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

Abstract

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 μm, which are important factors for the development of micropores and throats in tight sandstone. XCT scanning showed that as the content of clay 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.

Controlling Effect of Wave-Dominated Delta Sedimentary Facies on Unconventional Reservoirs: A Case Study of Pinghu Tectonic Belt in Xihu Sag, East China Sea Basin

“…The difference in dissolution in the study area depends on the intrusion of corrosive fluid and the changes in the opening and closing of the diagenetic system and is related to whether the acid-bearing body of organic matter can enter the reservoir smoothly [45]. The dissolution of the Pinghu Formation reservoirs is related to the Huagang Movement and the Longjing Movement [46]. Under the action of the Huagang Movement, when the oil and gas began to charge into the reservoir in the early stage, the organic acid fluid began to enter the reservoir.…”

Geochemical Characteristics and Environmental Implications of Trace Elements of the Paleocene in the West Lishui Sag, East China Sea Basin

“…Sr begins to precipitate at this time, and the Sr/Ba ratio in sediments will increase significantly. Therefore, it is feasible to judge the salinity of the sedimentary environment by the Sr/Ba ratio [20,[49][50][51]. It is generally considered that the Sr/Ba ratio of marine sediments is higher than that of continental sediments.…”

Study of Cretaceous Provenance Tracing and Sedimentary Patterns in the Western Qiantang Sag, East China Sea Shelf Basin

“…Current research mainly concentrates on the Fuzhou Sag in the southern part of the ECS Shelf Basin, while the study of Mesozoic sedimentation in the Qiantang Sag, located in the centralsouthern part of the ECS Shelf Basin, is relatively scarce due to the extensive development of 'red beds'. As a significant component of the ECS Shelf Basin, the Qiantang Sag retains substantial Mesozoic sedimentary strata [6,[34][35][36][37], potentially rich in geological records related to plate subduction. This makes the study of its provenance and sedimentary evolution of great significance for a deeper understanding of the subduction history of the West Pacific margin and the development of the basin.…”

“…Gao Dezhang et al, based on the 1:200,000 gravity and magnetic results of the Qiantang area in the East China Sea, used techniques such as wavelet multi-scale decomposition and full magnetic latitude tilt angle polar conversion to determine the presence of Mesozoic strata in the Qiantang Sag area, and speculated the possible existence of Paleozoic strata [34]. Zhao Lei and Xia Qingqing, through their study of seismic profile stratigraphic frameworks, believe that the Qiantang Sag is a structural unit with Mesozoic-Cenozoic sedimentary infill, where the Cenozoic sedimentation is thin and of relatively small scale, and it has a distinct double fault structure [35,36]. Jiang Yiming et al, in their research on the edge structure of the Xihu Sag, found that the sedimentary strata of the Qiantang Sag can be traced in the seismic profile to the Pinghu Main Fault of the Xihu Sag, but due to limitations in seismic data quality, the contact relationship is difficult to confirm [37].…”