北部湾盆地涠西南凹陷碳酸盐岩潜山表生岩溶储层特征与演化模式

Characteristics and Evolvement Model of Epigenetic Karst Reservoirs in Carbonate Buried Hill in Weixi’nan Sag,Beibuwan Basin

潜山储层是潜山油气成藏的重要条件,潜山领域是涠西南凹陷今后的重要勘探领域。本文综合运用岩心观察、薄片鉴定、碳-氧同位素测定、包裹体测温、钻录井及测井资料对涠西南凹陷碳酸盐岩潜山储层开展研究。研究表明,涠西南碳酸盐岩潜山储层主要为岩溶储层,并且发育同生-准同生期岩溶、埋藏岩溶和表生岩溶三种不同环境的岩溶作用,其中以表生岩溶作用为主;表生岩溶储层自上而下划分为表层岩溶带、垂直渗流带和水平潜流带;各个岩溶带在横向上具有可对比性。工区碳酸盐岩岩溶发育程度受沉积相、古地貌及后期构造运动控制:潮坪沉积环境下的白云岩的岩溶储层更发育;古地貌的岩溶斜坡区岩溶更发育;新生代断裂构造作用调整了原始岩溶储层带的分布深度,导致现今不同潜山间的岩溶储层带分布深度有差异。

Buried hill reservoirs are important conditions for buried hill hydrocarbon accumulations.Buried hill area is one of the important subsequent exploration areas in Weixi’nan Sag.This study comprehensively used core observation,thin section identification,carbon-oxygen isotope measurement,inclusion temperature measurement,and drilling and logging data to conduct research on carbonate buried hill reservoirs in Weixi’nan Sag.Results showed that the carbonate buried hill reservoirs in Weixi’nan were mainly karst reservoirs.There were three types of karstifications,and they included depositional-interregional karst,buried karst,and epikarst.Among them,the epikarst is the most common karstification in the work area.The epikarst reservoirs zones were vertically divided into subsurface zone,vadose zone,and lenticular phreatic zone.Each epikarst reservoirs zone can be compared horizontally.The controlling factors of carbonate karst reservoirs in the work area mainly contained sedimentary facies,paleo-geomorphic,and late tectonic movements.It was proposed that dolomites in the tidal-flat zone was a more favorable lithology for reservoirs development.The karst slopes were favorable paleo-geomorphic in the area.Cenozoic faults had adjusted the original distribution depths of the karst reservoirs zones and led to different distribution depths of the karst reservoirs zones among the different buried hills today.