柴达木盆地北缘马仙地区路乐河组风成砂岩识别及沉积相模式

Identification of eolian sandstone in the Lulehe Formation of Maxian area,Qaidam Basin,and its sedimentary model

基于岩心、岩石薄片、扫描电镜、粒度、X-射线衍射、孔渗和X-荧光7类数据,从岩性、沉积结构、矿物组分、主量元素和物性条件5个角度对比分析,证明柴达木盆地北缘马仙地区马西5井、马西6井、仙东1井和仙东2井路乐河组取心属于风成砂岩,首次揭示柴达木盆地路乐河组存在风成砂岩。这些风成砂岩为胶结疏松的棕黄色中细砂岩。与水成沉积相比,风成砂岩具有岩性单一、砂层厚、成分成熟度高、石英颗粒磨圆度好且具有风成砂的表面结构,以及粒度近似现代风成砂等方面的特征。在石英-钾长石-斜长石三元图、A-CN-K三元图、PCA分析和MFW三元图4类图解中,风成砂岩与水成砂岩沉积区别明显。另外,通过沉积和物源分析,认为风成砂岩是冲积扇-冲积平原沉积经由风营力的再次搬运、分选和再沉积过程就地形成,并发育于冲积扇-冲积平原的过渡地带,这一沉积模式在柴北缘地区具有较为广泛的适用性,能更好地应用于油气勘探开发涉及的沉积和储层研究。

Based on data from cores,rock slices,scanning electron microscope,granularity,X-ray diffraction,porosity and permeability,and X-ray fluorescence,this paper makes a comparative analysis of lithology,sedimentary textures,mineral composition,major elements and permeability,and then proves that the cores of Lulehe Formation from Wells of Maxi 5,Maxi 6,Xiandong 1 and Xiandong 2 in Maxian area belongs to aeolian sandstones,existence of which is the first time to be revealed in the Lulehe Formation of the Qaidam Basin.These aeolian sandstones are brown yellow medium-fine sandstones with loose cementation.Compared with the water-laid sedimentation,the aeolian sandstones have the characteristics of single lithology,thick sand layer,high compositional maturity,good roundness of quartz particles with surface textures of aeolian sand,and the particle size similar to modern aeolian sand.The aeolian sandstone is obviously distinguished from water-laid sedimentation in Zircon-kK-feldspar-plagioclase,A-CN-K ternary diagram,PCA analysis and MFW ternary diagram.In addition,according to the analysis of sedimentation and provenance,it is considered that aeolian sandstones are deposited in the transitional zone of the alluvial fan and alluvial plain,the sediments of which experience the process of re-transportation,sorting and re-deposition of wind.The sedimentary model can be widely applied to support the sedimentary and reservoir research during the process of petroleum exploration and development in the northern margin of Qaidam Basin.