Depositional Pattern and Reservoir Distribution of Changxing Formation Intra-platform Reef and Shoal in Wolonghe-Yangduxi Zone of eastern Sichuan Basin

Key words: 
• Wolonghe-Yangduxi tectonic zone /
• Changxing Formation /
• intra-platform reef and shoal /
• sedimentary patterns /
• favorable reservoir

Abstract: With vigorous promotion on the exploration for carbonate reef and shoal reservoirs in eastern Sichuan basin, the intra-platform reef shoal reservoir has become one focus in this area, but the study extent is lower. In this paper, based on the study on cores, field profiles and thin section data, it is ascertained that the principal sedimentation type of the study area mainly consists of Changxing Formation carbonate ramp sedimentation developed at early stage, and carbonate platform sedimentation developed at middle and late stages, open platform facies is the main sedimentation. The Changxing Formation can be divided into two third order sequences,the intra-platform reef and shoal bodies are mainly developed in Sq1-HST and Sq2-HST, and lateral distribution is not continuous, longitudinal development of phase changes, the west tectonic zone is mainly developed by Sq2-HST, whereas the east tectonic zone is developed by both Sq1-HST and Sq2-HST, and Sq1-HST is more developed. Physical analytic data show that grain dolomite and powder dolomite are the main reservoir rocks, the intra-platform is the main reservoir facies, sedimentary structure within reefs station controls the distribution of favorable reservoir. But the intra-platform highland plays a vital role in controlling the distribution of reef shoal. The vast majority of reef shoals recognized by geologic and seismic data are distributed along the Sui'ning and Guang'an intra-platform highlands, Wolonghe tectonic zone is already disclosed favorable reservoir zone, and the high zone in the south of the study area may be the important exploration direction of the intra-platform reef shoal reservoirs in this area in the future.