烃源岩中有效有机质的类型评价及意义

EVALUATION OF THE EFFECTIVE ORGANIC MATTER TYPES IN HYDROCARBON SOURCE ROCK AND ITS IMPLICATION

在经典干酪根质量划分方案的基础上,将原来的惰性干酪根进一步细分为"死碳"和无效碳,分别为不参与生烃和参与生烃但不作为油气产物的有机碳。新的干酪根质量划分方案可以很好地解释地质条件下氢质量分数与有机质丰度之间常见的协变关系。结合生、排烃模型,随着成熟度的增加,氢质量分数沿带状曲线逐渐降低,并不是沿某一条曲线逐渐降低,与地质数据相符,说明一套烃源岩原始的氢质量分数采用定值并不合适。烃源岩中有效有机质的类型定义为参与生烃的有机质类型,烃源岩有机质由有效有机质与无效有机质组成,后者无生烃潜力但会降低氢质量分数的计算值。一套烃源岩内氢质量分数的变化可能是有机质保存条件的波动(如硫酸盐还原强度的变化)的反映,并非一定是由于有机质类型输入的变化。有效有机质类型评价表明,有效有机质类型为倾油(油源岩),但原始氢质量分数低的烃源岩仍是形成滞留油裂解气型页岩气藏的有利烃源岩,常规有机质类型评价可能将这些烃源岩忽略。

On the basis of the classical classifying scheme of kerogen masses, the original inert kerogen can be further divided into dead carbon （DC） and null carbon （NC）. They are respectively defined as organic carbons that are not involved in petroleum generation and involved in the generation without acting as hydrocarbon product. The new classifying scheme of kerogen masses can much better interpret the common covariant relation between hydrogen index （HI） and total organic carbon content （ TOC ） in geological data. Integrating with hydrocarbon generating and discharging models, with the rise of the maturity, HI is gradually reduced along the belt-like curves, but not a curve, which is accordant with the geological data. This fact show that it is not reasonable for the original HI of a set of source rock to be defined as a definite value. The definition of the types of the effective organic matter in source rock is determined as the organic matter types involved in petroleum generation. The organic matters in the source rock are composed of effective and non-effective ones, the later has no potential to generate hydrocarbon, but can reduce the calculated value of HI. The changes of HI in a set of hydrocarbon source rock may be the up- and-down reflection of the preserving conditions of the organic matter （ such as the variation of the intensified sulfate reduction activity ） , but not the change resulted from the input of the organic matter types. The evaluation of the effective organic matter type shows that the type belongs to oil-prone one （oil source rock） , even though the source rock with low HIo can also be a favorable source rock for the formation of shale gas reservoir generated from the residual oil cracking. However, for the assessment of conventional organic matter types, these hydrocarbon source rocks may be neglected.