不同成因凝析油的地球化学鉴别

Condensate pools have been widely found in the world,although the genetic type of the condensate has been focused by geochemists all around the world, its geochemical criterion type has not been established systematically. Two views of condensate genetic types were hold by the geochemists, which are as follows: (1) thermal degradation of the organic matter including the thermal degradation of the kerogen and the cracking of the paleo-oil reservoirs; (2) migration fractionation. Due to the lack of a systematic division basis, it is difficult to distinguish the genetic types of the condensate, and thus to further undstand the formation progress of the condensate reservoirs. As a special type of hydrocarbon fluid,its internal liquid and gaseous hydrocarbons contain rich geochemical information, which is important clue for reflecting their genetic types and the formation progress of the condensates. This work would exploit the geochemical characteristic of the organic matter, the condensate and the associated natural gases, such as the composition of organic maceral, the biomarker, the carbon and hydrogen isotopes, and the light hydrocarbons, etc, to analyze the geochemical characteristics of condensate generated by different types of organic matter.On the basis of the geochemical research, the geochemical identification standard of condensates generated by different types of organic matters would be established. After the anatomy of the typical condensates pools originated from migration fractionation and the paleo-oil reservoir cracking and the geochemical characteristics of the condensates, geochemical identification criterion of these two types of condensates would be established too.

凝析气藏在国内外油气勘探中发现较为普遍，但目前尚未建立系统鉴别凝析油成因的地球化学标准。前人研究认为，凝析油具有两大类成因：一是有机质的热降解，包括干酪根的降解和古油藏的裂解；二是运移分馏作用。由于缺乏系统的划分依据，鉴别凝析油成因时面临诸多困难，因此制约了地质学家对某一地区凝析气藏的成藏认识。凝析油作为一类特殊的烃类流体，其液态烃和气态烃同时产出，内含丰富的地球化学信息，这些信息提供了认识其成因的重要线索。本文拟依据烃源岩、凝析油、天然气的有机显微组分、生物标志物、碳氢同位素、轻烃等地球化学特征分析以及典型的凝析气藏实例解剖，分析不同类型有机质生成凝析油的地球化学特征，并以此为依据建立划分不同类型有机质生成凝析油的地球化学标准。详细解剖由运移分馏作用以及古油藏裂解形成凝析油的地质过程和地球化学特征，建立区分上述两种凝析油的地球化学标准。

凝析气藏是一种重要的油气藏勘探类型，具有很高的工业应用价值和学术研究价值。不同成因类型的凝析油（凝析气藏）具有不同的形成条件和成藏过程，鉴别其成因类型在油气勘探中无疑具有重要的应用价值。在前人研究成果基础上，本文通过分析塔里木盆地、鄂尔多斯盆地、四川盆地、渤海湾盆地、莺琼盆地、珠江口盆地、东海盆地等国内重要的含油气盆地中100余口井凝析油的生物标志物、轻烃、全油碳同位素、轻烃单体烃碳同位素、金刚烷含量、原油成熟度，凝析油伴生气组分、碳同位素、轻烃组成和成熟度组成，结合烃源岩、热演化史、构造演化史以及典型凝析气藏的成藏过程，对不同成因类型的凝析油（凝析气藏）进行了研究，提出了相应的鉴别指标和图版。取得了如下认识：.1、按照母质类型，凝析油可以分为腐泥型和腐殖型两类；按照凝析气藏的形成过程，可以分为原生型（干酪根热降解直接生成凝析气）和次生型（运移分馏作用和古油藏热裂解形成凝析气）。.2、依据碳同位素、轻烃、生物标志物组成，建立了三大类25项腐殖型和腐泥型凝析油的综合鉴别指标。腐殖型凝析油碳同位素组成重于腐泥型凝析油，其全油、芳烃碳同位素均重于-27.5‰，后者则轻于-27.5‰；C4-7轻烃单体烃碳同位素，腐殖型凝析油分布区间为-28‰~ -17‰，腐泥型凝析油为-33‰ ~-29‰；甲基环己烷、环己烷、甲基环戊烷、甲苯和苯等五类轻烃的碳同位素中，腐殖型凝析油均重于-24‰，而腐泥型凝析油则轻于-24‰；轻烃组成中，腐殖型凝析油富含芳香烃类，甲基环己烷指数> 50±2%，在C7轻烃组成中富含甲基环己烷，而腐泥型凝析油则富含正构烷烃，甲基环己烷指数< 50±2%，腐殖型凝析油中可以检出丰富的杜松烷、双杜松烷和奥利烷，而腐泥型凝析油中没有，且其C29规则甾烷含量<C27规则甾烷。.3、运移分馏作用形成的凝析气藏原油成熟度低、金刚烷含量较低、伴生气成熟度高、甲苯/正庚烷值相对于正庚烷/甲基环己烷值变化迅速、原油同位素差异<1‰；古油藏裂解形成凝析气藏原油成熟度高、金刚烷含量很高（可达100ug/g以上）、油气轻烃组成相近、储层中存在大量高过成熟度的固体沥青、原油同位素差异达3‰以上。