Microscopic Characteristics of and Gas Occurrence in Coal Rock in Benxi Formation, Ordos Basin

doi:10.7657/XJPG20250301

Abstract

Abstract:

Coal rock gas (CRG) in the Upper Carboniferous Benxi formation in the Ordos Basin is currently in the early stage of exploration and development, and knowledge regarding the coal rock’s microscopic composition, pore structure, and their controls on gas occurrence remains limited. By using techniques including petrographic microscopy, X-ray diffraction (XRD), micro-CT scanning, low-temperature CO₂ adsorption, low-temperature N₂ adsorption, high-pressure mercury intrusion, and high-pressure autoclave-gold tube pyrolysis simulation, etc., the maceral composition, industrial component, pore structure, and gas occurrence states in the No. 8 coal seam of the Benxi formation in the study area were investigated. The results show that the No. 8 coal seam is dominated by bright and semi-bright coals, with average vitrinite, inertinite, and exinite contents of 78.8%, 18.2%, and 1.0%, respectively. The coal rock exhibits an average fixed carbon content of 70.00% and an ash content of 13.90%, indicative of low-ash coal. The micropores, mesopores, and macropores contribute 75.7%, 14.4%, and 9.9% to the total pore volume, respectively, while their specific surface area proportions are 98.3%, 1.0%, and 0.7%, respectively. The micropores contribute the most to both total pore volume and specific surface area. The adsorbed gas and free gas account for 74.7% and 25.3% of the total gas content, respectively. The adsorbed gas content is positively correlated with micropore volume and micropore specific surface area, while the free gas content shows an approximately positive correlation with macropore volume.

Key words: Ordos Basin, Carboniferous, Benxi formation, coal rock, microscopic characteristic, pore structure, gas occurrence

CLC Number:

TE122

HUANG Yougen, ZHENG Xiaopeng, ZHANG Daofeng, HU Weiwei, HE Mengqing, WANG Bing. Microscopic Characteristics of and Gas Occurrence in Coal Rock in Benxi Formation, Ordos Basin[J]. Xinjiang Petroleum Geology, 2025, 46(3): 253-262.

Figures/Tables 13

Fig. 1.

Fig. 2.

Fig. 3.

Fig. 4.

Fig. 5.

Fig. 6.

Fig. 7.

Fig. 8.

Table 1.

Fig. 9.

Fig. 10.

Fig. 11.

Table 2.

