海相、陆相油气及其成因概述

国外油气主要在海相地层中发现,而中国油气主要在陆相地层中找到,根本原因在于地层形成顺序两者相反,前者浅层以海相为主,后者浅层则以陆相为主,大量油气是通过壳深断裂从深部垂直向上运移所形成,储集于浅部的首先被勘探开发。中国海相油气勘探中面临三大问题:(1)海相碳酸盐岩的有机碳含量均很低,难以形成大规模的烃源岩;(2)无法解决碳酸盐岩中的油气运移问题;(3)一些海相地层油气田的油气来源存在争议。共可归纳出三种油气生成模式,即壳源有机质、壳—幔相互作用以及费-托合成。目前人们过于执着于壳源有机质生成,而对费-托合成模式还没有足够认识和重视,这种思维定势阻碍了油气勘探在理论和实践上的进一步发展。大量油气是在地幔深部通过费-托合成或在地壳深部通过壳—幔相互作用形成,并沿深大断裂向上运移,除了浅部有大量聚集,在地壳深部的花岗岩、火山岩、变质岩等基岩中,在我国深部的海相地层和国外深部的陆相地层中同样可以大量聚集。

A Discussion on Marine and Non-marine origin of Petroleum

Oil and gas abroad have been discovered mainly in the marine strata, but in China the oil and gas have been discovered mostly in the non-marine strata. The basic reason is the contrary sequence of the strata formation in China. As for the former, the shallow strata are mainly marine facies while for the latter the shallow strata are commonly non-marine facies. A huge amount of oil and gas could migrate up and accumulate into different reser- voirs from the deep along great crust fractures. The shallow reservoirs were firstly discovered and explored certainly. Three problems are faced to petroleum exploration of marine origin strata in China: ⑴Organic carbon content of marine carbonate rocks are too low to be large scales of hydrocarbon source rocks; ⑵Some problems of hydrocar- bon migration in carbonate rocks has not been well solved yet; ⑶Origin of hydrocarbon in the marine reservoir rocks has not been clear. Three models of hydrocarbon generation can be reduced to: crust-sourced organic matter, in- teraction between the crust and the mantle and Fisher-Tropsch synthesis. If we only rely on the organic generation theory and reject the other models of petroleum generation, the theory and practice in petroleum exploration would be hindered. Most of hydrocarbons were formed by Fisher-Tropsch synthesis in the mantle and the mid-crust or by the interaction between the crust and the mantle so that these hydrocarbons can migrate into the shallow from the deeper strata along large fractures and besides accumulating in the shallow, the hydrocarbon can accumulate in the deeper granites,volcanic rocks and metamorphic rocks and also in deeper marine strata in China and in deeper non-marine strata abroad.