Fractal characteristics of pore-throat structure and permeability estimation of tight sandstone reservoirs: A case study of Chang 7 of the Upper Triassic Yanchang Formation in Longdong area, Ordos Basin, China

The complex pore structure and high heterogeneity of ultra-low permeability sandstone reservoirs have a significant effect on reservoir quality evaluation and hydrocarbon resource assessment. We collected 10 reservoir samples from the Upper Triassic Yanchang Formation Chang 8 in the Zhenbei area of the Ordos Basin. We measured the pore size distribution (PSD) and fluid occurrence characteristics of the reservoir by Pressure-controlled porosimetry (PCP), rate-controlled porosimetry (RCP) and nuclear magnetic resonance (NMR), and then analyzed the results via the fractal theory to determine the pore space fractal characteristics. Our analysis indicates that the three major pore types of these reservoirs are residual intergranular pores, dissolution pores and intercrystalline pores. The pore structure of the ultra-low permeability sandstone reservoirs is highly heterogeneous with pore throats of various scales, and the corresponding fractal characteristics are notably different, exhibiting multi-fractal features. Compared to macropores and mesopores, micropores are more uniform and regular in terms of their PSD and thus only slightly influence the reservoir quality. The complexity of the throat distribution and whole pore space is attributed to the development of dissolution pores and the content of feldspar minerals. Fractal features depend on the movable fluid pore space and effective pores, whose fractal dimensions reflect the complexity of interconnected pores and correlate well with the porosity and permeability. The development of different types and sizes of pore throats in these ultra-low permeability sandstone reservoirs resulted in the observed pore structure heterogeneity. The difference in mineral composition and content of these reservoirs aggravates the pore structure complexity and affects reservoir quality evaluation and further oilfield development.

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Numerical simulation of remaining oil distribution in tight sandstone reservoirs: a case study of the upper Triassic Yanchang formation in the Ordos Basin, China

Arabian Journal of Geosciences ◽

10.1007/s12517-020-06325-3 ◽

2021 ◽

Vol 14 (1) ◽

Author(s):

Airong Li ◽

Qian Qiang ◽

Shuai Yin ◽

Jingong Zhang ◽

Fuli Wu ◽

...

Keyword(s):

Numerical Simulation ◽

Ordos Basin ◽

Upper Triassic ◽

Tight Sandstone ◽

Yanchang Formation ◽

Oil Distribution ◽

Remaining Oil ◽

The Ordos Basin ◽

Remaining Oil Distribution

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Fractures in sandstone reservoirs with ultra-low permeability: A case study of the Upper Triassic Yanchang Formation in the Ordos Basin, China

AAPG Bulletin ◽

10.1306/09240808047 ◽

2009 ◽

Vol 93 (4) ◽

pp. 461-477 ◽

Cited By ~ 105

Author(s):

Zeng Lianbo ◽

Li Xiang-Yang

Keyword(s):

Ordos Basin ◽

Upper Triassic ◽

Low Permeability ◽

Yanchang Formation ◽

The Ordos Basin ◽

Sandstone Reservoirs

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Difference of Microfeatures among Diagenetic Facies in Tight Sandstone Reservoirs of the Triassic Yanchang Formation in the Midwestern Region, Ordos Basin

Mathematical Problems in Engineering ◽

10.1155/2021/5611786 ◽

2021 ◽

Vol 2021 ◽

pp. 1-11

Author(s):

Jian Shi ◽

Xiaolong Wan ◽

Qichao Xie ◽

Shuxun Zhou ◽

Yan Zhou ◽

...

Keyword(s):

Pore Space ◽

Ordos Basin ◽

Water Flooding ◽

Pore Throat ◽

Tight Sandstone ◽

Throat Radius ◽

Yanchang Formation ◽

Fluid Saturation ◽

Sandstone Reservoirs ◽

Diagenetic Facies

Based on the background of sedimentary characteristics, a large amount of core and thin section analysis, taking Chang 6 reservoir of Yanchang Formation in the central and western Ordos Basin as an example, through the application of scanning electron microscopy, high-pressure mercury injection, nuclear magnetic resonance and microscopic water drive oil model, and other experimental test methods, the diagenetic facies types and microscopic pore structure characteristics of tight sandstone reservoirs are discussed and analyzed in depth. The results show that the average porosity loss rate caused by early diagenesis compaction in the study area is 50.62%, which is the main reason for reservoir compactness. The cementation further causes porosity loss, and the later dissolution increases the reservoir space in the study area to a certain extent. Different diagenetic facies reservoirs not only have obvious differences in porosity evolution characteristics but also have significant differences in pore throat radius distribution characteristics, movable fluid occurrence characteristics, and water drive oil characteristics. The pore throat distribution with radius greater than R50∼R60 determines the permeability. The difference in movable fluid saturation mainly depends on the connectivity of the relative large pore space corresponding to the relaxation time greater than the cut-off value of T2. The size of pore throat radius has a good control effect on water flooding efficiency.

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