope compositions of pyrite concretions δ34Spy) showed little variations (13.2‰–19.4‰) and small fractionations compared to coeval seawater δ34Sso4. Petrological and geochemical analyses indicated the pyrite concretions were formed in the sediment-water interface during the early diagenesis, with H2S diffusing from the euxinic water, and influenced by hydrothermal activity leading to the coexistence of barite, hyalophane, and tetrahedrite. These results imply euxinic bottom water featured by high primary productivity and increasing riverine flux of sulfate from chemical weathering during the Early Cambrian.
Rare earth minerals are important strategic resources to economic development all over the world. In this study, multiple linear regression and back propagation (BP) neural network methods are used to invert the contents of ion adsorbed rare earth elements (REEs) and exploring the feasibility of quantitative inversion of REEs through measured hyperspectral data in Liutang rare earth mines, South China. The result shows that the spectral curve of the rare earth ore samples has obvious absorption characteristics around 390, 930, 1 400, 1 900 and 2 200 nm, and continuum removal and the 1st derivative treatment can highlight the absorption characteristics. The modeling accuracies of BP neural network are higher than that of multiple linear regression model. The BP neural network model of the 1st derivative data in 400–1 000 nm bands has the best inversion result of the total content of REEs, R2 reaches 0.98, the ratio of the performance to deviation (RPD) is larger than 3.0. The quantitative inversion model of each REE (except for Ce) has high precision, R2 is greater than 0.90 and RPD is greater than 3.0. The results indicate that quantitative inversion of REEs using measured spectra not only has great potential and feasibility in the exploration of rare earth minerals, but also provides a rapid test method for the content of ion-adsorbed rare earth elements.
The Dong-Xi-Taijinaier Salt Lake (DXTSL) of Qaidam Basin is known as one of rich lithium reserves in China. However, the source of lithium deposits in this region remains unclear. The hydrochemistry and lithium isotopes (δ7Li) of water and solid samples along the Nalenggele River catchment were studied in combination with rock leaching experiments. The results showed the hot springs in the upstream contained high content of lithium and ratio of Li × 1 000/total dissolved solids (1.5–3.5), but the lower δ7Li values (4.33‰–11.59‰), meaning that it is one important lithium sources. The leaching experiments by the rich-lithium volcanic rocks (average content of 474.7 mg/kg) showed that under temperature of 20–80 ℃ and long time duration (24–96 h), the concentration of lithium released by leaching of the sampled volcanic rocks increased from 0.58 to 1.49 mg/L, with the leaching rate decreasing from 0.024 to 0.015 mg/(L·h) and the corresponding lithium release rate increasing from 29% to 74%. Calculation based on water-salt balance showed that the total amount of lithium contribution from hydrothermal fluids and volcanic rock weathering is about 4.99 and 0.29 Mt since 13.1 ka, respectively. Therefore, hot springs and leaching of volcanic rocks are main contributors to lithium deposit in DXTSL.
The prediction of sandstone distribution is the main target for hydrocarbon exploration and petroleum reservoir engineering, especially in a rift basin with a complex geological setting. During the Middle Eocene, the Dongying and Yong'an deltas converged in the Dongying depression of the Bohai Bay Basin, eastern China. So far, studies on the control of the existing syndepositional faults on the deltaic sandbodies of the two confluence deltas have been largely neglected. In this contribution, the sedimentary characteristics and spatial distribution of the two deltas, converging in the Dongying depression, were determined. In addition, the morphodynamic controlling factors of the deposits of the two deltas were identified based on core examination, log analysis, and seismic data analysis. During delta progradation, the sandbodies of the initially separated deltas were affected by the development of syndepositional tensional faults, which eventually also influenced the distribution of the sandstone reservoirs. The results of this study can not only be applied to petroleum reservoir engineering but also provide important new information for the studies on delta sandbody all over the world.
