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Characterization of multi-scale pore structure and analysis of adsorption capacity influencing factors in Zhaotong shallow shale gas reservoir

Zhang Jiayi, Zhang Liehui, Hu Shuyong, Qiu Tingting

Acta Geophysica

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2023

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Vol. 71, no. 5

2181--2196

EN

In order to explore the reservoir characteristics of shallow shale gas reservoir in Zhaotong and its differences with other shale gas blocks in Sichuan Basin, the pore structure of Zhaotong shale gas reservoir was comprehensively studied by various means, including X -ray diffraction, gas adsorption (CO2, N2), NMR, and field emission-scanning electron microscopy. In addition, the adsorption capacity of samples in this area was measured by volume method and the main controlling factors were analyzed. The results show that the shale reservoir in the Zhaotong demonstration area is dominated by clay and quartz minerals, with an average content of 23.1% and 34.3%, respectively. Pore-size distribution is concentrated in the range of 0.5–1000 nm, with micropore and mesopore as the main body. Scanning electron microscopy shows that the reservoir space types are mainly organic pores, intergranular pores, intragranular pores, and microfractures. Among them, organic pores are the most developed and most of them appear in large area network structures with good connectivity. The results of the methane isothermal adsorption test show that the adsorption capacity of shale in the Zhaotong area is positively correlated with TOC content, specific surface area, and micropore volume (D≤10nm), but poorly correlated with total pore volume. Due to the influence of mineral types and genesis, the adsorption capacity of shale in this area is negatively correlated with clay content and poorly correlated with quartz content. Through data comparison and analysis, the adsorption capacity of shale in the Zhaotong area is higher than that in the Fuling and Changning–Weiyuan areas. Additionally, due to the influence of mineral genesis, the changing trend of shale adsorption capacity with quartz content is also different in different regions.

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Applying the Tilt depth and Tilt Euler techniques of gravity data to decipher the basement depth in Sichuan Basin, China

Chen Qing, Dong Yunpeng, Tan Xianfeng, Wang Jiabei, Huang Xiaoyu, Chen Hao

Acta Geophysica

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2021

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Vol. 69, no. 6

2173--2186

EN

The tilt angle (i.e., TDR) provides an efficient way to recognize the horizontal locations of multi-source geological bodies at different depths and inclination angles. The tilt-depth method was initially derived by applying magnetic formulas and used to calculate the depth of magnetic sources. Recently researchers have attempted to extend this method to interpret depths in gravity field data. The tilt-depth method of gravity anomalies (i.e., GTilt-depth) could capture the depth of a buried source effectively, which makes it superior at deciphering the basement relief. Meanwhile, Tilt-Euler deconvolution (i.e., Euler deconvolution of TDR) has been utilized for estimating a source’s position from gridded data automatically, which requires no structural index. However, analytical singularities can be produced when performing inversion with the Tilt-Euler deconvolution owning to the derivatives of TDR being incalculable when the horizontal derivative is zero. The improved Tilt-Euler deconvolution provided an efficient way to eliminate analytical singularities and obtain more stable solutions. The results from the theoretical model show that the GTilt-depth method and improved Tilt-Euler deconvolution could be applied to calculate the buried depths more accurately and effectively. Application of these methods shows that they are able to capture more detailed features, and provide more straightforward and accurate results of depth, than traditional methods. Furthermore, the results obtained from the gravity data in Sichuan Basin show that the basement depth ranges from 3 to 11 km, and 3 to 7 km in the central uplift, which contains a local depression with a depth of 8 km. The basement exhibits a general pattern of “shallow in middle and deep in east and west”, which is consistent with the results revealed by gravityseismic jointly interpreted profile. This research provides a better indication of the basement structure when interpreting the regional geology in Sichuan Basin.

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Dinosaur assemblages from the Middle Jurassic Shaximiao Formation and Chuanjie Formation in the Sichuan-Yunnan Basin, China

Li K., Yang Ch., Hu F.

Volumina Jurassica

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2011

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Vol. 9, no. 1

21-42

EN

The Shaximiao Formation (Sichuan Basin, China), and the corresponding Chuanjie Formation of the neighboring Yunnan Basin (Sichuan-Yunnan Basin), representing continental Mesozoic strata, are distinguished from other Chinese Mesozoic units because of the large area over which they are distributed, their lithological characteristics and their abundant vertebrate fossils. This paper analyses and summarizes the dinosaur fossils from the Shaximiao Formation and compares them to other vertebrate groups of the same or similar ages, both in China and abroad. For the first time, this paper presents the viewpoint that the upper member of the Shaximiao Formation is of Middle Jurassic age (Bathonian–Callovian). Furthermore, we claim that the entire Shaximiao Formation is of Bajocian–Callovian age (middle-late part of Middle Jurassic). This conclusion is supported by the age inferred from invertebrate fossils and radiometric dating (165–178 Ma). The composition, evolution and geological age of the vertebrate fauna (particularly dinosaur fossils), as well as their comparison to the dinosaur fauna from the other parts of the Sichuan-Yunnan Basin (Chuanjie Fm.) is discussed. Middle Jurassic dinosaur assemblages from China show marked differences compared with other dinosaur assemblages in the world, and this is explained by geographical isolation.