二次生烃机理在中下扬子高演化烃源岩评价中的应用

APPLICATION OF THE MECHANISM OF HYDROCARBON REGENERATION TO EVALUATION OF SOURCE ROCKS OF HIGH MATURITY IN MIDDLE AND LOWER YANGTZE REGION

在野外地质观察、油气地球化学和样品分析的基础上,通过总结二次生烃特征和生烃机理,将其应用到中下扬子区海相高演化烃源岩生烃潜力的评价。模拟实验结果表明,二次生烃具有明显的迟缓现象,也仍具有相对的生烃高峰,二次生烃量与一次生烃量的总和小于连续热演化的生烃量,这些特征都与一次生烃的演化程度密切相关,初始演化程度成为评价高演化烃源岩二次生烃潜力的关键因素。中下扬子区中—古生界发育的6套烃源岩中,下二叠统、下志留统和下寒武统烃源岩具有较强的生烃能力,是主要的烃源层。下古生界烃源岩进入生烃时间较早,在强烈的构造运动背景下,生成的油气难以保存;上古生界烃源岩热演化程度相对较低,燕山—喜山期的再次沉降地区成为二次生烃的供源区。因此,下古生界台地相区和上古生界烃源岩具有一定的二次生烃潜力。

Mechanism of hydrocarbon regeneration, on the basis of geologic research in field, hydrocarbon geochemistry and sampling, was applied to evaluation of source rocks potential of high maturity in Middle and Lower Yangtze region. Through simulating, it is shown that there is obvious time lag in the performance of hydrocarbon regeneration and also there is peak of hydrocarbon generation. Relationship among the hydrocarbon regeneration quantity, first and second generation quantity and one-time successive generation relies on the degree of initial maturity of hydrocarbon regeneration that is the key factor to evaluate potential of hydrocarbon regeneration of source rocks of high maturity. In Mesozoic-Paleozoic, the Lower and Middle Yangtze region gave birth to six sets of source rocks, of which three sets（lower Cambrian Series, lower Silurian Series and lower Permian Series）are great in width, high in richness and potent in hydrocarbon generation, being the most important hydrocarbon source rocks in the region. The lower Paleozoic source rocks have high thermal evolutionary degrees,and very early enter the period of hydrocarbon generation. Against the background of intensive tectonic movements, the early period of lower Paleozoic（the thermal evolutionary hydrocarbon generation）did not have adequate conditions for hydrocarbon preservation. The upper Paleozoic source rocks have relatively lower thermal evolutionary degrees, did not enter oil generation stage until Indo-Chinese-Yenshan epoch, and reached the oil generation peak in Yenshan epoch, thus such area is the major supply area for hydrocarbon regeneration. So the lower Paleozoic stable platform and the upper Paleozoic source rocks have high potential of hydrocarbon regeneration.