Natural fractures in tight gas sandstones: a case study of the Upper Triassic Xujiahe Formation in Xinchang gas field, Western Sichuan Basin, China

Abstract

The Upper Triassic Xujiahe Formation is a typical tight gas reservoir in which natural fractures determine the migration, accumulation and production capacity of tight gas. In this study, we focused on the influences of natural fractures on the tight gas migration and production. We clarified characteristics and attributes (i.e. dips, apertures, filling degree and cross-cutting relationships) of the fractures based on image logging interpretations and core descriptions. Previous studies of electron spin resonance, carbon and oxygen isotopes, homogenization temperature of fluid inclusions analysis and basin simulation were considered. This study also analysed the fracture sequences, source of fracture fillings, diagenetic sequences and tight gas enrichment stages. We obtained insight into the relationship between fracture evolution and hydrocarbon charging, particularly the effect of the apertures and intensity of natural fractures on tight gas production. We reveal that the bedding fractures are short horizontal migration channels of tight gas. The tectonic fractures with middle, high and nearly vertical angles are beneficial to tight gas vertical migration. The apertures of fractures are controlled by the direction of maximum principal stress and fracture angle. The initial gas production of the vertical wells presents a positive correlation with the fracture abundance, and the intensity and aperture of fractures are the fundamental factors that determine the tight gas production. With these findings, this study is expected to guide the future exploration and development of tight gas with similar geological backgrounds.

Characteristics and Controlling Factors of Natural Fractures in Deep Carbonates of the Puguang Area, Sichuan Basin, China

“…The fracture analysis described above indicates that the development and distribution of tectonic fractures in the Feixianguan carbonates exhibit strongly longitudinal and horizontal heterogeneity in the Puguang area. Previous studies have demonstrated that the formation and development of tectonic fractures in carbonate reservoirs are closely relevant to the original sedimentary, diagenetic process, and tectonic movement. ,,− According to the characteristic disparity of tectonic fractures in the Feixianguan carbonates, this study identifies and discusses five geological factors that may primarily control the development and distribution of tectonic fractures, including lithology, rock mechanical stratigraphy, reservoir physical property, diagenetic cementation, and faults.…”

“…Lithology is the foundation for the formation of natural fractures and one of the key internal factors affecting the development characteristics of tectonic fractures. ,, Due to differences in the mineral composition, particle size, and rock structure, rocks with different lithologies display various rupture patterns and abilities under the same stress action. Numerous studies of mechanical experiments demonstrated that rocks with the higher brittle mineral contents, smaller grain sizes, and higher structural homogeneity were more likely to form brittle failure under the tectonic stress. , …”

Geomechanical Response Characteristics of Different Sedimentary Hydrodynamic Cycles—Exampled by Xujiahe Formation of Upper Triassic, Western Sichuan Basin

“…Tectonically, the Sichuan Basin, situated in the western part of the Yangtze Block, is a large composite superimposed basin with both gas-and oil-bearing characteristics (Figure 1A) [16,36]. It is bounded by the Longmenshan thrust belt and Longquanshan uplift belt.…”

Pore structure and reservoir physical properties for effective development of tight sandstone gas: A case study from the Central Sichuan Basin, China

“…The reservoirs in the second, fourth, and sixth members of the Xujiahe Formation discovered in Central Sichuan Basin are nonconventional tight reservoirs, with porosity of generally less than 10% and permeability of less than 1 mD. Many researchers have made significant contributions to the understanding of the Xujiahe Formation with respect to sedimentology, stratigraphy, reservoir characteristics, and diagenetic evolution (Bian et al, 2015; Li, Chen, Qiu, Su, & Wu, 2019; Yu et al, 2019; Zhang, 2021; Zhong, Huang, Ye, Lan, & Liu, 2020), including the impacts of sequence stratigraphy, sedimentary facies, and diagenesis on reservoir quality and the strong control of the changes in diagenesis (including coMPaction, cementation, and corrosion) on the heterogeneity of tight reservoirs.…”