Liang-Biao Ouyang

Steady-state gas flow in pipes

Abstract New general flow equations of simple form are developed to account for the pressure drops due to friction, elevation and kinetic energy change. Simplified forms are also presented for new flow equations for gas flow in pipelines or wells where the kinetic energy term can be neglected. The new general flow equations and their simplified forms are compared with the widely-used AGA equations and tested with field data. Results show that the new equations make excellent predictions of flow rates or pressure drops, and that they are applicable over a much broader range of gas types and gas flow rates than the AGA equation and old simplified flow equations. In addition, different empirical explicit correlations for the Fanning friction factor are compared. It is found that different correlations give quite different values of the friction factor. For smooth pipes, modified 1 9th power law, Blasius, Drew et al., and Panhandle equations are recommended for different Reynolds number ranges. For rough pipes, Serghides (I) and (II), Zigrang-Sylvester (I) and (II), Chen, and Haaland equations can be employed with confidence. Other friction factor correlations reported in the literature should be avoided because they can result in large errors.

A homogeneous model for gas-liquid flow in horizontal wells

Abstract Radial influx or outflux stands for the major difference between fluid flow in a pipe and fluid flow in a well. A homogeneous model for gas–liquid flow in a horizontal well is presented in this paper. In addition to frictional and gravitational components of total pressure drop, accelerational pressure drops due to fluid expansion and radial influx or outflux are considered. Effect of radial influx or outflux on wall friction is also taken account for. With a segmented approach, the new model and several existing pipe flow models have been applied to predict pressure drop along a wellbore, and predictions are compared with experimental data. It is found that the new homogeneous model outperforms existing models for gas–liquid flow in horizontal wells.

Transient gas-liquid two-phase flow in pipes with radial influx or efflux

Abstract A simplified model for transient gas–liquid flow in pipes with radial influx or efflux has been developed in this paper. The resulting governing equations are essentially hyperbolic with U tp + c s and U tp − c s as their eigenvalues. A finite-difference scheme based on the split coefficient matrix (SCM) approach is applied to solve the mass and momentum balance equations. Sample numerical simulation runs are performed. Simulation results agree with experimental observations and clearly show the features of variation in pressure drop, liquid holdup, and two-phase velocity during transient and steady state flow periods.

Development of New Wall Friction Factor and Interfacial Friction Factor Correlations for Gas-Liquid Stratified Flow in Wells and Pipelines

Stratified flow is one of the most basic flow pattern in the analysis of gas-liquid two-phase flow in pipes. In the present paper, different interfacial friction factor correlations were used to predict the liquid holdup and pressure gradients. The comparison of predictions with experimental observations shows that most existing correlations for the interfacial friction factor can lead to large deviations from measurements and that the standard method underestimates the liquid phase wall friction factors. New correlations for both the liquid phase wall friction factor and the interfacial friction factor were developed based on large amounts of available experimental data. The resulting correlations were used to predict liquid holdup and pressure gradient for different experiments. Considerable improvement in predictions was observed.

A MECHANISTIC MODEL FOR GAS–LIQUID FLOW IN HORIZONTAL WELLS WITH RADIAL INFLUX OR OUTFLUX

ABSTRACT A new mechanistic model for gas–liquid two-phase flow with mass transfer through the pipe wall, which accounts for the effects of wall inflow or outflow on wall friction, acceleration and flow pattern transition, has been developed. Four individual flow patterns, including stratified flow, annular-mist flow, bubble flow and intermittent flow, are considered in the mechanistic model. Models for individual flow patterns have been developed. Transition mechanisms among different flow patterns are discussed and new transition criteria are proposed. Predictions by the new mechanistic model are compared with experimental data obtained on a large industrial facility.

