伊拉克地区中上白垩统滩相灰岩颗粒组成特征及其对沉积环境的指示

Composition Characteristics of Middle-Upper Cretaceous Shoal Facies Limestone Grains and their Implications for Sedimentary Environment in Iraq Area

伊拉克地区白垩系广泛发育滩相灰岩储层,由于这类灰岩储层的颗粒类型复杂导致沉积相划分和预测难度较大。前人的研究结果发现,伊拉克地区中上白垩统主要发育似球粒、绿藻、棘皮,其次为有孔虫、圆笠虫、内碎屑。针对该地区中上白垩统开展不同颗粒的类型及其组合对沉积环境的指示有助于进一步厘清沉积微相和储层类型。该研究利用岩心和薄片观察,识别出了不同类型的颗粒,明确了中上白垩统Kh2层、Mi4层和Ma1层的颗粒类型。绿藻、薄壁瓣鳃类生物反映正常盐度海水或广盐度的浅海相对局限且水体能量较低的环境;有孔虫类中圆笠虫为移动底栖,分布范围广,反映水动力强;厚壳蛤这类厚壁瓣鳃类和内碎屑形成于浅海高能环境;棘皮类对沉积环境无选择性,分布范围广,各个层位中均可见。对中上白垩统典型层位不同颗粒类型的认识为我国在伊拉克地区油气开发和油气储层研究提供了岩相学依据。

Shoal limestone reservoirs are widely developed in the Cretaceous of Iraq,which are difficult to divide and predict because of the complex grain types of these reservoirs.Previous studies have shown that the Middle and Upper Cretaceous in Iraq mainly developed spheroids,green algae and echinoderms,followed by foraminifera,bonin and endoclast.It is helpful to further clarify the sedimentary microfacies and reservoir types to indicate the sedimentary environment of the middle and Upper Cretaceous.Using core and wafer observations,different types of particles were identified and the grain types of Kh2,Mi4 and Ma1 layers of the Middle Upper Cretaceous were defined.Green algae and thin-walled lamellibranchias reflect the environment of normal salinity sea water or shallow sea with wide salinity and relatively limited water energy.Among foraminifera,bonin is a mobile benthos,which is widely distributed and reflects strong hydrodynamics.The thick-walled lamellibranchias and endoclasts were formed in the high energy environment of shallow sea.Echinoderms are not selective to sedimentary environment and have a wide distribution range,which can be seen in every horizon.The understanding of different grain types of typical strata of middle and Upper Cretaceous provides petrographic basis for oil and gas development and reservoir research in Iraq.