A consensus has been reached through previous studies that organic matter (OM) pores are crucial to porosity in many shale gas reservoirs; however, their origins and types remain controversial. Here, ...we report the OM pore types hosted in algae, bitumen, graptolite and other fossil fragments in the Wufeng-Longmaxi Formations of the Sichuan Basin, Southwest China. Algae types mainly include multicellular algae, unicellular algae, etc. The OM pores in multicellular algae usually exhibit irregular, bubble-like, spherical and/or elliptical profiles, and their diameters vary between 300 and 800 nm. The shapes of the OM pores in unicellular algae are either irregular or oval, and the pores are hundreds of nanometres in size. The pores associated with solid bitumen are sporadic, isolated and variable in size, ranging from 500 nm to 3 μm. The pores in the graptolite, sponge spicule, radiolarian and other fossil fragments are much smaller and fewer. The pores may only have developed in the surface of the graptolite and bitumen by filling in the biological cavity of the sponge spicule. These new findings provide stronger evidence that multicellular algae are the main hydrocarbon generating organisms of OM pores development.
Based on the current research status of shale oil exploration and development at home and abroad, combing the field observations, dissection of typical shale oil regions, analysis and testing of ...organic-rich shale samples, etc., we compare the differences in geological and engineering characteristics of shale oil reservoirs in marine and continental basins between China and the United States. We put forward 8 issues worthy of attention in the exploration and development of lacustrine shale oil in typical basins of China, including the concept of tight oil and shale oil, differences between continental and marine shale oil reservoirs, medium-low maturity and medium-high maturity, vertical permeability and horizontal permeability, source-reservoir and source-caprock, geology and engineering, selection criteria of favorable areas and “sweet spots”, and basic scientific research and application research. By comparing and analyzing organic-rich shales in the Triassic Yanchang Formation of the Ordos Basin, the Permian Lucaogou Formation in the Jimsar Sag of the Junggar Basin, the Permian Fengcheng Formation in the Mahu Sag, the Cretaceous Qingshankou & Nenjiang Formation in the Songliao Basin and the Paleogene Kongdian & Shahejie Formation in the Bohai Bay Basin, from shale oil exploration to development, three key scientific issues must be studied in-depth in the future: (1) the physical, chemical and biological processes during the deposition of terrestrial fine-grained sediments and the formation mechanism of terrestrial organic-rich shale; (2) diagenesis-hydrocarbon-generation and storage dynamics, hydrocarbon occurrence and enrichment mechanism; (3) the fracturing mechanisms of terrestrial shale layers in different diagenetic stages and the multi-phase and multi-scale flow mechanism of shale oil in shale layers of different maturities. Clarifying the main controlling factors of shale oil reservoir characterization, oil-bearing properties, compressibility and fluidity of shale oil with different maturities and establishing a lacustrine shale oil enrichment model and the evaluation methodology can provide effective development methods, and theoretical foundation, and technical support for the large scale economical exploration and development of lacustrine shale oil resources in China.
The genetic identification of different types of natural gas is notably important for assessment of its sources and exploration potential. The chemical and isotopic (C and H, in particular) ...compositions of natural gas vary significantly due to the complexity of its generation, migration, and accumulation processes. The “coal-type” gas generated from humic matter is generally enriched in 13C as compared to "oil-type" gas generated from sapropelic organic matter. However, gas originating from fresh-brackish water environments is depleted in 13C whereas gas from saline environments is enriched in 13C. Notwithstanding organic precusors and sedimentary environments, both isotope compositions of alkanes tend to become enriched both in 13C and 2H with prograde thermal evolution. Therefore, in addition to thermal maturity, source material is the major controlling factor of carbon isotope compositions, whereas sedimentary environment is predominant in governing hydrogen isotopes. Secondary processes, including thermochemical sulfate reduction (TSR) and diffusion, result in an enrichment of the gases in 13C and 2H due to mass-dependent kinetic isotope effect. Microbial degradation causes a decrease in propane content and an enrichment in 12C and 2H of the residual propane. The abiogenic gases may include methane from deep mantle and high molecular weight hydrocarbons through Fischer-Tropsch type (FTT) synthesis. Methane of mantle origin possesses a narrow range of isotope compositions, although it is still a tall task to determine the exact values. In contrast, isotopes of alkane gases synthesized from FTT processes are in a wide range. In sedimentary basins, the mixing of gases from multiple sources and/or through different secondary processes may pose a challenage to identification of their origins. The detailed assessment is provided here with case studies from major oil and gas basins in China. This review provides identification of misconceptions in genetic types of natural gas using carbon and hydrogen isotopes of alkanes, and sheds insights into using isotope geochemistry as an important diagnostic tool for energy exploration as well.
