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Based on the characteristics of shallow buried, non-trap structure and close cover, non-diagenesis, weak cementation and easy fragmentation of natural gas hydrate deposits in China, a solid fluidization well testing and production scheme to develop these kind of natural gas hydrate is proposed. The main idea is to transfer the non-diagenetic natural gas hydrate sediments buried in shallow layer of deep-water into a closed multi-phase transporting and lifting system through mechanical crushing fluidization, during the lifting riser system from seabed to surface, hydrate will be dissociated gradually based natural rule of sea water temperature rising and the hydrostatic pressure decrease with the change of water depth during the lifting process, to turn the uncontrollable decomposition process of non-diagenetic hydrate into controllable, and to achieve safe field exploitation of natural gas hydrate in the surface and shallow layer of deep-water. After the validity was verified by the laboratory experimental study, CNOOC successfully implemented the world's first solid fluidization well testing and production of marine non-diagenetic hydrate with the water depth of 1310m and the hydrate sediments layers 117~196m depth in May 2017. It means China has found an innovation way about natural gas hydrate exploration and development with self-developed key technology and tools. The implementation relied on the Deepwater Engineering & Survey Vessel "HYSY708" at the station of Li Wan 3 in the South China Sea and it was supported by fully self-developed technology, process and facilities.

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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.

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