References 32

[1]	赵喆, 徐旺林, 赵振宇, 等. 鄂尔多斯盆地石炭系本溪组煤岩气地质特征与勘探突破[J]. 石油勘探与开发, 2024, 51(2):234-247.
	ZHAO Zhe, XU Wanglin, ZHAO Zhenyu, et al. Geological characteristics and exploration breakthroughs of coal rock gas in Carboniferous Benxi formation,Ordos Basin,NW China[J]. Petroleum Exploration and Development, 2024, 51(2):234-247.
[2]	李国欣, 张水昌, 何海清, 等. 煤岩气:概念、内涵与分类标准[J]. 石油勘探与开发, 2024, 51(4):783-795. doi: 10.11698/PED.20240424
	LI Guoxin, ZHANG Shuichang, HE Haiqing, et al. Coal-rock gas:Concept,connotation and classification criteria[J]. Petroleum Exploration and Development, 2024, 51(4):783-795.
[3]	张道锋, 王冰, 王华, 等. 鄂尔多斯盆地中东部深层煤层气成藏富集规律[J]. 西安科技大学学报, 2024, 44(6):1165-1175.
	ZHANG Daofeng, WANG Bing, WANG Hua, et al. Enrichment law of deep coalbed methane accumulation in central and eastern Ordos Basin[J]. Journal of Xi’an University of Science and Technology, 2024, 44(6):1165-1175.
[4]	刘新社, 黄道军, 虎建玲, 等. 鄂尔多斯盆地中东部地区石炭系本溪组煤岩气储层特征[J]. 天然气工业, 2024, 44(10):51-62.
	LIU Xinshe, HUANG Daojun, HU Jianling, et al. Reservoir characteristics of Carboniferous Benxi formation coal-rock gas in the central and eastern Ordos Basin[J]. Natural Gas Industry, 2024, 44(10):51-62.
[5]	汤达祯, 王生维, 金振奎, 等. 煤储层物性控制机理及有利储层预测方法[M]. 北京: 科学出版社, 2010.
	TANG Dazhen, WANG Shengwei, JIN Zhenkui, et al. The control mechanism of coal reservoir property and predictive methods for favorable reservoirs[M]. Beijing: Science Press, 2010.
[6]	胡雄, 邬长武, 杨秀春, 等. 低渗透煤层微观孔隙结构与煤层气解吸规律[J]. 特种油气藏, 2024, 31(2):129-135. doi: 10.3969/j.issn.1006-6535.2024.02.015
	HU Xiong, WU Changwu, YANG Xiuchun, et al. Microscopic pore structure and coalbed methane desorption law in low-permeability coal seams[J]. Special Oil & Gas Reservoirs, 2024, 31(2):129-135.
[7]	王兴刚, 范谭广, 焦立新, 等. 三塘湖盆地煤炭地下气化地质评价与有利区域[J]. 新疆石油地质, 2023, 44(3):307-313.
	WANG Xinggang, FAN Tanguang, JIAO Lixin, et al. Geological evaluation and favorable areas of underground coal gasification in Santanghu Basin[J]. Xinjiang Petroleum Geology, 2023, 44(3):307-313.
[8]	聂志宏, 徐凤银, 时小松, 等. 鄂尔多斯盆地东缘深部煤层气开发先导试验效果与启示[J]. 煤田地质与勘探, 2024, 52(2):1-12.
	NIE Zhihong, XU Fengyin, SHI Xiaosong, et al. Outcomes and implications of pilot tests for deep coalbed methane production on the eastern margin of the Ordos Basin[J]. Coal Geology & Exploration, 2024, 52(2):1-12.
[9]	曹岩刚, 苏成, 王庆, 等. 鄂尔多斯盆地清涧-宜川地区上石炭统本溪组混积特征及沉积演化[J]. 大庆石油地质与开发, 2024, 43(6):29-38.
	CAO Yangang, SU Cheng, WANG Qing, et al. Hybrid sediments characteristics and sedimentary evolution of Upper Carboniferous Benxi formation in Qingjian-Yichuan area of Ordos Basin[J]. Petroleum Geology & Oilfield Development in Daqing, 2024, 43(6):29-38.
[10]	沈柏坪, 李荣相, 白洪涛, 等. 鄂尔多斯盆地宜川地区本溪组8号煤岩特征及成煤环境分析[J]. 特种油气藏, 2024, 31(6):32-38. doi: 10.3969/j.issn.1006-6535.2024.06.004
	SHEN Baiping, LI Rongxiang, BAI Hongtao, et al. Analysis of coal rock characteristics and coal-forming environment of the No.8 coal seam in the Benxi formation in Yichuan area,Ordos Basin[J]. Special Oil & Gas Reservoirs, 2024, 31(6):32-38.
[11]	牛小兵, 赵伟波, 史云鹤, 等. 鄂尔多斯盆地本溪组天然气成藏条件及勘探潜力[J]. 石油学报, 2023, 44(8):1240-1257. doi: 10.7623/syxb202308004
