Hydrate Prevention In Deepwater High Pressure Gas Well Under Downhole Throttling Condition

The high pressure and low temperature at the wellhead will be faced in the test and production period of deepwater high pressure gas wells,and the risk of hydrate formation is high.At present,the main method used to prevent hydrate formation in deepwater gas wells is to inject thermodynamic inhibitors,but the high pressure at the wellhead increases the difficulty of inhibitor injection.By using the downhole throttling technology,the throttle valve can be lowered into the right position,not only reducing the wellhead pressure,but also making use of geothermal energy to reduce the temperature drop caused by throttling effect,so as to prevent the hydrate formation.But there is no systematic theoretical model and optimization design method.It is of great theoretical and practical significance to develop the downhole throttling for hydrate prevention in deepwater high pressure gas wells.This dissertation focuses on the actual conditions of deepwater high pressure gas wells,aiming at the annular mist flow dominated by gas phase,based on the calculation method of full diameter wellbore temperature and pressure,uses the node analysis method,introduces the throttling characteristic equation into the calculation model of full diameter temperature and pressure,establishes the calculation model of full diameter wellbore temperature and pressure considering the throttling effect,and establishes the corresponding numerical solution method The temperature,pressure,velocity and density of the gas along the wellbore are calculated.By means of Fluent numerical simulation,the distribution rules and characteristics of local temperature,pressure,velocity field and erosion degree of throttle subs with different structures are analyzed and characterized,and the suitable throttle valve type for downhole production is selected.Based on the premise of efficient hydrate prevention and injection in deepwater high pressure gas wells,the downhole throttle position and downhole stage are designed and optimized.The downhole throttling effect under different gas water cut,production and other factors is analyzed,and a reasonable and feasible hydrate inhibitor injection scheme is proposed.By using the established model and numerical method,the temperature profile,pressure profile,velocity field and erosion situation of streamline,orifice,step type and cone type throttle subs are compared.It is found that streamline throttle valve is more suitable for the situation of high pressure gas well production and severe erosion.According to different production and water cut,the multi-stage downhole throttle valve is put into the deep of the wellbore,which can reduce the wellhead pressure to a large extent on the premise of satisfying the economic production,and can use geothermal energy to raise the gas temperature of the high wellbore to a certain extent.Compared with the existing subsea choke in the subsea production system,through optimizing the ratio of the downhole choke size,the throttling stages and the depth of the downhole choke,the downhole throttling technology can effectively reduce the risk of hydrate formation and reduce the injection pump pressure of hydrate inhibitor,and has more obvious advantages for high temperature and high pressure deep wells.