Effect of paleoclimate and paleoenvironment on organic matter accumulation in lacustrine shale: Constraints from lithofacies and element geochemistry in the northern Qaidam Basin, NW China

Hou, Haihai; Shao, Longyi; Li, Yonghong; Liu, Lei; Liang, Guodong; Zhang, Wenlong; Wang, Xuetian; Wang, Weichao

doi:10.1016/j.petrol.2021.109350

Cited by 44 publications

(34 citation statements)

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“…Among them, the ranges of FC ad in Jiaozuo, Anhe, and Huaibei coals are 75.69–86.75% (82.94% on average), 65.68–80.39% (73.39% on average), and 56.87–80.94% (68.69% on average), respectively. FC ad can reflect the metamorphic degree of coals to a certain extent, so it has a good linear positive correlation with R o,max (Figure d).…”

Section: Resultsmentioning

confidence: 96%

Study on the Applicability of Reservoir Fractal Characterization in Middle–High Rank Coals with NMR: Implications for Pore-Fracture Structure Evolution within the Coalification Process

et al. 2021

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In order to evaluate the applicability of the pore-fracture structure fractal characterizations in coal reservoirs and confirm the internal relationships between the porosity, permeability, coal metamorphic grade, and pore-fracture structure, the pore-fracture features of 21 middle–high rank coal samples from Anhe, Jiaozuo, and Huaibei coalfields in northern China were investigated using a low-field nuclear magnetic resonance (NMR). All the coal samples are characterized by low moisture content (M ad), low and medium ash yield (A ad), and high vitrinite (V) in coal maceral. The adsorption space fractal dimension (D A) is positively correlated with the Langmuir volume (V L) under the three-peak transverse relaxation time (T 2) spectrum. The fractal dimension of all effective T 2 points under saturated water (D NMR) is positively correlated with V L and the adsorption pore volume, but negatively correlated with the volume ratio of seepage pores and fractures. The free flow space fractal dimension (D M) is negatively correlated with the porosity of full saturated water (ΦF) and the porosity of movable water (ΦM). There is a negative correlation between ΦF and the seepage space fractal dimension (D S) in the coal samples with one-peak and two-peak T2 spectra, but a positive correlation can be found with the three-peak T2 spectrum. Therefore, it is necessary to consider the types of T2 spectral peak as a prerequisite to analyze the correlations between pore-fracture parameters and NMR fractal dimensions. With the increase of coal rank, the adsorption pore content, ΦF, and bulk volume immovable (BVI) fraction first increase and then decrease, whereas the seepage pore content, fracture development, bulk volume movable (BVM) fraction, and BVM/BVI first decrease and then increase. The inflection points of these changes correspond to the maximum vitrinite reflectance (R o,max) at 2.6–2.8%, which would be attributed to the third coalification jump. Generally, D A is the fractal dimension representing the coal pore surface, and D S and D M are closely related to the pore structure. Furthermore, D NMR not only represents the roughness of the pore surface but also the complexity of the pore structure.

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Section: Resultsmentioning

confidence: 96%

Study on the Applicability of Reservoir Fractal Characterization in Middle–High Rank Coals with NMR: Implications for Pore-Fracture Structure Evolution within the Coalification Process

et al. 2021

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“…13, it was 1.723 m 2 /g (a difference of more than 20 times). Therefore, factors other than the coal macrolithotype (e.g., degree of metamorphism, pore filling, primary structure, and later structure) can also affect coal pore structures. ,, …”

Section: Discussionmentioning

confidence: 99%

Coal Macrolithotype Distribution and Its Genetic Analyses in the Deep Jiaozuo Coalfield Using Geophysical Logging Data

