Sources and occurrence patterns of hydrocarbons in the surrounding rocks of coal seams: A case study of the Jurassic Yan'an Formation in the Xinzhuang mine field, Longdong area

Authors

• ZHANG Peng, State Key Laboratory of Continental Evolution and Early Life, Department of Geology, Northwest University, Xi’an 710069, ChinaFollow
• CHEN Dongdong, CCTEG Xi’an Research Institute (Group) Co., Ltd., Xi’an 710054, China;School of Civil Engineering and Architecture, Xi’an University of Technology, Xi’an 710048, ChinaFollow
• ZHAO Junfeng, State Key Laboratory of Continental Evolution and Early Life, Department of Geology, Northwest University, Xi’an 710069, China
• ZHENG Kaige, CCTEG Xi’an Research Institute (Group) Co., Ltd., Xi’an 710054, China
• WANG Chunxin, Qingyang Xinzhuang Coal Industry Co., Ltd., Qingyang 745200, China
• ZHOU Xingtian, State Key Laboratory of Continental Evolution and Early Life, Department of Geology, Northwest University, Xi’an 710069, China

Abstract

Objective and Methods This study aims to ascertain abnormal hydrocarbon outflows from the surrounding rocks of coal seams in the Jurassic Yan'an Formation within the Xinzhuang mine field in the Longdong area, southwestern Ordos Basin. Based on the fundamental principles of petroleum geology, sedimentology, and coal geology, this study systematically analyzed the sources, occurrence patterns, and primary controlling factors of hydrocarbons in the surrounding rocks of coal seams using methods including core observation, sample analysis, and statistical mapping. Results and Conclusions In the Xinzhuang mine field, hydrocarbon outflows are primarily identified in the floor of the No. 8 coal seam in the Yan'an Formation. Their hydrocarbons originate from the mature source rocks of the underlying seventh oil group of the Triassic Yanchang Formation (also referred to as the Chang 7 oil group). The hydrocarbons occur primarily as isolated hydrocarbon pockets or gas pockets within the fine- to medium-grained sandstone reservoirs of subaqueous distributary channels in the Chang 4+5 oil groups, exhibiting a distribution characterized by distinct macroscopic heterogeneity and vertical stratification. The reservoir distribution is generally controlled by sedimentary microfacies. Furthermore, the sandstone reservoirs in the Yanchang Formation underwent significant denudation and modification due to the tectonic uplift induced by the Indosinian movement at the end of the Late Triassic. Then, the fine-grained sediments of the Early Jurassic Fuxian Formation were superimposed on the reservoirs, contributing to the formation of potential reservoir-cap rock assemblages in paleogeomorphic highs such as low residual paleo-hills and slope spurs. Structural traps, including nose-like structures and anticlines formed from the Yanshanian to the Himalayan, further intensified the differential hydrocarbon enrichment, while well-developed strike-slip faults and associated fractures provided pathways for hydrocarbon migration. Governed by the coupling effects of sedimentary microfacies, paleogeomorphology, and local structural morphologies, hydrocarbon enrichment occurs primarily in areas with subaqueous distributary channel sands of the Yanchang Formation lying beneath the low residual paleo-hills or slope spurs of the Fuxian Formation. Most especially, in parts with superimposed local structural traps, which exhibit thin cap rocks and are close to coal seam floors, hydrocarbon outflows are prone to occur under mining disturbance. Analysis of dominant factors controlling hydrocarbon occurrence reveals that the risks of potential hydrocarbon outflows can be classified into levels I to III. Furthermore, zones with various risk levels were predicted. This study provides insights and assessment methodology regarding the sources, occurrence patterns, and hazard prediction of hydrocarbons in the surrounding rocks of coal seams, offering a scientific basis for the prevention and control of hydrocarbon outflows in the surrounding rocks of coal seams in the Xinzhuang mine field and other mining areas with similar geological conditions.

