Wellbore Two-phase Flow Numerical Simulation Studies

Two-phase gas-liquid flow in pipes is of great practical importance in petroleum. This work focuses on the determination of flow pattern transitions and modeling in gas-liquid flow, which purpose is to estimate accurately the pressure drop and liquid holdup (gas volume fraction). Two-phase flow in pipes is a complex issue. For this reason, A model commonly used in simulators for well modeling is the no-slip homogeneous model, which predictions is inaccurate. Based on the feature of two-phase flow, influence on pattern transitions and a lot of experiment and investigation, this paper has established a drift-flux model for wellbores, which is easy, continuous and flow pattern included. A new formula for calculating the minimum liquid-carrying velocity and the producing rate for continuously withdrawing the liquid from gas well is derived by a new viewpoint that has analyzed the force and the shape of the droplet. The achievements we have got as follows:(l).The flow pattern prediction in Petalas & Aziz model is well. Based on the data considered, this model provided acceptable transition predictions. However, the transition to dispersed bubble flow and the transition between stratified flow and intermittent flow can be improved.(2).The mechanism for the transition to dispersed bubble flow is considered to be the turbulent fluctuation forces breaking up the gas phase into dispersed bubbles. Among the model developed from this mechanism, Barnea's model gave the most accurate result.(3).For the transition from intermittent flow to annular-mist flow, α_G > 0.75 model can provide reasonable transition boundaries. Its accuracy, however, may rely on the correlations used to calculate the in situ gas volume fraction. In the transitions for stratified flow, the interfacial friction factor has a strong effect on the transition. The simple approximation f_i = f_wG is recommended for the flow pattern prediction.(4).Based on the research of flow pattern and pattern transition, we have established a drift-flux model. The accuracy of this model is determined by the use of appropriate values for C_o and V_d . A method was proposed to develop correlations for C_o and V_d in which both C_o and V_d are function of α_G. The two parameters was determined by directly minimizing the errors between the experimental and the estimated α_G.(5). By the analysis of the force, the shape and the drag coefficient of the droplet, the formula related to the determination of terminal rate for continuous removal of liquids from gas well was proposed. The result of this formula is fit field data well.The prediction precision of pressure drop in two-phase flow in gas well wasimproved through this article's research, the critical producing rate for withdrawing the liquid from the gas well was obtained, which was suitable for field. The further study for theory of gas reservoir with water bottom is not only widely theory research, but also useful to production.