Cementation breaking and grit separation characteristics of weakly cemented natural gas hydrate by a new structure hydrocyclone

Solid fluidization exploitation technology is one of the most promising methods for the safe exploitation of shallow natural gas hydrates (NGH) in the deep sea. However, after primary jet breaking in the solid fluidization exploitation, the hydrate and argillaceous silt particles are in a state of weak cementation and agglomeration. When the argillaceous silt particles enter the offshore drilling platform with the drilling fluid, it causes substantial sand production, high energy consumption, and pipeline blockage, considerably affecting the development process of the NGH test. Therefore, in-situ desanding has become one of the key technologies of solid fluidization exploitation. In this study, a coupling method of hydrocyclone cementation breaking and hydrocyclone desanding was proposed, and a new structure of cementation breaking and grit separation hydrocyclone was designed. In a lab-designed cementation breaking and grit separation hydrocyclone system, the cementation breaking and grit separation characteristics of weakly cemented NGH similar materials in the swirl flow field were studied. The experimental results under the operating conditions studied show that the swirl flow field exhibits good cementation breaking and grit separation performance for weakly cemented NGH similar materials. For weakly cemented NGH similar materials with a compressive strength of 0.06–0.42 MPa, the cementation breaking efficiency of the cementation breaking and grit separation hydrocyclone is in the range of 27.17–99.61%. After the cementation breaking, the mixture of hydrate similar materials (hydrophilic polyethylene powder) and quartz sand was separated in the hydrocyclone. The separation efficiency of hydrate similar materials is 27.59–99.64%, and the desanding efficiency is 87.66–99.98%. The cementation breaking and grit separation of weakly cemented NGH similar materials were successfully realized. Based on the experimental data, a multiple regression model for the cementation strength of similar materials and the swirl flow field strength was established using the least squares method. This method is expected to provide new technical support for in-situ desanding and safe exploitation of the deep-sea shallow NGH production process.