Study On Multi-phase Flow In Supercritical Wellbore Annular

Supercritical Gas-liquid two-phase flow in wellbore is commonly encountered in the oil drilling & oil production engineering. The research of supercritical Gas-liquid two-phase flow is still in the primary state. As the acid gas and liquid two phase flow in wellbore becomes complicated, for example, the well blowout will be intense if it causes by supercritical natural gas. The existent multi-phase flow models can not be used satisfactorily in well kick calculation for Acid Gas drilling operation. So the study on multi-phase flow in wellbore of Supercritical Environment is very important.The phase transition law of acid gas in well bore is obtained under the conditions of different composition by theory analysis and simulation. The results indicate that the higher the acidic component content in nature gas the narrower the nature gas phase change zone is. The closer the location of transition occurrs the more serious the kick or blowout is and the more difficult well control is. Under condition of natural gas composition, the higher the mud density is, the the closer the location of transition occurs. The phase change curve move to low temperature zone with the increase of methane component in natural gas which makes the phase change zone decreased, early kick detection difficult, and well control more difficult.The characteristic void fraction wave fluctuation of two-phase flow is obtained above critical pressure through experiment and data analysis. Below critical pressure, bubble flow, cap bubble flow, cap churns flow are observed. Above critical pressure, bubble flow and churn-turbulent flow are observed. Below critical pressure and in the bubble flow zone, bubbly flow destabilizes and gas slip rate decreases with the increase of void fraction. Below critical pressure and in the cap bubble flow zone or cap churn flow zone, gas slip rate increases rapidly with the increase of void fraction. Under the same void fraction, the higher the pressure is, the lower the gas slip rate is. Above critical pressure, the gas slip rate variation in bubble flow zone is same as below critical pressure condition. But in churn-turbulent flow zone,the increase of gas slip rate is very small.Pressure inhibits on flow pattern transition is discovered through experiment. The gas superficial velocity and void fraction of flow pattern transition increase with the pressure increases. High pressure makes the bubble keep ball shape and more difficult collisioning. The critical void fraction of bubble flow destabilizes increases with the pressure increasing. The higher the pressure is, the higher the Critical mixed phase velocity is. Below critical pressure, the new model of bubble flow to cap flow transition is obtained by inducing reduced pressure. Above critical pressure,the boundary of bubbly flow to churn-turbulent flow is undefined.Based on the the mass conservation , momentum conservation , energy conservation equations, and combined with characteristics of natural gas drilling & well control, the supercritical wellbore multilphase flow control equation is built. On basis of the mathematical methods and using effective programming tools, the supercritical wellbore pressure prediction and well control parameters calculation software is developed, The well control parameters is calculated and analysised with the software and the variation of the parameters with the elapsed time of kick are analyzed. Under the same gas mass flow rate condition, the pit gain change rate decreases with the increasing of supercritical components. So it is important to find natural gas kick which contains supercritical components early in well control. In fact, the higher natural gas hydrogen sulfide content, the greater the gas density is. In the same bottom pressure conditions initial gas invaded volume is smaller. The gas volume fraction near the wellhead grows rapidly and mud density drops quickly because of the gas expansion and dissolved gas exhalation. The same volume fraction occurrence in the wellbore constantly drops down. Phase change and expanding location gradually deepen, and the blowout becomes sharp as a result of lower pressure.