et al. 2021

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Coal macrolithotypes are closely correlated with coal macerals and pore–fracture structures, which greatly influence the changes in gas content and the coal structure. Traditional macrolithotype identification in coalbed methane (CBM) wells mostly depends on core drilling observation, which is expensive, time-consuming, and difficult for broken core extraction. Geophysical logging is a quick and effective method to address this issue. We obtained coal cores from 75 wells in the deep regions of the Jiaozuo Coalfield, northern China, quantitatively analyzed the logging cutoff number corresponding to various macrolithotypes, and established natural γ (GR), deep lateral resistivity (LLD), and γ–γ log (GGL) response rules for each coal macrolithotype. The formation mechanisms of different coal macrolithotypes are discussed from the perspective of coal facies and pore structures. The results show that GGL decreased but GR and LLD increased from bright coal to dull coal. Most coal macrolithotypes can be distinguished based on the established thresholds of various logging curves. However, excessively high or low ash yields significantly affect the validity of identification. The vertical coal macrolithotypes attributed to the peat marsh environment in Shanxi Formation mostly comprise three to six sublayers; dull or semi-dull coals are predominant close to the 2 1 coal seam, and the bright or semi-bright types usually appear in the middle part. The semi-bright and bright coals are usually vitrinite rich, whereas the semi-dull and dull coals are primarily inertinite rich. For pore structure arguments, the highest average specific surface area ( S BET ) and the total pore volume ( V BJH ) are found in bright coals, followed by dull and semi-bright coals; those of semi-dull coals are the lowest. However, S BET and V BJH change significantly for different samples, even though the coal macrolithotype is the same. Therefore, the macrolithotype is not the key factor determining the coal parameters of pore structures. Rapid and effective identification of coal macrolithotypes can help determine the CBM enrichment area, the CBM well location, and the exploration horizon.

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“…Coal-bearing sequences were deposited along the southern Junggar Basin due to tectonic extension and subsidence during the Early and Middle Jurassic, when warm and humid climates were developed (Graham et al, 1990;Carroll et al, 2010;Hou et al, 2022a). The Lower and Middle Jurassic coal-bearing sequences of the southern Junggar Basin have a total thickness of about 2000 m (~6,600 ft).…”

Section: Coal-bearing Sequences and Coal Seamsmentioning

confidence: 99%

Coalbed methane accumulation, in-situ stress, and permeability of coal reservoirs in a complex structural region (Fukang area) of the southern Junggar Basin, China

Li²,

Pan³

et al. 2023

Front. Earth Sci.

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The enrichment of coalbed methane (CBM), in-situ stress field, and permeability are three key factors that are decisive to effective CBM exploration. The southern Junggar Basin is the third large CBM basin in China but is also known for the occurrence of complex geological structures. In this study, we take the Fukang area of the southern Junggar Basin as an example, coalbed methane accumulation and permeability, and their geological controls were analyzed based on the determination of geological structures, in-situ stress, gas content, permeability, hydrology and coal properties. The results indicate that gas contents of the Fukang coal reservoirs are controlled by structural framework and burial depth, and high-to-ultra-high thickness of coals has a slightly positive effect on gas contents. Perennial water flow (e.g., the Baiyanghe River) favors gas accumulation by forming a hydraulic stagnant zone in deep reservoirs, but can also draw down gas contents by persistent transportation of dissolved gases to ground surfaces. Widely developed burnt rocks and sufficient groundwater recharge make microbial gases an important gas source in addition to thermogenic gases. The in-situ stress field of the Fukang area (700–1,500 m) is dominated by a normal stress regime, characterized by vertical stress > maximum horizontal stress > minor horizontal stress. Stress ratios, including lateral stress coefficient, natural stress ratios, and horizontal principal stress ratio are all included in the stress envelopes of China. Permeability in the Fukang area is prominently partitioned into two distinct groups, one group of low permeability (0.001–0.350 mD) and the other group of high permeability (0.988–16.640 mD). The low group of permeability is significantly formulated by depth-dependent stress variations, and the high group of permeability is controlled by the relatively high structural curvatures in the core parts of synclines and the distance to the syncline core. Meanwhile, coal deformation and varying dip angles intensify the heterogeneity and anisotropy of permeability in the Fukang area. These findings will promote the CBM recovery process in China and improve our understanding of the interaction between geological conditions and reservoir parameters and in complex structural regions.

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Effect of paleoclimate and paleoenvironment on organic matter accumulation in lacustrine shale: Constraints from lithofacies and element geochemistry in the northern Qaidam Basin, NW China

Cited by 44 publications

References 54 publications

Study on the Applicability of Reservoir Fractal Characterization in Middle–High Rank Coals with NMR: Implications for Pore-Fracture Structure Evolution within the Coalification Process

Study on the Applicability of Reservoir Fractal Characterization in Middle–High Rank Coals with NMR: Implications for Pore-Fracture Structure Evolution within the Coalification Process

Coal Macrolithotype Distribution and Its Genetic Analyses in the Deep Jiaozuo Coalfield Using Geophysical Logging Data

Coalbed methane accumulation, in-situ stress, and permeability of coal reservoirs in a complex structural region (Fukang area) of the southern Junggar Basin, China

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