Study on Organic Petrology Characteristics of the Wufeng-Longmaxi Formation Black Shale, Sichuan Basin

doi:10.19657/j.geoscience.1000-8527.2022.046

Abstract

Abstract:

At present, there is no unified classification and definition of organic macerals in the Wufeng-Longmaxi Formation black shale, which made it difficult for regional shale gas exploration and evaluation. In this study, organic macerals in the Wufeng-Longmaxi Formation black shale from the Sichuan Basin were identified and summarized via optical microscopic observation of polished blocks and organic geochemistry (TOC, δ¹³C_org), and their origins and organic matter types were determined. Our results show that organic macerals are mainly composed of the marine vitrinite, sapropelinite, organic zooclast and secondary groups. Among them, marine vitrinite group consists of round-/rod-shaped structureless vitrinite, and displays strong light reflection, but it is only locally distributed. The sapropelinite group is mainly composed of structureless sapropelinite, and is widely developed in organic-rich shale, which is the product of algal materials that underwent geological processes of thermal degradation. The organic zooclast group includes graptolite epidermis, chitinozoans and radiolarians. Meanwhile, the secondary group is composed of secondary bituminites, which is widely developed in matrix porosity of shales and is amorphous. The sapropelinite and secondary groups are the major types of organic macerals in the shales of Wufeng-Longmaxi Formation, whereas organic zooclast and marine vitrinite groups are less common. The organic matter type of studied shales is predominately type Ⅰ-Ⅱ₁ kerogen. Moreover, the relative contents of sapropelinite and secondary groups increase, and organic matter type tends to oil-prone, contributing to their greater potentials of hydrocarbon generation.

Key words: organic maceral, organic matter type, organic carbon isotope, shale gas

CLC Number:

LIU Siyi, GAO Ping, XIAO Xianming, LIU Ruobing, QIN Jing, YUAN Tao, WANG Xu. Study on Organic Petrology Characteristics of the Wufeng-Longmaxi Formation Black Shale, Sichuan Basin[J]. Geoscience, 2022, 36(05): 1281-1291.

Figures/Tables 10

Fig.1 Palaeogeographic map of the Late Ordovician-Early Silurian Sichuan Basin and sampling locations (modified from reference [2])

Table 1 Basic information and organic geochemical results of samples

井位	样品号	深度 /m	层位	岩性	TOC /%	δ¹³C_org /‰	BR_o /%	EqV $R o *$ /%
PS1 井	PS1-02	5 964.50	五峰组	黑色页岩	4.58	-30.9	/	/
	PS1-03	5 963.00	五峰组	黑色页岩	2.91	-30.0	/	/
	PS1-05	5 959.20	龙马溪组	黑色页岩	5.43	-30.9	2.73	2.83
	PS1-16	5 943.76	龙马溪组	黑色页岩	2.51	-29.7	/	/
	PS1-18	5 939.66	龙马溪组	黑色页岩	1.44	-30.1	/	/
	PS1-22	5 933.36	龙马溪组	黑色页岩	3.61	-30.2	2.80	2.90
DY5 井	DY5-01	3 816.69	五峰组	黑色页岩	4.94	-30.9	/	/
	DY5-03	3 813.60	五峰组	黑色页岩	4.85	-31.0	/	/
	DY5-04	3 811.20	龙马溪组	黑色页岩	5.25	-30.6	/	/
	DY5-10	3 801.60	龙马溪组	黑色页岩	3.37	-29.9	/	/
	DY5-16	3 789.40	龙马溪组	黑色页岩	2.28	-29.3	2.95	3.04
JY4 井	JY4-02	2 594.80	五峰组	黑色页岩	4.71	-30.3	/	/
	JY4-05	2 591.70	五峰组	黑色页岩	5.38	-30.4	/	/
	JY4-07	2 588.21	龙马溪组	黑色页岩	7.10	-30.7	3.30	3.38
	JY4-19	2 565.80	龙马溪组	黑色页岩	3.55	-30.5	/	/
	JY4-30	2 545.20	龙马溪组	黑色页岩	1.88	-29.9	/	/