The provenance and tectonic implications of Late Paleozoic sedimentary rocks in the South Qinling Belt (SQB) provide important clues for understanding the timing and mechanism of the collision between North China Block (NCB) and South China Block (SCB). Here we report new LA-ICP-MS zircon U-Pb ages and geochemical composition of metasedimentary rocks from the Foping area in the SQB. The results indicate that the depositional age of the Wenquan Group can be limited to the Early Devonian by the youngest U-Pb age of 398 Ma, whereas those of the quartz schist from the Changjiaoba Group could be constrained after the Carboniferous by the youngest 206Pb/238U peak age of 306 Ma. Therefore, much of the previously-assumed "Neoarchaean or Paleoproterozoic" strata, including the Wenquan and Changjiaoba groups, were actually deposited in the Late Paleozoic. Based on analysis and comparison of the detrital zircon ages of the Devonian tectonic units in the SQB, we found that most prominent peak ages of detrital zircons from metasedimentary rocks in the Foping area shared similar characteristics with others. They mainly derived from the North Qinling Belt and South Qinling Belt-Yangtze Block, with a minor source probably from the North China Block, implying that the Shangdan Ocean between NCB and SCB had closed in the Early Devonian. Combined with regional geological background and geochemical data, we inferred that these Devonian strata formed in the foreland basin after the amalgamation of the North China Block and South China Block.
Glacial diamictite may provide important information on paleoenvironment and average composition of the upper continental crust (UCC). In this study, we report sedimentary facies, petrological and geochemical characteristics of Neoproterozoic diamictite from a profile of the Luoquan Formation on the southern margin of the North China Block (NCB). Upwards the sampling profile, lithostratigraphic strata vary from massive diamictite with poorly sorted carbonate gravels to laminated diamictite with small gravels of terrestrial detrital materials. Along the profile, CaO-MgO-LOI-Sr values decrease with the increase of SiO2-Al2O3-K2O contents. All these petrological and geochemical variations indicate a change from lodgement till deposition in the proximal of ice sheet to ice-rafting deposition in glacial-marine environment with less dolomite to supply their source. Together with previous studies on diamictite from other outcrops on the NCB, the deposition of Luoquan diamictite reflects that the glaciation on the NCB vanished and the ice-rafting effect weakened with glacial transgression process. In addition, significant co-variations of various elements with La and Al2O3 confirm the significant conservation of most analyzed elements during the sedimentary processes to produce diamictite.
The Daba Shan orocline is located at the northeastern margin of the Sichuan Basin and has been inferred as a foreland thrust-fold belt of the Qinling Orogen since the Late Triassic. A complete understanding of rock exhumation history is critical to elucidate how and when this typical orocline structure is developed. Detrital apatite fission-track dating of modern river sands is employed to reveal the regional exhumation history of the Daba Shan orocline. Four age peaks are identified and interpreted as the results of tectonic exhumation. Two older age peaks at ~150–140 and ~116–86 Ma are agreement with two main shortening deformation episodes of the Yanshanian Movement in the eastern China. The other two younger age peaks at ~69 and ~37 Ma support that the Daba Shan was reactivated by the Late Cretaceous to Cenozoic deformation which were likely related to the subduction of the Pacific Ocean and eastward growth of the Tibetan Plateau, respectively. It is worth noting that in contrast to the ~150–140 Ma rapid rock uplift and exhumation, the Middle Cretaceous exhumation (~116–86 Ma) shifted southward and continued to spread to southern tips of the Daba Shan. These exhumation variations in temporal and spatial allow a southward thrust deformation with piggyback style during the Yanshanian.
The nature of lithosphere mantle beneath North China Craton (NCC) has been changed during the Mesozoic. We investigated the mafic dykes in Jiaodong to put constraint on the origin of them and reveal the mantle evolution of the NCC. Zircons from Kunyushan and Nansu mafic dykes give concordia U-Pb ages of 114.9 and 52.8 Ma, respectively. The Kunyushan mafic dyke has high MgO (~8.0 wt.%) and Cr (> 380 ppm) but lower FeO (< 10 wt.%) contents. Large ion lithophile elements (LILE) are enriched compared to primitive mantle. The εHf(t) values of zircons are between -15.0 and -20.1. All these geochemical data imply an old and enriched lithosphere mantle source. In contrast, the Nansu mafic dyke has lower concentrations of MgO (< 7.0 wt.%) and Cr (200 ppm–230 ppm) but higher FeO (> 11 wt.%) contents. The LILE and light rare earth elements (LREE) are not so strongly enriched relative to the mafic dyke from Kunyushan but display slight enrichment compared to the primitive mantle. Positive zircon εHf(t) values are obtained (from +11.7 to +19.5, with one outlier of +3.4). It is suggested that the Nansu dyke sourced from an enriched MORB mantle and was generated by fluid flux melting.