Classification of natural gas and traditional geochemical methods for genetic identification of natural gas are reviewed.The effect of geological background and secondary alteration on δ13C and δ2H of light alkanes is assessed.New diagnostic tools for genetic classification of natural gas are suggested.
In recent years, theoretical geologic research has made important progress in shale gas exploration and development, and new discoveries, such as the Jiaoshiba, Weiyuan and Changning shale gas ...fields, provide geological cases to define key controls on shale gas accumulation in Wufeng Formation-Longmaxi Formation marine shale strata. A mechanism coupling source and seal development for shale gas enrichment is proposed in this study based on detailed research results of isochronous stratigraphic distribution of source rock and seals and source-seal dynamic evolution. Great thickness, wide distribution and high total organic carbon content (TOC) of sources are key controls on the shale gas content, and storage capacity in organic matter-hosted pores, micro-cracks and bedding fissures is intensively developed. The Wufeng Formation and the lower part of the first member of the Longmaxi Formation (WF2-LM4 graptolitic zone) are favorable sources that feature a slow deposition rate, well graptolitic zone, favorable organic organism type and high TOC. The organic matter type is benefit to the development of organic-matter pores because the planktonic algae tends to generate and expulse large amounts of hydrocarbon and form many organic-matter pores. Both high biogenic quartz and high TOC ensure development of abundant organic matter-hosted pores and result in a three-dimensional network of interconnected organic matter pores that allows shale gas storage and flow. The seal can be divided into direct and indirect seals. The direct seal refers to the middle and upper parts of the first member of the Longmaxi Formation (LM5 and higher graptolitic zone) that are characterized by low TOC and low porosity. The indirect seal refers to the regionally distributed Lower-Middle Triassic gypsum layer(s) and mudstone that maintain regional geopressure systems. The shale gas fields of Jiaoshiba, Fushun-Yongchuan and Changning have high geopressure coefficient factors (1.5, 2.0 and 1.5, respectively). In the absence of the Lower-Middle Triassic gypsum layer(s) and mudstone regional seals, the high-pressure system was destroyed and resulted in low-normal geopressure shale gas reservoirs, for instance, the Pengshui and Zhaotong wells. The static match and dynamic match of source and seal constrain the location of shale gas reservoirs and the degree of shale gas enrichment. The model of a mechanism coupling source and seal for shale gas enrichment provides new ideas and methods for the assessment of shale gas. This model promotes the evaluation of shale gas from the static parameters approach to the source and seal dynamic approach. In the Sichuan Basin and its peripheral areas, the promising areas for shale gas accumulation are those with favorable sources in the WF2-LM4 graptolitic zone and the presence of the Lower-Middle Triassic gypsum layer(s) and mudstone regional seal.
•The mechanism of source and seal coupling for shale gas enrichment was analyzed.•The WF2-LM4 graptolitic zone is a favorable source for shale gas enrichment.•Spatiotemporal evolution of direct and indirect seals is critical for shale gas reservoirs.•Static-dynamic match of source and seal controls the location and enrichment of shale gas.
Depositional environment highly affects the geochemical feature of sediments recording the information of paleoenvironment and its evolution. Geochemical data for Ordovician Wufeng Formation and ...Silurian Longmaxi Formation black shale deposition in the Sichuan Basin are presented and applied as proxies for deciphering paleoenvironment (detrital influx, redox conditions, paleoproductivity) and providing insight to paleoenvironmental conditions responsible for organic carbon accumulation. These data suggest that siliceous shale in the Wufeng and Longmaxi Formations reveals high TOC content, whereas silty, argillaceous, and limey shale display relatively low TOC contents. Major element and petrological evidences indicate that most of quartz in siliceous shales is biogenic origin (as shown by excess silica concentrations); therefore, Si is an unreliable indicator of detrital influx. The similar distribution of detrital influx proxies (Ti/Al, Ce, Hf, La, Nb Th and Zr) suggests a rather homogeneous coarse-grained detrital fraction supply. Redox proxies (Mo, Th/U, Ni/Co, V/Cr, and V/(V+Ni)) indicate that siliceous shales were deposited in a relatively dysoxic/anoxic environment, whereas the argillaceous, silty, and limey shales were deposited in a relatively oxic environment. Barium was solubilized under reducing conditions and cannot be applied confidently as a paleoproductivity indicator in high-TOC siliceous shales. Productivity proxies (Cu/Al, Ni/Al, excess Si) suggest that paleoproductivity was high during siliceous shales deposition, and weak during argillaceous and limey shales deposition. Our data suggests that high paleoproductivity and dysoxic/anoxic conditions controlled organic matter accumulation in Wufeng and Longmaxi shales.