Table 1 Basic information and organic geochemical results of samples

井位	样品号	深度 /m	层位	岩性	TOC /%	δ¹³C_org /‰	BR_o /%	EqV $R o *$ /%
PS1 井	PS1-02	5 964.50	五峰组	黑色页岩	4.58	-30.9	/	/
	PS1-03	5 963.00	五峰组	黑色页岩	2.91	-30.0	/	/
	PS1-05	5 959.20	龙马溪组	黑色页岩	5.43	-30.9	2.73	2.83
	PS1-16	5 943.76	龙马溪组	黑色页岩	2.51	-29.7	/	/
	PS1-18	5 939.66	龙马溪组	黑色页岩	1.44	-30.1	/	/
	PS1-22	5 933.36	龙马溪组	黑色页岩	3.61	-30.2	2.80	2.90
DY5 井	DY5-01	3 816.69	五峰组	黑色页岩	4.94	-30.9	/	/
	DY5-03	3 813.60	五峰组	黑色页岩	4.85	-31.0	/	/
	DY5-04	3 811.20	龙马溪组	黑色页岩	5.25	-30.6	/	/
	DY5-10	3 801.60	龙马溪组	黑色页岩	3.37	-29.9	/	/
	DY5-16	3 789.40	龙马溪组	黑色页岩	2.28	-29.3	2.95	3.04
JY4 井	JY4-02	2 594.80	五峰组	黑色页岩	4.71	-30.3	/	/
	JY4-05	2 591.70	五峰组	黑色页岩	5.38	-30.4	/	/
	JY4-07	2 588.21	龙马溪组	黑色页岩	7.10	-30.7	3.30	3.38
	JY4-19	2 565.80	龙马溪组	黑色页岩	3.55	-30.5	/	/
	JY4-30	2 545.20	龙马溪组	黑色页岩	1.88	-29.9	/	/

Table 2 Organic maceral classification for the shales of the Wufeng-Longmaxi Formation, Sichuan Basin

显微组分类别	显微组分组	显微组分
内源类 (海相的)	海相镜质组	无结构海相镜质体
	腐泥组	无结构腐泥体
		笔石表皮体
	动物有机碎屑组	几丁虫壳壁体
		放射虫有机碎屑体
次生类(成岩的)	次生组	次生沥青体

Fig.2 Microphotographs of organic petrological characteristics of the marine vitrinite group in the Wufeng-Longmaxi Formation shale

Fig.3 Microphotographs of organic petrological characteristics of the sapropelinite group in the Wufeng-Longmaxi Formation shale

Fig.4 Microphotographs of organic petrological characteristics of the organic zooclast group in the Wufeng-Longmaxi Formation shale

Fig.5 Microphotographs of organic petrological characteristics of the secondary group in the Wufeng-Longmaxi Formation shale

Table 3 Relative organic macerals contents in the Wufeng-Longmaxi Formation shale

样品	(腐泥组+次生组)/%	动物有机碎屑组/%	海相镜质组/%
PS1-02	82.77	17.23	0
PS1-03	84.98	13.36	1.66
PS1-05	88.14	6.96	4.90
PS1-16	47.34	45.08	7.58
PS1-18	73.65	22.99	3.36
PS1-22	76.67	18.37	4.96
JY4-02	69.12	18.65	12.23
JY4-05	70.50	25.94	3.56
JY4-07	61.91	26.94	11.15
JY4-19	68.13	23.67	8.20
JY4-30	50.65	40.40	8.95
DY5-01	60.32	27.49	12.19
DY5-03	65.83	21.38	12.79
DY5-04	50.93	40.43	8.64
DY5-10	85.86	13.15	0.99
DY5-16	50.72	33.77	15.51

Fig.6 Ternary plot for the various organic macerals in the Wufeng-Longmaxi Formation shale from the Sichuan Basin (unit:%)

Fig.7 Scatter plots of relative contents of organic macerals and organic geochemical parameters of the Wufeng-Longmaxi Formation shale from Sichuan Basin

