加拿大Alberta盆地下白垩统油砂沉积特征分析及隔夹层识别

Sedimentary characteristics analysis and interlayer identification of the Lower Cretaceous oil sands in the Alberta basin, Canada

加拿大Alberta盆地下白垩统油砂储量巨大,但基于泥质含量对油砂开展的沉积相划分不能准确预测储层与隔夹层分布,难以指导油田开发。本文以多口取心井岩心描述为基础,结合测井资料,对研究区下白垩统油砂的沉积特征和隔夹层类型进行了研究,将油砂层段划分为潟湖、潮汐影响的曲流河、潮坪和正常海相等4种沉积相,进一步划分为8种沉积亚相、20余种沉积微相,并对每种沉积微相的测井响应、孔隙性及含油性进行了精细分析。研究认为,研究区潟湖内可形成滩坝砂岩-泥岩储盖组合,砂岩内基本无隔夹层;在潮汐影响的曲流河、潮坪及海相泥岩储盖组合中,曲流砂坝、低潮砂岩、潮道砂岩为主要储层,可以识别出3类8种隔夹层,即强隔层(包括弱改造河漫、河道侧翼、高潮泥岩)、弱隔层(包括中改造河漫、中潮层理状砂岩)和夹层(包括强改造河漫、曲流砂坝中的泥砾、滞留沉积体)。通过测井曲线上不同沉积相带及隔夹层类型的识别,可为研究区无取心井的测井曲线沉积微相分析奠定基础,据此建立的沉积模式对于指导油田开发、提高储层与隔夹层预测精度具有重要意义。

The Lower Cretaceous oil sand reserves in the Alberta basin of Canada are huge, but the sedimentary facies division for oil sand on the basis of shale content cannot accurately predict the distribution of reservoirs and interlay-ers;it is difficult to guide the oilfield development. Based on the cores description from multiple coring wells and com-bined with the logging data, this paper studies the sedimentary characteristics and interlayer types of the Lower Creta-ceous oil sands in the study area. and divides the oil sand layers into four sedimentary facies, such as the lagoon, tide affecting meandering river, tidal flat and normal sea, which can be further divided into eight sedimentary subfacies and more than 20 sedimentary microfacies. The logging response, porosity and oil content of each sedimentary microfacies are analyzed. According to the study, the beach dam sandstone-mudstone reservoir-caprock combination can be formed in the lagoon of the study area, and there is no interlayer in the sandstone. Among the reservoir-caprock combinations of tide affecting? meandering river, tidal flat and marine mudstone, the meandering sand dam, low tide sandstone and tidal channel sandstone are the main reservoirs, and three categories (8 types) of interlayers can be identified, namely, the strong interlayers (including weak flood transformation, channel flank, high tide mudstone), weak interlayers (in-cluding medium flood transformation, middle tidal bedded sandstone) and interbeds (including strong flood transfor-mation, gravel in the meandering sand dam, retained sediment). Through the identification of different sedimentary facies and interlayer types on the logging curves, it lays a foundation for analyzing the sedimentary microfacies of wells free of cores in the study area. The sedimentary model established by this method can be of great significance in guiding oilfield development and improving the prediction accuracy of reservoirs and interlayers.