	NIU Xiaobing, ZHAO Weibo, SHI Yunhe, et al. Natural gas accumulation conditions and exploration potential of Benxi formation in Ordos Basin[J]. Acta Petrolei Sinica, 2023, 44(8):1240-1257. doi: 10.7623/syxb202308004
[12]	席胜利, 闫伟, 刘新社, 等. 鄂尔多斯盆地天然气勘探新领域、新类型及资源潜力[J]. 石油学报, 2024, 45(1):33-51. doi: 10.7623/syxb202401003
	XI Shengli, YAN Wei, LIU Xinshe, et al. New fields,new types and resource potentials of natural gas exploration in Ordos Basin[J]. Acta Petrolei Sinica, 2024, 45(1):33-51. doi: 10.7623/syxb202401003
[13]	徐凤银, 王成旺, 熊先钺, 等. 鄂尔多斯盆地东缘深部煤层气成藏演化规律与勘探开发实践[J]. 石油学报, 2023, 44(11):1764-1780. doi: 10.7623/syxb202311002
	XU Fengyin, WANG Chengwang, XIONG Xianyue, et al. Evolution law of deep methane reservoir formation and exploration and development practice in the eastern margin of Ordos Basin[J]. Acta Petrolei Sinica, 2023, 44(11):1764-1780. doi: 10.7623/syxb202311002
[14]	李芙蓉, 刘文汇, 王晓锋, 等. 鄂尔多斯盆地古生界天然气地球化学特征与成因[J]. 石油实验地质, 2023, 45(4):809-820.
	LI Furong, LIU Wenhui, WANG Xiaofeng, et al. Geochemical characteristics and genesis of Paleozoic natural gas in the Ordos Basin[J]. Petroleum Geology & Experiment, 2023, 45(4):809-820.
[15]	张晓莉. 鄂尔多斯盆地中部上古生界沉积相演化[J]. 地球科学与环境学报, 2005, 27(3):26-29.
	ZHANG Xiaoli. Sedimentary facies evolution of Upper Palaeozoic formation in Ordos Basin[J]. Journal of Earth Sciences and Environment, 2005, 27(3):26-29.
[16]	张晓波, 孙佳. 深部煤层气储层测井解释技术及应用分析[J]. 云南化工, 2021, 48(1):125-127.
	ZHANG Xiaobo, SUN Jia. Logging interpretation technology and application analysis of deep coalbed methane reservoir[J]. Yunnan Chemical Technology, 2021, 48(1):125-127.
[17]	邢亚楠, 张松航, 唐书恒, 等. 滇东老厂矿区煤层气储层地应力特征研究[J]. 煤炭科学技术, 2020, 48(6):199-206.
	XING Yanan, ZHANG Songhang, TANG Shuheng, et al. Study on in-situ stress characteristics of coalbed methane reservoir in Laochang mining area,eastern Yunnan[J]. Coal Science and Technology, 2020, 48(6):199-206.
[18]	郑小鹏, 王蕾蕾, 刘道天, 等. 基于分形理论的高煤阶煤层气储层气-水相渗计算方法及应用[J]. 煤矿安全, 2019, 50(7):10-13.
	ZHENG Xiaopeng, WANG Leilei, LIU Daotian, et al. Application and calculation method of gas-water relative permeability for high-rank coalbed methane reservoirs based on fractal theory[J]. Safety in Coal Mines, 2019, 50(7):10-13.
[19]	郭小军. 鄂尔多斯盆地石炭—二叠纪聚煤规律与煤层气勘探有利区优选[D]. 山东青岛: 中国石油大学(华东), 2010.
	GUO Xiaojun. Coal accumulation and target optimization for exploration of CBM in Permo-Carboniferous,Ordos Basin[D]. Qingdao, Shandong: China University of Petroleum(East China), 2010.
[20]	张鹏飞, 张仲达, 邱贻博, 等. 华北地区煤系地层油气资源研究现状及启示[J]. 油气地质与采收率, 2024, 31(4):96-111.
	ZHANG Pengfei, ZHANG Zhongda, QIU Yibo, et al. Research progress of oil and gas resources in coal-bearing strata in north China and its implications[J]. Petroleum Geology and Recovery Efficiency, 2024, 31(4):96-111.
[21]	徐长贵, 季洪泉, 王存武, 等. 鄂尔多斯盆地东缘临兴-神府区块深部煤层气富集规律与勘探对策[J]. 煤田地质与勘探, 2024, 52(8):1-11.
	XU Changgui, JI Hongquan, WANG Cunwu, et al. Enrichment patterns and exploration countermeasures of deep coalbed methane in the Linxing-Shenfu block on the eastern margin of the Ordos Basin[J]. Coal Geology & Exploration, 2024, 52(8):1-11.
