论“定凹探边”与“定凹探隆”

生油层、储油层和盖油层的存在、它们之间的组合关系以及它们在空间上的分布和时间上的变化,对于油气藏的形成有决定性的作用。其中,生油层是主要的。生油层形成的条件为:第一,要有大的水体,即,有大型盆地或大型凹陷区;第二,这个水体需要在一定时期封闭,处于还原环境,以使大量生油母质得以保存并进行厌氧细菌的发酵及化学作用;第三,生油盆地应具有持续的大幅度的沉降及快速堆积。从我国一些生油盆地的生油层位来看,其堆积速度都是相当大的(表1)。大幅度的沉降和快速堆积,不仅提供了巨大的生油岩体积,而且使有机质在上覆沉积岩的厚度及荷重不断增大的情况下,具有足够的温度(主要条件)和压力,导致了生油母质的热裂化反应而得烃类。本文第一作者早已指出,深的内陆凹陷、海陆交替相的泻湖盆地以及滨海古河口三角洲是生物大量繁殖并成为油源的地区;而沉积环境的快速和突然变化以及适当的地温梯度和压力是生物大量死亡和快速埋藏并向油气转化的主要条件。所以,我们勘探油气藏必须首先确定生油凹陷,恢复原生古盆地面貌。“定凹”就是这样提出来的。

THE SIGNIFICANCE OF "DELIMITING THE DEPRESSION AND ITS BOUNDARIES" AND "DELIMITING THE DEPRESSION AND UPLIFT" IN PROSPECTING OIL AND GAS

It was about in 1950’s to the beginning of the 60’s that Prof.Zhang Wen-you gradually summed up the experiences in prospecting oil and gas and first introduced the idea "delimiting the depression and its boundaries" and "delimiting the depression and uplift",relying on abundant geological data from basins in China.The distribution of oil and gas within a basin is chiefly controlled by the mode of activity of the fractures in the basement.The basement with vertical or inclined fault-planes slided down and up formed depressions and uplifts in facilitating the accumulation of hydrocarbons.From practical experience,the deep depression with thick sediments in a basin is usually favorable for generation of oil and gas and the higher margin and subswell in depression is usually good for accumulation of oil and gas,while high productive wells are often located at the intersections of the margins of depressions and central subs-wells therein.Examples of these oil and gas fields are riot rare in the basins of various orders of magnitude in China,such as oil and gas fields,namely the Liaohe,the Dagon and the Shungli,etc.along the margin of the great Bohai depression and the Daqing oil field on the central subswell of the great Songliao basin in eastern China.Similar cases are also found in other parts of China.