基于图像分析技术的页岩微观孔隙特征定性及定量表征

doi:10.11867/j.issn.1001-8166.2016.07.0751.

在有限的条件下,为了更经济有效地评价页岩微观孔隙特征,同时利用扫描电镜(SEM)、氩离子抛光场发射扫描电镜(FESEM)方法对四川盆地彭水地区龙马溪组页岩孔隙特征进行了定性观察,并借助专业的图像分析软件IamgeJ2x 提取页岩SEM和FESEM图像蕴含的孔隙定量信息,结合统计学方法分析页岩全孔径分布特征,计算页岩孔隙分形维数,探讨孔隙结构特征以及分析维数与有机碳含量、矿物成分、孔隙吸附能力等的相关性,研究发现:扫描电镜下,彭水地区龙马溪组页岩微米级孔隙发育,主要孔隙类型有粒间孔、黏土矿物层间孔、粒内孔以及微裂缝等;氩离子抛光场发射扫描电镜下,可见大量纳米级孔隙,主要发育有机质孔、无机矿物孔(黄铁矿晶间孔、粒内孔、黏土矿物层间孔、粒间孔等)和微裂缝,两者综合分析更有利于页岩孔隙定性表征;页岩孔隙全孔径分布特征呈4个主峰,主要分布区间为3~9 nm,10~40 nm,100~400 nm,1~4 μm;页岩有机质孔隙形状系数分布区间为0.9~1,孔隙呈圆形、近圆形,无机矿物孔形状系数分布在0.5~0.7,多呈三角形、多边形、狭缝形等,孔隙形状较有机质孔复杂,主要受页岩孔隙成因不同所致;彭水地区龙马溪组页岩孔隙符合分形特征,有机质孔隙分形维数较无机矿物孔分形维数小,孔隙结构相对简单;分形维数与有机质含量、矿物成分、孔隙度及吸附气含量都有一定的相关性,随有机质含量的增加,孔隙分形维数增加,孔隙结构复杂化,随分形维数增加,页岩孔隙的最大吸附气含量也随之增加,孔隙吸附能力增强。

关键词: 图像分析技术, 扫描电镜, 页岩, 孔隙特征, 分形维数

In order to evaluate the shale microscopic pore characteristics more economically and effectively in limited circumstances, the pore characteristics of Longmaxi Formation in Pengshui area, Sichuan Basin, were qualitatively observed and analyzed with Scanning Electron Microscopy (SEM) and Field Emission Scanning Electron Microscopy (FESEM) with argon ion polishing method at the same time. Pore quantitative information were extracted from shale SEM and FESEM images with the help of a professional image analysis software IamgeJ2x, and combined with statistical methods, the whole pore size distribution as well as shale pore fractal dimension and the relevance between fractal dimension and organic matter content, mineral composition and pore adsorption capacity and the corresponding pore structure characteristics of Longmaxi Formation in Pengshui area were analyzed. The study shows that under SEM, there are mostly micro pores of Longmaxi Formation in Pengshui area. The main pore types include intergranular pore, clay mineral layer pore, intragranular pore and micro cracks, etc. Through argon ion polishing FESEM, there mainly develop nanoscale pores. The main pore types contain organic pore, inorganic mineral pore (pyrite intergranular pore, intragranular pore, clay mineral layer pore and intergranular pore, etc.) and micro cracks. The use of both of the two methords is more advantageous to qualitatively analyze shale pore. The whole pore size distribution of shale pore has four main peaks and the main distribution range is 3~10 nm, 10~40 nm, 100~400 nm, 1~4 μm, respectively. The shape factor of shale organic matter pore is distributed between 0.9~1 and inorganic mineral pore is distributed between 0.5~0.7. It shows that the organic matter pore is circular, nearly circular and inorganic mineral pore shape is triangle, polygon, slit shape and so on. The inorganic mineral pore shape is relativly complex because of the different pore causes. The shale pore of Longmaxi Formation in Pengshui area conforms to the fractal features, and the organic pore fractal dimension is smaller than that of inorganic mineral pore, showing that the organic matter pore structure is relatively simple. There is a certain relevance between fractal dimension and organic matter content, mineral composition, porosity, and adsorbed gas content. With the increase of the organic matter content, the shale pore fractal dimension increase, the pore structure characteristics become complicated. With the shale pore fractal dimension increasing, the biggest gas adsorption quantity increases and the ability of pore adsorption strengthens.

Key words: Image analysis, SEM, Shale, Pore characteristics, Fractal dimension.

中图分类号:

P618.13

表1 页岩样品测试数据

Table 1 Test data of shale sample

样品编号	黏土矿物含量/%				脆性矿物含量/%						有机地化参数
样品编号	伊利石		伊蒙混层		绿泥石	总量占比	石英	方解石	白云石	长石	黄铁矿	TOC含量/%	R_O/%	干酪根类型
P-1	60	15	25	45	42	1	2	7	3		2.08	2.75	II2
P-3	56	22	22	45	41	3	2	7	2		1.77	4.4	II1
P-4	73	14	13	14	46	4	12	23	1		0.46	-	II2
P-6	56	29	15	24	42	8	8	14	4		0.964	3.2	II2
P-7	62	26	12	31	40	4	5	18	2		1.18	2.84	II2
P-9	66	20	14	23	49	3	5	19	1		0.841	3.4	II2
P-10	61	23	16	32	48	3	2	12	3		-	-	-
P-11	64	30	6	28	50	7	3	8	4		2.56	3.4	II1
P-12	75	16	9	26	48	7	4	11	4		2.85	3.64	II1
P-13	69	22	9	24	52	4	6	12	2		2.77	3.25	II2
P-14	74	16	10	22	66	4	6	1	1		3.52	2.53	II1