References 46

[1]	聂海宽, 张金川, 包书景, 等. 四川盆地及其周缘上奥陶统-下志留统页岩气聚集条件[J]. 石油与天然气地质, 2012, 33(3): 335-345.
[2]	郭彤楼, 张汉荣. 四川盆地焦石坝页岩气田形成与富集高产模式[J]. 石油勘探与开发, 2014, 41(1): 28-36.
[3]	肖贤明, 王茂林, 魏强, 等. 中国南方下古生界页岩气远景区评价[J]. 天然气地球科学, 2015, 26(8): 1433-1445.
[4]	龙胜祥, 冯动军, 李凤霞, 等. 四川盆地南部深层海相页岩气勘探开发前景[J]. 天然气地球科学, 2018, 29(4): 443-451.
[5]	何治亮, 聂海宽, 胡东风, 等. 深层页岩气有效开发中的地质问题--以四川盆地及其周缘五峰组-龙马溪组为例[J]. 石油学报, 2020, 41(4): 379-391. DOI
[6]	LOUCKS R G, REED R M, RUPPEL S C, et al. Spectrum of pore types and networks in mudrocks and a descriptive classification for matrix-related mudrock pores[J]. AAPG Bulletin, 2012, 96: 1071-1098. DOI URL
[7]	曾庆辉, 钱玲, 刘德汉, 等. 富有机质的黑色页岩和油页岩的有机岩石学特征与生、排烃意义[J]. 沉积学报, 2006, 24(1): 113-122.
[8]	魏志红. 富有机质页岩有机质孔发育差异性探讨--以四川盆地五峰组-龙马溪组笔石页岩为例[J]. 成都理工大学学报(自然科学版), 2015, 42(3): 361-365.
[9]	腾格尔, 卢龙飞, 俞凌杰, 等. 页岩有机质孔隙形成、保持及其连通性的控制作用[J]. 石油勘探与开发, 2021, 48(4): 687-699.
[10]	唐相路, 姜振学, 李卓, 等. 渝东南地区龙马溪组高演化页岩微纳米孔隙非均质性及主控因素[J]. 现代地质, 2016, 30(1): 163-171.
[11]	赵建华, 金之钧, 金振奎, 等. 岩石学方法区分页岩中有机质类型[J]. 石油实验地质, 2016, 38(4): 514-520,527.
[12]	谢国梁, 刘树根, 焦堃, 等. 受显微组分控制的深层页岩有机质孔隙:四川盆地五峰组-龙马溪组有机质组分分类及其孔隙结构特征[J]. 天然气工业, 2021, 41(9): 23-34.
[13]	钟宁宁, 秦勇. 碳酸盐岩有机岩石学--显微组分特征、成因、演化及其与油气关系[M]. 北京: 科学出版社, 1995: 14-33.
[14]	肖贤明, 刘德汉, 傅家谟. 海相镜质体--海相烃源岩中一种重要生烃母质[J]. 石油学报, 1997, 18(1): 46-50.
[15]	陶树, 汤达祯, 伍大茂, 等. 中、上扬子区下组合烃源岩有机岩石学特征[J]. 中国矿业大学学报, 2010, 39(4): 575-581,590.
[16]	罗情勇, 郝婧玥, 李可文, 等. 下古生界有机质成熟度评价新参数:笔石表皮体光学特征再研究[J]. 地质学报, 2019, 93(9): 2362-2371.
[17]	LUO Q, FARIBORZ G, ZHONG N, et al. Graptolites as fossil geo-thermometers and source material of hydrocarbons: An overview of four decades of progress[J]. Earth-Science Reviews, 2020, 200: 103000. DOI URL
[18]	LUO Q, ZHANG L, ZHONG N, et al. Thermal evolution behavior of the organic matter and a ray of light on the origin of vitrinite-like maceral in the Mesoproterozoic and Lower Cambrian black shales: Insights from artificial maturation[J]. International Journal of Coal Geology, 2021, 244: 103813. DOI URL
[19]	HACKLEY P C, CARDOTT B J. Application of organic petrography in North American shale petroleum systems: A review[J]. International Journal of Coal Geology, 2016, 163: 8-51. DOI URL
[20]	仰云峰. 川东南志留系龙马溪组页岩沥青反射率和笔石反射率的应用[J]. 石油实验地质, 2016, 38(4): 466-472.
[21]	周圆圆. 南方志留系龙马溪页岩成熟度研究[D]. 北京: 中国石油大学(北京), 2017.
[22]	王晔, 邱楠生, 仰云峰, 等. 四川盆地五峰-龙马溪组页岩成熟度研究[J]. 地球科学, 2019, 44(3): 953-971.
[23]	SCHOENHERR J, LITTKE R, URAI J L, et al. Polyphase thermal evolution in the Infra-Cambrian Are Group (South Oman Salt Basin) as deduced by maturity of solid reservoir bitumen[J]. Organic Geochemistry, 2007, 38(8): 1293-1318. DOI URL
[24]	BUCHARDT B, LEWAN M D. Reflectance of vitrinite-like macerals as a thermal maturity index for Cambrian-Ordovician Alum shale, Southern Scandinavia[J]. AAPG Bulletin, 1990, 74(4): 394-406.
[25]	XIAO X, WILKINS R W T, LIU D, et al. Investigation of thermal maturity of lower Palaeozoic hydrocarbon source rocks by means of vitrinite-like maceral reflectance: a Tarim Basin case study[J]. Organic Geochemistry, 2000, 31: 1041-1052. DOI URL
