Pore-Throat Size Distribution and Classification of the Paleogene Tight Sandstone in Lishui Sag,East China Sea Shelf Basin,China

摘要

The characteristics of tight sandstone reservoirs are closely influenced by the complex pore structure and the widths of pore-throat size distributions (P-TSDs). Because of the limitations of various techniques, it is difficult to characterize the morphology and size distribution jointly of the pore-throat structure. In this study, thin section, scanning electron microscopy, X-ray fluorescence diffraction, high-pressure mercury injection, and constant speed mercury injection were combined to analyze the pore throat structure characteristics of the Lishui tight sandstone reservoir in the southern East China Sea Shelf Basin, and joint characterization of morphology and size distribution of the pore-throat structure was established based on X-ray computed tomography (XCT) analysis. The results showed that the Paleocene tight sandstone in Lishui Sag generally has a high content of lithic and feldspar, which provides a good material basis for the development of clay minerals in the reservoir. Autogenic illite and kaolinite occupy the majority of pore-throat space in tight sandstone reservoirs and form intergranular micropores of clay minerals with a radius less than 1 mu m, which are important factors for the development of micropores and throats in tight sandstone. XCT scanning showed that as the content of day mineral increased, the number of throats developed per unit volume decreased, the isolated point-like micropores significantly increased, and the connectivity between micropores deteriorated. Based on the pore and throat information obtained by XCT scanning, the pore and throat radius frequency and volume distribution curves were generated. According to the distribution characteristics of the curves, the pore size distribution types of tight sandstone are divided into two types: peak type and flat type, and throat size distribution types are divided into three types: right peak type, left peak type, and bimodal type.