珠江口盆地深水区CO_2成因、分布规律与风险带预测

深水区油气勘探高成本要求尽量规避CO_2风险,其风险带的分布预测属世界性难题。在珠江口盆地CO_2和伴生稀有气体组分与同位素组成分析的基础上,查明CO_2来源(幔源岩浆脱气)和成因;在火成岩年龄和气藏40 Ar/36 Ar计算获得的CO_2生成年龄双重约束下,运用与CO_2包裹体同期盐水包裹体均一温度—埋藏史投影法估算了CO_2气藏的充注年龄(14.5~0.3Ma);通过其运聚模式、分布规律分析与总结,发现了其具有新生代火成岩展布、断裂展布和砂岩输导体系展布及CO_2聚集时限与圈闭形成时空匹配关系等4个主控因素。根据揭示的这一分布规律,预测了深水区恩平组、珠海组和珠江组存在多个NNW向分布的高CO_2风险带,从而为珠江口盆地下一步油气勘探部署规避高CO_2风险带提供了依据。

Genesis,distribution and risk belt prediction of CO2 in deep-water area in the Pearl River Mouth Basin

The high cost of oil and gas exploration in deep-water area requires that the risk of CO₂ should be prevented to the greatest extent, and the distribution prediction of its risk belt is a worldwide problem. In this study, the source (degassing of mantle-derived magma) and genesis of CO₂ were identified first based on the analysis of CO₂ and associated rare gas composition and isotope composition in the Pearl River Mouth Basin. Then, under the double restraints of age of igneous rock and the CO₂ generation age obtained from the calculation of ⁴⁰Ar/³⁶Ar in gas reservoir, the injection age (14.5-0.3 Ma) of the CO₂ gas reservoir was estimated using the projection method of homogenization temperature and burial history of the saline water inclusions coeval with CO₂ inclusions. Moreover, through analysis and summary of CO₂ migration and accumulation model and distribution law, it is found that there are four main controlling factors, i.e., Cenozoic igneous rock distribution, fault distribution, sandstone transport system distribution and spatial temporal matching relation of CO₂ accumulation time limit and trap formation. Finally, according to the revealed accumulation and distribution law, it is predicted that there are several NNW-trending high CO₂ risk belts in Enping Formation, Zhuhai Formation and Zhujiang Formation in the deep-water area, providing a reference for avoiding the high CO₂ risk belts in the next deployment of oil and gas exploration in the Pearl River Mouth Basin.