桑托斯盆地盐下CO2聚集条件及对油气成藏影响

巴西桑托斯盆地盐下层系是近几年世界油气勘探的热点地区，但盐下已发现的油气田中普遍含有CO₂。通过对CO₂含量、CO₂碳同位素和伴生氦气同位素分析，明确桑托斯盆地盐下油气田中的CO₂成因类型主要为幔源无机成因。从CO₂成因类型出发，结合对桑托斯盆地盐下已发现油气田中CO₂含量与基底断裂展布关系，提出紧邻基底大断裂的油气田中CO₂含量往往高于远离基底断裂的油气田。同时，通过对桑托斯盆地盐下典型油气田中的CO₂形成条件和聚集成藏特征分析后，认为火山活动和晚期活化的基底断裂是桑托斯盆地盐下CO₂聚集成藏的主要控制因素，其中火山活动为CO₂的聚集成藏提供气源条件，晚期活化的基底断裂为CO₂聚集成藏提供了有利通道条件。受后期大量幔源CO₂源源不断地注入影响，油气藏中的油气组分发生蒸发分馏作用，并形成高含CO₂的凝析气顶和下部的稠油油环。

Accumulation Conditions of CO2 and Its Influence to Pre-salt Oilfields,Santos Basin

In recent years, the pre-salt sequence of Santos Basin is the focused exploration area, but CO₂ is generally found in the pre-salt oil fields. After analysis of CO₂ content, carbon isotope and helium isotope, the generation type of CO₂ in Santos basin pre-salt layers is inorganic mantel. Based on generation type and the comprehensive analysis of the correlation of CO₂ content with basement faults distribution, we found that fields closed to faults are generally high in CO₂ content. Meanwhile, the analysis of generation factors and accumulation elements of CO₂ in the typical fields displays that volcano activities and basement faults are the controlling factors for the accumulated CO₂ gas cap. And the volcano provides CO₂ source, faults acting as migration pathways. Affected by a large amount of inflow of continuous CO₂, evaporation and diffluence occurred in oil and gas composition and generated gas cap of high CO₂ content.