Keywords

hydrocarbon source, occurrence pattern, Jurassic coal seam, paleogeomorphology, structural trap, Ordos Basin

DOI

10.12363/issn.1001-1986.26.02.0098

Recommended Citation

ZHANG Peng, CHEN Dongdong, ZHAO Junfeng, et al. (2026) "Sources and occurrence patterns of hydrocarbons in the surrounding rocks of coal seams: A case study of the Jurassic Yan'an Formation in the Xinzhuang mine field, Longdong area," Coal Geology & Exploration: Vol. 54: Iss. 8, Article 12.
DOI: 10.12363/issn.1001-1986.26.02.0098
Available at: https://cge.researchcommons.org/journal/vol54/iss8/12

Reference

[1] 刘池阳. 鄂尔多斯盆地演化–改造动力学与多种能源矿产共存成藏(矿)[M]. 西安：西北大学出版社，2009.

[2] 邓军,王庆飞,高帮飞,等. 鄂尔多斯盆地多种能源矿产分布及其构造背景[J]. 地球科学,2006,31(3):330−336 DENG Jun,WANG Qingfei,GAO Bangfei,et al. Distribution and tectonic background of various energy resources in Ordos Basin[J]. Earth Science,2006,31(3):330−336

[3] 孙四清,陈冬冬,龙威成,等. 煤油气共存矿井油型气精准治理技术及工程实践[J]. 煤炭科学技术,2021,49(5):60−66 SUN Siqing,CHEN Dongdong,LONG Weicheng,et al. Technology of precise control of oil–type gas and engineering practice in coal mine with coal–oil–gas coexistence[J]. Coal Science and Technology,2021,49(5):60−66

[4] 赵继展,张群,郑凯歌,等. 黄陵矿区煤矿井下围岩喷涌气体致灾机理及防治措施[J]. 天然气工业,2018,38(11):114−121 ZHAO Jizhan,ZHANG Qun,ZHENG Kaige,et al. Disaster–causing mechanism of surrounding rock gas flowing underground in the Huangling coal mine and prevention measures[J]. Natural Gas Industry,2018,38(11):114−121

[5] 陈冬冬. 煤油气共生矿井围岩气多因素耦合区域预测技术:以鄂尔多斯盆地黄陵矿区为例[J]. 煤田地质与勘探,2018,46(2):49−53 CHEN Dongdong. Prediction technology of surrounding rock gas zones by multiple factor coupling in coal mines with coal–oil–gas coexistence[J]. Coal Geology & Exploration,2018,46(2):49−53

[6] 郑凯歌,孙四清,赵继展,等. 黄陵矿区围岩气体成因及致灾机理研究[J]. 煤炭科学技术,2021,49(8):139−146 ZHENG Kaige,SUN Siqing,ZHAO Jizhan,et al. Study on genetic and destructive mechanism of gas from surrounding rock in Huangling mining area[J]. Coal Science and Technology,2021,49(8):139−146

[7] 孙四清,曲少东,陈冬冬,等. 陕西黄陵二号煤矿203工作面煤层底板沉积微相与瓦斯展布规律研究[J]. 中国煤炭地质,2017,29(1):31−34 SUN Siqing,QU Shaodong,CHEN Dongdong,et al. Working face No. 203 coal floor sedimentary microfacies and gas distribution pattern study in Huangling No. 2 coalmine,Shaanxi[J]. Coal Geology of China,2017,29(1):31−34

[8] 王生全. 煤油气共生矿井的采面瓦斯涌出预测[J]. 煤田地质与勘探,2003,31(3):13−16 WANG Shengquan. The prediction of gas emission from combined mining face of the mine with coal and oil–gas symbiosis association[J]. Coal Geology & Exploration,2003,31(3):13−16

