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Coal macrolithotypes control the heterogeneity of coal physical properties in coalbed methane (CBM) reservoirs and have a significant effect on the success of hydraulic fracturing stimulation. However, only a few studies have focused on this heterogeneity, and the propagation mechanism of hydraulic fractures related to the coal macrolithotype is not well understood. In this study, we considered the Hancheng area, Ordos Basin, China, as an example to understand macrolithotype differences, establish finite element numerical models of the cohesive zone, and evaluated the hydraulic fracture initiation and vertical propagation behavior of laminated coal reservoirs. We used physical experiments, such as direct shear test and Digital Image Correlation (DIC), along with finite element simulation and a finite element model; the results show that the tensile strength of bright coal is the lowest and that of dull coal is the greatest; the average cohesion and shear strength of the bright-dull coal interface are 0.418 MPa and 1.3778 MPa (σ = 3 MPa), respectively. Notably, behavioral differences are likely to impact the geometric evolution of hydraulic fractures. In the numerical models of hydraulic fracturing for a laminated coal reservoir, the hydraulic fracture propagates predominantly vertically as the interlayer has a lower elastic modulus and higher tensile strength. Because the interfacial shear strength is weak, the fractures can easily penetrate and propagate into the bedded interface between layers, and often, the distance of lateral slip increases into the interlayer interface. Thus, when dull coal is fractured, the geometry of the hydraulic fracture is often characterized as an isolated fracture distribution. The fracture then, rapidly propagates into the interlayer, activating the natural fractures in the bright coal reservoir, thus improving the fracture scale in the interlayers (model 2). However, as bright coal is a productive strata, the geometry of the hydraulic fracture is also dominated by crisscross network structures, and the fractures preferentially propagate along the interface (model 1). • The differences of mechanical properties that linked to the macrolithotype contribution were investigated systematically. •The impact of these sensitivity factors on hydraulic fracture geometry evolution was evaluated. •The influences of coal macrolithotype on hydraulic fracture geometry evolution were investigated. [ABSTRACT FROM AUTHOR]

Liang, Z.; Ji, D.; Zhang, X.; Lingyun, W.; Zhang, T.; Li, S.; Yong, J.; Luo, J.; Liu, Y., and Zeng, J., 2023. Carboniferous oceanic basin sediment-gravity flows in the margin of the Junggar Basin, NW China: Characterisation and implications for hydrocarbon potential and evolution pacing. Journal of Coastal Research, 39(5), 890–906. Charlotte (North Carolina), ISSN 0749-0208. Several Carboniferous deep-marine-sandstone reservoirs have recently been discovered in the Junggar Basin, NW China. These reservoir sandstones were deposited by sediment-gravity flows that occurred on the continental slope of the Junggar Basin, and they have high hydrocarbon exploration potential. In this study, careful observations and petrological and geochemical analyses of samples from outcrop sections of Carboniferous rocks from the Junggar Basin were conducted to establish the deep-marine sedimentary characteristics, depositional environments, and mechanism of these gravity-flow deposits, as well as a sedimentary model for their occurrence. The deep-marine, gravity-flow deposit types include those of turbidity currents, debris flows, and slumps. The debris-flow deposits can be divided into pebbly debris-flow deposits and sandy debris-flow deposits. Results allow the relationship between the type and nature of gravity flows and ocean basin evolution to be established. During the early Carboniferous, the ocean basin had sufficient space to accommodate incoming sediment, and the sediment transport distance was long. The gravity-flow sediments of this period are dominated by sandy debris-flow deposits and turbidity-flow deposits characterised by thin individual layers but thick accumulations of multiple deposits. With continuous narrowing of the oceanic basin during the late Carboniferous, the basin had a smaller accommodation space. The main types of gravity-flow deposition during this period were pebbly and sandy debris flows, with rare thin turbidity-flow deposits. These deposits were coarser grained than their early Carboniferous equivalents, and their cumulative thicknesses were smaller. The results of the study provide insights into the prediction of deep-marine reservoir sandstones and the distribution of hydrocarbons in the Junggar Basin. [ABSTRACT FROM AUTHOR]

