Pore Characteristics and Pore Structure of the Upper Paleozoic Coal-bearing Shale Gas Reservoir in the Wuxiang Block, Qinshui Basin

doi:10.19657/j.geoscience.1000-8527.2022.222

Abstract

Abstract:

Reservoir pore characteristics and pore structure are the important factors affecting the occurrence and accumulation of shale gas. In order to evaluate the properties of high evolution coal-bearing shale reservoir and shale gas reservoir performance from the marine-continental transitional facies, the pore microscopic characteristics and pore structure of the Upper Paleozoic coal-bearing shale gas reservoir in the Wuxiang block of Qinshui Basin were studied by means of scanning electron microscope, high pressure mercury injection, low temperature N₂ and CO₂ gas adsorption, micron CT scanning and nuclear magnetic resonance experiments. The results show that various types of microscopic pores are developed in the Upper Paleozoic coal-bearing shale samples in the Wuxiang block of Qinshui Basin, including intergranular pores, intragranular pores and microfractures, and organic matter pores are almost not developed. The total pore volume of the samples of coal-bearing shale gas reservoir in the Wuxiang block is distributed 0.021,9~0.073,5 mL/g, with an average of 0.039,9 mL/g, and the total specific surface area is mainly distributed 11.94~46.83 m²/g, with an average of 29.16m²/g, of which mesopore (2-50 nm) and micropore (<2 nm) are the main carriers of the coal-bearing shale gas reservoir. The higher coordination number pores in coal-bearing shale, the larger the corresponding pore volume and specific surface area, and the better the pore connectivity. On the premise of little difference between the number of pores and the total pore volume, the pore structure and connectivity of the Shanxi Formation coal-bearing shale are slightly better than that of the Taiyuan Formation coal-bearing shale.

Key words: shale gas reservoir, coal-bearing shale, pore characteristics, pore structure, Upper Paleozoic, Wuxiang Block, Qinshui Basin

CLC Number:

TE132.2

ZHANG Jinqing, LI Xianqing, ZHANG Boxiang, ZHANG Xueqing, YANG Jingwei, YU Zhenfeng. Pore Characteristics and Pore Structure of the Upper Paleozoic Coal-bearing Shale Gas Reservoir in the Wuxiang Block, Qinshui Basin[J]. Geoscience, 2022, 36(06): 1551-1562.

Figures/Tables 16

Fig.1 Regional structure of Qinshui Basin(a), well location map of the Wuxiang Block(b), and stratigraphic histogram of the study area(c)

Table 1 Basic geochemical characteristics of coal-bearing shale samples in the Wuxiang Block, Qinshui Basin

样品号	层位	埋深/m	TOC/%	R_o/%	全岩矿物成分含量 /%
样品号	层位	埋深/m	TOC/%	R_o/%	石英	碳酸盐矿物	黏土矿物	其它矿物
W18-03	山西组	1 581.6	6.61	2.35	34.2	2.9	54.2	8.7
W18-06	山西组	1 600.3	0.29	2.41	63.0	2.0	32.5	2.5
W18-08	山西组	1 614.4	7.42	2.48	60.6	0.0	28.3	11.1
W18-11	山西组	1 652.7	1.74	2.33	51.8	2.2	40.7	5.3
W27-02	山西组	1 502.3	2.23	2.61	49.1	19.7	20.5	10.7
W27-07	山西组	1 623.5	2.75	2.55	55.6	1.8	33.2	9.4
W27-09	太原组	1 677.9	1.81	2.63	48.5	0.0	47.3	4.2
W28-02	山西组	1 738.2	2.01	2.39	56.0	0.9	35.3	7.8
W28-07	山西组	1 748.5	8.36	2.33	46.5	23.1	22.0	8.4
W28-13	太原组	1 884.4	1.57	2.59	59.8	2.4	34.1	3.7
W28-15	太原组	1 888.0	2.82	2.54	57.5	5.1	35.3	2.1
W28-19	太原组	1 900.6	6.30	2.63	59.7	0.0	36.4	3.9