•Multiple sedimentary geochemical proxies were investigated for paleoenvironment interpretation.•Biogenic silica make silica or Si/Al ratios an unreliable indicator of clastic influx.•The low Batot and Babio concentrations does not suggest the lower paleoproductivity.•Anoxic conditions plays a significant role in organic matter accumulation.
Subsurface gas storage is crucial for achieving a sustainable energy future, as it helps to reduce CO2 emissions and facilitates the provision of renewable energy sources. The confinement effect of ...the nanopores in caprock induces distinctive thermophysical properties and fluid dynamics. In this paper, we present a multi‐scale study to characterize the subsurface transport of CO2, CH4, and H2. A nanoscale‐extended volume‐translated Cubic‐Plus‐Association equation of state was developed and incorporated in a field‐scale numerical simulation, based on a full reservoir‐caprock suite model. Results suggest that in the transition from nanoscale to bulk‐scale, gas solubility in water decreases while phase density and interfacial tension increase. For the first time, a power law relationship was identified between the capillary pressure within nanopores and the pore size. Controlled by buoyancy, viscous force and capillary pressure, gases transport vertically and horizontally in reservoir and caprock. H2 has the maximum potential to move upward and the lowest areal sweep efficiency; in short term, CH4 is more prone to upward migration compared to CO2, while in long term, CH4 and CO2 perform comparably. Thicker caprock and larger caprock pore size generally bring greater upward inclination. Gases penetrate the caprock when CH4 is stored with a caprock thickness smaller than 28 m or H2 is stored with a caprock pore size of 2–10 nm or larger than 100 nm. This study sheds light on the fluid properties and dynamics in nanoconfined environment and is expected to contribute to the safe implementation of gigatonne scale subsurface gas storage.
Plain Language Summary
Aiming at the ambitious targets of net‐zero emission and global energy transition, effective technologies need to be developed and deployed with huge efforts. Subsurface gas storage is expected to play a critical role in reducing CO2 emission and providing large‐scale renewable energy. However, unforeseen gas leakage can cause potential environmental risks and energy efficiency concerns. Despite its importance, the mechanisms governing gas transport and distribution within caprocks, particularly under nanoconfinement conditions, are poorly understood. From nano‐scale and bulk‐scale thermodynamic properties predictions to field‐scale numerical simulations, this work carried out a comprehensive multi‐scale analysis to evaluate the storage security of CO2, CH4, and H2. Relationships between VLE, phase density, interfacial tension, capillary pressure and pore size, temperature, pressure and wettability were discussed, offering novel perspectives on the mechanisms governing gas leakage. Furthermore, loss potentials of different gases were compared and evaluated and the impacts of caprock thickness and pore size were examined, providing valuable insights for screening eligible storage sites. Overall, this work contributes to the development of secure and reliable gas storage techniques, supporting the goals of climate change mitigation and facilitating the transition to a net‐zero energy future.
Key Points
A multi‐scale analysis is carried out to assess the loss potential of CO2, CH4, and H2 during subsurface storage
Migration and distribution characteristics of gases in the caprock are investigated
Short‐term and long‐term gas storage security are analyzed and compared
Ovarian cancer is one of the most common gynecologic cancers with high morbidity and mortality in women. Glycogen metabolism plays a critical role in cancer development and glycogen phosphorylase B ...(PYGB) has reported to be involved in various tumors. Here, we explored the role of PYGB in ovarian cancer.
PYGB mRNA expression were examined in ovarian cancer tissue and also analyzed using the dataset from The Cancer Genome Atlas cohort. Correlations between PYGB expression and prognosis of ovarian cancer patients were analyzed. PYGB was silenced to evaluate the ovarian cell proliferation, invasion and migration in vitro and tumorigenesis in vivo. MiR-133a-3p targeting PYGB was identified using online tools and confirmed with luciferase reporter experiment. MiR-133a-3p overexpression using miRNA mimics was conducted to evaluate its function on ovarian cancer cells.
We showed that PYGB was upregulated in ovarian cancer tissue and high level of PYGB expression is markedly correlated with poor prognosis of ovarian cancer patients. PYGB knockdown significantly suppressed ovarian cancer cell proliferation, invasion and migration. Xenograft tumor formation further demonstrated that knockdown PYGB inhibited ovarian tumor development. Bioinformatics analysis revealed that PYGB regulated Wnt/β-catenin signaling pathway in ovarian cancer cells. Mechanistically, miR-133a-3p directly bound to 3′-untranslated region of PYGB and overexpression miR-133a-3p suppressed proliferation, invasion and migration in ovarian cancer cells.
