四川盆地东南部中、下寒武统膏岩盖层分布特征及封盖有效性

Distribution and sealing effectiveness of Middle-Lower Cambrian evaporite cap rocks in the southeastern Sichuan Basin

通过野外剖面、钻井剖面的精细对比,结合宽带约束的地震资料反演,对四川盆地东南地区中、下寒武统膏岩盖层的分布特征进行了研究,并在四川盆地及周缘构造演化的基础之上对中、下寒武统膏岩盖层的封盖有效性进行了探讨。四川盆地东南地区中、下寒武统膏岩连片分布,呈北东向展布,发育两个膏岩厚度中心,膏岩展布和圈闭分布完全匹配。在加里东期和印支期,四川盆地东南地区中、下寒武统膏岩层未遭受破坏,能够有效封盖震旦系古油(气)藏;在燕山期和喜马拉雅期,则膏岩层遭受破坏,失去了对丁山-林滩场地区古油(气)藏的封盖作用。同时指出,七跃山断裂以西地区膏岩层在后期构造运动中未被完全破坏,能够对盐下油气藏起到封盖作用,是川东南地区寒武系盐下的有利勘探区带。

Based on correlation of outcrop section with wellbore pofile and in combination with seismic inversion under the constraint of broadband,this paper analyzed the distribution of the Middle-Lower Cambrian evaporite cap rocks in the southeast of Sichuan Basin.It also discussed the sealing effectiveness of the evaporite cap rocks based on study of the tectonic evolution of Sichuan Basin and its periphery.In the southeastern Sichuan Basin,the Middle-lower Cambrian evaporites are widely distributed in northeast direction with two thickness centers,and the distribution of evaporites coincides perfectly with the trap distribution.During the Caledonian and Indosinian period,sealing capacity of the Middle-Lower Cambrian evaporites was not destroyed,so they could serve as effective seals for the Sinian ancient oil（gas） accumulations.Whereas,their sealing capacity was lost during the Yanshan and Himalayan period,thus the ancient oil（gas） accumulations in the Dingshan-Lingtanchang area were not effectively preserved.As the Middle-Lower Cambrian evaporite cap rocks to the west of Qiyueshan fault were not destroyed completely post-Indosinian movement,they could effectively seal the presalt Sinian oil（gas） accumulation,thus this area is favorable for petroleum exploration in the pre-salt strata in southeastern Sichuan Basin.