| Sinian Dengying formation is an important marine carbonate gas reservoir in Sichuan basin, the exploration of Moxi-Gaoshiti gas field shows a great potential for further exploration. Affected by Tongwan movement, the inner and top of Dengying Formation is under weathering and eluviation, and moud-shoal carbonate with reconstruction by crust karst is thought to be the premium reservoir of Dengying Formation, and the location of the premium reservoir is controlled by the crust karst paleogeomorphy. So restorating crust karst paleogeomorphy and studying the karst reservoir of the Sinian Dengying Formation have important directive to carbonate reservoir exploration. Based on newly drilled well data in the Gaoshiti area in the central Sichuan Basin, profile data of more than150field outcrops of the regional geological survey, and stratigraphic division and correlation of more than30wells in the Sichuan Basin and its adjacent areas, combined with regional seismic data, moldic methods are comprehensively used to restore the karst paleogeomorphy of the Dengying Formation, and thus studying the pale geographic pattern and the significance of oil and gas exploration. The Sichuan Basin was surrounded by paleo-lands/underwater highlands in the late Sininan Dengying period-the early cambrain, such as Kangdian paleo-land in the west, Songpan paleo-land in the northwest, Hannan paleo-land in the north, Qianjiang-Zheng’an, Zhenba and Wuxi-Jianshi underwater highlands in the southeast and northeast. The Sichuan Basin was adjacent to Jiangnan Basin southeastwards and Qinling paleo-ocean northeastwards respectively. Affected by the separation of NS-striking Zitong-Junlian Aulacogen, NE-striking Langzhong-Tongjiang and ChongqingKaixian depressions in this basin, the Sichuan Basin shows the NS-trending framework of "three uplifts (Zhenba, Chuanzhong and Qianjiang-Zhengan) and two depressions (Langzhong-Tongjiang and Chongqing-Kaixian)" and is divided into two relatively isolated EW-trending paleo-uplift systems (NS-striking Mianyang-Leshan-Xichang paleo-uplift and nearly NE-striking Chuanzhong paleo-uplift). Controlled by karst paleogeomorphy of the Sinian Dengying Formation, the pattern of karst landscape consists of five secondary geomorphic units, such as karst highland, karst platform, karst slope, karst depression and karst basin, of which the karst platform and karst slope are the favorable zones for the development of karst reservoirs, providing advantages for the formation of large gas fields. |
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