近地表轻烃来源判识模型及其油气勘探应用基础研究

Whether the light hydrocarbon anomalies delineated in Surface Geochemistry Exploration (SGE) are derived from the deep oil and gas reservoirs or just from various near-surface reactions is one of the most concerns of the explorationists. In order to identify the sources of light hydrocarbon, researchers have proposed some identification cross plots using the genetic identification model of natural gas in the reducing environment underground for reference. But the near-surface weak oxidizing environment where light hydrocarbons are occurring is ignored. The ratios and carbon isotopes of near-light hydrocarbons are altered because of migration effect, microbial oxidation, mixture of multisource gas, etc. Consequently, it will lead to misjudgment of the sources of light hydrocarbon in surface if the genetic identification model of natural gas underground are used for reference. The modification degree of microseepage hydrocarbons by vertical migration and surface environmental factors lacks the reliable support of the simulation experimental data. The genetic identification cross plots for surface hydrocarbons based on simulation data in laboratory and survey data in known areas has not been established yet. This project is proposed on the basis of the previous research projects. The relationship between light hydrocarbon anomalies and quantitive environmental factors, the sources and geochemical characteristics of light hydrocarbon in surface will be studied in oil and gas field. Meanwhile, the migration processes of different sources of hydrocarbons under different surface conditions will be simulated in laboratory. The microseepgae processes and surface geochemical evolution mechanisms of light hydrocarbon will be explored through integration of above results. This study is to establish the identification model of the sources of light hydrocarbons in surface, improve the reliability of geochemical anomalies.

基于微渗漏理论的化探技术圈定的轻烃异常到底是深部油气信息还是表生作用形成的假象，是勘探者最关注的问题之一。如何判识近地表轻烃的来源，目前主要是借用地下处于还原环境的天然气成因类型判识图版，却忽视了近地表轻烃处于一个弱氧化环境，微渗漏轻烃的组构和稳定碳同位素特征除了受运移效应影响，还会因近地表喜氧微生物氧化等因素发生改变。因此，借用的图版会导致地表轻烃来源的误判。地下垂向运移过程和地表环境因子对微渗漏轻烃的影响程度一直缺乏可靠的实验依据，尚未建立基于模拟实验和已知区实测结果相结合的近地表轻烃异常判识图版，制约了油气化探的应用效果。本项目拟在前期工作基础上，开展已知油气田地表定量环境因子与轻烃异常之间的关系、近地表轻烃来源判识研究，同时对不同表层环境、不同源轻烃的微渗漏过程进行实验模拟，综合研究不同源轻烃地表地球化学演化机制，建立地表轻烃来源判识模型，提高油气化探异常信息的可信度。

油气地球化学勘探技术经过几十年的发展，虽然取得了很大进步，但仍然备受地质家质疑，其中近地表轻烃来源的判识是关键问题。当前近地表轻烃来源判识在干扰因素研究方面基本以定性校正为主，尚未系统开展轻烃与定量环境影响因子关系研究，没有定量校正。地表轻烃来源判识基本仍以烃类同位素和组构方法为主，对影响因素研究尚不够深入，成因判识仍模棱两可。上述问题很大程度上影响了油气化探的应用效果。.针对干扰因素问题，以川西坳陷新场地区、济阳坳陷惠民凹陷南坡临南-钱官屯地区为试验区，开展了油气田地表轻烃与定量环境因子的关系研究，用定量校正法有效地抑制了干扰因素，提高了近地表油气信息提取的精度，取得了较好的效果。针对地表微渗漏轻烃受运移效应和微生物氧化作用的影响程度问题，基于油气微渗漏的理论模型，首次建立了不同渗漏源类型烃类微渗漏模拟实验装置，包括气源、储层、盖层、上覆多重岩性叠置、潜水面、土壤层、采样探头等为一体的实验系统，为开展不同源轻烃微渗漏及其响应机理研究提供了实验技术手段。通过不同源类型（气田气、油田气、生物气）烃类微渗漏模拟实验，揭示了潜水面上下地球化学指标变化规律和“似源组构”，同时将室内模拟结果与已知油气田实测结果综合研究，建立了适用于地表轻烃来源判识图版，为化探异常判识提供了重要的理论依据。利用轻烃微渗漏的动力学方程，编制有限差分计算程序来对模拟实验中的轻烃微渗漏过程及垂向地球化学特征进行了数值模拟。数值模拟结果与实验模拟结果吻合度较好，进一步验证和揭示了轻烃垂向微渗漏机理，夯实了油气化探的基础理论。.上述研究成果在今后油气勘探中具有良好的应用前景，可以提高油气化探异常的可信度，以及解释评价的精度和预测成功率。