Tectonic framework and oil-gas geological significance of Late Permian Changxing Period in Sichuan Basin

doi:10.13745/j.esf.sf.2024.12.81

Abstract

Abstract:

The Sichuan Basin during the Late Permian Changxing Period was influenced by multiple tectonic systems. However, few studies have established the correlation between the basin’s tectonic pattern and reef reservoirs from the perspective of basin and orogenic evolution. Based on previous geotectonic studies, this research establishes the genetic relationship between plate tectonics, basin tectonic patterns, and reef reservoir formation through analysis of geophysical and well-log data from the Sichuan Basin. The results show: (1) During the Changxing Period, the northern and southern parts of the Sichuan Basin were influenced by the tectonic evolution of the Mianlüe Ocean and the Emeishan mantle plume. Basement NWW-trending faults were reactivated, forming the Kaijiang-Liangping Trough and the Pengxi-Wushengtao Depression through extension and strike-slip, respectively. (2) The trough exhibits a semi-graben structure with a steep eastern flank and a gentle western flank. NEE- and NW-trending faults developed in the overlying area of the eastern boundary faults, while small folds developed at the bends of the western boundary faults. Strike-slip motion along the boundary faults within the depression formed a Riedel shear structure, including P-shears (NEE-trending faults). (3) Reefs on the steep western slope of the trough are stacked vertically along the boundary fault, whereas reefs on the gentle slope migrated laterally. Reefs also develop near the eastern and western boundary faults of the platform depression, near the internal NEE-trending faults, and in the cores of folds located at the bends of the boundary faults. (4) The boundary faults of the trough and depression connect with Cambrian and Permian hydrocarbon sources. Reefs in the nearby Changxing Formation form “lower-generation and upper-storage” accumulation assemblages. Reefs on the platform margin and source rocks within the trough form “side-generation and side-storage” assemblages. The NEE-trending faults within the platform connect Changxing Formation organic reefs with the Longtan Formation hydrocarbon source, forming a “lower-generation and upper-storage” assemblage. In contrast, reefs in the small fold cores at the bends of the platform depression boundary faults lack underlying fault-connected hydrocarbon sources and are predominantly water-bearing. (5) In the northern Sichuan area between the Kaijiang-Liangping Trough and the Chengkou-West Hubei Trough, the extension direction during the Changxing Period intersected at a low angle with pre-existing Caledonian faults, reactivating these fault segments and forming transtensional faults. This study enriches our understanding of the tectonic evolution related to the Emeishan mantle plume and the Paleo-Tethys Ocean, providing a theoretical basis for hydrocarbon exploration and development of reef-beach reservoirs in the Changxing Formation.

Key words: Sichuan Basin, Changxing Period, structure framework, Kaijiang-Liangping Trough, Pengxi- Wusheng Depression, oil and gas reservoir, reef

CLC Number:

CHEN Youzhi, ZANG Dianguang, HU Gang, FENG Xukui, WANG Xiaoyang, XIAO Dong, CHEN Ying, XU Min, LIANG Hong, WU Yulin, CHEN Hui, GUO Haiyang, ZHAO Zhenwei, GUO Shuang, ZHOU Yuezong, TAO Jun. Tectonic framework and oil-gas geological significance of Late Permian Changxing Period in Sichuan Basin[J]. Earth Science Frontiers, 2025, 32(5): 28-37.

Figures/Tables 9

Fig.1 (a) Fault distribution diagram of Changxing Period on the west side of Pengxi-Wushengtai Depression and Kaijiang-Liangping Trough in Sichuan Basin; (b) Tectonic location map of the Sichuan Basin at the end of the Late Permian (sedimentary facies in a modified from reference [16]; Basalt distribution map quoted in references [17]; b modified from reference [18])

Fig.2 Synthetic seismic records of well Ql7, Sichuan Basin

Fig.3 Geological interpretation map of seismic section

Fig.4 Stress model diagram of Sichuan Basin during Changxing Period (dike location modified from reference [26])

Fig.5 Structural sketch

Fig.6 Seismic coherence map of local Changxing Formation fault in Pengxi-Wusheng Depression

Fig.7 Thickness map of Changxing Formation, Sichuan Basin

Fig.8 Seismic profile of North Sichuan region

Fig.9 Structure and reef development model map of North Sichuan during Changxing Period

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