Lithologic Reservoirs ›› 2024, Vol. 36 ›› Issue (3): 1-18.doi: 10.12108/yxyqc.20240301

• PETROLEUM EXPLORATION • Previous Articles    

Characteristics and significance of micron pores and micron fractures in shale oil reservoirs of Cretaceous Qingshankou Formation in Gulong sag，Songliao Basin

HE Wenyuan1, ZHAO Ying2, ZHONG Jianhua3,4, SUN Ningliang3   

  1. 1. China National Oil and Gas Exploration and Development Company Ltd., Beijing 100032, China;
    2. Heilongjiang Provincial Key Laboratory of Continental Shale Oil, Daqing 163712, Heilongjiang, China;
    3. Ocean Engineering Research Institute, Northeastern University, Qinhuangdao 066004, Hebei, China;
    4. School of Geosciences, China University of Petroleum (East China), Qingdao 266580, Shandong, China
  • Received:2023-03-13 Revised:2023-08-22 Published:2024-04-30

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Abstract: By means of core observation, thin section identification, electron backscattering, secondary imaging and energy spectrum analysis, the micron pores and micron fractures in shale oil reservoirs of Cretaceous Qing‐ shankou Formation in Gulong sag of Songliao Basin were studied. The results show that:（1）The lithologies of shale oil reservoirs in Gulong sag are fine-grained clastic rocks dominated by shale, and the mineral composition is mainly clay and felsic, showing the characteristics of mudstone or shale in structure, and the whole reservoir is felsic shale. Micron pores and micron fractures are developed in reservoirs with various types.（2）The diameter of micron pores in the study area is generally 1-2 μm, and the maximum can reach 70 μm, and they are nearly round, oblate, polygonal and irregular. According to the genesis, they can be divided into six types:compaction stress shielding pores, diagenetic authigenic pores, dissolved pores, hydrocarbon generation and expulsion expansion pores, organic matter pores and diatom residual pores. Compaction stress shielding pores are mostly developed on both sides of rigid minerals. Diagenetic authigenic pores are often developed in authigenic minerals such as dolo‐ mite, chlorite and illite, mainly intergranular pores. Dissolved pores are mostly developed in carbonate minerals, and secondary mycelial floccules can be seen inside. Hydrocarbon generation and expulsion expansion pores are mostly produced in vertical or nearly vertical rows, which is related to the secondary hydrocarbon generation and expulsion formed by light oil. Organic matter pores develop in organic matter and are related to residual cells of plants and filling of light oil and natural gas. Diatom residual pores mainly develop in the interior and edge of dia‐ toms, with large sizes ranging from several microns to tens of microns.（3）The micron fractures in the study area are mainly bedding, with a width of 1-10 μm and a maximum of 100 μm, and a length of several microns to tens of microns. They can be divided into four types:diagenetic shrinkage fractures, dissolved fractures, hydrocarbon generation and expulsion expansion fractures and structural/shear fractures. The diagenetic shrinkage fractures are mainly tensile fractures, with curved fractures and uneven fracture wall. The width of dissolved fractures can reach 60-70 μm, authigenic clay can be seen in the fractures, and authigenic minerals such as pyrite, apatite and dolomite can be found on both sides of the fracture. Both sides of hydrocarbon generation and expulsion expan‐ sion fractures are jagged and uneven, bypassing rigid minerals. Structural/shear micron fractures are generally straight, accompanied by other fractures related to shear.（4）The connectivity between pores and fractures of dif‐ ferent scales in the study area is good, forming a three-level reservoir and transport system of“nano-pores + nanofractures, micron-pores + micron-fractures, millimeter-pores + millimeter-fractures”.

Key words: micron pore, micron fracture, reservoir space, connectivity, shale oil reservoir, Qingshankou Formation, Cretaceous, Gulong sag, Songliao Basin

CLC Number: 

  • TE122.2
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