厄瓜多尔Oriente盆地北部区块T段地层沉积演化特征

Sedimentary evolution characteristics of T Member in north block,Oriente basin,Ecuador

厄瓜多尔Oriente盆地白垩纪T段地层具有丰富的油气资源,是北部区块油气勘探的重要目的层段,但目前T段地层沉积演化研究程度较低,尚未形成统一认识,极大地制约了该区块的进一步勘探开发。运用沉积岩石学理论方法,结合扫描电镜矿物定量评价方法,依据岩心、薄片、测井、录井等资料,通过描述岩心岩性、结构等岩石学特征以及沉积构造、生物遗迹化石、沉积韵律等沉积学特征,分析测井相标志,认为北部区块T段地层中LT层发育海侵期的外潮控河口湾亚相,包括潮汐砂坝、潮汐水道和潮汐砂坝间3种微相,而MT层和UT层发育潮控内陆棚亚相,包括潮汐沙脊、潮汐砂席和内陆棚泥3种微相。T段地层储层物性主要受沉积微相控制,各沉积微相的储层物性由好到差依次为潮汐砂坝/潮汐沙脊、潮汐水道、潮汐砂席,潮汐砂坝和潮汐沙脊微相发育区为最有利的储集相带。北部区块T段地层发育于以潮汐作用为主、坡度极缓的海陆过渡环境,从而形成了海侵型潮控河口湾-潮控陆棚相沉积模式。本文研究成果可为Oriente盆地北部区块下一步有利储集砂体的分布及预测提供科学依据。

The Cretaceous T Member of Oriente basin in Ecuador,which is rich in petroleum resource,is the main exploration target in north block. However,the further exploration and development are restricted due to the low study of sedimentary evolution characteristics and without a unified understanding in this area. Integrating sedimentary petrology theory and quantitative evaluation of mineral by SEM,petrology characteristics,including lithology and texture,and sedimentology characteristics,including sedimentary structure,trace fossil and sedimentary rhythm,are described and facies marks of logging are analyzed based on the comprehensive analyses of cores,thin section and well logs. Then,the sedimentary evolution characteristics are clarified. The LT layer of Cretaceous T Member develops outer tide-dominated estuary and three lithofacies types are identified,including tidal bar,tidal channel,and interbar. The MT and UT layers develop tide-dominated inner shelf,including tidal ridge,tidal sheet and inner shelf mudstone. The reservoir physical properties of the Cretaceous T Member are controlled by microfacies. The microfacies with reservoir properties from good to poor are tidal bar/tidal ridge,tidal channel and idal sheet,and the developed areas of tidal bar and tidal ridge are the most favorable reservoirs. The Cretaceous T Member in north block is developed in tide-dominated transitional environment with a very low slope gradient,and therefore it develops a transgressive depositional model of tide dominated estuary-tide dominated shelf. The research results can provide scientific basis to predict the distribution of favorable reservoir in north block,Oriente basin.