Design And Experiment Of Deep Water Multi-gradient Drilling Downhole Cyclone Separator

At present,deepwater drilling faces many challenges such as shallow geological disasters,deep water and low temperature environments,unstable seabeds and narrow safety density windows.In order to solve the problem of narrow water safety density window in deep water,double gradient drilling technology is often used at home and abroad.However,the pressure gradient generated by this technique is limited,and the intersection of the two gradient lines is located near the seabed mud line,and the annular pressure at the lower part of the mud line cannot be precisely controlled.Therefore,as the water depth and formation depth increase,double gradient drilling annulus pressure will be difficult to match with narrow density windows.Aiming at this problem,a multi-gradient drilling technology that adapts to a narrower density window is proposed.The core of the multi-gradient drilling technology is the downhole hollow ball cyclone separator.By installing multiple separators under the well,multiple pressure gradient line intersections can be generated in the lower annulus of the mud line,which can achieve precise control of the annulus pressure.Make it better match the narrowdensity window of the formation.By analyzing the limitations of existing designs,this paper designs an axial hollow ball cyclone separation device,focusing on the design of the guide vanes and improving the separation performance of the device.Using numerical simulation software to analyze the structural parameters of the new cyclone separator: swirl chamber length,overflow tube diameter,overflow tube insertion depth,cone angle,number of blades,operating parameters: split ratio,displacement,hollow sphere content The results show that the flow field of the new cyclone separator is more stable,the pressure consumption of the overflow port is smaller,and the separation effect of the hollow sphere is better.According to the preferred result,the device is processed and manufactured,and the relevant experimental platform is established to test the separation efficiency of the device under different split ratios,different displacements,different hollow sphere concentrations and sizes.The experimental results show that increasing the split ratio and hollow sphere size will obviously affect the separation efficiency.It is recommended to use a 30-mesh hollow sphere with a split ratio of 15%.The increase of drilling fluid displacement and hollow sphere concentration has little effect on it.According to the experimental results,the feasibility of the device is first proved,and then the basis for further optimization of the device is provided.The above research provides a theoretical basis for the further improvement of the new cyclone separator and the development of deepwater multi-gradient drilling technology.