[9] 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

[10] 李得路,王行哲,孙学阳,等. 鄂尔多斯盆地煤油气共生矿井中原油来源及时空演化:以芦村矿区为例[J]. 煤炭学报,2025,50(9):4432−4449 LI Delu,WANG Xingzhe,SUN Xueyang,et al. Origin and spatial–temporal evolution of crude oil in coal–oil–gas symbiotic mines in Ordos Basin:Taking Lucun mining area as an example[J]. Journal of China Coal Society,2025,50(9):4432−4449

[11] 唐恩贤. 黄陵矿区煤层底板异常涌出气体成因类型[J]. 煤田地质与勘探,2015,43(6):8−11 TANG Enxian. Genetic type of abnormal gas emission from coal seam floor in Huangling mining area[J]. Coal Geology & Exploration,2015,43(6):8−11

[12] 牟全斌. 煤油气共生矿井底板油型气赋存特征及防治[J]. 能源与环保,2020,42(12):76−80 MOU Quanbin. Occurrence characteristics and prevention of oil–type gas in coal–gas symbiosis mine floor[J]. China Energy and Environmental Protection,2020,42(12):76−80

[13] 胡伯良. 塔里木盆地石油有机地球化学特征和油源问题探讨[J]. 石油与天然气地质,1981,2(4):359−368 HU Boliang. On the organic geochemical characteristics and oil–source correlations in Tarim Basin[J]. Oil & Gas Geology,1981,2(4):359−368

[14] 王启军. 油气运移的地质、地球化学(上)[J]. 地质科技情报,1984,3(3):157−166

[15] 张尚虎,黄建军,李昆,等. 西湖凹陷孔雀亭地区复合圈闭发育模式与油气富集差异控制因素[J]. 海洋地质与第四纪地质,2023,43(1):128−137 ZHANG Shanghu,HUANG Jianjun,LI Kun,et al. The model of compound traps development and controlling factors of hydrocarbon enrichment in Kongqueting area of the Xihu Sag[J]. Marine Geology & Quaternary Geology,2023,43(1):128−137

[16] 戴金星. 各类天然气的成因鉴别[J]. 中国海上油气(地质),1992,6(1):11−19 DAI Jinxing. Identification of various genetic natural gases[J]. China Offshore Oil and Gas (Geology),1992,6(1):11−19

[17] 戴金星,李剑,罗霞,等. 鄂尔多斯盆地大气田的烷烃气碳同位素组成特征及其气源对比[J]. 石油学报,2005,26(1):18−26 DAI Jinxing,LI Jian,LUO Xia,et al. Alkane carbon isotopic composition and gas source in giant gas fields of Ordos Basin[J]. Acta Petrolei Sinica,2005,26(1):18−26

[18] 宋岩,徐永昌. 天然气成因类型及其鉴别[J]. 石油勘探与开发,2005,32(4):24−29 SONG Yan,XU Yongchang. Origin and identification of natural gases[J]. Petroleum Exploration & Development,2005,32(4):24−29

[19] 刘恺德,姚凯文,陈能远,等. 黄陇煤田大佛寺井田煤层气成因机制研究[J]. 煤田地质与勘探,2022,50(11):115−124 LIU Kaide,YAO Kaiwen,CHEN Nengyuan,et al. Formation mechanism of coalbed methane in Dafosi mine field,Huanglong coalfield[J]. Coal Geology & Exploration,2022,50(11):115−124

[20] 刘厚宁,曹惠锋. 大佛寺井田煤层气地球化学特征及其成因分析[J]. 煤炭技术,2020,39(11):60−63 LIU Houning,CAO Huifeng. Dafosi mine field coalbed methane geochemical characteristics and genesis analysis[J]. Coal Technology,2020,39(11):60−63

[21] 孙丽娜,张中宁,吴远东,等. 生物标志化合物热成熟度参数演化规律及意义:以Ⅲ型烃源岩HTHP生排烃热模拟液态烃产物为例[J]. 石油与天然气地质,2015,36(4):573−580 SUN Lina,ZHANG Zhongning,WU Yuandong,et al. Evolution patterns and their significances of biomarker maturity parameters:A case study on liquid hydrocarbons from type Ⅲ source rock under HTHP hydrous pyrolysis[J]. Oil & Gas Geology,2015,36(4):573−580

