Evaluation of Physical Parameters and Construction of the Classification System of Natural Gas Hydrate in the Northern South China Sea

摘要

Marine gas hydrate is a potential alternative energy. As the 173rd new mineral species, it can be qualitatively divided into diagenetic and non-diagenetic types. Because of its few drilling and production cases, high sampling cost, and great difficulty in heat preservation and pressure preservation technology, the in situ test of reservoir physical properties and the quantitative classification and evaluation of resource grade are not clear, and the relationship between resource-grade division and development-mode response is not clear. Therefore, in this paper, to solve this problem and technical difficulties, in combination with the actual hydrate sampling core data in the South China Sea, using the indoor hydrate acoustoelectric testing device, the physical parameters, such as acoustic wave, resistivity, saturation, permeability, partial stress and strain of hydrate deposits with different composition and saturation, were measured. An entropy weight comprehensive evaluation model for the sensitivity of physical parameters of natural gas hydrate is established on the basis of the decomposed hierarchy process. The order of sensitivity of hydrate parameters from high to low is stress, partial stress, decomposed gas, longitudinal wave, resistivity, permeability, and shear wave. In this paper, the evaluation method of physical parameters of marine natural gas hydrate and the five-grade classification standard of natural gas hydrate are established according to the law of parameter variation and the results of sensitivity analysis. Finally, the Liwan hydrate reservoir in the northern South China Sea is taken as a case study and defined as non-diagenetic grade II, which belongs to argillaceous shallow sedimentary hydrate with high saturation and high methane content without complete trap structure. This study provides an important technical method and theoretical guidance for the evaluation and classification of marine gas hydrate resources and the optimization of corresponding suitable development methods in the future.