Two-phase Flow In Wellbore Research Articles

Lattice Boltzmann Method simulation of wellbore gas–liquid​ phase transition

Whenever the drilling wellbore is at the state of gas–liquid two-phase flow, gas slips and migrates along the drilling fluid. Due to the decreased wellbore temperature and pressure during gas migration, gas volume will gradually increase. When the temperature and pressure reach the critical value of gas–liquid phase, phase change occurs. The volume of natural gas expands suddenly, and a large amount of gas is generated. It easily leads to a well blowout, which is a great challenge to well control. Therefore, analyzing the gas–liquid phase changes in drilling wellbore has important practical significance for realizing well control safety. In this paper, Lattice Boltzmann Method (LBM) is applied to simulate phase transition of wellbore gas–liquid​ two-phase system. Research results show that gas–liquid distribution after phase transition is closely related to the system original density. Compared to the critical density of gas–liquid phase change, when the system original density is lower, continuous gas forms in wellbore. While the system original density is higher, gas phase breaks out into small bubbles and migrates along the wellbore. Phase distribution directly determines gas–liquid two-phase flow pattern in wellbore, which is crucial to wellbore pressure accurate prediction. Some valuable attempts are conducted to investigate gas–liquid two-phase flow in wellbore by using LBM in this research.

A transient hydro-thermo-bubble model for gas kick simulation in deep water drilling based on oil-based mud

Accurate prediction of wellbore gas-liquid two-phase flow behaviors is significant for gas kick detection and well control treatment, particularly in oil-based mud. Considering the synergy of mass transfer, heat transfer and bubble-bubble interaction, a fully coupled hydro-thermo-bubble model was developed to simulate the wellbore gas-liquid two-phase flow during gas kick in oil-based mud. In this model, the impact of gas flow on heat transfer was considered. Also, the variation in the gas concentration in the mass transfer boundary layer based on the bubble hydrodynamics was used to quantify the mass transfer rate. The integrated model was solved using the fully-implicit finite difference method. The accuracy and capability of the model were verified using the field and experimental measurement data. Using this model, the wellbore two-phase flow behaviors and temperature distribution characteristics during gas kick in oil-based mud were analyzed. Additionally, the mutually coupled effects between mass transfer, heat transfer and bubble-bubble interaction were investigated. Moreover, the impacts of mass transfer, heat transfer and bubble-bubble interaction on two-phase flow characteristics were compared.

Change mechanism of transient gas-liquid two-phase flow in wellbore during marine natural gas hydrate reservoir drilling

In the drilling process of a marine natural gas hydrate reservoir, the original temperature and pressure condition of the hydrate will change due to the influence of construction, and gas will be released from the hydrate. The decomposition gas makes the wellbore flow into a complex gas-liquid-solid multiphase flow after entering into the wellbore, and thus poses a great threat to the well control security. Accordingly a transient gas-liquid two-phase flow drift flux mathematical model is established in this paper. The numerical method is proposed and verified, and an example analysis is carried out. Finally the change mechanism of transient gas-liquid two-phase flow in wellbore is obtained. This study provides an important foundation for the safe design of an offshore gas hydrate. Meanwhile, it is of great positive significance to find the decomposition gas and to optimize drilling parameters in the drilling process of a marine natural gas hydrate reservoir.

Numerical simulation of gas-liquid two-phase flow in wellbore based on drift flux model

A general model and computational code for transient gas-liquid two-phase flow in wellbore are developed in this paper. The model consists of mass conservation equation for each phase and mixture momentum conservation equation. The interactions of each phase are taken into account by invoking the Shi slip relation in the proposed model. The model is numerically solved by the second order AUSMV scheme, which is obtained by using classical MUSCL technique. The computational code is validated by the classical numerical cases, Zuber–Findlay tube and complex mass transport problem. The simulation results show good agreement with the references which are obtained by using first-order flux-limited Roe scheme with refined grids. The computational code also succeeds in obtaining the transient behavior of each phase for a normal gas-kick occurrence in wellbore. The simulation results illustrate the degree of pressure variation in the upper wellbore is greater than that in the lower wellbore. The pressures of wellbore increase before the corresponding gas mass flow rate reach max inlet gas mass flow rate, then decrease.

Investigation of pressure wave propagation and attenuation characteristics in wellbore gas-liquid two-phase flow

Pressure waves have many important applications in the oil and gas drilling engineering field. This paper aims to discuss the propagation and attenuation of pressure waves transmitted in wellbore gas-liquid two-phase flow. In this study, a mathematical model is proposed that estimates the pressure wave propagation and attenuation in wellbore two-phase fluid flow. The model is based on a two-fluid model and considers the interactions between two phases, wall shear force, and gravitational effect. The wave speed and attenuation coefficient are calculated and compared to previous experimental results. The comparison of the results shows satisfactory compliance. Based on the model, the effects of void fraction, angular frequency, system pressure, and temperature on wave speed and attenuation coefficient are discussed. The results indicate that pressure wave dispersion is obvious in wellbore two-phase fluid flow. The wave speed first decreases with an increase in the void fraction and then exhibits a flat transition. Next, the wave speed increases notably after the void fraction exceeds 90%, showing a characteristic U-shape curve. The pressure wave attenuation shows the inverse variation trends than that of wave speed. Lower angular frequency and temperature, and higher system pressure are observed to benefit the transmission of a pressure wave in wellbore two-phase flow. Furthermore, the propagation and attenuation behaviors of pressure waves in wellbore two-phase flow during aerated underbalanced drilling are discussed as a case study. The pressure wave attenuation rises with respect to the gas injection rate. The amplitude of the pressure wave at the wellhead decreases to 8.1% of the initial value when the gas injection rate reaches 13 m3 min−1. This wave amplitude is almost undetectable during drilling operations. This is the cause of failure for mud pulse telemetry in aerated underbalanced drilling. Stronger attenuation is observed when the pressure wave travels close to the wellhead.