[22]	孔令印, 李剑锋, 吴凯, 等. 鄂尔多斯盆地黄陵—铜川地区延安组煤矿原油成因[J]. 新疆石油地质, 2024, 45(1):35-46.
	KONG Lingyin, LI Jianfeng, WU Kai, et al. Origin of crude oil from coal mine of Yan’an formation in Huangling-Tongchuan area,Ordos Basin[J]. Xinjiang Petroleum Geology, 2024, 45(1):35-46.
[23]	姚征, 李华兵, 李宁. 韩城矿区山西组煤层气储层特征研究[J]. 煤炭技术, 2021, 40(5):96-99.
	YAO Zheng, LI Huabing, LI Ning. Study on coalbed methane reservoir characteristics of Shanxi formation in Hancheng mining area[J]. Coal Technology, 2021, 40(5):96-99.
[24]	李伟, 申建, 李超, 等. 沁水盆地榆社-武乡区块深部煤层气赋存条件及开发甜点预测[J]. 大庆石油地质与开发, 2023, 42(4):9-19.
	LI Wei, SHEN Jian, LI Chao, et al. Occurrence conditions and development sweet spots prediction of deep coalbed methane in Yushe-Wuxiang block of Qinshui Basin[J]. Petroleum Geology & Oilfield Development in Daqing, 2023, 42(4):9-19.
[25]	蔡杰, 沈云飞. 响水煤矿煤层气储层特征研究[J]. 中外能源, 2020, 25(8):23-27.
	CAI Jie, SHEN Yunfei. Study on characteristics of coalbed methane reservoir in Xiangshui coal mine[J]. Sino-Global Energy, 2020, 25(8):23-27.
[26]	朱文涛, 李小刚, 任勇, 等. 基于CT扫描的煤岩孔隙结构全孔径表征[J]. 特种油气藏, 2024, 31(4):71-80. doi: 10.3969/j.issn.1006-6535.2024.04.009
	ZHU Wentao, LI Xiaogang, REN Yong, et al. Full pore size characterization of coal pore structure based on CT scanning[J]. Special Oil & Gas Reservoirs, 2024, 31(4):71-80.
[27]	邓泽, 王红岩, 姜振学, 等. 深部煤储层孔裂隙结构对煤层气赋存的影响:以鄂尔多斯盆地东缘大宁-吉县区块为例[J]. 煤炭科学技术, 2024, 52(8):106-123.
	DENG Ze, WANG Hongyan, JIANG Zhenxue, et al. Influence of deep coal pore and fracture structure on occurrence of coalbed methane:A case study of Daning-Jixian block in eastern margin of Ordos Basin[J]. Coal Science and Technology, 2024, 52(8):106-123.
[28]	刘大锰, 李振涛, 蔡益栋. 煤储层孔-裂隙非均质性及其地质影响因素研究进展[J]. 煤炭科学与技术, 2015, 43(2):10-15.
	LIU Dameng, LI Zhentao, CAI Yidong. Study progress on pore-crack heterogeneity and geological influence factors of coal reservoir[J]. Coal Science and Technology, 2015, 43(2):10-15.
[29]	侯雨庭, 周国晓, 黄道军, 等. 鄂尔多斯盆地纳林河地区煤岩气成藏地质特征[J]. 石油与天然气地质, 2024, 45(6):1605-1616.
	HOU Yuting, ZHOU Guoxiao, HUANG Daojun, et al. Geological characteristics of coal-rock gas accumulation in the Nalinhe area,Ordos Basin[J]. Oil & Gas Geology, 2024, 45(6):1605-1616.
[30]	李阳, 张玉贵, 张浪, 等. 基于压汞、低温N₂吸附和CO₂吸附的构造煤孔隙结构表征[J]. 煤炭学报, 2019, 44(4):1188-1196.
	LI Yang, ZHANG Yugui, ZHANG Lang, et al. Characterization on pore structure of tectonic coals based on the method of mercury intrusion,carbon dioxide adsorption and nitrogen adsorption[J]. Journal of China Coal Society, 2019, 44(4):1188-1196.
[31]	李明瑞, 史云鹤, 范立勇, 等. 鄂尔多斯盆地上古生界本溪组8#煤岩煤岩气与致密砂岩气主要气藏特征对比[J]. 石油与天然气地质, 2024, 45(6):1590-1604.
	LI Mingrui, SHI Yunhe, FAN Liyong, et al. Comparison of main reservoir characteristics between deep coal-rock gas of the No.8 coal seam of the Upper Paleozoic Benxi formation and tight sand gas reservoirs,Ordos Basin[J]. Oil & Gas Geology, 2024, 45(6):1590-1604.
[32]	黄文魁. 库车坳陷煤系烃源岩生烃动力学和地球化学特征研究[D]. 广州: 中国科学院广州地球化学研究所, 2019.
	HUANG Wenkui. Hydrocarbon generation kinetics and geochemical characteristics of coaly source rocks in the Kuqa depression[D]. Guangzhou: Guangzhou Institute of Geochemistry,Chinese Academy of Sciences, 2019.

