厄瓜多尔Oriente盆地白垩系Napo组LU亚段沉积模式

The sedimentary model of the LU Sub-member of Cretaceous Napo Formation in Oriente Basin,Ecuador

厄瓜多尔Oriente盆地北部白垩系Napo组LU亚段地层油气资源极其丰富,具有较大的油气勘探潜力,由于目前对LU亚段地层沉积模式认识不清晰,极大程度上限制了研究区进一步勘探开发。依据LU亚段岩芯观察、测井、成熟度分析以及镜下薄片等资料,通过岩芯岩性、结构等岩石学特征,沉积构造、生物遗迹化石、沉积韵律等沉积学特征,以及测井相标志认为,研究区LU亚段地层发育于潮汐作用为主的海陆过渡环境,并在前人研究基础上提出潮控河口湾与陆棚之间存在过渡带沉积,形成了潮控河口湾-过渡带-陆棚沉积体系,识别出潮汐水道、潮汐砂坝、砂坪、海绿石砂席、混合坪、陆棚泥和灰质滩共7种沉积微相,其中,优势储层相带为潮汐水道和潮汐砂坝,砂坪次之。建立研究区潮控河口湾-过渡带-陆棚沉积模式,以期对Oriente盆地白垩系Napo组油气勘探提供有利的科学依据。

The LU Sub-member(LUSM)of the Cretaceous Napo Formation in the northern part of Oriente Basin,Ecuador,is extremely rich in hydrocarbon resources and has a large potential for hydrocarbon exploration.However,the depositional pattern of the LUSM remains poorly understood,which had largely limited the further exploration and development of the area.Based on the core observation,logging,maturity analysis,and thin-section study,the petrological and sedimentary features were described;the biological relics and fossils,sedimentary structure and rhythm,and the logging phase signatures were analyzed.Results show that the LUSM strata were developed in a transitional environment between sea and land,in which tidal action was dominated.Referring to previous studies,we proposed that there was a transitional zone between tide-dominated estuary and a continental shelf,forming a tide-dominated estuary-transitional zone-continental shelf sedimentary system,showing seven sedimentary microfacies:tidal channel,tidal sand bar,sand flat,glauconite sand sheet,mixed flat,shelf mud,and calcareous beach.Among them,the tidal channel and tidal sand bar are sweet reservoir facies,followed by sand flat.By analyzing the depositional system,a tidal-dominated estuarine-transition zone-shelf depositional model was established for the study area.This study provided a favorable scientific basis for oil and gas exploration in the Cretaceous Napo Formation in the Oriente Basin.