[22] 游君君,杨希冰,雷明珠,等. 珠江口盆地珠三坳陷不同沉积环境下烃源岩和原油中长链三环萜烷、二环倍半萜烷分布特征及地球化学意义[J]. 天然气地球科学,2020,31(7):904−914 YOU Junjun,YANG Xibing,LEI Mingzhu,et al. The characteristics and significances of cheilanthane tricyclic terpanes and bicyclic sesquiterpanes in source rocks and oils under different depositional environments in Zhu Ⅲ Depression,Pearl River Mouth Basin[J]. Natural Gas Geoscience,2020,31(7):904−914

[23] 苏鹏,胡守志,李水福,等. 走滑断裂对原油性质的控制作用:以鄂尔多斯盆地南部泾河油田为例[J]. 地球科学,2023,48(6):2310−2323 SU Peng,HU Shouzhi,LI Shuifu,et al. Control of strike–slip faults on crude oil properties:Exemplified by Jinghe oilfield in south Ordos Basin[J]. Earth Science,2023,48(6):2310−2323

[24] 伍岳，秦学杰，夏冬冬，等. 鄂尔多斯盆地南缘中生界断缝体地质特征与油气富集主控因素[J/OL]. 吉林大学学报(地球科学版)，2025：1–12 [2025-06-24]. https：//doi. org/10. 13278/j. cnki. jjuese. 20250067. WU Yue，QIN Xuejie，XIA Dongdong，et al. Geological characteristics and main controlling factors of oil and gas enrichment in the Mesozoic fracture–bodies in the southern margin of the Ordos Basin[J/OL]. Journal of Jilin University (Earth Science Edition)，2025：1–12 [2025-06-24]. https：//doi. org/10. 13278/j. cnki. jjuese. 20250067.

[25] 董丽红,杜彦军,李军,等. 鄂尔多斯盆地中部延长组烃源岩生物标志化合物特征[J]. 西安科技大学学报,2018,38(4):604−610 DONG Lihong,DU Yanjun,LI Jun,et al. Biomarker characteristics of hydrocarbon source rocks of Yanchang Formation in central Ordos Basin[J]. Journal of Xi’an University of Science and Technology,2018,38(4):604−610

[26] 陆骋. 鄂尔多斯盆地彬长区块延长组原油地球化学特征及成因分析[J]. 石油地质与工程,2020,34(5):25−29 LU Cheng. Geochemical characteristics and cause analysis of crude oil from Yanchang Formation in Binchang Block,Ordos Basin[J]. Petroleum Geology and Engineering,2020,34(5):25−29

[27] 杨华,张文正. 论鄂尔多斯盆地长7段优质油源岩在低渗透油气成藏富集中的主导作用:地质地球化学特征[J]. 地球化学,2005,34(2):147−154 YANG Hua,ZHANG Wenzheng. Leading effect of the Seventh Member high–quality source rock of Yanchang Formation in Ordos Basin during the enrichment of low–penetrating oil–gas accumulation:Geology and geochemistry[J]. Geochimica,2005,34(2):147−154

[28] 张新乐,平宏伟,杨鑫,等. 鄂尔多斯盆地南缘泾河油田长7段烃源岩生、排烃期与油气成藏期对比[J]. 地质科技通报,2024,43(1):108−121 ZHANG Xinle,PING Hongwei,YANG Xin,et al. Comparison of hydrocarbon generation,expulsion periods,and accumulation periods of source rocks in Member 7 of the Yanchang Formation in the Jinghe oilfield,southern Ordos Basin[J]. Bulletin of Geological Science and Technology,2024,43(1):108−121

