四川盆地东部深层盐下震旦系—寒武系天然气成藏条件与勘探方向

Accumulation conditions and exploration directions of natural gas in deep subsalt Sinian-Cambrian System in the eastern Sichuan Basin, SW China

基于四川盆地东部（川东）周缘野外露头与钻井资料综合分析,通过对区内逾6×104 km2地震资料进行深层构造精细解释,刻画川东中下寒武统膏盐岩层平面展布,探讨川东深层盐下震旦系—寒武系天然气成藏条件,指出近期有利勘探方向。川东深层中下寒武统发育两套区域展布含膏盐岩层,其是川东区域性滑脱层,滑脱层之上发育断层相关褶皱,之下发育宽缓背斜;盐下发育6~7排北北东、北东向展布大面积构造圈闭。川东深层盐下具备良好天然气成藏条件,生储盖空间配置好：发育陡山沱组、灯三段与水井沱组3套烃源岩,以水井沱组为主;发育灯二段、灯四段与石龙洞组3套风化壳岩溶与颗粒滩型储集层;发育中下寒武统膏盐岩与水井沱组区域性盖层。川东深层盐下勘探应首选灯四段,石龙洞组与灯二段居次,首选油气运聚指向区、埋深适中且远离盆缘区域,红花店—华蓥山北、凉水井—蒲包山—雷音铺、大天池等3排构造是近期最有利勘探区带。

Based on comprehensive analysis of outcrops and drilling data, and interpretation of more than 6×104 km2 seismic data, this paper delineates the regional distribution of the gypsum-salt layers in Middle-Lower Cambrian in eastern Sichuan Basin, and discusses accumulation conditions for natural gas in deep subsalt Sinian-Cambrian System in eastern Sichuan Basin, and points out favorable exploration directions. There are two sets of regional gypsum-salt layers in the Middle-Lower Cambrian in eastern Sichuan Basin, which are regional detachment layers, with fault-related folds occurring above and broad anticlines occurring below. There are 6-7 rows of NNE and NE trending large traps developed under the salt. Good space configuration of source rocks, reservoirs and cap rocks provide favorable accumulation conditions for natural gas in the deep subsalt in this region： three sets of hydrocarbon source rocks including Sinian Doushantuo Formation, the third Member of Sinian Dengying Formation, and dominant Cambrian Shuijingtuo Formation; three sets of weathering crust karst reservoirs and grain beach reservoirs including the second and fourth Members of Sinian Dengying Formation, and Cambrian Shilongdong Formation; and the regional cap of gypsum-salt in the Middle-Lower Cambrian and shale in Shuijingtuo Formation. The top target in deep subsalt exploration in eastern Sichuan Basin should be the fourth Member of Dengying Formation, followed by Shilongdong Formation and the second Member of Dengying Formation, and areas on migration direction with appropriate burial depth and being far away from the edge of the basin should be the first choices in exploration. Therefore, the favorable hydrocarbon exploration areas in the near future are the Honghuadian-North Huaying Mountain, Liangshuijing-Pubao Mountain-Leiyinpu, and Datianchi structural belts.