Abstract: The subdivision of hydrocarbon evolution stage and the resource potential evaluation of source rocks are of great significance for deep conventional and unconventional petroleum exploration and studies on deep basic petroleum geology. The hydrocarbon evolution of deep source rocks can be divided into four stages, i.e., light oil (volatile oil), condensate, wet gas and dry gas, corresponding to four types of deep hydrocarbons that may be sourced from the source rocks in crude oil reservoirs. Using thermal simulation, this paper evaluates the hydrocarbon generation potential of deep source rocks, and then puts forward indexes for the division of four hydrocarbon evolution stages. In view of the fact that the evaluation of resource potential of deep source rocks needs to consider whether normal crude oil is expelled and how much the expulsion is, an experimental scheme of first performing oil expulsion at peak of normal oil generation and then starting heating of oil expelled source rock in a confined pyrolysis system is adopted to establish the hydrocarbon evolution mode of deep source rocks. This mode can be used to roughly evaluate the hydrocarbon resource potential of deep source rocks. Based on the experience of reservoir classification according to the gas over oil ratio in reservoir (GORr), the gas over oil ratio in source rock (GORs) and the methane content of source rock pyrolysis simulation products are used as the classification indexes of hydrocarbon evolution stage under laboratory thermal simulation conditions. The rapidly rising GORs values, i.e., 142 m³/m³ (800 scf/bbl), 890 m³/m³ (5 000 scf/bbl) and 3 562 m³/m³ (20 000 scf/bbl), and 95% methane content were taken as the upper GORs limits of light oil, condensate, wet gas and dry gas, respectively. Considering that GORs cannot be obtained directly from component analysis of core samples, these limit values cannot be used for dividing the hydrocarbon evolution stages of actual sections. Since the vitrinite reflectance (R_o) or equivalent vitrinite reflectance (R_oE) is commonly used by explorers to classify hydrocarbon generation stages of source rocks, the Ro range of the above GORs limits can be obtained by converting the laboratory temperature into R_o using the oil inhibition R_o model. It is worth noting that the R_o value obtained from the thermal simulation experiment in a confined pyrolysis system is higher than the R_oE value measured in the actual formation. Light oil and condensate can be divided into four categories according to their geneses. Among them, type A is formed by type Ⅰ to type Ⅱ organic matter after oil expulsion, type B is formed by type Ⅱ to type Ⅲ organic matter without hydrocarbon expulsion, type C is formed by crude oil cracking, and type D is formed by secondary alteration. At present, the researches on primary light oil and condensates (type A, B and C oil and gas) are insufficient and need to be strengthened. Deep light oil and condensate resources are not only affected by the organic matter content, type and maturity of source rocks, but also related to the following geological factors of deep strata:(1) hydrocarbon expulsion efficiency of normal oil (black oil); (2) large-scale oil cracking in reservoir; (3) mixture of oil and gas from different sources. Various genetic types of light oils and condensates are found in China, showing broad exploration prospects in the fields of light oil and condensate resources.

Key words: hydrocarbon evolution stage, oil cracking hydrocarbon, deep oil and gas, light oil, condensate, genetic type, resource potential

摘要： 烃源岩油气演化阶段的细分与资源潜力评价对深层常规和非常规油气勘探、深层基础石油地质学问题的研究具有重要意义。深层烃源岩的油气演化可划分为4个阶段，即轻质油（挥发性油）、凝析油气、湿气和干气，也对应着深层的4种油气类型。烃源岩和储层中的原油体系均可形成这些油气。通过模拟实验评价深层烃源岩的生烃潜力，提出了4个油气演化阶段的划分指标。鉴于深层烃源岩的油气资源潜力评价需要考虑正常原油是否排出和排出量多少等问题，采用先进行生烃高峰排烃、再进行限定体系加热的实验方案，建立了基于排烃作用的深层油气演化模式。该模式可粗略用于深层烃源岩油气资源潜力评价。借鉴基于开采气油比（GORr）划分油气藏类型的经验，利用烃源岩裂解模拟产物的气油比（GORs）和甲烷含量作为实验室热模拟油气演化阶段的划分指标。将GORs快速上升时的值142 m³/m³（800标准立方英尺/桶）、890 m³/m³（5 000标准立方英尺/桶）、3 562 m³/m³（20 000标准立方英尺/桶）以及甲烷含量95%分别作为轻质油、凝析油气、湿气、干气的上部界限值。考虑到无法通过岩心样品直接获取GORs，因此，这些界限值还不能用于实际剖面的油气演化阶段的划分。鉴于勘探家常用镜质体反射率（R_o）或等效镜质体反射率（R_oE）划分烃源岩的生烃阶段，因此，采用抑制的R_o模型将实验室的温度标尺转化为R_o，求出上述界限值的R_o范围。值得注意的是，通过限定体系热模拟实验求出的R_o值比实际地层测定的R_oE值要高。轻质油和凝析油气按成因可分为4类，其中，A类由Ⅰ—Ⅱ型有机质经排烃后形成，B类由未经排烃的Ⅱ—Ⅲ型有机质形成，C类由原油裂解形成，D类由次生改造形成。目前对原生轻质油、凝析油气（A类、B类和C类油气）的研究还很不够，需要加强。深层轻质油、凝析油气资源除受烃源岩的有机质含量、类型和成熟度影响外，还与下列深层地质因素有关：①正常油（黑油）的排烃效率；②是否存在大规模的油藏裂解；③是否有来自不同烃源层的油气混合。中国发育有多种成因类型的轻质油和凝析油气，具有广阔的轻质油、凝析油气资源勘探前景。

关键词: 油气演化阶段, 原油裂解烃, 深层油气, 轻质油, 凝析油气, 成因类型, 资源潜力