A Drift-Flux Model for Upward Two-Phase High-Velocity Flow in Large Diameter Pipes

Abstract

Abstract This study proposes the evaluation and development of a drift-flux model for upward two-phase high-velocity flow in large diameter pipes. A case where the proposed model is applicable is WCD (Worst-Case-Discharge) calculations for offshore wells. WCD assumes relatively larger pipe diameters and higher flow rates than the flow experiments at laboratory conditions utilized to develop most of the flow models available in the literature. Most of the two-phase flow models describe flow regime transitions as discrete processes by assigning the required void fraction or velocity for each flow regime transition. Therefore, for each flow regime, flow-regime-dependent correlations or fixed drift-flux parameters are applied, which lead to a wide variety of flow regime maps and complications of flow models. Unlike others, the model proposed does not have sudden pressure surge or reduction along with flow regime transitions from bubbly to non-bubbly flow regimes. Also, it doesn't have fixed drift-flux coefficients for each flow regime. Further, rather than assigning a fixed void fraction or velocity for bubbly/churn flow transition, it applies the minimum pressure gradient estimated by the bubbly flow model to determine bubbly/non-bubbly flow transition. The proposed drift-flux model is validated for a wide range of experimental and field data and compared with pressure loss models in commercial software. Among all the models, the proposed model gives the lowest average absolute pressure error (2%) and standard deviation (4.5%) for the tested 279 field data points.