Work

Origin and Reservoir Significance of Authigenic Minerals in Lacustrine Shales: A Case Study from the Paleogene Dongying Sag, Bohai Bay Basin, East China

Year: 2025

Type: article

Abstract: Authigenic minerals in shale are products of the co-evolution of organic and inorganic components, affecting the heterogeneity of shale reservoirs. However, due to their fine granularity and complex rock composition, studies on these minerals in shale are still insufficient. This research focuses on the lacustrine shales from the upper sub-member of the fourth member in the Eocene Shahejie Formation, Dongying Sag, East China. Utilizing core samples, thin sections, scanning electron microscope, X-ray diffraction, elemental geochemistry, and organic geochemistry, we systematically characterized the features and origins of authigenic minerals. The results identified several typical authigenic minerals, including authigenic quartz, framboidal and euhedral pyrite, ferroan dolomite, kaolinite, chlorite, and albite. Authigenic quartz is predominantly diagenetic silica formed through smectite illitization, acidic dissolution of K-feldspar, and alkaline dissolution of detrital quartz. Pyrite is a product of microbial sulfate reduction, with framboidal pyrite forming during an early diagenetic stage under conditions with sufficient solute supply and euhedral pyrite forming during a later stage under conditions with insufficient solute supply. Ferroan dolomite originates from the precipitation of Fe and Mg during smectite illitization, with slight contributions from the acidic dissolution of chlorite and calcite. Kaolinite stems from the acidic dissolution of K-feldspar, while chlorite results from the transformation of kaolinite. Albite primarily arises from the alkaline alteration of anorthite and K-feldspar. Most non-clay authigenic minerals likely enhance reservoir quality by slightly reducing the effects of compaction, whereas authigenic clay minerals typically exert detrimental effects on reservoir properties. This study constrains the genesis of authigenic minerals to assess their influence on reservoir quality in lacustrine shale.

Source: Minerals

DOI: 10.3390/min15050493

Authors: Jihua Yan, Shiyue Chen, Zhiyun Yu, Pengfei Zhang, Guozheng Feng

Institutions: China University of Petroleum, East China, China University of Petroleum, Beijing, Sinopec (China), Research Institute of Petroleum Exploration and Development

Language: English

Topic: Hydrocarbon exploration and reservoir analysis

Subfield: Mechanics of Materials

Field: Engineering

Domain: Physical Sciences

Open Access status: gold

Estimated APC paid: $2,896

Funder: National Natural Science Foundation of China