油气藏上方地层中不同赋存态微渗漏轻烃特征初步模拟实验研究

油气藏的微渗漏烃类在岩石和土壤中的赋存状态，现阶段都已经建立起相应的分析方法，包括酸解烃、热释烃、顶空气轻烃、游离烃等，但各方法分析的静态数据尚不能准确描述微渗漏烃类在上覆地层和土壤介质中的赋存状态及特征。以往对于微渗漏轻烃赋存机理大多数研究限于理论层面，一直缺乏可靠的模拟实验结果支持，导致化探工作者对上述各类轻烃指标在应用上存在不同认识，以及对指标具有独立性存在质疑，从而影响了方法的合理应用和化探异常的解释。针对上述问题，以烃类微渗漏的简化理论模型为基础，开展烃类通过盖层及上覆地层垂向微渗漏模拟实验，对实验后的模拟柱体进行解剖，根据不同类别样品（气、岩）的分析测试结果，对游离烃、顶空气轻烃、热释烃、酸解烃在地层中的赋存机理进行了初步研究。结果表明，游离烃指标最能反映烃类垂向微渗漏的现今面貌，酸解烃指标短期内不受气体运移的影响，热释烃指标短期内受到气体运移的影响，顶空气轻烃指标受气体运移影响最显著。不同相态的烃类在岩石和土壤中赋存机理不同，受到影响因素不同，能从不同侧面反映油气微渗漏特征。上述实验结果有助于加深对油气化探不同类型轻烃指标的认识，更好地解释地球化学异常的地质意义。 

Simulation of microseepage of light hydrocarbon of different occurrence states in strata above reservoirs

Several geochemical methods to analyze light hydrocarbons in subsurface rock and soil microseeping from hydrocarbon reservoirs were set up. The hydrocarbons included adsorbed and thermally-released hydrocarbon, head space gas, and free gas, etc., but the static data analyzed through these methods could not accurately describe the occurrence states and features of microseeping hydrocarbons in the overlying strata and soil. Most past studies on the occurrence mechanism of microseeping hydrocarbons were limited to a theoretical level, and lacked the support of reliable simulation, resulting in different understandings of the application of the light hydrocarbon indexes and the independence among them, which affected the interpretation of geochemical anomalies and proper application of the methods. An experiment was conducted to simulate hydrocarbon vertical microseepage through cap rocks and overlying strata based on a simplified theoretical model of hydrocarbon microseepage. The cylinder was dissected to recover subsamples after the experiment. According to the test results of gas and rock samples, the occurrence mechanisms of free gas, head space gas, thermally-released hydrocarbon, and adsorbed hydrocarbon in the strata overlying a reservoir were studied. The results showed that the free gas indicators were best in reflecting the present features of vertical microseepage, and the adsorbed hydrocarbon indicators were not affected by gas vertical migration in the short term, whereas the thermally-released hydrocarbon indicators and the head space gas indicators were affected by gas micro-migration, with the latter being most significantly affected. Because the occurrence mechanisms and the influence factors of these hydrocarbons in rock and soil are different, the characteristics of hydrocarbon microseepage can be reflected by using these light hydrocarbon indicators from different aspects. These experiment results can help geochemical explorers deepen the understanding of different types of light hydrocarbon indicators, and to explain the geological significance of geochemical anomalies better.