潮控河口湾岩相类型及沉积模式——以厄瓜多尔Oriente盆地北部区块上白垩统Napo组LU段为例

Lithofacies and Sedimentary Model of Tidal⁃dominated Estuary:A case study of LU interval from Upper Cretaceous Napo Formation,northern Oriente Basin,Ecuador

潮控河口湾是厄瓜多尔Oriente盆地北部上白垩统Napo组的主力储层,当前对其识别标志、岩相及沉积分布规律认识不清,建立可靠的潮控河口湾的沉积模式,对于预测油气储层有重要意义。通过研究区LU碎屑岩段岩芯、粒度、测井、薄片以及地化资料的综合分析发现:(1)综合岩相类型、地化、垂向序列特征认为其发育潮控河口湾和陆棚;(2)研究区潮控河口湾主要发育中河口湾亚相及外河口湾亚相,中河口湾亚相发育潮汐河道、潮坪、高流态沙坪等微相,在测井曲线上呈钟形;外河口湾轴部发育潮汐沙坝、高流态沙坪微相,测井曲线上为箱型;外河口湾两侧为泥质潮坪微相,测井曲线上呈指形;浪基面之下发育泥质陆棚沉积和风暴形成的海绿石席状砂;(3)研究区倾向西南,中河口湾的潮汐河道边滩沉积发育在东北部;向西南河道逐渐拓宽,外河口湾轴部潮汐沙坝南北向展布,向两翼泥质含量增高,发育泥质潮坪,呈席状展布。

A predominantly tidal estuary is the main reservoir type in the Upper Cretaceous Napo Formation,north⁃ern Oriente Basin,Ecuador,although its identification,lithofacies and sedimentary distribution are unclear at pres⁃ent.Establishing a reliable sedimentary model of the estuary is of great significance for predicting the presence of oil and gas reservoirs.A comprehensive analysis of the core,including grain size,well logging,thin section and geo⁃chemical data,found that:(1)The combination of lithofacies,geochemical and vertical sequence characteristics in⁃dicates the development of a tidal⁃dominated estuary⁃shelf sedimentary system.(2)The tidal⁃dominated estuary con⁃tains middle⁃and outer estuary subfacies.The middle estuary contains tidal channels with an overbanked mixture of flat and salt⁃marsh microfacies,the distribution shown as bell-shaped on the logging curve.Along the axis of the out⁃er estuary,tidal sand bar and upper⁃flow⁃regime sand flat microfacies were developed,producing a box⁃shaped log⁃ging curve.Muddy tidal flat microfacies occur on both flanks of the outer estuary,shown as finger⁃shaped logging curve.A muddy shelf and storm⁃formed glauconitic sheet sand developed under the normal wave base.(3)The paleo⁃geography of the study area leans towards the southwest.Tidal channels developed in the middle estuary in the north⁃east.The southwestern channel gradually widened and north⁃south tidal bars were distributed along the axis of the out⁃er estuary.A sheet⁃like muddy tidal flat developed on the flanks of the estuary.