journal article Apr 10, 2026

Controlling Factors and Distribution Patterns of Natural Fractures in the Paleogene Lacustrine Shale of the Subei Basin, China

Abstract
ABSTRACT

In this study, the characteristics of different types of natural fractures were characterized through an integrated analysis of core, thin sections, imaging logs and laboratory tests. The main controlling factors and distribution patterns of natural fractures in lacustrine shale reservoirs were systematically investigated. The results indicate the presence of two main fracture types: structural fractures and diagenetic fractures. Structural fractures are predominantly high‐angle to sub‐vertical, with large scale and well‐defined features. In contrast, diagenetic fractures are mostly sub‐horizontal, with irregular and curved fracture surfaces. The development of structural fractures in these continental shales is controlled by multiple factors, including lithology, mineral composition and the mechanical stratigraphy. Among these, lithology and mineral composition form the material basis for fracturing, with brittle mineral content showing a significant positive correlation with structural fracture density. The mechanical stratigraphy plays a critical role in regulating the distribution and vertical extension of fractures. Within a mechanical unit of relatively uniform lithology, greater layer thickness correlates with larger fracture length, lower fracture density and increased vertical connectivity. The Palaeocene Second Member of the Funing Formation (E
1
f
2
) within the Qintong Sag, the interplay between sedimentation‐controlled lithology and rock structure results in a distinct vertical zonation from Sub‐members I to V: fracture types become simpler, average fracture length increases, while fracture density and filling degree decrease. This study provides valuable insights for understanding fracture distribution in lacustrine shale reservoirs and offers guidance for hydrocarbon exploration and development.
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