A comprehensive model is formulated to predict the flow behavior for upward two-phase flow. This model is composed of a model for flow-pattern prediction and a set of independent mechanistic models for predicting such flow characteristics as holdup and pressure drop in bubble, slug, and annular flow. The comprehensive model is evaluated by using a well data bank made up of 1,712 well cases covering a wide variety of field data. Model performance is also compared with six commonly used empirical correlations and the Hasan-Kabir mechanistic model. Overall model performance is in good agreement with the data. In comparison with other methods, the comprehensive model performed the best.
A comprehensive model is formulated to predict the flow behavior for upward two-phase flow. The comprehensive model is composed of a model for flow pattern prediction and a set of independent models for predicting the flow characteristics such as holdup and pressure drop in bubble, slug and annular flows. The comprehensive model is evaluated by using a well databank that is composed of 1775 well cases covering a wide variety of field data. The performance of the model is also compared with the six commonly used empirical correlations. The overall performance of the model is in good agreement with the data. In comparison with the empirical correlations, the comprehensive model performs the best, with the least average error and the smallest scattering of the results. INTRODUCTION Two-phase flow is commonly encountered in petroleum, chemical and nuclear industries. The frequent occurrence of two-phase flow presents engineers with the challenge of understanding, analyzing and designing two phase systems. Due to the complex nature of two-phase flow, the problem was first approached through empirical methods. Recently the trend has shifted towards the modeling approach. The fundamental postulate of the modeling approach is the existence of flow patterns or flow configurations. Various theories have been developed for the prediction of flow patterns. Separate models were developed for each flow pattern to predict the flow characteristics such as holdup and pressure drop. By considering flow mechanics, the resulting models can be applied to flow conditions other than used for their development with more confidence. The only studies published on comprehensive mechanistic modeling of two-phase flow in vertical pipes are by Ozon et al. and Hasan and Kabir. Nevertheless, more work is needed in order to develop models which describe the physical phenomena more rigorously. The purpose of this study is to formulate a detailed comprehensive mechanistic model for upward two-phase flow. The comprehensive model first predicts the existing flow pattern and then calculates the flow variables by taking into account the actual mechanisms of the predicted flow pattern. The model is evaluated against a wide range of experimental and field data available in the updated TUFFP well databank. The performance of the model is also compared with six empirical correlations used in the field.
Different permutations of the single and the two-fold dam-break flow have been investigated using the mesh-free smoothed-particle hydrodynamics and the experimental setup. The free-surface deformation in the case with the wet bed for five different downstream water heights has been investigated and respective numerical and experimental results were presented. The results demonstrate that the increase of the water height over the wet bed leads to the reduction of the flow front velocity. Effect of considering or omitting the dam gate during the numerical simulation has also been examined, which proves that the simulations including the dam gate show improved agreement with the experimental results. Influence of the three-dimensional cubic, triangular, circular and square cylindrical obstacles and their position on flow characteristics has been investigated. As the distance between the triangular obstacle and the gate increases, a bore is created at the position closer to the top of the triangle. In addition, it is found that larger force is exerted on the circular cylinder in comparison to the square cylinder.
The flow of gas-liquid mixtures in vertical pipes is widely encountered in the petroleum industry. In most oil wells gas is produced simultaneously and the oil production rate is dependent upon the gas rate. As the gas rate is increased from zero, the gas is dispersed as discrete bubbles that increase steadily in number and, with coalescence and pressure drop, may increase in size. This flow pattern is called bubble flow. At progressively higher gas velocities slug, froth, and annular-mist flow patterns occur.For a given gas rate the volume fraction of the gas phase or gas void fraction is dependent upon the oil rate. For a naturally producing oil well, the oil production rate depends upon the difference between the flowing bottom hole pressure and the surface pressure. This difference is dependent upon the flow pattern and the holdup, which are dependent upon the oil and gas rates, the fluid properties, the depth and diameter of the well, and the absolute pressure and temperature.Numerous empirical correlations are available (Brill and Beggs, 1982) for predicting flow pattern, holdup, and pressure drop in oil wells. It has only been in recent years that researchers have begun to consider the basic hydrodynamic phenomena involved in two-phase flow and to develop theoretical models for determining flow pattern, holdup, and pressure drop. Mechanistic models have been developed for flow pattern (Taitel et al., 1980), holdup (Barnea andBrauner, 1985), and pressure drop in slug flow (Fernandes et al., 1983;Sylvester, 1987) and annular-mist flow (Yao and Sylvester, 1987) in vertical pipes.The purpose of this paper is to formulate and evaluate a mechanistic model for two-phase bubble flow in vertical pipes that permits calculation of liquid holdup and pressure drop.(1982) have developed relations that delineate the bubble flow pattern. At low gas and liquid rates bubble flow exists provided the pipe diameter is larger thanAccording to this relation bubble flow does not exist for smalldiameter pipes because the small bubbles rise faster than the Taylor bubbles, which causes coalescence.Taitel et al. considered two distinct bubble flow patterns, bubbly and dispersed bubble flow, depending upon the gas and liquid rates and the gas void fraction. At low liquid and gas rates the transition from bubbly to slug flow is based on a liquid holdup of 0.25. This transition in terms of superficial liquid and gas velocities is given bywhere u, is the slip or bubble rise velocity given by Harmathy (1 960) (3) At higher gas and liquid rates both bubbly and slug flow become dispersed bubble flow. The transition to dispersed bubble flow is given by Flow Pattern Transition BoundariesThe model is formulated based on the assumDtion that theflow is fully developed and stable. It is further assumed that a t any given location the gas is discretely and uniformly dispersed as bubbles in the liquid phase.When gas and liquid flow concurrently upward a t a low gas rate, bubble flow occurs. Taitel et al. (1980) and Barnea et al. This relation was ...
Pakistan, a developing country, has gone through various phases of fonnulating gas pricing policies during its 4O-year history of natural gas production and consumption. This paper identifies critical factors that influenced gas pricing policies in Pakistan and adverse effects experienced when any of these factors was not given proper consideration. For instance, on the producer's side, discounted pricing fonnulas discouraged further exploration and development, leaving high-potential areas unexplored and discovered fields donnant for more than a decade. On the consumer's side, subsidized gas prices encouraged consumption to rise steeply without new discoveries to offset additional surplus consumption. The paper also discusses various short-and long-tenn variables that should go into a gas pricing policy for developing countries. References to recent policies are also given, indicating how these variables were incorporated in real tenns. The conclusions and recommendations, based on Pakistan's long experience with the gas industry, should be useful for other oil-importing countries rich in indigenous gas resources.
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