Using the gravity/GNSS data of 318 stations observed in 2020, this paper optimizes the Bouguer and free-air gravity anomalies around the 2021 Yangbi Ms 6.4 Earthquake, inverses the lithospheric density structure of the focal area, and obtains the distribution of isostatic additional force borne by the lithosphere. The results show that the Bouguer gravity anomaly in western Yunnan varies from -120 to -360 mGal. As a whole the anomalies are large in the north and small in the south, and the value in the source area of the 2021 Yangbi Ms 6.4 Earthquake is about -260 mGal. Significant lateral differences indicates that the crust around the great earthquake does not belong to a solid and stable tectonic unit. The lithosphere in the source area is basically in equilibrium, indicating that the occurrence of the great event is not relative to the lithospheric equilibrium, but to the differential movement of the crust in the horizontal direction. In addition, we obtain the teleseismic SKS phases of 51 stations. As a whole, the polarization direction of fast wave in western Yunnan is approximately vertical to the maximum gradient change direction of regional Bouguer gravity anomaly that reflects the change of Moho.
Chahuaqingolepis magniporus gen. et sp. nov., a new taxon of Bothriolepididae (Placodermi: Antiarcha), is described from the Middle Devonian in Luquan County, Yunnan Province, South China. The phylogenetic analysis shows that Chahuaqingolepis is the sister group of Wufengshania with the synapomorphy of the large obtected nuchal area. Together with the findings of other associated antiarchs including Dianolepis, Bothriolepis, and Hunanolepis, the new bothriolepid antiarch is assigned to the Bothriolepis sinensis-Hunanolepis fish assemblage, which characterizes the Eifelian of the Middle Devonian in South China. The fish-bearing Tanglishu Formation can be well correlated with the Tiao-majian Formation in Changsha, Shangshuanghe Formation and lower part of the Haikou Formation in Qujing, and Laohutou Formation in Shaoguan and Lechang areas. This discovery not only enriches the Middle Devonian diversity of bothriolepids, but also provides reliable paleoichthyological evidence on the division and correlation of the fish-bearing Devonian strata in South China and deepens the understanding of the biogeography of the Devonian bothriolepids.
Assembly processes of prokaryotic and microeukaryotic community is an important issue in microbial ecology. However, unclear remains about the relative contribution of deterministic and stochastic processes to the shaping of prokaryotic and microeukaryotic communities in saline lake water. Here, we systematically investigated the assembly processes governing the prokaryotic and microeukaryotic communities in Qinghai Lake with the use of Illumina sequencing and a null model. The results showed that both deterministic and stochastic processes play vital roles in shaping the assemblies of prokaryotic and microeukaryotic communities, in which stochastic processes appeared to dominate (> 70%). Prokaryotic communities were mainly governed by non-dominant processes (60.4%), followed by homogeneous selection (15.8%), variable selection (13.6%) and dispersal limitation (10.2%), whereas microeukaryotes were strongly driven by non-dominant processes (68.9%), followed by variable selection (23.6%) and homogenizing dispersal (6.3%). In terms of variable selection, nutrients (e.g., ammonium, dissolved inorganic carbon, dissolved organic carbon and total nitrogen) were the major factors influencing prokaryotic and microeukaryotic community structures. In summary, prokaryotes and microeukaryotes can be predominantly structured by different assembly mechanisms, in which stochasticity is stronger than deterministic processes. This finding helps to better comprehend the assembly of prokaryotic and eukaryotic communities in saline lakes.
