Characteristics of High-Gamma-Ray Sandstone Reservoirs for Yanchang Formation in Ordos Basin

2010 ◽  
Vol 53 (1) ◽  
pp. 154-163 ◽  
Author(s):  
Xiao-Li ZHANG ◽  
Qiao FENG ◽  
Pei SUN ◽  
Wei LI
Keyword(s):  
Gamma Ray ◽  
Ordos Basin ◽  
Yanchang Formation ◽  
High Gamma ◽  
Sandstone Reservoirs

Pore structure and fractal characteristics of ultra-low permeability sandstone reservoirs in Upper Triassic Yanchang Formation, Ordos Basin

2021 ◽  
pp. 1-59
Author(s):  
Quanpei Zhang ◽  
Tao Jiao ◽  
Hao Huang ◽  
Zhao Qi ◽  
Tao Jiang ◽  
...  
Keyword(s):  
Pore Structure ◽  
Quality Evaluation ◽  
Pore Space ◽  
Ordos Basin ◽  
Upper Triassic ◽  
Reservoir Quality ◽  
Low Permeability ◽  
Yanchang Formation ◽  
Fractal Characteristics ◽  
Sandstone Reservoirs

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.

scholarly journals Genesis Analysis of High-Gamma Ray Sandstone Reservoir and Its Log Evaluation Techniques: A Case Study from the Junggar Basin, Northwest China

2013 ◽  
Vol 2013 ◽  
pp. 1-6 ◽  
Author(s):  
Liang Wang ◽  
Zhiqiang Mao ◽  
Zhongchun Sun ◽  
Xingping Luo ◽  
Yong Song ◽  
...  
Keyword(s):  
Gamma Ray ◽  
Physical Property ◽  
Junggar Basin ◽  
Northwest China ◽  
Uranium Enrichment ◽  
Water Sensitivity ◽  
High Gamma ◽  
Sandstone Reservoir ◽  
Sandstone Reservoirs ◽  
Evaluation Techniques

In the Junggar basin, northwest China, many high gamma-ray (GR) sandstone reservoirs are found and routinely interpreted as mudstone non-reservoirs, with negative implications for the exploration and exploitation of oil and gas. Then, the high GR sandstone reservoirs’ recognition principles, genesis, and log evaluation techniques are systematically studied. Studies show that the sandstone reservoirs with apparent shale content greater than 50% and GR value higher than 110API can be regarded as high GR sandstone reservoir. The high GR sandstone reservoir is mainly and directly caused by abnormally high uranium enrichment, but not the tuff, feldspar or clay mineral. Affected by formation’s high water sensitivity and poor borehole quality, the conventional logs can not recognize reservoir and evaluate the physical property of reservoirs. Then, the nuclear magnetic resonance (NMR) logs is proposed and proved to be useful in reservoir recognition and physical property evaluation.

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