井名	深度/m	低温CO₂吸附		低温N₂吸附		高压压汞
井名	深度/m	孔体积/ （cm³·g^-1）	比表面积/ （m²·g^-1）	孔体积/ （cm³·g^-1）	比表面积/ （m²·g^-1）	孔体积/ （cm³·g^-1）	比表面积/ （m²·g^-1）
A32井	3 400.8	0.041 0	135.52	0.002 2	1.08	0.005 4	0.93
A36井	2 804.6	0.062 2	199.40	0.003 0	1.11	0.004 8	0.84
A36井	2 805.6	0.063 2	206.71	0.004 1	0.81	0.003 5	0.97
A36井	2 809.9	0.053 3	172.11	0.004 1	1.00	0.003 9	0.99
A55井	2 178.8	0.029 4	89.22	0.013 0	2.32	0.005 7	1.32
A78井	2 353.2	0.031 7	96.03	0.006 3	1.01	0.005 1	0.84
A78井	2 354.4	0.049 5	150.61	0.005 2	0.64	0.007 1	1.38
A88井	2 505.1	0.068 2	239.60	0.007 2	2.21	0.007 1	1.46
G11井	3 258.1	0.011 7	36.14	0.006 0	1.10	0.005 6	1.22
G11井	3 261.7	0.023 1	72.73	0.030 4	2.52	0.006 4	1.13

镜质体反射率/%	总有机碳产气率/（mg·g^-1）	面孔率/%		不同孔隙占比/%
镜质体反射率/%	总有机碳产气率/（mg·g^-1）	有机孔	无机孔	微孔	介孔	宏孔
0.55	2.1	0.9	2.3	20.3	32.4	47.3
0.85	4.3	1.5	2.7	17.9	31.2	50.9
1.02	8.6	2.0	3.0	22.1	32.5	45.4
1.41	19.4	3.2	2.8	33.2	29.8	37.0
1.59	26.4	3.6	2.4	45.5	29.2	25.3
1.90	42.9	4.0	1.9	57.1	27.1	15.8
2.14	54.4	4.3	1.4	75.9	18.5	5.6
3.52	102.4	3.9	0.4	78.6	6.2	15.2