Fractal Characteristics and Main Controlling Factors of Wufeng-Longmaxi Formation Shale in Luobu Syncline, Southern Sichuan Basin

doi:10.7657/XJPG20220204

Abstract

Abstract:

In the Luobu syncline, southern Sichuan basin, the shale in the Upper Ordovician Wufeng formation (O₃w)-Lower Silurian Longmaxi formation (S₁l) is characterized by large thickness, high organic carbon content, wide distribution range and moderate thermal evolution of organic matter, making it an important target for subsequent shale gas exploration. In order to better characterize the heterogeneity of shale pore structure and clarify the influence of heterogeneity on shale gas enrichment in the study area, the fractal characteristics of the shale in layers of O₃w-S₁l11 in the study area were analyzed using the rock-mineral analysis, geochemical and well logging data, and CO₂ and N₂ adsorption analysis. The results show that the layers in the study area are very different in TOC content, mineral compositions and porosity, and the reservoir is highly heterogeneous. The fractal dimension of shale pores ranges from 2.711 0 to 2.794 8, with an average of 2.747 0; the value is relatively high for O₃w and Layer #1 in S₁l11, and the lowest for Layer #4 in S₁l11. The organic carbon and bio-quartz can promote the development of shale micropores. The smaller the average pore size of shale, the more the pores, and the more complex the pore structure, and the larger the fractal dimension.

Key words: Sichuan basin, Dianqianbei depression, Luobu syncline, Wufeng formation, Longmaxi formation, shale, heterogeneity, pore structure, fractal characteristic

CLC Number:

TE122.23

DUAN Wengang, LIN Wen, TIAN Jijun, MA Jinghui, DU Meng, LUO Jinchang. Fractal Characteristics and Main Controlling Factors of Wufeng-Longmaxi Formation Shale in Luobu Syncline, Southern Sichuan Basin[J]. Xinjiang Petroleum Geology, 2022, 43(2): 153-159.

Figures/Tables 7

Table 1

Test results of main component content and porosity of shale samples in the study area"

样品编号	深度/ m	层位	总有机碳含量/%	矿物含量/%							孔隙度/ %
样品编号	深度/ m	层位	总有机碳含量/%	石英	钾长石	斜长石	方解石	白云石	黄铁矿	黏土矿物	孔隙度/ %
YS1-8	2 234.81	龙一41小层	2.10	39.10	5.40	5.50	12.60	5.60	3.60	28.10	1.05
YS2-8	3 003.75		1.76	33.10	1.00	6.50	11.10	1.70	4.60	42.00	0.51
YS2-11	3 010.46		2.28	31.00	0	4.60	12.60	1.70	4.60	45.50	0.77
YS2-15	3 017.74		3.41	39.30	0	3.60	18.80	4.70	5.60	28.00	0.93
YS3-21	2 972.94		1.30	31.90	1.20	8.30	8.80	5.20	4.00	40.60	0.46
YS3-23	2 977.27		1.60	30.40	1.10	5.40	10.20	5.90	4.00	43.00	0.62
YS3-25	2 981.25		1.97	31.10	0.70	4.80	10.50	6.70	4.50	41.70	0.54
YS4-52	2 986.30		3.38	39.60	0.80	2.70	17.90	5.30	4.60	29.10	3.19
YS6-1	2 191.80		3.89	31.10	2.70	5.70	14.60	5.50	7.80	32.60	3.07
YS6-2	2 194.25		1.52	29.90	1.80	6.40	10.00	4.00	4.80	43.10	3.73
YS6-3	2 196.51		2.44	28.60	1.40	6.80	8.90	7.70	7.90	38.70	3.82
YS6-4	2 198.05		1.93	27.90	0.60	5.40	11.70	4.60	6.30	43.50	3.73
YS6-5	2 199.54		2.49	31.60	0.60	3.80	17.70	8.60	5.40	32.30	3.88
YS1-14	2 245.95	龙一31小层	3.80	39.10	5.40	5.50	12.60	5.60	3.60	28.10	1.55
YS2-18	3 023.85		3.50	41.60	0	3.70	18.30	4.50	5.60	26.30	0.63
YS2-20	3 026.83		3.68	46.50	0	3.00	14.00	4.20	5.70	26.60	1.00
YS3-27	2 986.32		3.19	36.30	0.70	4.40	15.50	11.00	4.70	27.40	1.14
YS3-29	2 989.49		3.70	40.00	0	2.80	17.90	8.20	4.70	26.40	1.00
YS3-31	2 993.25		3.40	35.20	0.70	3.50	16.40	15.60	3.30	25.30	1.00
YS6-6	2 204.00		3.55	31.40	0.60	4.60	16.90	7.50	5.20	33.80	4.40
YS6-9	2 209.23		3.37	37.30	0.70	3.90	14.40	13.00	5.40	25.30	5.16
YS1-18	2 251.67	龙一21小层	3.70	45.70	5.30	4.80	15.60	7.40	3.80	17.40	1.76
YS2-22	3 031.73		3.28	55.50	0	2.40	13.20	5.70	4.20	19.00	1.55
YS3-33	2 997.14		3.65	41.90	0	4.30	17.20	13.10	4.10	19.40	1.12
YS3-35	3 000.85		3.53	43.00	0	1.50	25.40	13.80	2.10	14.20	0.75
YS4-58	2 999.07		3.73	53.90	0	2.80	13.90	4.70	3.30	21.40	3.78
YS6-10	2 211.35		3.76	40.20	0	5.20	14.30	8.90	4.50	26.90	4.46
YS6-11	2 213.13		3.75	25.70	0.80	5.40	16.80	19.40	5.20	26.70	4.91
YS6-12	2 215.07		3.01	27.30	1.80	3.70	23.50	21.20	3.10	19.40	3.88
YS6-13	2 216.13		4.98	53.80	0	4.40	10.50	8.60	2.90	19.80	5.94
YS6-14	2 217.36		3.79	32.00	0	6.60	21.90	10.90	5.10	23.50	3.96
YS1-20	2 255.55	龙一11小层	4.50	40.90	5.40	5.60	24.40	4.40	3.00	16.20	3.26
YS2-24	3 036.04	龙一11小层	4.77	35.10	1.10	3.60	26.70	8.90	4.00	20.60	2.46
YS1-21	2 257.27	五峰组	4.30	28.30	3.40	10.40	33.30	8.50	4.40	11.70	1.91
YS1-23	2 261.40		1.30	22.20	6.30	7.60	27.30	11.50	3.30	21.80	1.17
YS2-26	3 039.78		2.30	18.30	0	8.70	8.90	19.10	12.40	32.60	0.84
YS3-37	3 003.16		3.98	18.10	0	2.70	34.40	16.70	2.70	25.40	1.43
YS6-17	2 223.63		0.78	22.50	0.50	4.50	27.20	16.90	0.70	27.70	0.37

Table 1

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Fig.6.

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