1 College of Energy,Chengdu University of Technology,Chengdu 610059,China; 2 State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation,Chengdu University of Technology,Chengdu 610059,China; 3 Research Institute of Exploration and Development, PetroChina Southwest Oil & Gas Field Company,Chengdu 610041,China
Abstract：The carbonate rocks of the Permian Maokou Formation in the Sichuan Basin are crucial for oil and gas exploration. Significant breakthroughs have been achieved in the exploration of the Maokou Formation in the Bajiaochang-Moxi-Longnüsi area of central Sichuan Basin. However,the unclear stratigraphic structure impedes the study of sedimentary evolution and reservoir prediction of the Maokou Formation. This research is based on high-precision lithofacies characteristics of the Maokou Formation at the Er’ya section in the Huaying Mountain of Guang’an in central Sichuan Basin. It integrates actual drilling data to analyze the sedimentary facies and sequence stratigraphic framework of the Maokou Formation,explaining the influence of the sequence framework on the development characteristics and distribution patterns of the reservoirs. The research findings indicate that: (1)The carbonate rocks of the Maokou Formation in the central Sichuan Basin can be divided into eight lithofacies. During the late stage of deposition of the Maokou Formation,tectonic activity facilitated the transition from a gentle slope sedimentary system to a “platform-platform interior sea trough” sedimentary system. (2)The upper sequence interface SB1 of the Qixia Formation and the upper sequence interface SB2 of the lower submember of Member 2 of the Maokou Formation are both classified as type II lithofacies transition interfaces. The top interface SB3 of the upper submember of Member 2 of the Maokou Formation is identified as a type I drowning unconformity interface,while the top interface SB4 of Member 3 of the Maokou Formation is classified as a type I erosion unconformity interface. (3)The Maokou Formation in the Er’ya section can be divided into three third-order sequences and five fourth-order sequences. Member 1 of the Maokou Formation constitutes the transgressive system tract of third-order sequence SQ1. The middle to lower parts of the lower submember of Member 2 correspond to the high-position system tract of third-order sequence SQ1,while the upper part develops the transgressive system tract of third-order sequence SQ2 at the margin of the continental shelf. The upper submember of Member 2 and Member 3 of the Maokou Formation correspond to third-order sequences SQ2 and SQ3,respectively. (4)In the Moxi-Longnüsi area,the dolomitized reservoirs of the lower submember of Member 2 of the Maokou Formation are distributed in the high-position system tract of third-order sequence SQ1 and the continental shelf margin system tract of third-order sequence SQ2. These reservoirs are primarily dominated by late diagenetic dolomitization and early diagenetic dolomitization,controlled by type II sequence boundary SB2. In the Guang’an-Bajiaochang area,the dolomite reservoirs of the upper submember of Member 2 of the Maokou Formation in the platform margin shoal facies are found in the high-position system tract of third-order sequence SQ2 and are controlled by type I sequence boundary SB3. These reservoirs undergo stages of early diagenetic matrix dolomitization,late diagenetic grain dissolution,and burial dolomitization. This study provides constraints on sequence and sedimentation for predicting the distribution patterns and investigating the genesis of dolomite reservoirs in the Maokou Formation in the Sichuan Basin,which is significant for oil and gas exploration in the Maokou Formation.
KUANG Mingzhi,ZHANG Xiaobing,YUAN Haifeng et al. Sequence stratigraphy and sedimentary facies characteristics of the Maokou Formation carbonate rocks in central Sichuan Basin[J]. JOPC, 2024, 26(5): 1201-1220.
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