Lamination Texture and Its Effects on Reservoir and Geochemical Properties of the Palaeogene Kongdian Formation in the Cangdong Sag, Bohai Bay Basin, China

• Published in: Minerals (Basel) 2021-12, Vol.11 (12), p.1360
• Main Authors: Li, Mengying, Wu, Songtao, Hu, Suyun, Zhu, Rukai, Meng, Siwei, Yang, Jingru
• Format: Article
• Language: English
• Subjects: Carbonates; Chronic lymphocytic leukemia; Classification; Clay; Clay minerals; Distribution; Electron microscopy; Emission analysis; Feldspars; Field emission microscopy; fine-grained sedimentary; Geochemistry; Grain size; lacustrine shale oil; Laminates; Lamination; Lithology; Minerals; nano-pores; Oil exploration; Oil shale; Organic matter; Palaeogene; Permeability; Pores; Porosity; Properties; Quartz; R&D; Research & development; Reservoirs; Scanning electron microscopy; Sedimentary rocks; Shale; Shales; sweet spot; Technical services; Texture; Total organic carbon; unconventional geology; Vertical distribution; X-ray diffraction
• ISSN: 2075-163X; 2075-163X
• DOI: 10.3390/min11121360

The characteristics of laminae are critical to lacustrine shale strata. They are the keys to the quality of source rocks and reservoirs, as well as engineering operations in shale plays. This study uses organic geochemistry, thin section identification, X-ray diffraction, field emission scanning electron microscopy, and other analytical methods, to reveal the detailed lamination texture and vertical distribution of laminae in the second Member of the Kongdian Formation in Cangdong Sag. The principal results are as follows: (1) A classification of laminae is proposed to characterize reservoir and geochemical properties. The five types of laminae are as follows: feldspar-quartz laminae (FQL), clay laminae (CLL), carbonate laminae (CAL), organic matter laminae (OML), and bioclastic laminae (BCL). There are also four significant lamina combinations (with the increasing TOC values): FQL-CLL combination, FQL-CLL-BCL combination, FQL-CLL-OML combination, and FQL-CAL-CLL-OML combination; (2) differences between laminae occur because of the variability in pore types and structures. There appears to be a greater abundance of intercrystalline pores of clay minerals in the FQL, CAL, BCL, and OML, and well-developed organic pores in the CAL and CLL, and the counterparts of intragranular pores of bioclastic material in the BCL. This detailed characterization provides the following comparative quantification of the thin section porosity of laminae in the second Member of the Kongdian Formation can be differentiated: CAL > FQL > OML > BCL > CLL; (3) differentiation between vertical distributions of laminae is carried out in a single well. The FQL and CLL are widely distributed in all the samples, while the BCL is concentrated in the upper part of the second Member of the Kongdian Formation, and CAL is concentrated in the lower part. This detailed classification method, using geochemical analysis and vertical distribution descriptions, offers a detailed understanding of lamination texture and its effects on reservoir and geochemical properties, which will provide a scientific guidance and technical support to better estimate reservoir quality and to identify new sweet spots in the second Member of the Kongdian Formation in the Cangdong Sag.