表1 页岩样品测试数据

Table 1 Test data of shale sample

样品编号	黏土矿物含量/%				脆性矿物含量/%						有机地化参数
样品编号	伊利石		伊蒙混层		绿泥石	总量占比	石英	方解石	白云石	长石	黄铁矿	TOC含量/%	R_O/%	干酪根类型
P-1	60	15	25	45	42	1	2	7	3		2.08	2.75	II2
P-3	56	22	22	45	41	3	2	7	2		1.77	4.4	II1
P-4	73	14	13	14	46	4	12	23	1		0.46	-	II2
P-6	56	29	15	24	42	8	8	14	4		0.964	3.2	II2
P-7	62	26	12	31	40	4	5	18	2		1.18	2.84	II2
P-9	66	20	14	23	49	3	5	19	1		0.841	3.4	II2
P-10	61	23	16	32	48	3	2	12	3		-	-	-
P-11	64	30	6	28	50	7	3	8	4		2.56	3.4	II1
P-12	75	16	9	26	48	7	4	11	4		2.85	3.64	II1
P-13	69	22	9	24	52	4	6	12	2		2.77	3.25	II2
P-14	74	16	10	22	66	4	6	1	1		3.52	2.53	II1

图1 扫描电镜照片

Fig.1 SEM images

图2 氩离子抛光扫描电镜照片

Fig.2 FESEM images

表2 四川盆地彭水地区龙马溪组页岩孔隙分类及特征

Table 2 Pore classification of Longmaxi Formation shale in Pengshui area, Sichuan Basin

孔隙类型		孔径分布	孔隙形态	成因机制
无机矿物孔	粒间孔	百纳米—微米	三角形,多边行,狭缝型	矿物颗粒不完全胶结或成岩作用
	粒内孔	十几纳米—微米	椭圆形或近圆形	后期成岩改造
	黄铁矿晶间孔	几十纳米—几百纳米	多边形	晶体生长不致密或成岩收缩
	黏土矿物层间孔	百纳米—微米	狭缝形、不规则状	原生孔隙或后期压实成岩改造
有机质孔		数纳米—几百纳米,少量微米级	近圆形、椭圆形、凹坑状、串珠状、不规则多边形	有机质生烃演化
微裂缝		百纳米—几十微米	长条状	沉积、成岩、微构造等应力作用

表2 四川盆地彭水地区龙马溪组页岩孔隙分类及特征

Table 2 Pore classification of Longmaxi Formation shale in Pengshui area, Sichuan Basin

孔隙类型		孔径分布	孔隙形态	成因机制
无机矿物孔	粒间孔	百纳米—微米	三角形,多边行,狭缝型	矿物颗粒不完全胶结或成岩作用
	粒内孔	十几纳米—微米	椭圆形或近圆形	后期成岩改造
	黄铁矿晶间孔	几十纳米—几百纳米	多边形	晶体生长不致密或成岩收缩
	黏土矿物层间孔	百纳米—微米	狭缝形、不规则状	原生孔隙或后期压实成岩改造
有机质孔		数纳米—几百纳米,少量微米级	近圆形、椭圆形、凹坑状、串珠状、不规则多边形	有机质生烃演化
微裂缝		百纳米—几十微米	长条状	沉积、成岩、微构造等应力作用

图3 利用IamgeJ2x软件定量分析SEM图像

Fig.3 Analyzing the SEM images quantitatively through the software ImageJ2x

图4 利用IamgeJ2x软件定量分析FESEM图像

Fig.4 Analyzing the FESEM images quantitatively through the software ImageJ2x

图5 3号样品孔径分布特征
(a) FESEM图像孔径分布;(b) SEM图像孔径分布

Fig.5 Shale pore size distribution of sample 3 in Pengshui area, Sichuan Basin
(a)Pore size distribution of FESEM images;(b)Pore size distribution of SEM images

图6 四川盆地彭水地区龙马溪组页岩孔径分布特征
(a) FESEM图像孔径分布;(b) SEM图像孔径分布

Fig.6 Shale pore size distribution of Longmaxi Formation in Pengshui area,Sichuan Basin
(a)Pore size distribution of FESEM images;(b)Pore size distribution of SEM images

图7 四川盆地彭水地区龙马溪组页岩样品全孔径大致分布特征

Fig.7 Shale whole pore size distribution of Longmaxi Formation in Pengshui area,Sichuan Basin

图8 不同类型孔隙周长与面积分维关系
(a) 无机矿物孔;(b) 有机质孔

Fig.8 Fractal dimension relationship of perimeter and area of different types of pore
(a) Inorganic mineral por ;(b) Organic mineral por

图9 不同类型孔隙形状系数
(a)无机矿物孔;(b)有机质孔

Fig.9 Shape factor of different pore types
(a) Inorganic mineral por; (b) Organic mineral por

图10 分形维数相关性分析
(a)分形锥数与有机质含量的关系;(b)分形锥数与黏土矿物含量的关系;(c)分形锥数与长石含量的关系;(d)分形锥数与石英含量的关系;(e)分形锥数与孔隙度的关系;(f)分形锥数与最大吸附量的关系

Fig.10 Relationship between fractal dimension and other content of shale sample
(a) Relationship between Fractal dimension and TOC;(b) Relationship between Fractal dimension and Clay minerals content;(c) Relationship between Fractal dimension and Feldspar content;(d) Relationship between Fractal dimension and Quartz content;(e) Relationship between Fractal dimension and Porisity;(f) Relationship between Fractal dimension and the maxmum adsorption amount

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Qualitative and Quantitative Characterization of Shale Microscopic Pore Characteristics Based on Image Analysis Technology