Theoretical Study on the Separation of New Hydrate Downhole In Situ Desander

To solve the problem that the theory of in situ separation and sand removal of marine hydrate is not perfect enough, the formulas of fluid tangential velocity and particle radial migration were derived based on the separation theory of rotating fluid and equilibrium orbit. Under certain assumptions, theoretical prediction models of fluid tangential velocity, particle radial migration and separated particle size under different operation and physical parameters were established. Then the theoretical results were compared with the numerical simulation results. The results show that the key factors affecting the tangential velocity are the inlet spiral pitch, the number of spiral blades, the diameter of the overflow pipe, the thickness of the spiral blades, and the main diameter of the desander. The tangential velocity is proportional to the flow rate. When the particle diameter is fixed, the radial migration velocity of the particle decreases with the increase in the rotation radius. When the rotation radius is fixed, the radial migration velocity of particles increases with the increase in particle diameter. The larger the hydrate particle size, the shorter the time to reach the center, and the larger the sand particle size, the shorter the time to reach the wall. The particle size is inversely proportional to the tangential velocity of the fluid in the equilibrium orbit. The determination of fluid velocity, liquid–solid density difference and particle size is the key factor affecting particle equilibrium trajectory and particle size separation. The numerical simulation results are basically consistent with the theoretical values. The obtained results enrich the theoretical model of hydrate in situ sand removal.