Numerical Investigation of the Impacts of Wall Fluid Entry on Fluid Flow Characteristics and Pressure Drop along a Wellbore

Abstract Single-point or limited-point wall fluid entry in a wellbore has been observed in different oil and gas wells all over the world through downhole video logging. The wall fluid entry is expected to affect both the fluid flow characteristics in a wellbore and the pressure drop along the wellbore. In order to investigate the impacts of the single-point wall fluid entry, a numerical simulation model has been set up and a series of numerical simulations have been conducted by using a commercial computational fluid dynamics (CFD) software package. Flow velocity profiles, streaklines, pressure distribution along the wellbore, and so on have been thoroughly investigated. The simulation results clearly demonstrate the influence of the wall fluid entry on the fluid flow as well as the pressure drop along the wellbore. The impacts on the pressure drop along the wellbore have further been quantified.

Prediction of the Occurrence of Oil–Water Countercurrent Flow in Deviated Wells

Abstract Water circulation and oil–water countercurrent flow in a deviated well has been investigated in the present article. Flow patterns for the countercurrent flow have been identified. Two practical criteria based on the transport mechanisms of a liquid layer and a liquid droplet have been developed for determining the occurrence of oil–water countercurrent flow in deviated or multilateral wells. The criteria can also be applied to determine the liquid loading-up conditions of gas wells. Well deviation, well size, and oil density are the three major factors that affect the occurrence of oil–water countercurrent flow. The smaller the wellbore size, the larger the well deviation, or the denser the oil phase, the lower the minimum oil flow rate is required to avoid the occurrence of oil–water countercurrent flow or water circulation. Excellent agreement has been achieved between the model prediction and the field and laboratory observations. A modified equation has also been proposed for determining the water droplet size in oil–water wells.

Modeling Oil–Water Countercurrent Flow in Deviated Wells Using Mechanistic and Simplified Approaches

Abstract Water circulation and oil–water countercurrent flow in a deviated or multilateral well has been investigated in the present paper. Flow patterns for the countercurrent flow have been identified. Two practical criteria for determining the occurrence of countercurrent flow in deviated wells are introduced. Five categories of flow patterns for the countercurrent flow in pipes or wells are identified. Transitions among different flow patterns are proposed. Both a mechanistic model and a simplified model are developed for describing the oil–water countercurrent flow in deviated and multilateral wells. Solution procedure for using the newly-developed models is discussed.

SOLUTION NONUNIQUENESS FOR SEPARATED GAS–LIQUID FLOW IN PIPES AND WELLS. I. OCCURRENCE

ABSTRACT The occurrence of multiple solutions has been investigated and discussed in this paper. Multiple solution regions are displayed by either a U SL–U SG map or a X–Y map. It is found that many parameters impose influence on the multiple solution regions, including fluid properties, pipe ID, pipe inclination angle, wall inflow or outflow, empirical correlations for wall friction and interfacial friction factors, and so on. For example, the multiple solution region could change significantly if different interfacial friction factor correlations are applied. Multiple solutions are only possible for upward flow for separated flow in a pipe without wall mass transfer. However, for wellbore flow case, depending on wall inflow or outflow of fluids and their flow rates, multiple solutions may also exist for horizontal and downward flow. More specifically, for wall inflow case (production well), multiple solutions only exist for upward flow for the gas inflow-dominant case, whereas they may exist for upward, horizontal and downward flow for liquid inflow-dominant situations. The opposite is expected for wall outflow (injection well) case.

PRODUCTIVITY OF HORIZONTAL AND MULTILATERAL WELLS

This paper introduces a new semi-analytical technique that can be applied to calculate the productivity of vertical, horizontal and multilateral wells. The well location and profile can be arbitrary. The reservoir region containing the well must be homogeneous (isotropic or anisotropic) and it may have constant potential or no-flow outer boundaries. Constant rate, constant bottom hole pressure and a combination of these constraints can be imposed on the wells. It is shown that under certain conditions the well productivity is strongly influenced by the pressure drop in the well and the type of conditions that exist at the reservoir boundaries. For multilateral wells the interaction among laterals can also influence productivity. In many cases, conventional techniques can result in large errors.