门限控烃作用及其在有效烃源岩判别研究中的应用

Threshold Control over Hydrocarbons and Its Application in Distinguishing Valid Source Rock

油气在生排运聚成藏过程中需经历生烃门限、排烃门限、成藏门限和资源门限 .某一确定的油气运聚成藏系统进入任一门限都将损耗一部分烃量 ,实际地质条件下源岩生成的烃量只有超过进入各个门限时损耗烃量之和后才能大规模聚集成藏 ,构成油气勘探的远景区 ;只有提供的油气满足成藏过程中各种油气损耗形成工业油气聚集的源岩才称为有效烃源岩 .阐明了各门限的地质含义、判别标准和控油气作用机理 ,并将门限控烃作用在塔里木盆地台盆区古生界碳酸盐岩源岩评价中进行了应用 .研究表明 ,不存在一个放之四海而皆准的最小有机质丰度下限 ,最小有机质丰度下限受源岩自身条件及成藏地质条件的共同影响 .

A series of thresholds, such as thresholds of hydrocarbon generation, expulsion, accumulation and resources, may occur during reservoir formation. Part of hydrocarbons are consumed in certain reservoir system of petroleum when reaching a threshold. Oil and gas supplied by source rocks in practical geological conditions can be accumulated to form reservoir in larger scale and be of promising oil and gas exploration future only after hydrocarbon generation amount from the source rock is more than the sum of hydrocarbon lost across each threshold. Source rocks can be called valid source rock only when the excessive oil and gas come from them can form a commercial reservoir after the amount of hydrocarbons generated by the source rock meets the need of all kinds of wasting during the process of reservoir formation. The paper presents geologic meanings, judging standards, mechanisms of controlling oil and gas of thresholds and their application in Paleozoic carbonate source rock evaluation in Tarim basin. Researches indicate that there is not a minimum lower limit of organic matter abundance which can be used validly everywhere. While the minimum lower limit of organic matter abundance was affected by conditions of the source rock itself, together with the geological conditions of reservoir formation.