[Display omitted] (a) μ-XRF mapping and Nb content distribution maps of dolomite-type Nb-REE-(Fe) ore, displaying the representative magmatic Nb mineralization; (b) μ-XRF mapping and Nb content distribution maps of fluorite-type (banded) Fe-REE-Nb ore, showing the typical hydrothermal Nb mineralization; (c) back-scattered-electron images of different kinds of niobium-bearing minerals in Bayan Obo Fe-REE-Nb deposits; (d) niobium-bearing mineral compositions (Wt %) of various Fe-REE-Nb ores in Bayan Obo deposit. • The Bayan Obo Fe-REE-Nb deposit contains huge amount of niobium resources. • Niobium occurrence and typical mineral compositions of different types of Fe-REE-Nb ores are determined. • Hydrothermal process plays an important role in controlling the migration and mineralization of niobium. The Bayan Obo Fe-REE-Nb deposit is the largest rare earth deposit in the world, which also contains huge amounts of niobium resources, hosting 83% of industrial reserves in China. The previous researches focused on the REE mineralogy, mineralization age and REE source, whereas only a few studies paid attention to the genesis of Nb mineralization. The REE and Nb might present systematic mineralization difference as the degree of REE and Nb mineralization is distinct in different types of ores in host dolomite. Many complicated factors such as low grade, fine-grained dissemination and complex mineral composition are the main obstacles to hinder the effective utilization of Nb. In this study, a variety of niobium-bearing minerals have been identified, including aeschynite, fergusonite, columbite, pyrochlore, fersmite, baotite, and ilmenorutile. The distribution regularity of niobium in various types of ores in the giant Bayan Obo Fe-REE-Nb deposit is asserted. In massive Nb-REE-Fe ore and dolomite-type Nb-REE-(Fe) ore, niobium-bearing minerals are represented by columbite, while niobium mineralization in aegirine-type Nb-REE-Fe ore is characterized by pyrochlore and aeschynite. The major niobium-bearing mineral in the riebeckite -type Nb-REE-(Fe) ore and fluorite-type (banded) Nb-REE-Fe ore is aeschynite, and major niobium-bearing mineral in biotite-type Nb-REE-Fe ore and diopside-type niobium ore is fergusonite. The μ-XRF results and SEM observations display that columbite contains dolomite, magnetite and monazite inclusions and show obvious genetic links with apatite. Columbite, apatite and magnetite in massive Fe-REE-Nb ore and dolomite-type Nb-REE-(Fe) ore occur at same mineral generation, both having magmatic origins. Pyrochlore from aegirine-type Fe-REE-Nb ore also showsclose genetic relationship with apatite, which is formed by fractional crystallization during the magmatic stage of carbonatite. Aeschynite in fluorite-type (banded) Fe-REE-Nb ore, riebeckite-type Nb-REE-(Fe) ore, and fergusonite in biotite-type Fe-REE-Nb ore and diopside-type niobium ore are large in grain size and have hydrothermal origins. Moreover, intensive Nb mineralization in a series of ores related to fluoritization and alkali-metasomatism demonstrates the critical role of hydrothermal process in niobium enrichment in the Bayan Obo deposit. Fluid-rock interaction leads to the generation of alteration minerals, such as fluorite, biotite and aegirine, and contributes to a slash of K, Na and/or F in hydrothermal fluids, facilitating precipitation of niobium-bearing minerals. By using scanning electron microscope (SEM), X-ray energy dispersive analysis (EDS), Micro-XRF spectral analysis (μ-XRF) and TESCAN Intergrated Mineral Analysis (TIMA), detailed mineralogical study on niobium occurrence and typical niobium mineral compositions in various types of Fe-REE-Nb ores was conducted to provide an important reference for mineral processing and niobium prospecting and give a deeper understanding of the niobium anomalous enrichment mechanism of the Bayan Obo Fe-REE-Nb deposit. [ABSTRACT FROM AUTHOR]

The Shanxi Rift System is an intracontinental rift system located between the North China Plain and Ordos Plateau, which was infilled with thousands of meters of Cenozoic fluvio-lacustrine deposits. A comprehensive chronological framework will help better understand the formation and evolutionary process of the rift system. Here, we present a new magnetochronology for the Datong Basin sedimentary sequence in the northern Shanxi Rift System based on high-resolution magnetostratigraphic investigations of the DY-1 core. Correlation of the recognized magnetic polarity sequence of the DY-1 core with the Astronomically Tuned Neogene Time Scale shows that the fluvio-lacustrine sequence in the Datong Basin spans from Chron C3Bn to Chron C1n. The age of the Datong Basin sedimentary sequence can thus be paleomagnetically constrained to an interval from the late Late Miocene to Middle Pleistocene. The basal age of the sediments is ca. 7.0 Ma, which indicates that the initial extension of the northern segment of the Shanxi Rift System was no later than 7.0 Ma. The Datong Basin in the northern Shanxi Rift System has experienced a three-stage evolution: During the initial stage (7.0–4.2 Ma), fluvial environments are dominant. Then during 4.2–1.8 Ma, lacustrine environments are developed due to dip-slip fault activities, as part of the Nihewan paleolake. After 1.8 Ma, the lake gradually shrank. The northeastward progressive growth and expansion of the Tibetan Plateau may have driven the evolution of the Shanxi Rift System. • We present a new magnetochronology for the Datong Basin sedimentary sequence. • The initial extension of the northern Shanxi Rift System was no later than 7.0 Ma. • The northeastward progressive growth of the Tibetan Plateau may have driven the evolution of the Shanxi Rift System. [ABSTRACT FROM AUTHOR]

The article presents a study on formation of Bayan Obo iron (Fe)-REE-Niobium (Nb) ore deposit in the Inner Mongolia, North China. Topics discussed include the Bayan Obo Group divided into two parts that is a lower regressive series (H1?H10) and an upper transgressive series (H11?H17), origin of H8 dolomite formation that is as crystallization of carbonatitic magma in origin and analysis of the REE mineralization using a model based on metasomatism caused by extreme REE-enriched fluids.