巴西桑托斯盆地CO2区域分布及主控因素

桑托斯盆地盐下油气田中发现了大量CO₂，给油气勘探开发和生产都带来诸多困难和挑战.利用地层测试、样品分析及文献资料等，明确了CO₂成因及来源，统计分析了其区域分布特征，并基于区域重磁和深源地震等资料，剖析了控制CO₂分布的地质因素.盆内CO₂主要为幔源—岩浆成因，且幔源CO₂贡献了至少92%的CO₂总量.区域上，CO₂自陆向海呈增加趋势，并相对集中在盆地东部隆起带上.地壳减薄和地幔局部隆升是控制CO₂宏观分布最重要的背景因素.极端的地壳伸展造成了圣保罗地台下部陆壳强烈拉伸减薄，形成了一个面积约5.1×104 km2的地壳减薄区，造成了富含CO₂的地幔物质上拱进入陆壳，宏观上决定了盆内CO₂区域分布.此区域之外，出现高含量CO₂的可能性大幅降低.岩浆侵入和活动断层都是沟通隆升地幔和浅部储层的重要路径，但以断裂沟通最常见.NW-SE向区域走滑断裂和NE-SW向I-II级正断层对CO₂在浅部地层中的分配起控制作用，两组断裂交汇部位或周缘是幔源岩浆或CO₂最集中发育区. 

Distribution and Main Controlling Factors of CO2 in Santos Basin,Brazil

An extraordinarily high amount of CO₂found in pre-salt section in Santos basin poses great challenges to the oil and gas exploration and development. In this study, combining regional gravity and magnetic database, deep-seismic lines, well drilling, formation test and samples dataset of the basin, the origin of CO₂ was clarified firstly, and its regional distribution patterns were statistically analyzed and their main controlling factors were explored as well. The widely distributed CO₂ in pre-salt reservoirs in Santos basin is mainly sourced from mantle, and mantle-derived CO₂ contributes at least 92% of the total volume of CO₂. Regionally, CO₂ abundance gradually increases from continent to ocean, and is relatively concentrated in the eastern uplift of the basin. On its margin usually occurs the current maximum CO₂ content values. The extra-high CO₂ abundance in Santos basin is the result of the combined action of various geological factors such as crust & mantle transition, regional tectonic evolution, magma events and fault activity. Among them, continental crust thinning and mantle uplifting are the most important background factors, controlling the regional distribution of CO₂. The intensive extension of crust caused a strong stretching and thinning of the lower continental crust of Sao Paulo platform, forming a crustal thinning area, around 5.1×104 km2, which caused the CO₂-rich mantle material to intrude upward into the continental crust. This uplifted mantle has directly controlled the regional distribution of CO₂ in Santos basin. Outside this area, the risk of CO₂ is significantly reduced. Magma injection or active faults are both important pathways for CO₂ migration and accumulation, with most common cases involving active faults leading CO₂ from "uplifted" mantle to shallower reservoirs. The NW-SE strike-slip faults and the NE-SW class I-II normal faults have an obvious control effect on distribution of CO₂ in shallower formation: NW-SE strike-slip fault could extend into deep mantle, while the NE-SW normal faults distribute these CO₂ in shallower layers. So that their intersection points or periphery areas are the most favorable areas for accumulation of magma and CO₂.