Petrography and Quality Characteristics of Lower-Middle Jurassic Coal Seam in the Southeastern Tarim Basin

doi:10.19657/j.geoscience.1000-8527.2018.05.10

Abstract

Abstract:

Petrology and quality of the Lower-Middle Jurassic coal seams in the southeastern margin of the Tarim basin (distributed intermittently along the Altyn Tagh) are very different from the Jurassic coal seams in northwestern China. To characterize these coal seams, various experiments including coal petrography, coal quality identification and coalification index have been conducted on a large amount of coal samples collected from the Hetian Buya, Yutian Pulu and Qiemo Hongliugou coal mines. The results reveal that the main mining layer consists mainly of clarain and semi-bright coal, followed by durain and semi-dull coal. The macerals are mainly characterized by vitrinite, with minor exinite and middle-high V/I. In addition, the total sulfur content in the coal increases with the vitrinite content, due to the lower degree of coal-forming swamp that promotes the formation of inorganic sulfur. Moreover, it is obvious that the content of coal seam sulfur decreases with the ash content. Similarly, the volatile content of coal seam affected by various sulfur contents is significantly different. The analyses also show that the main component of sulfur in the medium-high sulfur coal of the Minfeng sag is inorganic sulfur, and that the volatile fraction increases with increasing sulfur content. However, the productivity of volatile influence of organic sulfur is not obvious in the medium-low sulfur coal in the Washixia sag. It is found that the ash composition index in the coal seam of the Minfeng sag is higher than that of the Washixia sag, which suggests that the water table of the coal-forming swamp of the latter is much higher. Our results confirm that the change of coal petrology and coal quality diversity in the southeastern Tarim basin are controlled by the faulted lacustrine basin and the local water depth in the reducing swamp environment, which led to the medium-high volatility, medium-low ash, medium-low sulfur, and the rich vitrinite-poor inertinite coal features there.

Key words: Tarim basin, Lower-Middle Jurassic, coal petrography, maceral, coal quality

CLC Number:

P618.11

WANG Di, TIAN Jijun, FENG Shuo, LU Xingyu. Petrography and Quality Characteristics of Lower-Middle Jurassic Coal Seam in the Southeastern Tarim Basin[J]. Geoscience, 2018, 32(05): 975-984.

Figures/Tables 8

Fig.1 Structural division of the depression in southeast Tarim basin(according to the ref.[14])

Fig.2 Photomicrographs showing microstructural features of macerals in the coal

Fig.3 Distribution map of the vitrinite and inertinite contents of the Lower-Middle Jurassic coal seams in southeast Tarim basin

Table 1 Coal quality indices of the major coal seam in southeast Tarim basin

地区	煤矿		煤层号	水分/%	灰分/%	挥发分/%	硫分/%	镜质组含量/%	镜质组反射率/%	最高古地温值/℃	煤类
民丰凹陷	和田布雅		A1	6.44	18.27	33.51	1.63	68.90	0.52	115.86	31号不粘煤
			$A 21$	5.96	17.33	33.65	1.89	69.60	0.54	117.95	31号不粘煤
			$A 22$	5.97	26.95	35.13	2.67	77.80	0.55	118.97	31号不粘煤
			A3	5.60	33.42	35.73	0.46	72.40	0.58	121.92	31号不粘煤
	于田普鲁		A1	0.44	50.67	25.41	—	94.30	1.45	172.81	24号焦煤
			A2	0.45	37.16	20.16	0.28	93.90	1.43	172.04	24号焦煤
			A3	0.75	47.79	18.08	—	93.60	1.68	180.99	13号瘦煤
			B1	1.03	24.13	15.59	0.52	93.50	1.64	179.65	13号瘦煤
			B2	0.48	17.88	15.51	0.82	98.40	1.65	179.99	13号瘦煤
	乌鲁克赛		A1	1.86	20.96	36.57	0.83	95.10	0.84	142.49	34号气煤
			A2	2.38	13.58	32.62	1.64	94.60	0.86	143.80	34号气煤
			A3	1.86	24.98	40.78	1.45	97.10	0.87	144.44	45号气煤
			A4	1.77	20.31	26.78	0.92	95.40	0.86	143.80	34号气煤
			A5	1.44	26.48	37.68	1.06	95.30	0.84	142.49	43号气煤
			A6	2.03	21.40	40.78	0.74	95.60	0.83	141.83	45号气煤
瓦石峡凹陷	其格勒克		B4	6.23	27.41	44.36	0.58	87.20	0.66	129.10	41号长焰煤
			$B 51$	7.46	31.84	47.22	0.53	87.60	0.65	128.25	41号长焰煤
			$B 52$	6.55	28.34	46.46	0.61	87.50	0.67	129.93	41号长焰煤
			$B 53$	6.28	31.28	43.98	0.63	86.90	0.66	129.10	41号长焰煤
			B6	1.66	45.99	51.15	0.31	89.20	0.68	130.76	41号长焰煤
	红柳沟	向斜北翼	A1	14.27	16.51	46.12	0.87	87.50	0.58	121.92	41号长焰煤
			A2	12.26	14.46	45.73	1.04	87.50	0.55	118.97	41号长焰煤
			A3	11.12	11.45	45.26	0.74	87.30	0.56	119.97	41号长焰煤
			A4	10.60	11.33	44.68	0.74	87.40	0.57	120.96	41号长焰煤
			A5	3.67	12.16	42.94	0.83	86.80	0.59	122.87	41号长焰煤
			A6	4.20	10.10	43.50	0.86	87.10	0.57	120.96	41号长焰煤
			A7	9.92	13.93	44.08	0.91	87.30	0.57	120.96	41号长焰煤
		向斜南翼	A3	3.52	15.46	45.68	0.97	86.90	0.82	141.15	45号气煤
			A4	4.02	7.86	46.54	1.04	87.20	0.86	143.80	43号气煤
			A5	3.88	13.11	44.80	0.89	87.20	0.78	138.38	45号气煤
			A6	3.49	24.68	47.08	0.83	87.60	0.56	119.97	41号长焰煤

