中非走滑裂谷盆地群石油地质特征与勘探方向

Petroleum geological characteristics and exploration orientation in strike-slip rift basin group in central Africa

中非走滑裂谷盆地群是在中非剪切带影响下形成的中、新生代陆相裂谷盆地,构造复杂多样且勘探程度较低,成藏规律认识不清制约了该区的油气勘探发现。基于盆地构造、沉积、成藏组合特征和已发现油气田解剖,总结盆地油气富集规律和主控因素,并分析了勘探潜力和方向。研究认为,中非走滑裂谷盆地群在早白垩世以来经历了多期伸展、走滑和反转等构造活动,对沉积地层、构造特征和油气成藏具有较强的控制作用;受储盖组合和构造演化的影响,中非走滑裂谷盆地群不同盆地的油气发现和成藏组合有较大差异,总体表现为“西富东贫、下稀上稠”的特点;油气富集的主控因素是有效生烃灶、构造活动和断层;西部Doba盆地油气最为富集,发育多套成藏组合,上、下白垩统均已经获得规模发现,未来主要勘探方向包括下白垩统岩性圈闭和基岩圈闭;中部Doseo盆地上白垩统缺乏有效盖层,主要勘探目标为下白垩统砂泥岩组合,圈闭类型为走滑形成的断背斜、断块圈闭,基岩潜山是潜在的勘探目的层;东部的Salamat盆地尚未证实有效的成藏组合,勘探潜力有限。

The central African strike-slip rift basin group was composed of the Mesozoic-Cenozoic continental rift basins influenced by the Central African Shear Zone(CASZ),showing complex and diverse structures,as well as low exploration degree.The unclear understanding of hydrocarbon accumulation rules restricted the exploration and discovery in the region.Based on the analysis of basin structure,sedimentary system,hydrocarbon accumulation assemblage characteristics,as well as the discovered oil and gas fields,the hydrocarbon enrichment rules and main controlling factors are summarized,and the exploration potential and orientation are analyzed.The study results show that the central African strike-slip rift basin group experienced multi-stage extensional,strike-slip and reversed tectonic activities after the Early Cretaceous,which significantly controlled the sedimentary strata,structural features and hydrocarbon accumulation;Influenced by reservoir-cap rock assemblages and tectonic evolution,there are great differences in oil discoveries and plays in various basins in the central African strike-slip rift basin group,showing hydrocarbon distribution characteristics of“rich in the west and poor in the east,and light in the lower part and heavy in the upper part”;The main controlling factors for hydrocarbon enrichment include the effective hydrocarbon kitchen,tectonic activity and fault;Doba Basin in the west has the most abundant oil and gas resources,with several sets of hydrocarbon accumulation assemblages developed and large-scale oil and gas resources discovered in the Upper and Lower Cretaceous,and the Lower Cretaceous lithologic and buried-hill traps are the main exploration orientation in the future;For Doseo Basin in the central part,there is a lack of the regional cap rocks in the Upper Cretaceous,and the main exploration targets include the Lower Cretaceous sand-mudstone association,and fault anticline and fault block traps formed by strike-slip activities,as well as the potential bedrock buried hill;Salamat Basin in the east has no proved effective hydrocarbon accumulation assemblage,which shows a limited exploration potential.