Fig.2 Image analysis of scanning electron microscopy from coal-bearing shale samples in the Wuxiang Block, Qinshui Basin

Table 2 Development degree of different types of coal-bearing shale in the Wuxiang Block, Qinshui Basin

样品号	粒间孔		粒内孔		有机质孔		微裂缝
样品号	发育程度	大小/nm	发育程度	大小/nm	发育程度	大小/nm	发育程度	长度/μm	宽度/nm
W18-08	+++	80~430	++	70~530	-	-	+	13~42	70~310
W18-11	+++	90~530	++	80~610	-	-	+	7~28	40~290
W28-02	+++	110~440	+	110~730	+	30~370	+	11~59	60~510
W28-07	+++	50~330	++	50~520	+	50~160	+	7~31	110~370
W28-19	+++	110~630	++	80~210	-	-	+	2~14	30~430

Fig.3 Proportions of different pores of coal-bearing shale in the Wuxiang Block, Qinshui Basin

Table 3 Pore structure characteristics of coal-bearing shale in the Wuxiang Block, Qinshui Basin

样品编号	平均孔径 /nm	总孔容/ (mL·g^-1)	总比表面积/ (m²·g^-1)	孔容/(mL·g^-1)				比表面积/(m² ·g^-1)
样品编号	平均孔径 /nm	总孔容/ (mL·g^-1)	总比表面积/ (m²·g^-1)	微孔	介孔	宏孔		微孔	介孔	宏孔
W18-03	33.46	0.043 7	46.83	0.013 8	0.024 3	0.005 6	29.49		16.67	0.67
W18-06	25.19	0.029 6	16.76	0.003 9	0.019 5	0.006 2	7.17		8.60	0.99
W18-08	24.22	0.073 5	33.91	0.009 8	0.017 1	0.046 6	21.68		11.46	0.77
W18-11	63.13	0.056 8	42.72	0.009 0	0.036 9	0.010 9	16.04		25.99	0.69
W28-02	29.35	0.029 9	17.60	0.003 9	0.021 1	0.004 9	7.62		9.32	0.66
W28-07	30.81	0.021 9	11.94	0.003 2	0.012 7	0.006 0	5.94		5.22	0.78
W28-13	36.52	0.031 7	25.79	0.005 3	0.021 6	0.004 8	12.05		13.21	0.53
W28-15	40.72	0.033 3	28.95	0.006 3	0.021 9	0.005 1	14.52		13.93	0.50
W28-19	40.23	0.038 8	37.92	0.009 6	0.023 8	0.005 4	21.63		15.76	0.53

Fig.4 Distribution of pore volume and specific area of the coal-bearing shale in the Wuxiang Block, Qinshui Basin

Fig.5 Characterization of macropore volume change rate distribution with different pore diameters (high pressure mercury intrusion method)

Fig.6 N2 adsorption-desorption isotherms of the coal-bearing shale samples in the Wuxiang Block, Qinshui Basin

Fig.7 Characterization of the change rate distribution of pore volume and specific surface area with different pore diameters (N2 adsorption method)

Fig.8 CO2 adsorption curve of the coal-bearing shale samples in the Wuxiang Block, Qinshui Basin

Fig.9 Characterization of the change rate distribution of pore volume and specific surface area with different pore diameters (CO2 adsorption method)

Fig.10 Full pore size distribution of the coal-bearing shale in the Wuxiang Block, Qinshui Basin and its comparison with North American shale

Fig.11 Distribution characteristics of pore roar radius and pore coordination number of coal-bearing shale in the Wuxiang Block, Qinshui Basin

Fig.12 Normalized accumulation curve of T2 spectrum of coal-bearing shale in the Wuxiang Block, Qinshui Basin

Fig.13 Distribution map of 3D reconstruction of coal-bearing shale samples from Shanxi Formation and Taiyuan Formation in the Wuxiang Block, Qinshui Basin

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