Pore Structure Characteristics of Yanchang Formation Shale Gas Reservoir in Yanchang Exploration Area of Ordos Basin

Abstract

Abstract:

In order to evaluate the space and the gas storage capacity of terrestrial shale gas reservoirs,many shale samples were taken from the Chang 7 and Chang 9 members of the Upper Triassic Yanchang Formation in Yanchang exploration area of Ordos basin, and the pore type and pore structure of these samples and their influence factors were studied by the use of scanning electron microscope (SEM), high pressure mercury injection and low-temperature gas adsorption experiments with CO₂ and N₂. The results reveal the following aspects: (1)There are many types of microscopic pores in these shale samples, mainly including intergranular pores and intragranular pores,and a small amount of crystal particle pores and dissolution pores exists, and organic matter pores are less development. These pores provide the main storage spaces for the shale gasreservoir. (2)Mesopores (2-50 nm) contribute to the main pore volume and specific surface area of Yanchang Formation, accounting for 74.34% of the total pore volume and 64.40% of the total surface area. The shale samples from the Chang 9 Member have a greater total pore volume and total specific surface area than those from the Chang 7 Member. (3)The pore structure is dominated by slit type pores and plate pores, and the pore size distribution mainly falls in 0.4-0.9 nm,3-25 nm and 5-200 μm. The average pore size of Yanchang Formation shale is 8.53 nm,and the Chang 7 Member shale has a greater average pore size than the Chang 7 Member shale.(4)The organic carbon content, organic matter maturity and mineral composition content affect the pore development of the Yanchang Formation shale.The mineral composition content is the main controlling factor of the pore development of Yanchang Formation shale which is predominated by the mesopore. The increase of the organic carbon content and maturity of shales mainly play a positive role in the development of the micropore in Yanchang Formation shale.

Key words: terrestrial shale gas reservoir, pore structure, pore type, pore size distribution, Yanchang Formation shale, Yanchang exploration area

CLC Number:

XU Hongwei, LI Xianqing, QI Shuai, ZHOU Baogang, WANG Zhe, GAO Wenjie, CHEN Jinming. Pore Structure Characteristics of Yanchang Formation Shale Gas Reservoir in Yanchang Exploration Area of Ordos Basin[J]. Geoscience, 2017, 31(02): 328-337.

Figures/Tables 11

References 37

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样品号	层位	深度/m	TOC/%	R_o/%	全岩矿物成分含量/%						脆性矿物含量/%
样品号	层位	深度/m	TOC/%	R_o/%	石英	长石	黏土	碳酸盐	黄铁矿	其他	脆性矿物含量/%
YY4-1	长7段	1 370.25	4.13	0.897	36.0	13.9	37.2	9.3	3.6	微	57.2
YY5-6	长7段	1 451.10	4.18	0.923	12.3	11.2	56.3	18.0	2.2	微	39.2
YY5-10	长7段	1 452.07	6.77	0.926	19.1	14.0	44.2	19.2	0.4	微	53.2
YY5-23	长7段	1 456.60	4.45	0.924	33.6	5.8	31.5	27.5	0.0	1.6	64.0
YY7-1	长7段	1 139.10	3.79	0.835	19.9	18.0	52.3	8.0	1.8	微	45.9
YY7-8	长7段	1 146.16	2.73	0.840	28.4	10.9	41.1	19.2	0.4	微	53.2
YY7-12	长7段	1 150.25	3.17	0.845	23.5	21.0	39.1	15.4	1.0	微	54.7
YY8-2	长7段	1 442.45	5.51	0.915	13.7	10.2	52.6	20.9	0.6	2.0	42.7
YY8-7	长7段	1 445.46	4.07	0.913	11.6	9.2	38.5	40.0	0.7	微	50.2
YY9-6	长7段	1 515.92	4.68	1.018	21.6	15.7	36.6	24.0	2.1	微	57.0
YY12-5	长7段	1 613.94	7.77	0.975	21.9	17.7	59.7	0.0	0.7	微	39.6
YY12-11	长7段	1 620.10	8.82	0.960	20.4	26.2	47.9	0.0	5.5	微	46.6
YY4-5	长9段	1 533.21	4.75	1.030	13.7	14.5	43.2	27.1	1.5	微	49.0
YY5-31	长9段	1 604.42	6.91	1.063	23.5	15.2	49.6	4.0	7.7	微	42.7
YY8-17	长9段	1 597.20	5.09	1.046	18.6	8.4	36.6	33.7	2.5	0.2	43.4
YY9-16	长9段	1 668.27	3.37	1.095	15.4	13.1	24.7	46.1	0.7	微	57.7
YY12-21	长9段	1 752.40	6.07	1.012	32.2	13.0	42.0	7.1	5.7	微	52.3
YY13-21	长9段	1 361.15	4.42	0.889	20.2	5.4	39.9	31.7	2.8	微	45.8

