Fractal Characteristics and Main Controlling Factors of Pore Throat of Chang 6 Tight Sandstone in Jiyuan Area

doi:10.12422/j.issn.1006-396X.2026.02.004

Abstract

Abstract:

Microscopic pore throat structure is the key focus and challenge of tight sandstone reservoir research.Regarding the Chang 6 tight sandstone in the Jiyuan area of the Ordos Basin,casting thin sections,scanning electron microscopy,and constant rate mercury injection experiments were used,and fractal theory was introduced to study its pore throat characteristics.The study shows that the pore throat of tight sandstone can be divided into two types:large⁃scale and small⁃scale.The large⁃scale pore throats are mainly dissolution pores,composite pores and curved lamellar throats.The pore throat has large storage space,obvious pore throat deformation,strong heterogeneity and large fractal dimension.The small⁃scale pore throats are strongly compacted and cemented, and mainly consist of intergranular pores,intercrystalline pores and necked throats with little deformation of pore⁃throat space,weak heterogeneity and small fractal dimension.There is a good positive correlation between the fractal dimension and the effective reservoir space.The better the reservoir is,the stronger the heterogeneity will be,and the larger the fractal dimension will be.There is also a good correlation between the fractal dimension and the pore throat structure parameter.The pore throat distribution is uneven,the connectivity is poor,the larger the fractal dimension will be.The mass fraction of clay minerals is an important factor affecting the fractal dimension of pore throat,which in turn reflects the quality and pore throat characteristics of reservoirs.

Key words: Jiyuan area, Tight sandstone, Constant rate mercury injection, Pore throat structure, Fractal dimension, Ordos Basin

摘要：

微观孔喉结构是致密砂岩储层研究的重点和难点。针对鄂尔多斯盆地姬塬地区长6致密砂岩，运用铸体薄片、扫描电镜及恒速压汞实验，并引入分形理论对其孔喉特征进行了研究。结果表明，致密砂岩孔喉分为大尺度和小尺度两种类型；大尺度孔喉以溶蚀孔、复合孔和弯片状喉道为主，孔喉储集空间较大，变形明显，非均质性强，分形维数较大；小尺度孔喉受压实、胶结作用强烈，以粒间孔、晶间孔和缩颈状喉道为主，孔喉空间变形较少，非均质性弱，分形维数较小；分形维数与有效储集空间有较好的正相关性，储集性越好，非均质性强，分形维数越大；分形维数与孔喉结构参数之间也存在较好的相关性，孔喉分布不均匀，连通性越差，分形维数越大；黏土矿物质量分数是影响孔喉分形维数大小的重要因素，同时也反映储层的质量和孔喉特征。

关键词: 姬塬地区, 致密砂岩, 恒速压汞, 孔喉结构, 分形维数, 鄂尔多斯盆地

CLC Number:

TE122.2

Yunyun BAI, Lu WANG, Feng GAO, Ke ZHAO, Qinghua ZHENG. Fractal Characteristics and Main Controlling Factors of Pore Throat of Chang 6 Tight Sandstone in Jiyuan Area[J]. Journal of Petrochemical Universities, 2026, 39(2): 31-40.

白云云, 王路, 高锋, 赵科, 郑庆华. 姬塬地区长6致密砂岩孔喉分形特征及主控因素[J]. 石油化工高等学校学报, 2026, 39(2): 31-40.

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URL: https://journal.lnpu.edu.cn/syhg/EN/10.12422/j.issn.1006-396X.2026.02.004

https://journal.lnpu.edu.cn/syhg/EN/Y2026/V39/I2/31

Figures/Tables 11

Fig.1 Geographical location of Jiyuan area

Fig.2 The pore morphology of Chang 6 tight sandstone reservoir space in the Jiyuan area

Fig.3 The microscopic characteristics of the throat and the mineral characteristics of Chang 6 tight sandstone in the Jiyuan area

Table 1 The pore throat structure parameters of core samples of Chang 6 tight sandstone in the Jiyuan area

样品编号	深度/m	孔隙度/%	渗透率×10³/μm²	平均喉道半径/μm	平均孔隙半径/μm	平均孔喉半径比
S1	2 435.2	10.54	0.11	0.58	127.74	265.06
S2	2 349.4	12.04	0.18	0.89	130.94	191.86
S3	2 338.3	8.85	0.04	0.43	135.28	369.47
S4	2 467.7	11.18	0.42	0.57	129.79	278.15
S5	2 269.1	13.42	1.57	0.64	129.20	256.02
S6	2 560.2	11.75	0.38	0.69	129.58	237.81

Fig.4 Porosity permeability relationship diagram of Chang 6 tight sandstone in the Jiyuan area

Fig.5 Core pore throat distribution curves of Chang 6 tight sandstone in the Jiyuan area

Fig.6 Fractal characteristics curves of pore throat at different scales of Chang 6 tight sandstone in the Jiyuan area

Table 2 The results of pore throat fractal dimension of core samples of Chang 6 tight sandstone in the Jiyuan area

样品编号	小尺度孔隙		小尺度喉道		大尺度孔隙		大尺度喉道		小尺度孔喉占比/%	大尺度孔喉占比/%
样品编号	D₁	R $12$	D₂	R $22$	D₃	R $32$	D₄	R $42$	小尺度孔喉占比/%	大尺度孔喉占比/%
S1	2.14	0.44	2.94	0.91	12.54	0.92	8.75	0.95	91	9
S2	2.08	0.47	2.87	0.94	8.99	0.93	7.44	0.97	93	7
S3	2.18	0.44	2.98	0.91	20.15	0.87	16.99	0.87	92	8
S4	2.18	0.48	2.97	0.94	11.70	0.95	7.77	0.85	89	11
S5	2.19	0.51	2.90	0.92	10.48	0.96	7.44	0.89	91	9
S6	2.16	0.52	2.95	0.94	13.20	0.99	9.98	0.93	94	6

Table 2 The results of pore throat fractal dimension of core samples of Chang 6 tight sandstone in the Jiyuan area

样品编号	小尺度孔隙		小尺度喉道		大尺度孔隙		大尺度喉道		小尺度孔喉占比/%	大尺度孔喉占比/%
样品编号	D₁	R $12$	D₂	R $22$	D₃	R $32$	D₄	R $42$	小尺度孔喉占比/%	大尺度孔喉占比/%
S1	2.14	0.44	2.94	0.91	12.54	0.92	8.75	0.95	91	9
S2	2.08	0.47	2.87	0.94	8.99	0.93	7.44	0.97	93	7
S3	2.18	0.44	2.98	0.91	20.15	0.87	16.99	0.87	92	8
S4	2.18	0.48	2.97	0.94	11.70	0.95	7.77	0.85	89	11
S5	2.19	0.51	2.90	0.92	10.48	0.96	7.44	0.89	91	9
S6	2.16	0.52	2.95	0.94	13.20	0.99	9.98	0.93	94	6

Fig.7 Core mercury entry curve of Chang 6 tight sandstone in the Jiyuan area

Fig.8 Relationship between fractal dimension and pore throat structure parameters of Chang 6 tight sandstone in the Jiyuan area

Fig.9 Relationship between fractal dimension and clay mineral mass fraction of Chang 6 tight sandstone in the Jiyuan area

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