Abstract: 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 evapo-rites 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.

Key words: fault, sealing effectiveness, evaporite, Middle-Lower Cambrian, southeastern Sichuan Basin