[26]	王飞宇, 何萍, 程顶胜, 等. 镜状体反射率可作为下古生界高过成熟烃源岩成熟度标尺[J]. 天然气工业, 1996, 16(4): 24-28.
[27]	BETRAND R, HEROUX Y. Chitinozoan, graptolite, and scolecodont reflectance as an alternative to vitrinite and pyrobitumen reflectance in Ordovician and Silurian strata, Anticosti island, Quebec, Canada[J]. AAPG Bulletin, 1987, 71: 951-957.
[28]	PETERSEN H I, SCHOVSBO N H, NIELSEN A T. Reflectance measurements of zooclasts and solid bitumen in Lower Paleozoic shales, southern Scandinavia: Correlation to vitrinite reflectance[J]. International Journal of Coal Geology, 2013, 114: 1-18. DOI URL
[29]	GOODARZI F, FOWLER M, BUSTIN M, et al. Thermal Maturity of Early Paleozoic Sediments as Determined by the Optical Properties of Marine-Derived Organic Matter:A Review, Early Organic Evolution[M]. Berlin: Springer, 1992: 279-295.
[30]	张爱云, 伍大茂, 郭丽娜, 等. 海相黑色页岩建造地球化学与成矿意义[M]. 北京: 科学出版社, 1987: 40-45.
[31]	李苗春, 丁海, 焦堃, 等. 湘西三岔地区牛蹄塘组黑色岩系有机岩石学特征[J]. 天然气地球科学, 2012, 23(6): 1077-1089.
[32]	金奎励, 刘大锰, 涂建琪, 等. 有机岩石学研究: 以塔里木为例[M]. 北京: 地震出版社, 1997: 107-122.
[33]	REYES J, JIANG C, LAVOIE D, et al. Organic petrographic analysis of artificially matured chitinozoan and graptolite-rich Upper Ordovician shale from Hudson Bay Basin, Canada[J]. International Journal of Coal Geology, 2018, 199: 138-151. DOI URL
[34]	JACKSON D. Amplexograptus and Glyptograptus isolated from Ordovician limestones in Manitoba[J]. Geological Survey of Canada Bulletin, 1973, 22: 1-8.
[35]	ARDAKANI O H, SANEI H, GHANIZADEH A, et al. Do all fractions of organic matter contribute equally in shale porosity? A case study from Upper Ordovician Utica Shale, southern Quebec, Canada[J]. Marine and Petroleum Geology, 2018, 92: 794-808. DOI URL
[36]	黄莫, 李明, 杨振京, 等. 湖南益阳奥陶系五峰-志留系周家溪群笔石[J]. 现代地质, 2021, 35(5): 1343-1353.
[37]	王子轶, 高志前, 石文睿, 等. 四川盆地五峰组-龙马溪组笔石与页岩气关系探讨[J]. 现代地质, 2019, 33(2): 379-388.
[38]	杨雪英, 龚一鸣. 莓状黄铁矿:环境与生命的示踪计[J]. 地球科学--中国地质大学学报, 2011, 36(4): 643-658.
[39]	卢龙飞, 秦建中, 申宝剑, 等. 川东南涪陵地区五峰-龙马溪组硅质页岩的生物成因及其油气地质意义[J]. 石油实验地质, 2016, 38(4): 460-465,472.
[40]	CARDOTT B J, LANDIS C R, CURTIS M E. Post-oil solid bitumen network in the Woodford Shale, USA: A potential primary migration pathway[J]. International Journal of Coal Geology, 2015, 139: 106-113. DOI URL
[41]	GAO P, LIU G, LASH G G, et al. Occurrences and origin of reservoir solid bitumen in Sinian Dengying Formation dolomites of the Sichuan Basin, SW China[J]. International Journal of Coal Geology, 2018, 200: 135-152. DOI URL
[42]	MASTALERZ M, DROBNIAK A, STANKIEWICZ A B. Origin, properties, and implications of solid bitumen in source-rock reservoirs: A review[J]. International Journal of Coal Geology, 2018, 195: 14-36. DOI URL
[43]	吴朝东, 陈其英, 雷家锦. 湘西震旦-寒武纪黑色岩系的有机岩石学特征及其形成条件[J]. 岩石学报, 1999, 15(3): 453-461.
[44]	侯读杰, 冯子辉. 油气地球化学[M]. 北京: 石油工业出版社, 2011: 109-124.
[45]	SCHOELL M. Recent advances in petroleum isotope geochemistry[J]. Organic Geochemistry, 1984, 84(6): 645-663.
[46]	黄籍中. 干酪根的稳定碳同位素分类依据[J]. 地质地球化学, 1988, 16(3): 66-68.