Numerical Simulation Of Liquid-solid Two-phase Hydrodynamic Characteristics Of Deep-sea Drilling

With the massive exploitation and consumption of oil and gas resources in the world,marine oil and gas development will become an important area of global energy development.Due to the loose and high sediment levels in the seafloor stratum,the margin between the pore pressure and the fracture pressure of the stratum is small.It is difficult for conventional drilling technology to keep the pressure in the annulus between them.The appearance of Dual Gradient Drilling method of Hollow Glass Spheres(HGS)has solved this problem very well.Because the flow in the annulus is difficult to observe,the Two-Fluid Model(TFM)based on the principle of Kinetic.In this thesis,the Eulerian-Eulerian two-fluid model combined with particle dynamics and SST k-ω turbulence model is used to simulate the hollow sphere injection system.Through the analysis of the pressure drop in the annulus and the law of solid phase migration,the effects of different physical parameters and operating parameters on the HGS were studied.The results show that the overall concentration of cuttings in annulus increases with the increase of cuttings diameter.An increase in the diameter of the hollow sphere will increase the pressure drop in the riser,which will also reduce the concentration of cuttings in the annulus,but the reduction is very limited.The increase of cuttings concentration leads to the decrease of solid phase velocity and the increase of granular temperature of particles in the annulus.As the probability of collision increases,the momentum loss increases,and the pressure drop in the annulus increases.There is a nonlinear relationship between the pressure drop value and the inlet cuttings concentration,but after the hollow sphere is injected into the annulus,there is a more obvious dual gradient phenomenon in the annulus.As the concentration of the hollow sphere decreases,the pressure drop in the annulus increases.Increasing the rotating speed of the drill string can increase the concentration of the solid phase in the annular and increase its migration speed,which will not have too much effect on the pressure.When the velocity of the bottom inlet fluctuates,a large amount of energy loss occurs in the annulus,resulting in a higher pressure drop.As the fluid behavior index n of the drilling fluid decreases,the cuttings in the annulus are more evenly mixed with the hollow spheres.The hollow spheres mainly occupy the central area of the annulus,while the cuttings are mainly distributed in the area close to the wall.This thesis aims to provide a practical theoretical basis for the HGS.