ADVANCES IN MULTIPHASE SEEPAGE CHARACTERISTICS OF NATURAL GAS HYDRATE SEDIMENTS

Natural gas hydrate, as a kind of clean and environmental-friendly energy, has large reserves and attract great attention in recent years. In the past 20 years, exploration and reserves prediction for natural gas hydrate reservoirs have been widely conducted within mainland and offshore areas in China. In 2017, China Geological Survey carried out the tentative production for natural gas hydrate based on depressurizing seepage theory in Shenhu Area of the South China Sea. In worldwide, the hydrate tentative production are faced with the typical problems like low gas production and sand production. One of the main reasons is that the complex mechnisams of multiphase flow in sediments during development are still unclear. In this paper, we review parallel capillary model and Kozeny particle model which are widely used in seepage analysis during natural gas hydrate development. Then we analyze the multiscale simulation methods for hydrate seepage and briefly describe experimental advances in terms of permeability measuremnts, evolutionary process for physical properties of sedimens during seepage and laboratory production simulation for hydrate production. Afterwards, we summarize the numerical simulation methods for gas production during the exploitation of gas hydrate reservoirs at the field scale. Future works and challenges are proposed for multiphase seepage model, in situ testing of hydrate samples, evolutionary process for structural and physical properties, field scale numerical simulation and horizontal well fracturing technology applications.