Characteristics and formation mechanism of the tight tuff reservoirs of the Upper Triassic Chang 7 member in the southern Ordos Basin, China

Li, Qing; Lu, Hao; Li, Jiangshan; Wu, Shenghe; Wu, Yue; Wen, Lang; He, Yu; Qi, Fengqiang

doi:10.1016/j.marpetgeo.2022.105625

Cited by 12 publications

(4 citation statements)

References 38 publications

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“…Generally, the fine‐grained sedimentary rock with particle size <0.0039 mm is referred to as shale (Li, Lu, et al, 2022; Zou et al, 2013). In this study, the particle size of the fine‐grained rock sample of Lucaogou Formation in Malang Sag is generally <0.0039 mm, which can be classified as shale (Liu et al, 2020).…”

Section: Results and Interpretationmentioning

confidence: 99%

Pore structure and oil‐bearing property of laminated and massive shale of Lucaogou Formation in Malang Sag, Santanghu Basin

Guo,

Zhou,

Pan

et al. 2023

Geological Journal

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Exploration and development effects of Lucaogou Formation laminated shale are not ideal in the Santanghu Basin, and the reasons are not clear. Therefore, in this study, laminated and massive shales were systematically sampled, and experiments of cryogenic adsorption of nitrogen and multi‐dimensional nuclear magnetic resonance comparison were carried out. The results show that Lucaogou Formation shale is rich in volcanic ash and low content of clay, which can be divided into tuff, dolomite, tuffaceous dolomite, dolomitic tuff, and other lithologic types. The laminar structure is developed in tuffaceous dolomite and dolomitic tuff. The pores of Lucaogou Formation shale with a diameter of more than 10 nm can be used as an effective storage space for movable oil. The oil saturation and mobile oil ratio of laminated shale are lower than that of massive shale. Movable oil is controlled by carbonate content, and the higher the content, the higher the proportion of movable oil. Millimetre laminae are rich in organic matter and have poor interlaminar pore connectivity, which leads to strong adsorption capacity for oil. Therefore, the migration of oil between laminae is blocked, and oil mainly distributes or migrates in the bedding plane between laminae in laminated shale, which cannot be used as favourable reservoirs.

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Section: Results and Interpretationmentioning

confidence: 99%

Pore structure and oil‐bearing property of laminated and massive shale of Lucaogou Formation in Malang Sag, Santanghu Basin

Guo,

Zhou,

Pan

et al. 2023

Geological Journal

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“…Because the content of feldspar in tuffaceous mudstone is high and feldspar is easily dissolved, the main storage spaces of tuffaceous mudstone are secondary pores formed by feldspar dissolution (Li et al, 2022). A large number of macropores with a diameter greater than 50 nm are shown in tuffaceous mudstones, mainly associated with feldspars.…”

Section: Effect Of Feldsparsmentioning

confidence: 99%

Shale Lithofacies and Its Effect on Reservoir Formation in Lower Permian Alkaline Lacustrine Fengcheng Formation, Junggar Basin, NW China

Tang

Zheng

et al. 2022

Front. Earth Sci.

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Lower Permian Fengcheng Formation is considered to be a high-quality alkaline lacustrine shale oil resource in the Junggar Basin, NW China. Based on core and thin section observation, X-ray diffraction, scanning electron microscope, low-pressure N2 adsorption, and high-pressure mercury intrusion porosimetry, different shale lithofacies, and pore structures were examined. According to the mineral composition, shales in well My 1 are divided into five types: dolomitic mudstone, calcareous mudstone, siliceous mudstone, tuffaceous mudstone, and argillaceous mudstone, each of which shows its pore structure distribution. Intragranular pores, inter-crystalline pores associated with clays and pyrites, dissolution pores, and microfractures were commonly observed. There are three segments of pore structures including <50 nm, 50 nm-4 μm, and >4 μm. Clay minerals mainly contribute to mesopores, especially in argillaceous mudstones. The dissolution of carbonate minerals and feldspars is significant for macropores predominantly in dolomitic mudstones and tuffaceous mudstones, respectively. Micron-scale microfractures associated with laminae dominate in dolomitic mudstones. Therefore, the dolomitic mudstones, especially with lamination, and tuffaceous mudstones are proposed to be favored shale lithofacies with great exploration potential in the Mahu Sag.

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“…In the past few decades, research on the sedimentary and reservoir characteristics of shale reservoirs has also become a hot topic in the field of unconventional oil and gas geology [2,3]. The composition of minerals, rock texture, and sedimentary structure in shale formations commonly display strong heterogeneity, as well as reservoir qualities of shale reservoirs [4][5][6][7].…”

Section: Introductionmentioning

confidence: 99%

Pore Structure and Factors Controlling Shale Reservoir Quality: A Case Study of Chang 7 Formation in the Southern Ordos Basin, China

Li,

You,

et al. 2024

Energies

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The lithofacies types, pore structure differences, and main controlling factors on the shale reservoirs are vital problems that need to be addressed in the process of shale oil exploration and development. This study explores the Luohe oilfield in the southern Ordos Basin, which is composed of organic-rich shale in the Chang 7 member, to clarify the reservoir properties and analyze major factors affecting the reservoir quality. The shale reservoir can be divided into five lithofacies using ternary diagrams of TOC, argillaceous minerals, and siliceous minerals: high organic-rich siliceous shale (HOSS), high organic-rich argillaceous shale (HOAS), medium organic-rich siliceous shale (MOSS), medium organic-rich argillaceous shale (MOAS), and low organic-rich shale (LOS). The type of organic matter in the studied samples is mainly Type I kerogen and Type II kerogen, predominantly Type II1 kerogen. The kerogen mostly lie within the mature zone in the study area. Various types of pores have been identified in the studied shale: intergranular pores, intragranular pores, intercrystalline pores, organic matter pores, and seams around organic matter. The pores are commonly nanoscale to micrometer in scale, with diameters ranging from 10 nm to several microns. The S1 content in shale is positively correlated with the macropore content, indicating that macropores in shale are the main effective oil storage spaces and are important for oil-bearing reservoirs. There is a good positive relationship between the macropore volume of shale and the content of organic matter. Organic matter in the shale can be beneficial for generating organic matter pores, dissolution pores, and seams at organic matter edge, resulting in better physical properties of shale reservoirs. There is a negative relationship between the quartz/feldspar content and macropores content, indicating that quartz and feldspar are detrimental for the macropore volume development. The lithofacies type is one of the important factors controlling the macropore volume. MOAS and HOAS are favorable lithofacies for the development of macropores. The findings of this study can be utilized for hydrocarbon exploration and development in the lacustrine shale formation of the Ordos Basin and other similar basins.

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Characteristics and formation mechanism of the tight tuff reservoirs of the Upper Triassic Chang 7 member in the southern Ordos Basin, China

Cited by 12 publications

References 38 publications

Pore structure and oil‐bearing property of laminated and massive shale of Lucaogou Formation in Malang Sag, Santanghu Basin

Pore structure and oil‐bearing property of laminated and massive shale of Lucaogou Formation in Malang Sag, Santanghu Basin

Shale Lithofacies and Its Effect on Reservoir Formation in Lower Permian Alkaline Lacustrine Fengcheng Formation, Junggar Basin, NW China

Pore Structure and Factors Controlling Shale Reservoir Quality: A Case Study of Chang 7 Formation in the Southern Ordos Basin, China

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