在天然气成因研究和勘探中,确定有效烃源岩和有效成藏组合是非常重要的。对于原型盆地来说 ,无论是碳酸盐岩还是泥岩 ,其有效烃源岩有机碳丰度下限值均为 0 .5 %。对于多旋回叠合残留盆地来说 ,该有机碳下限值对于二次生烃已不适用。有机质的成熟度不同 ,二次生烃有效烃源岩有机碳的下限值也不同 ,有机质成熟度 Ro 值在 1 .0 %～ 1 .2 %之间时 ,有机碳下限值为 1 .5 %～1 .8% ,Ro 值在 1 .2 %～ 2 .0 %之间时 ,有机碳下限值为 1 .8%～ 3 .2 % ,Ro 值在 2 .0 %～ 3 .0 %之间时 ,有机碳下限值为 3 .1 %～ 8.4% ,有机质成熟度 Ro 大于 4.0 %、H/C比值小于 0 .3的地区 ,无论有机碳丰度有多高 ,找气藏的希望则相当小。另一类有效烃源是古油气藏的储层沥青和局部残留的液态烃 ,由其裂解生成的烃类可以形成轻质油藏和天然气藏 ,这些次生油气藏有的再次被改造则形成晚期的天然气藏。因此 ,有效烃源岩或有效烃源生、排烃中心的叠加决定了次生油气藏的分布。

In the study of natural gas genesis and exploration, it is still our major task to determine effective hydrocarbon source rocks and accumulation assemblage. In terms of primitive basin, the low limit of organic carbon in effective hydrocarbon source rocks (whether carbonate rock limit or shale) is 0.5%. While in polycyclic superimposed sarsen basin, this value is not suitable to secondary hydrocarbon generation. The limits of secondary hydrocarbon generation in different maturation stages are as follows: when Ro is 1.0%～1.2%, the limit is 1.0%; when R-o is 1.2%～2.0%, the limit is 2.0%; when Ro is 2.0%～3.0%,the limit is 4.0%; While when Ro is more than 4.0% and H/C is less than 0.3, there are little probability to find gas reservoir regardless organic carbon abundance. The other effective hydrocarbon sources are reservoir bitumen and local residual liquid hydrocarbons in palaeoreservoirs. They can crack into light oil pools and gas reservoirs. And a few of these secondary pools were reformed once again into late gas reservoirs. So, the distribution of secondary reservoirs are d
etermined by effective hydrocarbon source rocks and center superposition of generation and migration of effective hydrocarbon sources.