巴西大坎波斯盆地盐下碳酸盐岩油气成藏规律与勘探启示

Hydrocarbon accumulation rules and exploration inspiration of pre-salt carbonate reservoirs in the Great Campos Basin,Brazil

巴西大坎波斯盆地盐下深海领域自2006年发现Lula特大型油田以来,已经发现了一系列大型油气田,成为全球勘探的热点地区之一。通过勘探发现、油气特征等分析,对盐下油气系统的成藏条件进行研究,认为盐下湖相泥页岩生烃条件优越,形成多个生烃中心、强充注油气系统;巨厚膏盐岩层延缓烃源岩演化,有效保存油气;湖相微生物岩储层大规模发育是油气富集的关键。采用规模序列法对盐下油气资源潜力进行了重新评价,待发现油气可采资源量约为331×10^8bbl。系统总结勘探历程与经验后,提出勘探思路转变、持续投入和技术进步是盐下大油气田发现的关键,商业性油气发现风险主要受优质储层规模、油气藏类型和经济储量规模的影响。裂谷期隆起区背景下的构造圈闭是最重要勘探目标,其次为地层—岩性圈闭,超深海远洋高隆带具有非常大的勘探潜力。

Since the discovery of Lula giant oil fi eld in 2006,a series of large oil and gas fi elds have been discovered in deep-water pre-salt strata in the Great Campos Basin in Brazil,which has become one of the hot spots of global exploration.Through the analyses of exploration discoveries and oil and gas characteristics,hydrocarbon accumulation conditions of pre-salt oil/gas systems are studied.The results show that,the hydrocarbon generation conditions of pre-salt lacustrine shales are excellent,forming multiple hydrocarbon generation centers and strong oil/gas charging systems.The extremely-thick gypsum-salt strata delayed the evolution of source rocks and effectively preserved oil and gas.Large-scale development of lacustrine microbial reservoirs is the key to oil and gas enrichment.The pre-salt oil and gas resource potential was re-evaluated by scale sequence method,with the yet-to-discovered recoverable oil and gas resources about 331×10^8bbl.Based on the systematic summary of exploration history and experiences,it is proposed that the key factors to the discovery of pre-salt large oil and gas fi elds are the transformation of exploration ideas,continuous investment and technology progress.The risk of commercial oil and gas discovery is mainly affected by the scale of high-quality reservoirs,the type of oil and gas reservoirs and the scale of economic reserves.The structural traps under the background of uplifted area during rift-period are the most important exploration targets,followed by the stratigraphic-lithologic traps.The high positions in ultra-deep ocean are of great exploration potential.