Sedimentary structure characteristics and logging identification method for the first member of Qingshankou Formation shale strata in Gulong sag
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摘要: 沉积构造类型的精细划分与定量表征是页岩油勘探开发中的一个关键问题。为此,以松辽盆地古龙凹陷青山口组一段(K2qn1)陆相页岩层系为例,基于岩心和薄片观察、全岩矿物X射线衍射和电成像测井资料,明确了岩性差异下的沉积构造特征,建立了适用于陆相页岩层系的沉积构造测井定量识别方法。结果表明,K2qn1页岩层系的不同岩性下沉积构造特征的差异主要体现在纹层的矿物组成和层理(纹理)的厚度变化上,沉积构造类型基于单层厚度的大小可分为纹层状(单层≤1cm)、层状(1cm<单层<10cm)和块状(单层≥10cm);充分依托电成像测井切片图像的高分辨率优势,利用边缘检测和霍夫变换识别电成像切片中的层界面,基于层界面厚度的大小,实现沉积构造类型的定量划分;该方法不仅克服了传统动静态成像测井图像对毫米级纹层表征精度不足的难题,同时弥补了以往利用纹层密度不能对测井单位窗长内层状和纹层状沉积构造进行精细划分的弊端。总体上,本文提出的基于电成像切片的沉积构造测井识别方法,精度高、推广性好,可为后续陆相页岩储层有效性评价提供有力支撑。Abstract: [Objective] The fine classification and quantitative characterization of sedimentary structure types is a crucial issue in the exploration and development of shale oil. [Methods] To this end, taking the continental shale strata of the first member of Qingshankou Formation (K2qn1) in Gulong sag of Songliao Basin as an example, based on core and thin section observations, whole-rock mineral X-ray diffraction and electrical imaging logging data, the sedimentary structure characteristics under lithological differences were clarified, and a quantitative logging identification method for sedimentary structures applicable to continental shale strata was established. [Results] The result shows that the differences in sedimentary structure characteristics under different lithologies of K2qn1 shale strata are mainly reflected in the mineral composition of the laminae and the thickness variation of the bedding (texture). The sedimentary structure types can be divided into laminar (single layer ≤1 cm), lamellar (1 cm < single layer < 10 cm), and massive (single layer ≥ 10 cm) based on the size of the single-layer thickness. Relying on the high resolution advantage of electrical imaging logging slice image, the layer interface in electrical imaging slice is identified by edge detection and Hough transform, and the sedimentary structure type is quantitatively divided based on the thickness of the layer interface. This method not only overcomes the problem of insufficient characterization accuracy of millimeter-scale laminae in traditional dynamic and static imaging logging images, but also compensates for the drawback that the previous use of laminae density cannot effectively divide the lamellar and laminar sedimentary structures within the logging unit window length. [Conclusion] Overall, the sedimentary structure logging identification method based on electrical imaging slices proposed in this paper has high accuracy and good generalization, which can provide strong support for the subsequent continental shale reservoir effectiveness evaluation.
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