Table 1 Coal quality indices of the major coal seam in southeast Tarim basin

地区	煤矿		煤层号	水分/%	灰分/%	挥发分/%	硫分/%	镜质组含量/%	镜质组反射率/%	最高古地温值/℃	煤类
民丰凹陷	和田布雅		A1	6.44	18.27	33.51	1.63	68.90	0.52	115.86	31号不粘煤
			$A 21$	5.96	17.33	33.65	1.89	69.60	0.54	117.95	31号不粘煤
			$A 22$	5.97	26.95	35.13	2.67	77.80	0.55	118.97	31号不粘煤
			A3	5.60	33.42	35.73	0.46	72.40	0.58	121.92	31号不粘煤
	于田普鲁		A1	0.44	50.67	25.41	—	94.30	1.45	172.81	24号焦煤
			A2	0.45	37.16	20.16	0.28	93.90	1.43	172.04	24号焦煤
			A3	0.75	47.79	18.08	—	93.60	1.68	180.99	13号瘦煤
			B1	1.03	24.13	15.59	0.52	93.50	1.64	179.65	13号瘦煤
			B2	0.48	17.88	15.51	0.82	98.40	1.65	179.99	13号瘦煤
	乌鲁克赛		A1	1.86	20.96	36.57	0.83	95.10	0.84	142.49	34号气煤
			A2	2.38	13.58	32.62	1.64	94.60	0.86	143.80	34号气煤
			A3	1.86	24.98	40.78	1.45	97.10	0.87	144.44	45号气煤
			A4	1.77	20.31	26.78	0.92	95.40	0.86	143.80	34号气煤
			A5	1.44	26.48	37.68	1.06	95.30	0.84	142.49	43号气煤
			A6	2.03	21.40	40.78	0.74	95.60	0.83	141.83	45号气煤
瓦石峡凹陷	其格勒克		B4	6.23	27.41	44.36	0.58	87.20	0.66	129.10	41号长焰煤
			$B 51$	7.46	31.84	47.22	0.53	87.60	0.65	128.25	41号长焰煤
			$B 52$	6.55	28.34	46.46	0.61	87.50	0.67	129.93	41号长焰煤
			$B 53$	6.28	31.28	43.98	0.63	86.90	0.66	129.10	41号长焰煤
			B6	1.66	45.99	51.15	0.31	89.20	0.68	130.76	41号长焰煤
	红柳沟	向斜北翼	A1	14.27	16.51	46.12	0.87	87.50	0.58	121.92	41号长焰煤
			A2	12.26	14.46	45.73	1.04	87.50	0.55	118.97	41号长焰煤
			A3	11.12	11.45	45.26	0.74	87.30	0.56	119.97	41号长焰煤
			A4	10.60	11.33	44.68	0.74	87.40	0.57	120.96	41号长焰煤
			A5	3.67	12.16	42.94	0.83	86.80	0.59	122.87	41号长焰煤
			A6	4.20	10.10	43.50	0.86	87.10	0.57	120.96	41号长焰煤
			A7	9.92	13.93	44.08	0.91	87.30	0.57	120.96	41号长焰煤
		向斜南翼	A3	3.52	15.46	45.68	0.97	86.90	0.82	141.15	45号气煤
			A4	4.02	7.86	46.54	1.04	87.20	0.86	143.80	43号气煤
			A5	3.88	13.11	44.80	0.89	87.20	0.78	138.38	45号气煤
			A6	3.49	24.68	47.08	0.83	87.60	0.56	119.97	41号长焰煤

Fig.4 Comparison of the coal-bearing strata and coal quality in southeast Tarim basin

Fig.5 Diagram showing the trend of the sulfur and ash contents of the Lower-Middle Jurassic coal seams in southeast Tarim basin

Fig.6 Diagram showing the trend of the sulfur and volatile contents of the Lower-Middle Jurassic coal seams in southeast Tarim basin

Fig.7 Diagram showing the ash index variation trend of the Lower-Middle Jurassic coal seams in southeast Tarim basin

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