# Sand Production Characteristics of Hydrate Reservoirs in the South China Sea
## 8 Conclusions and Recommendations  
In summary, the pressure drop rate and water production are the main factors affecting sand production. There is a coupling effect between them. The technical difficulties of hydrate sand prevention compared with that of conventional oil and gas development are mainly reflected in the fine grain size and high mud content of the formation sand. The favourable factor is that the sand-carrying performance of gas-water flow is significantly weaker than that of crude oil. In addition, compared with the sand-carrying gas-water flow, the carrying capacity of low-production gas is weaker than that of agglomerated wetted fine particles. Therefore, reservoir water content is one of the key factors limiting the effectiveness of sand control in hydrate test mining. The permeability and flow rate increase will increase the sand carrying capacity of the fluid with water output as a carrier and replacement flow as a carrying power. When the replacement flow rate becomes smaller, the reservoir particle transport from the \"large channel seepage\" to the \"umbrella seepage\" and then to the \"uniform fine flow\". \"Uniform fine flow\". In the actual production process, it should be controlled by the influencing factors such as differential pressure and flow rate, and the lowering amplitude and period, in order to minimize the unfavourable factors of sand discharge and improve the gas production by penetrating the reservoir permeability under the mode of uniform fine flow. Our major findings can be summarized as:  
1. The hydrate reservoirs in the South China Sea belong to unconsolidated strata, and will face the risk of sanding or serious sanding under mining conditions;
2. As the replacement flow rate becomes smaller, the reservoir particle transport changes from \"large-channel seepage\" to \"umbrella seepage\" and then to \"uniform fine flow\", which indicates that the risk of reservoir sand outflow due to large-channel seepage is not to be underestimated when the flow rate increases to a certain order of magnitude (especially under industrial mining conditions). 3. When gas and liquid phases coexist, the disturbance to the formation is greater than that of the single-phase displacement process, and its pore sand morphology and particle transport pattern are also different from that of the single-phase flow. Fluid flow and gas-liquid ratio are the key factors affecting particle transport. * When the pressure reduction rate is lowered to a certain range, the rate of sand and water production no longer decreases significantly but tends to be constant, and there is an optimal interval for the pressure reduction rate. It is possible to establish a quantitative prediction model of water production and sand output through experiments, and orthogonal experiments with multiple parameters can be carried out in the future to enrich the quantitative prediction model of sand output and provide guidance for the implementation of test mining. Conceptualisation, H.S., Y.Z. and Q.L. ; methodology, H.S., Y.Z. and Y.Y. ; software, H.S., B.L. and L.L. ; resources, Z.L., F.N. and W.X. ; data curation, H.S., Y.Z., Z.Z. and Q.L. ; supervision, Z.L. and F.N. ; funding acquisition, Y.Y. and W.X. All authors have read and agreed to the published version of the manuscript. This research was jointly supported by the Nansha District, Guangzhou City, the coordinators of \"The Key Areas of the Science and Technology Programme Project\", entitled \"Research and development of key technologies and equipment for stable gas production from silty-clayey hydrate reservoir\" (2023 ZD017); Guangdong Province, the major project of basic and applied basic research, \"Shenhu Pilot Pilot Area of natural gas hydrate production test mining key (2020B0301030003); special hydrate project of China Geological Survey \"Productive Trial Mining of Natural Gas Hydrate in the Northern South China Sea\" (DD20230063). Not applicable. The raw data supporting the conclusions of this article will be made available by the authors upon request.