Study On Annular Pressure Recovery Of Gas Well And Floating Dynamic Behavior Of Gas Bubble

The large-scale oilfields has highly exploited in China.However,the sustained casing pressure(SCP)of oil and gas wells becoming more and more serious.SCP not only threatens the wellbore safety,but also affects the ultimate recovery of reservoirs.The present investigation experimentally researched the recovery and discharge of pressure in the A annulus of gas wells.The phenomenon of gas floating behaviour in the annulus protection fluid during the recovery of annular pressure is studied to provide a theoretical reference for the problem of SCP in practice.The domestic and foreign research focus on SCP,gas-liquid two-phase flow problem,two-phase flow problem of annulus wellbores,the phenomenon of bubble rising in static water,and the classic models about recovery and discharge of the pressure in well annulus.In order to simulate wellbore annulus,the experimental device has been designed,and the experiments about recovery-discharge of the pressure in well annulus and bubbles rising were conducted.In the process of the experiment,the effects of gas column height,gas flow channel size and wellbore size were taken into account.The rule of recovery and discharge pressure in annulus were obtained.In the meanwhile,high-speed camera has captured the flow path of gas bubbles in the annulus protection fluid and dynamic floating behaviour were obtained.According to SCP mechanism and experimental conditions,three-part mathematical models have been established,these models include flow model of residual gas at leak point,multiphase flow model in annulus wellbore and recovery model of pressure in gas column.The reliability of models has been confirmed by experimental results.The conclusions of this thesis are as follows:(1)the process of recovery and discharge of the pressure in annulus is influenced by gas channelling traffic volume,gas column height,pressure of leakage point and wellbore dimensions.With bigger gas channelling traffic volume and smaller gas column volume,the period of recovery of the pressure annulus decreases.With higher pressure of leakage point,the final balanced pressure of gas column increase.When the gas column volume and pressure of gas column was high,the period of discharge of the pressure annulus becomes longer.(2)The multiphase flow in annulus wellbore during the recovery of annulus pressure is a transient process.With the decrease of pressure difference on the two sides,the volume of gas crossing into annulus wellbore through the leak point decreases.(3)During the process of channelling bubbles float in annulus protection fluid,bubbles size and lift speed are closely related to annulus pressure.(4)The coupled mathematical model about channelling gas at leak and multiphase flow model in annulus wellbore and recovery model of pressure in gas column could be used to describe the process of pressure recovery in annular.The model could also calculate the annular wellbore multiphase flow in the process of annular pressure recovery and predict the annular pressure balance time and final balanced pressure.The prediction values agree well with the experimental results.