Geological factors controlling the occurrence of Carboniferous-Permian tar-rich coals in the Ningdong coalfield

Authors

HUANG Pengcheng, Institute of Geological Survey, China University of Geosciences, Wuhan 430074, China; Ningxia Hui Autonomous Region Bureau of Coal Geology, Yinchuan 750002, China; Ningxia Unconventional Natural Gas Exploration and Development Innovation Team, Yinchuan 750002, ChinaFollow
GUO Weiyong, Ningxia Hui Autonomous Region Bureau of Coal Geology, Yinchuan 750002, China
JI Xiaoyan, Ningxia Hui Autonomous Region Bureau of Coal Geology, Yinchuan 750002, China; Ningxia Unconventional Natural Gas Exploration and Development Innovation Team, Yinchuan 750002, China
CAI Feifei, Institute of Geological Survey, China University of Geosciences, Wuhan 430074, China; Ningxia Hui Autonomous Region Bureau of Coal Geology, Yinchuan 750002, China
ZHANG Zhifeng, Institute of Geological Survey, China University of Geosciences, Wuhan 430074, China; Ningxia Hui Autonomous Region Bureau of Coal Geology, Yinchuan 750002, China; Ningxia Unconventional Natural Gas Exploration and Development Innovation Team, Yinchuan 750002, China
HUANG Kang, Institute of Geological Survey, China University of Geosciences, Wuhan 430074, China; Ningxia Hui Autonomous Region Bureau of Coal Geology, Yinchuan 750002, China; Ningxia Unconventional Natural Gas Exploration and Development Innovation Team, Yinchuan 750002, China
CHENG Yunqiang, Ningxia Hui Autonomous Region Bureau of Coal Geology, Yinchuan 750002, China
LIU Zheng, Ningxia Hui Autonomous Region Bureau of Coal Geology, Yinchuan 750002, China
WANG Bei, Ningxia Hui Autonomous Region Bureau of Coal Geology, Yinchuan 750002, China; Ningxia Unconventional Natural Gas Exploration and Development Innovation Team, Yinchuan 750002, China
CHEN Rong, Ningxia Hui Autonomous Region Bureau of Coal Geology, Yinchuan 750002, China; Ningxia Unconventional Natural Gas Exploration and Development Innovation Team, Yinchuan 750002, China
SHI Qingmin, College of Geology and Environment, Xi’an University of Science and Technology, Xi’an 710054, ChinaFollow

Abstract

Objective The Ningdong Coalfield of the Ordos Basin boasts abundant tar-rich coal resources, of which tar-rich coals in the Carboniferous-Permian coal seams exhibit unique occurrence characteristics due to differences in thermal evolution and sedimentary environments. Methods This study analyzed the occurrence characteristics and critical material composition of tar-rich coals in the Hongdunzi and Siguquan mining areas. Based on this, it explored the controlling effects of the degree of coalification and sedimentary environment on the tar yield. Results and Conclusions The results indicate that the Carboniferous-Permian coal seams in the Ningdong Coalfield exhibit average tar yields ranging from 7.15% to 11.07%, which generally vary in different zones, different coal seams, and even different parts of the same coal seam. The degree of coalification is identified as a core geologic factor controlling the occurrence of tar-rich coals in the study area. With an increase in the degree of coalification, the tar yield trended upward initially and then downward, peaking at C_daf=84%. Under the action of coalification, a similar evolutionary trend can be observed between the H/C and O/C ratios and the tar yield. Meanwhile, there were significant positive correlations between active components (i.e., vitrinite and exinite) and the tar yield merely under C_daf <84%. Coal-forming parent materials, climatic conditions, and paleosalinity of water bodies exert minor impacts on the tar yield. In contrast, the reducibility and hydrodynamic conditions of water bodies indirectly affect the discreteness of the tar yield of coals at the same ranks. The vitrinite/inertinite ratio (V/I), gelification index (GI), ash composition index (K), U/Th ratio, and δU values indicate that coal-forming environment features deep water, occlusion, moisture, strong reducibility, and small quantities of woody tissues, which are conducive to the formation of tar-rich coals with a high tar yield. In contrast, indices such as ash yield and SiO₂+Al₂O₃ indicate strong hydrodynamic conditions and substantial quantities of terrigenous clast inputs, which are unfavorable for the formation of tar-rich coals with a high tar yield.

Keywords

tar-rich coal, tar yield, coalification degree, coal-forming environment, Carboniferous-Permian, Ningdong Coalfield

DOI

10.12363/issn.1001-1986.24.02.0106

Recommended Citation

HUANG Pengcheng, GUO Weiyong, JI Xiaoyan, et al. (2024) "Geological factors controlling the occurrence of Carboniferous-Permian tar-rich coals in the Ningdong coalfield," Coal Geology & Exploration: Vol. 52: Iss. 7, Article 13.
DOI: 10.12363/issn.1001-1986.24.02.0106
Available at: https://cge.researchcommons.org/journal/vol52/iss7/13

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