巴西桑托斯盆地C区块火成岩发育特征及对油气成藏的影响

桑托斯盆地盐下碳酸盐储层中火成岩分布广泛，以盆地C区块为解剖区，通过对区内火成岩岩石学、年代学以及CO₂气体同位素测试分析等，明确了区内火成岩发育特征，剖析了其对油气成藏的影响。C区块至少经历了阿普特期和圣通-坎潘期2期岩浆活动，其中阿普特期岩浆以喷发岩为主，经历了多次喷发，并伴有多次侵入；圣通-坎潘期岩浆规模较小，侵入比较随机。阿普特期岩浆多次喷发改造古地形，形成局部凸起，促成并控制了Itapema组介壳灰岩的沉积发育，形成了巨厚的火山岩-介壳灰岩复合体，不仅造成了局部构造反转和圈闭高点迁移，而且也促成了Barra Velha组优质微生物灰岩的发育。区块北翼属早期古隆，Barra Velha组也发育一定规模微生物灰岩滩体。圣通-坎潘期及之后岩浆活动伴生的CO₂大规模侵入，对烃类流体进行萃取和抽提改造，形成含凝析油的CO₂气藏。 

Characteristics of igneous rocks and their significance in hydrocarbon accumulation in Block C of Santos Basin,SE Brazil

Santos Basin is characterized by multiple phases of magmatic events and widespread distribution of igneous rocks, which have significant affect of hydrocarbon accumulation. Taking Block C of Santos Basin as a typical and representative example, this paper focused on the characteristics of igneous rocks and their roles in hydrocarbon accumulation through the analysis of igneous rock petrology, geochronology, petrogeochemistry, and gas isotopes. In Block C, at least two main stages of magma events were developed: Aptian magma (122.8±0.6-110.8±0.6 Ma) and Santonian-Campanian magma (84.2±0.7-77.4±0.4). The Aptian magma is dominated by eruptive rocks and has experienced dozens of eruptions, accompanied by several layers of subvolcanic rocks. In comparison, Santonian-Campanian magma is distributed in a relatively random pattern. The multipulse eruption of Aptian magma formed an igneous rock-coquinas complex of more than 600 meters in thickness, inducing a local paleohigh in Itapema Formation. This directly caused the trap crest to shift and contributed to the development of high-quality carbonate deposition in Barra Velha Formation. Before the eruption of Aptian magma, the north flank of Block C was paleohigh, where a particular scale of microbial carbonate reservoirs was anticipated to develop in the Barra Velha Formation as well. These carbonate reservoirs were favorable for hydrocarbon accumulation. The later Santonian-Campanian intrusions also impact carbonate reservoirs through hydrothermal fluid circulation and contact metamorphism. Meanwhile, a large amount of associated CO₂ accumulated in the trap led to a high GOR (gas oil ratio) and high CO₂ content and changed the fluid composition through the extraction process.A CO₂ gas reservoir with condensed oil was eventually formed in the current crest in Block C, as proven by drilled well A.Another pool with high CO₂ content is also expected in its north flank, to be demonstrated in the future.