油气生成后运移的结果有3种:1)聚集成藏;2)散于岩层和流体中;3)与途经的流体-围岩相互作用所耗损或暴露地表而散失,后者称之为“耗散”。在油气运移过程中,耗散部分最为活跃,与聚集成藏的油气联系最为密切;为油气地质研究、勘探部署和资源评价等不可或缺的重要研究内容。根据油气耗散前、后数量和性质等方面的差异,将油气耗散划分为数量减少、相态转变、成份改变和性质转化4种类型,分别不同程度地体现了油气耗散的环境、条件和特点等方面的差异。其中性质转化类通常发生在埋藏不很深的表浅层或地表,油气与围岩、流体或大气等相互作用所形成的各种还原蚀变等后生产物及矿产,一般已不具烃类的表观特征。但其油气耗散量通常十分巨大,应给以足够的重视。将这类一般不具烃类特征的产物与直接显示油气耗散的结果(如油气苗、沥青、稠油等)相结合,对其追根溯源,可能为探讨和解决油气耗散及其规模这一国际难题的重要途径;也是示踪、发现和预测相关矿床的有效线索和重要标志。本文探讨了鄂尔多斯盆地东北部与上古生界天然气耗散有关的各种后生产物的类型、基本特征、地球化学性质、形成环境和分布特点等。
Hydrocarbon migration may have three results: (1)accumulation, (2)diffusion in rocks and fluids,or (3) loss due to interactions with fluids and surrounding rocks or surface exposure. The latter is defined here as dissipation. The dissipation is most active during hydrocarbon migration and is closely linked to hydrocarbon accumulation, thus study of the phenomenon become an indispensible part of petroleum geology research, and petroleum exploration and resource assessment. Hydrocarbon dissipations can be divided into four types according to the differences of quantity and quality of hydrocarbons before and after dissipation : quantity decrease, phase transformation, composition alteration, and quality conversion, reflectting the differences in environment, conditions and characteristics of dissipation. The quality conversion often occurs at surface or near surface, where hydrocarbons will interact with surrounding rocks, pore fluids or air. The epigenetic products and minerals resulted from these interactions generally have no apparent features of hydrocarbons, but the amount of dissipated hydrocarbons is huge, thus much attention should be given to this phenomenon. These products in combination with direct evidences of hydrocarbon dissipation( such as seepage, bitumen and heavy oil)can not only serve as an important means to address the puzzle of hydrocarbon dissipation and its scale, but also provide effective clues and significant indicators for tracing hydrocarbon pathways, searching for oil and gas pools, and evaluating the scale of dissipations. This paper analyzes and discusses the types, basic characteristics, geochemical properties, environments of formation and distributions of various epigenetic products related with gas dissipation in the Upper Paleozoic in northeastern Ordos Basin.