[29] 王成龙,张创. 鄂尔多斯盆地志丹地区延长组长6段滩坝沉积特征与生长模式[J]. 西安科技大学学报,2025,45(6):1222−1230 WANG Chenglong,ZHANG Chuang. Sedimentary characteristics and growth model of beach–bar sandbodies of Yanchang Formation Chang 6 Member in Zhidan area,Ordos Basin[J]. Journal of Xi’an University of Science and Technology,2025,45(6):1222−1230

[30] 郑庆华,刘乔,梁秀玲,等. 鄂尔多斯盆地陇东地区长4+5油层组沉积相展布特征[J]. 岩性油气藏,2019,31(6):26−35 ZHENG Qinghua,LIU Qiao,LIANG Xiuling,et al. Sedimentary facies distribution characteristics of Chang 4+5 reservoir in Longdong area,Ordos Basin[J]. Lithologic Reservoirs,2019,31(6):26−35

[31] 王锋,李刚,马瑶. 定靖地区侏罗系延安组辫状河沉积微相与储层构型[J]. 西安科技大学学报,2025,45(5):1008−1017 WANG Feng,LI Gang,MA Yao. Braided river microfacies and reservoir architecture of Jurassic Yan’an Formation in Dingbian–Jingbian area[J]. Journal of Xi’an University of Science and Technology,2025,45(5):1008−1017

[32] 李元昊,杨桂茹,彭建,等. 鄂尔多斯盆地前侏罗纪古地貌形成演化及沉积充填特征[J]. 世界地质,2020,39(1):56−71 LI Yuanhao,YANG Guiru,PENG Jian,et al. Formation and evolution of pre–Jurassic palaeogeomorphology and characteristics of sedimentary filling in Ordos Basin[J]. Global Geology,2020,39(1):56−71

[33] 袁珍,李文厚,朱静,等. 鄂尔多斯盆地陇东地区侏罗系古地貌恢复及其对石油聚集的影响[J]. 地质通报,2013,32(11):1806−1814 YUAN Zhen,LI Wenhou,ZHU Jing,et al. The restoration of pre–Jurassic paleogeomorphology and its influence on oil accumulation in Longdong area[J]. Geological Bulletin of China,2013,32(11):1806−1814

[34] 王建民,李文厚,任占利,等. 陕北志丹地区长2油藏油气富集规律研究[J]. 矿物岩石,2011,31(2):79−85 WANG Jianmin,LI Wenhou,REN Zhanli,et al. Research on regularity of petroleum accumulation and distribution for Chang 2 oil reservoir in Zhidan region,northern Shanxi[J]. Journal of Mineralogy and Petrology,2011,31(2):79−85

[35] 陈贺贺,朱筱敏,陈纯芳,等. 鄂尔多斯盆地彬长区块延长组生储盖组合与油气富集特征[J]. 岩性油气藏,2016,28(2):56−63 CHEN Hehe,ZHU Xiaomin,CHEN Chunfang,et al. Characteristics of source–reservoir–caprock assemblage and hydrocarbon accumulation of Yanchang Formation in Binchang Block,Ordos Basin[J]. Lithologic Reservoirs,2016,28(2):56−63

[36] 何发岐,齐荣,袁春艳,等. 鄂尔多斯盆地南部地区断裂构造与油气成藏关系再认识:以彬长地区为例[J]. 地球科学,2024,49(11):4082−4097 HE Faqi,QI Rong,YUAN Chunyan,et al. Further understanding of relationship between fault characteristics and hydrocarbon accumulation in Binchang area,Ordos Basin[J]. Earth Science,2024,49(11):4082−4097

[37] 杨桂林,任战利,何发岐,等. 鄂尔多斯盆地西南缘镇泾地区断缝体发育特征及油气富集规律[J]. 石油与天然气地质,2022,43(6):1382−1396 YANG Guilin,REN Zhanli,HE Faqi,et al. Fault–fracture body growth and hydrocarbon enrichment of the Zhenjing area,the southwestern margin of the Ordos Basin[J]. Oil & Gas Geology,2022,43(6):1382−1396