Our data suggest that miR-133a-3p/PYGB/Wnt-β-catenin axis plays a critical role in human ovarian cancer, which might serve as a promising therapeutic target of ovarian cancer treatment in the future.
As two essential controls on the formation of organic matter (OM)-enriched shales, both paleoproductivity and preservation models remain controversial for the Wufeng and Longmaxi shales in the ...Sichuan Basin, southwest China. This study provides geochemical parameters as proxies for the paleoproductivity characteristics (Ba, P/Al, and (Ni+Cu)/Al), bottom water redox status (U/Th, V/(V+Ni), V/Cr, and Mo), and terrigenous clastic flux (Th and Al) of the Wufeng–Longmaxi Formations in the Sichuan Basin, a back-deep basin in a foreland basin system in southwest China. Combining these data with total organic carbon (TOC) content and sedimentation rate data obtained from graptolite zones allowed us to discuss the validity of these popular indices and to identify the main factors that controlled OM enrichment in the formations. TOC contents exceed 4 wt% in the upper Wufeng Formation to the bottom part of the Longmaxi Formation (LM1-3), which are the most OM-rich intervals. The average P/Al ratio for well JY2 in the Jiaoshiba area is 0.009, which is lower than those for well YY1 (0.028) in the Yongchuan area and well DY1 (0.02) in the Dingshan area, indicating the lowest productivity levels were in the Jiaoshiba area. Based on the redox proxies, the samples from well DY1 reflect less reducing bottom water conditions than those from wells JY2 and YY1. The Th and Al indices increase upwards, indicating that the terrigenous clastic input increased, and that those in the Yongchuan area were lower than those in the Jiaoshiba and Dingshan areas. The sedimentation rate was too low to dilute the OM in the Sichuan Basin, especially during the depositional time of the OM-rich intervals, such that the redox status of the water became more critical. Given the more strongly reducing conditions of the sedimentary environment and the high thermal maturity of the OM in this formation, the Ba concentrations appeared anomalously low and became inaccurate as a paleoproductivity index, as well as the validity of V, V/Cr, and V/(V+Ni) anomalously decreased as redox indices.
•Geochemical study on the Wufeng–Longmaxi Formations in the Sichuan Basin was conducted.•Geochemical data are provided as proxies for paleoproductivity characteristics.•Total organic carbon and sedimentation rates for graptolite zones were obtained.•Validities of Ba and V are discussed.
The linkages between the astronomical forcing of sea-level oscillations, the environment, and climate change during the Late Paleozoic Ice Age (LPIA) add to our understanding of the complicated ...mechanisms and patterns of current global sea-level change, climate transition, and biological evolution. However, due to the complexity and internal nonlinearity of the Earth's climate system, the million-year-scale oceanic and continental moisture transport patterns and carbon cycle processes during icehouse states are still controversial. Here, we utilize high-resolution gamma ray (GR), density (DEN) logs and total organic carbon (TOC) datasets to conduct a study on the cyclostratigraphy and organic carbon burial processes in the Lucaogou Formation of the Early Permian Junggar Basin in the Northern Hemisphere. An ∼4.2 Myr high-resolution astronomical time scale is developed by astronomical tuning of DEN log and TOC series to the stable 405-kyr long-eccentricity cycles. A comparative study of the sedimentary noise model and the SediRate-Fischer (SR-Fischer) plot finds similar patterns of lake-level changes for the first time, further demonstrating the utility and robustness of the sedimentary noise model and the SR-Fischer plot in tracking water-level variations. The antiphase correlation of sedimentary noise curve with the obliquity modulation and relative sea-level cycles demonstrates that the changes in land-ocean water exchange associated with variations in poleward flux of moisture dominated by s4-s3 obliquity amplitude modulation (AM) cycles may be a major driver for regulating inland lake levels in the Northern Hemisphere during the Late Paleozoic Ice Age. Additionally, we find a robust cyclicity of ∼170 kyr in the TOC series, which is modulated by the combined s4-s3 and s3-s6 astronomical signals and is nonlinearly amplified by internal climate responses of the carbon cycle under varying climate conditions. Our results strengthen knowledge of the connection of Myr-scale sea- and lake-level variations to astronomically induced climate change during the Late Paleozoic Ice Age and further elucidate the nonlinear climate feedback of the carbon cycle under obliquity forcing.
•An ∼4.2-Myr high-resolution ATS was constructed during the Early Permian.•A robust cyclicity of ∼170 kyr (s3-s6) in the TOC series was found.•∼1.2 Myr obliquity minima correspond to high lake levels during the icehouse world.•The s4-s3 and s3-s6 power maximum intervals are favorable for OC burial.•TOC series cycles are nonlinearly amplified by internal climate responses.
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