样品号	层位	深度/m	TOC/%	R_o/%	全岩矿物成分含量/%						脆性矿物含量/%
样品号	层位	深度/m	TOC/%	R_o/%	石英	长石	黏土	碳酸盐	黄铁矿	其他	脆性矿物含量/%
YY4-1	长7段	1 370.25	4.13	0.897	36.0	13.9	37.2	9.3	3.6	微	57.2
YY5-6	长7段	1 451.10	4.18	0.923	12.3	11.2	56.3	18.0	2.2	微	39.2
YY5-10	长7段	1 452.07	6.77	0.926	19.1	14.0	44.2	19.2	0.4	微	53.2
YY5-23	长7段	1 456.60	4.45	0.924	33.6	5.8	31.5	27.5	0.0	1.6	64.0
YY7-1	长7段	1 139.10	3.79	0.835	19.9	18.0	52.3	8.0	1.8	微	45.9
YY7-8	长7段	1 146.16	2.73	0.840	28.4	10.9	41.1	19.2	0.4	微	53.2
YY7-12	长7段	1 150.25	3.17	0.845	23.5	21.0	39.1	15.4	1.0	微	54.7
YY8-2	长7段	1 442.45	5.51	0.915	13.7	10.2	52.6	20.9	0.6	2.0	42.7
YY8-7	长7段	1 445.46	4.07	0.913	11.6	9.2	38.5	40.0	0.7	微	50.2
YY9-6	长7段	1 515.92	4.68	1.018	21.6	15.7	36.6	24.0	2.1	微	57.0
YY12-5	长7段	1 613.94	7.77	0.975	21.9	17.7	59.7	0.0	0.7	微	39.6
YY12-11	长7段	1 620.10	8.82	0.960	20.4	26.2	47.9	0.0	5.5	微	46.6
YY4-5	长9段	1 533.21	4.75	1.030	13.7	14.5	43.2	27.1	1.5	微	49.0
YY5-31	长9段	1 604.42	6.91	1.063	23.5	15.2	49.6	4.0	7.7	微	42.7
YY8-17	长9段	1 597.20	5.09	1.046	18.6	8.4	36.6	33.7	2.5	0.2	43.4
YY9-16	长9段	1 668.27	3.37	1.095	15.4	13.1	24.7	46.1	0.7	微	57.7
YY12-21	长9段	1 752.40	6.07	1.012	32.2	13.0	42.0	7.1	5.7	微	52.3
YY13-21	长9段	1 361.15	4.42	0.889	20.2	5.4	39.9	31.7	2.8	微	45.8

样品号	层位	平均孔径 /nm	总孔容/ (10^-3mL/g)	总比表面积/ (m²/g)	孔容/(10^-3mL/g)				比表面积/(m²/g)
样品号	层位	平均孔径 /nm	总孔容/ (10^-3mL/g)	总比表面积/ (m²/g)	微孔	介孔	宏孔		微孔	介孔	宏孔
YY4-1	长7段	6.13	14.01	6.56	0.54	11.47	2.00	1.89		4.18	0.49
YY5-10	长7段	9.60	11.34	7.87	0.85	7.49	3.00	2.90		4.49	0.47
YY7-8	长7段	8.68	11.80	4.71	0.39	9.41	2.00	1.33		3.10	0.27
YY7-12	长7段	12.18	16.61	7.01	0.44	12.17	4.00	1.54		4.75	0.73
YY8-7	长7段	9.74	7.72	5.08	0.51	6.21	1.00	1.76		3.19	0.13
YY9-6	长7段	8.49	13.81	7.94	0.46	11.35	2.00	1.57		6.13	0.24
YY12-5	长7段	9.83	6.16	4.91	0.66	4.80	0.70	2.26		2.64	0.01
YY4-5	长9段	7.88	18.65	11.04	0.71	13.94	4.00	2.52		8.08	0.44
YY5-31	长9段	8.95	15.95	11.74	0.83	11.12	4.00	2.82		8.13	0.79
YY8-17	长9段	9.76	24.99	11.96	0.59	17.40	7.00	2.00		8.58	1.38
YY9-16	长9段	6.47	22.99	14.31	0.72	15.27	7.00	2.46		10.45	1.39
YY12-21	长9段	5.76	14.33	11.39	0.84	9.49	4.00	2.80		7.69	0.90
YY13-21	长9段	7.42	17.10	11.39	0.66	13.44	3.00	2.44		8.32	0.63

样品号	层位	平均孔径 /nm	总孔容/ (10^-3mL/g)	总比表面积/ (m²/g)	孔容/(10^-3mL/g)				比表面积/(m²/g)
样品号	层位	平均孔径 /nm	总孔容/ (10^-3mL/g)	总比表面积/ (m²/g)	微孔	介孔	宏孔		微孔	介孔	宏孔
YY4-1	长7段	6.13	14.01	6.56	0.54	11.47	2.00	1.89		4.18	0.49
YY5-10	长7段	9.60	11.34	7.87	0.85	7.49	3.00	2.90		4.49	0.47
YY7-8	长7段	8.68	11.80	4.71	0.39	9.41	2.00	1.33		3.10	0.27
YY7-12	长7段	12.18	16.61	7.01	0.44	12.17	4.00	1.54		4.75	0.73
YY8-7	长7段	9.74	7.72	5.08	0.51	6.21	1.00	1.76		3.19	0.13
YY9-6	长7段	8.49	13.81	7.94	0.46	11.35	2.00	1.57		6.13	0.24
YY12-5	长7段	9.83	6.16	4.91	0.66	4.80	0.70	2.26		2.64	0.01
YY4-5	长9段	7.88	18.65	11.04	0.71	13.94	4.00	2.52		8.08	0.44
YY5-31	长9段	8.95	15.95	11.74	0.83	11.12	4.00	2.82		8.13	0.79
YY8-17	长9段	9.76	24.99	11.96	0.59	17.40	7.00	2.00		8.58	1.38
YY9-16	长9段	6.47	22.99	14.31	0.72	15.27	7.00	2.46		10.45	1.39
YY12-21	长9段	5.76	14.33	11.39	0.84	9.49	4.00	2.80		7.69	0.90
YY13-21	长9段	7.42	17.10	11.39	0.66	13.44	3.00	2.44		8.32	0.63