With a warming climate, temperature extremes have been a main global issue in recent decades due to their potential influence on the sustainable development of human life and natural ecosystems. In this study, 12 indicators of extreme temperature events are used to evaluate the spatiotemporal distribution, periodic structure and teleconnections with large-scale atmospheric circulation in Xinjiang, Northwest China by combining wavelet coherence (WTC) analysis based on continuous wavelet transform (CWT) analysis with the sequential Mann-Kendall test. We find that over the past six decades, the climate in Xinjiang has become warmer and has suffered from increases in the frequency of warm extremes and decreases in the frequency of cold extremes. Warm extremes have mainly occurred in the southern Tianshan Mountains surrounding the Tarim Basin and western part of the Taklamakan Desert, and cold extremes have primarily occurred in the southwestern Altai Mountains and northern foot of the Tianshan Mountains. Extreme temperature events, including warm extremes, cold extremes, and other temperature indices, have significant interannual variability, with the main oscillation periods at smaller (2–4-year band), intermediate (4–7-year band), and greater time scales in recent decades. Furthermore, cold-extreme indices, including frost days, cool days, and cool nights all show a clear changepoint during 1990–1997 at the 95% confidence level, and both ice days and cold spell duration indicator have a potential changepoint during 1981–1986. However, the changing points for warm-extreme indices are detected during 1992–1998. The temperature variables are significantly correlated with the EI Niño-Southern Oscillation (ENSO) and Arctic Oscillation (AO), but less well correlated with the Pacific Decadal Oscillation (PDO). The phase difference in the WTC spectra is not uniform between temperature extremes and climatic oscillations. Our findings will have important implications for local governments in taking effective measures to mitigate the potential effects of regional climate warming due to human activities in Xinjiang.
The pan-Arctic region has the largest number of lakes in the world, which is rather sensitive to changing climate. It is urgently needed to understand how these lakes were changing in the long term. However, there are few lakes with long-term historical monitoring of water level, understanding the hydrologic changes of pan-Arctic lakes over the past century requires the data reconstruction by state-of-art techniques. This study used machine learning algorithms to reconstruct the water level of pan-Arctic lakes on a centennial scale. It further investigated their relationship with long-term hydrological and climatic variables. Comparison of the reconstructed results by four different machine learning models shows that the extreme gradient boosting tree (XGBoost) is better than other three models. Overall, the centennial-scale reconstruction using the XGBoost model performs best for most study lakes. Based on the reconstructed results, we can observe that water level changes of several North American lakes are correlated with potential evapotranspiration, followed by precipitation, while the Eurasian lakes are more strongly associated with temperature and wet day frequency. The water level dynamics of pan-Arctic lakes could be largely attributed to Arctic Oscillation and Atlantic Multidecadal Oscillation. This study is expected to advance our understanding of the pan-Arctic lake water level changes in the past century and to provide a feasible method for reconstructing the regional lake water level in the long term.
The groundwaters within the ophiolite nappes in the southwestern part of Turkey have different physical and geochemical characteristics and are divided into five different groundwater facies. These are (1) Mg-HCO3, (2) Mg-HCO3-CO3, (3) Mg-CO3-HCO3, (4) Na-Ca-Cl-CO3, and (5) Ca-Mg-HCO3. The waters interact with ophiolites, mainly made up of basic-ultrabasic rocks, are characterized by alkaline and hyperalkaline character. Alkaline waters have high Mg, HCO3 contents and Μg/Ca ratio, and hyperalkaline water has high Na, Ca contents, and low Μg/Ca ratio. The waters in the study area formed by the interaction of meteoric waters with variously serpentinized ultramafic rocks under low-temperature conditions. Silicate weathering is the main hydrogeochemical process that plays a role in the chemical composition of water. Mg-HCO3-type groundwaters are produced under open-system conditions with respect to CO2 due to meteoric water-serpentinized peridotite interactions in a shallow environment. Deep-seated groundwaters are Na-Ca-Cl-CO3-type waters with high pH (TN-8 sample with pH 10.72), depleted in terms of Mg due to water-peridotite interaction under closed-system conditions with respect to CO2. Salda Lake with an alkaline character and high Mg and Na content is characterized by high evaporation and hydromagnesite deposition.
Understanding controls on river planform changes can help to build predictive models for distributive fluvial systems, and then guide the oil and gas exploration. To do this we have undertaken a detailed investigation of the modern Great Halten River distributive fluvial system from the Sugan Lake Basin, Qinghai, China. Unmanned aerial vehicle (UAV) photography, satellite remote sensing data and elemental analysis were used to determine differences in the sedimentary characteristics of the distributive fluvial system. From the apex to the toe, the changes in the slope, river morphology, sedimentary characteristics and element content in different regions were determined and three facies belts: "proximal", "medial" and "distal" were identified. We found that the sedimentary structure and elemental content characteristics of each facies differ greatly. We compare the large-scale evolution of rivers from braided to meandering rivers, and the fine description of sedimentary characteristics in combination with each observation, we strengthen our overall understanding of the modern DFS from macro to micro scale. At the same time, we summarize the sedimentation model of the Great Halten River DFS, and our study provides a reference for establishing the sedimentary model in continental petroliferous basins.
