Integrated multiphase flow modeling in wellbore for downhole pressure predictions

Abstract

Throughout the life of the well, when designing many aspects of various disciplines that pertain to the flow of fluids within a conduit, knowing the bottomhole flowing pressure (P_wf) and pressure profile in the wellbore are of undeniable significance. One would ask why not deploy downhole pressure gauges to obtain P_wf readings. Unfortunately, it is not economical or practical to do so. The harsh in-situ conditions are not optimal for such gauges, resulting in high failure rates. Thus, the common practice is to apply hydraulic models to predict P_wf given surface measurements. To do so, predicting the fluid flow behavior is vital. The prediction of such behavior is quite simple when dealing with single-phase fluid flow. Unfortunately, such is rarely the case in the petroleum industry. The existence of multiple phases introduces multiple complexities hindering the accuracy of the predictions. Even the most sophisticated models pertain to a considerable amount of error when applied to some conditions. To solve this issue, comprehensive mechanistic models that integrate fluid flow mechanisms to vastly increase the accuracy of the predictions could be used. Although the mechanistic models can be considered the most accurate multiphase flow model, they cause major difficulties when coupled with simulators due to their discontinuous nature. In this work, a new integrated multiphase flow model was developed. The aim of the new model is to produce relatively accurate downhole pressure predictions under all flow conditions while maintaining a simple, differentiable, and continuous form. In this study, the performance of widely used multiphase flow point models has been evaluated with five different field datasets. Then the integrated model was put together by incorporating the state-of-the-art onset of liquid loading model. Unlike the existing models, the new model classifies the flow based on the onset of liquid loading. If liquid loading occurs, then the model uses a sophisticated drift-flux model which proved to be both simple and relatively accurate when dealing with high liquid flow. On the other hand, if liquid loading does not occur, an improved two-fluid model will be used. The proposed two-fluid model was developed by improving on the wetted perimeter and the liquid wall shear stress of existing two-fluid models. The proposed model outperformed five other models in predicting the liquid holdup and pressure gradient of 11 experimental datasets (1478 data points). In addition, the model succeeds capturing the effects of inclination angle, gas density, and liquid and gas superficial velocities on liquid holdup and pressure gradient. With the improved two-fluid model, the new integrated model was completed. Moreover, the new integrated model outperformed the other multiphase flow models in predicting the downhole pressure of 313 field data points. When dealing with wells that have both segregated and intermittent flow, the new model produces outstanding results. In addition, it succeeds in finding the location and amount of liquid loading in a well. Ultimately, the new integrated model paves the way for the design and optimization of artificial lift processes that require knowing the location and amount of liquid loading.