Microscopic Reservoir Characteristics of the Lacustrine Calcareous Shale: An Example from the Es4 s Shale of the Paleogene Shahejie Formation in Boxing Sag, Dongying Depression

Yang Yong; Danish Khan; Longwei Qiu; Du Yushan; Jiang Long; Li Weizhong; Tehseen Zafar; Fahad Ali; Azizullah Shaikh

doi:10.1021/acsomega.2c05055

Microscopic Reservoir Characteristics of the Lacustrine Calcareous Shale: An Example from the Es₄ ^s Shale of the Paleogene Shahejie Formation in Boxing Sag, Dongying Depression

ACS Omega. 2022 Oct 4;7(41):36748-36761. doi: 10.1021/acsomega.2c05055. eCollection 2022 Oct 18.

Authors

Yang Yong¹, Danish Khan², Longwei Qiu², Du Yushan¹, Jiang Long¹, Li Weizhong¹, Tehseen Zafar³, Fahad Ali², Azizullah Shaikh⁴

Affiliations

¹ Hekou Oil Production Plant, SINOPEC Shengli Oilfield Company, Dongying 257000, China.
² School of Geosciences, China University of Petroleum, Qingdao 266580, China.
³ School of Earth and Space Sciences, Peking University, Beijing 100870, China.
⁴ Department of Petroleum and Gas Engineering, Engineering and Management Sciences, Balochistan University of Information Technology, Quetta, Balochistan 87300, Pakistan.

Abstract

The Es₄ ^s shale is taken as the main research object to understand and describe the reservoir characteristics in Boxing Sag, Dongying Depression. Through core observation, X-ray diffraction, thin section observation, field-emission scanning electron microscopy analysis, and low-pressure nitrogen gas adsorption experiment, the reservoir space of the Es₄ ^s shale including pore types, pore size, and pore structure characteristics was elucidated. The study shows that the shale in the Boxing Sag has the following characteristics: (1) the reservoir space in the study area is diverse, with the development of inorganic pores, organic pores, and microfractures. The higher the content of calcite and organic matter, the more favorable the development of intergranular pores, dissolution pores, and organic matter pores and (2) complex pore structure. The average Barrett-Joyner-Halenda pore size of calcareous shale is 6.5-22.8 nm, and the Brunauer-Emmett-Teller cumulative specific surface area is 0.7588-4.744 m²/g. According to the morphological analysis of the adsorption and desorption curve, it is found that the shale samples in the target interval are mainly ink-bottle-shaped, cylindrical, and slit-shaped pores. The shale samples with relatively well-laminated intervals are mainly composed of ink-bottle-shaped and cylindrical pores, while the samples with relatively unlaminated intervals and high clay mineral content are mainly composed of slit-shaped pores. The contents of clay minerals and calcite are correlated with pore volume, specific surface area, and pore size, which further indicates the controlling effect of clay minerals and carbonate mineral components on pore structure parameters. This study not only helps us to understand the distribution of various micropores/nanopores in the lacustrine shale but also acts as a guiding note for the characterization of the shale oil reservoir, which ultimately offers a theoretical foundation for lacustrine shale oil exploration and development.