The determination of channel evolutions and the causes is important for reconstructing the evolutionary history of river landforms. This study aimed to elucidate the downstream channel evolution of the Yuan River in Hunan Province, China, during the Qing Dynasty via Landsat 8 satellite image data and relevant literature. The objective was to establish the modes of channel evolution and discuss the significance of historical climate change. The downstream paleochannel of the Yuan River was identified in the Late Ming Dynasty and Early Qing Dynasty (1600–1644 AD), the Kangxi-Qianlong periods of the Qing Dynasty (1661–1796 AD), the Late Qing Dynasty (1840–1912 AD), and the World War Ⅱ (1939–1945 AD), and three main modes of river evolution were determined. Using remote sensing data and the ancient literature, the evolution characteristics of the paleochannel in the Lower Yuan River were analyzed and its distribution across historical periods was comprehensively revealed. The findings reveal a strong correlation between channel evolution, flood events, and climate change. Numerous flood events that occurred from the Late Qing Dynasty to the World War Ⅱ caused a high rate of channel evolution, demonstrating the combined effects of climate change and human activities. These findings will help adopt robust and resilient hydrological management methods in the future of a changing climate.
The compression and creep characteristics of moraine soil are important mechanical properties of geomaterials to be analyzed during the construction process of engineering projects. However, related references about these characteristics through large-size in-situ tests have rarely been reported. In this study, in-situ tests of particle size distribution, compression deformation, and compression creep were conducted at the Xingkang Bridge, West Sichuan, China. The results show that the uniformity coefficient of moraine soil ranges from 12.1 to 183.3, and gradation coefficient ranges from 0.4 to 2.8. The total compression deformations of moraine samples during the conventional compression deformation test are 4.70, 4.07, and 0.47 mm, and their residual deformations are 2.81, 2.45, and 0.22 mm, respectively. The deformation modulus ranges from 127.3 to 676.4 MPa, and elastic modulus ranges from 316.3 to 765.7 MPa. During compression creep tests, moraine soil enters the steady creep stage after 3.8 h of loading pressure at 445 kPa, and it keeps steady after 14 h of loading pressure at 900 kPa. The Burgers model and generalized Kelvin model predict the deformation well in transient, deceleration and steady creep stages. Results provide a valuable reference for the analysis of the compression deformation and creep behavior of moraine soil during engineering construction and management.
Columnar jointed basalt (CJB) widely distributes in the dam site of the Baihetan Hydropower Station. The columnar joint structure and fracture development of CJB have significant influence on the mechanical properties of rock mass, and the mechanical properties of CJB are of great significance to the Baihetan Hydropower Project. Therefore, in-situ direct shear tests were carried out on ten test adit at different locations in the dam site area to study the shear behavior of CJB. In this study, 21 sets of in-situ direct shear tests were conducted for rock types of type Ⅱ2, type Ⅲ1 and type Ⅲ2, with horizontal and vertical shear planes and two different specimen sizes of CJB. Shear strength parameters of CJB were obtained by linear fitting of in-situ direct shear test results based on the Mohr-Coulomb strength criterion. The results indicate that the shear strength parameters of CJB with horizontal shear plane increase as the increase of rock type grade. The shear strength parameters of CJB show obvious anisotropy and the friction coefficient of the horizontal shear plane is greater than the vertical shear plane. The friction coefficient in the horizontal direction of the shear plane is 1.27 times that in the vertical direction of the shear plane. With the increase of rock type grade, the difference of friction coefficient becomes larger. However, the cohesion changes little whether the shear plane is horizontal or vertical. In addition, the size effect of CJB in this area is significant. The shear strength parameters of large size (100 cm × 100 cm) specimens are lower than those of regular size (50 cm × 50 cm) specimens. The reduction of cohesion is greater than that of the friction coefficient. For rock type Ⅲ2, the cohesion of large-size specimens is 0.637 of the regular-size specimens. The reduction percentage of the friction coefficient for type Ⅲ2 is 1.66 times that of type Ⅲ1. The reduction percentage of the cohesion for type Ⅲ2 is 1.27 times that of type Ⅲ1. The size effect decreases with the increase of rock type grade. The research results of this study can provide an important basis for the selection of rock mechanics parameters in the dam site area of Baihetan Hydropower Station and the stability analysis of the dam foundation and rocky slopes.