Sand production is one of the main problems restricting the safe, efficient and sustainable exploitation of marine natural gas hydrate. To explore the sand-control effects of gravel packing, experiments that simulate hydrate extraction in the water-rich environment were conducted with designed hydrate synthesis and exploitation devices. Three sand control completion methods, including 120 mesh sand screen, 400 mesh sand screen, 120 mesh sand screen combined with gravel packing, are adopted. Sand and gas production rates were compared under different well types and sand control completion methods. Results show that the gas production modes of radial wells and vertical wells are almost the same at the same time due to the small experimental scale and high permeability. The sand production of the vertical well with gravel packing combined with a sand-control screen is 50% lower than that of the vertical well with sand-control screens only. Radial well with gravel packing combined with sand-control screens produced 87% less sand than screen mesh alone. The cumulative gas production and recovery rates of a radial well with the composite sand control method are better than those without gravel packing in the same development time.

The effects of 40 Chinese herbs on Microcystis aeruginosa growth were monitored spectrophotometrically. Golden thread (Coptis chinensis) exhibited the best inhibitory effects. Cell density of M. aeruginosa decreased with the increasing concentrations of golden thread and the prolongation of exposure time. Decreases in protein content, carbohydrate content, and chlorophyll a content were observed in a golden thread concentration-dependent manner after 96 h exposure. Changes in cell density, protein content, carbohydrate content, and chlorophyll a content of M. aeruginosa exposed to berberine, the main component of golden thread, were also investigated. It was observed that berberine exhibited the same inhibitory effects on M. aeruginosa. The results suggested that golden thread could inhibit M. aeruginosas growth effectively, and berberine might be the main allelochemical implementing the inhibitory effects of golden thread.