Gas reservoir evaluation for underbalanced horizontal drilling

A set of surface equipment for monitoring the parameters of fluid and pressure while drilling was developed, and mathematical models for gas reservoir seepage and wellbore two-phase flow were established. Based on drilling operation parameters, well structure and monitored parameters, the wellbore pressure and the gas reservoir permeability could be predicted theoretically for underbalanced horizontal drilling. Based on the monitored gas production along the well depth, the gas reservoir type could be identified.

T2Well—An integrated wellbore–reservoir simulator

At its most basic level, management of subsurface fluid resources involves a system comprising the wellbore and the target reservoir. As discrete pathways through geologic formations, boreholes and wells are critical to the success of many water, energy, and environmental management operations. Although many stand-alone simulators for two-phase flow in wellbores with various levels of sophistication have been developed, simulating non-isothermal, multiphase, and multi-component flows in both the wellbore and in the porous or fractured media reservoir as an integrated system remains a challenging yet important task. The difficulties include (1) different governing equations apply to the wellbore and the reservoir that need to be solved efficiently in a uniform framework, (2) the significant contrast in temporal and spatial scales between the wellbore and the reservoir that results in a very challenging set of stiff partial differential equations, and (3) other complexities (e.g., dry-out) that can be caused by flow processes between the wellbore and the reservoir. To address the need to simulate coupled wellbore–reservoir flow, we have developed T2Well, a numerical simulator for non-isothermal, multiphase, and multi-component flows in the integrated wellbore–reservoir system. The new model extends the existing numerical reservoir simulator TOUGH2 to calculate the flow in both the wellbore and the reservoir simultaneously and efficiently by introducing a special wellbore sub-domain into the numerical grid. For grid blocks in the wellbore sub-domain, we solve the 1D momentum equation of the mixture (which may be two-phase) as described by the drift-flux model (DFM). A novel mixed implicit–explicit scheme for friction in the wellbore is applied to facilitate the solution of the momentum equation, while other variables are calculated fully implicitly. Applications of the new simulator to problems in various fields are presented to demonstrate its capabilities.

Development of a Transient Mechanistic Two-Phase Flow Model for Wellbores

SummaryA great deal of research has been focused on transient two-phase flow in wellbores. However, there is lack of a comprehensive two-fluid model in the literature. In this paper, we present an implementation of a pseudo-compositional, thermal, fully implicit, transient two-fluid model for two-phase flow in wellbores. In this model, we solve gas/liquid mass balance, gas/liquid momentum balance, and two-phase energy balance equations to obtain five primary variables: liquid velocity, gas velocity, pressure, holdup, and temperature. This simulator can be used as a stand-alone code or can be used in conjunction with a reservoir simulator to mimic wellbore/reservoir dynamic interactions. In our model, we consider stratified, bubbly, intermittent, and annular flow regimes using appropriate closure relations for interphase and wall-shear stress terms in the momentum equations. In our simulation, we found that the interphase and wall-shear stress terms for different flow regimes can significantly affect the model's results. In addition, the interphase momentum transfer terms mainly influence the holdup value.The outcome of this research leads to a more accurate simulation of multiphase flow in the wellbore and pipes, which can be applied to the surface facility design, well-performance optimization, and wellbore damage estimation.

A New Method Using Wellhead Measurement to Approximate Unsteady- State Gas-Water Two-Phase Flow in Wellbore to Calculate Inflow Performance

Abstract An accurate analysis of the pressure and water inflow at the bottomhole of a gas well with free water influx is important for determining an optimized artificial lift method. The commonly used two-phase flow correlations based on steady-state flow have been successfully applied to gas wells in homogeneous reservoirs. However, for reservoirs with a high degree of heterogeneity, such as fractures, the existing techniques often fail due to the unsteady-state flow behaviour from reservoir to wellbore. This paper presents a new method that is derived based on the unsteady-state two-phase flow phenomena and the conservation of mass, taking into consideration the slippage effect of the two phases. In this method, the fluid flow is divided into a number of segments at which pressure drop and gas-liquid distribution under unsteady-state flow conditions can be calculated utilizing the measured data at the wellhead. In this case, more representative bottomhole pressures and water inflow rate changes with time can be calculated, permitting the selection of an optimum artificial lift method. The new method has been successfully tested. A field case is presented involving a gas well in the Sichuan Field in China. The results of the new calculation method and the steady-state calculations were compared with field measurements to determine the accuracy of the method. Introduction The total amount of gas that can be produced from a gas well with free water influx largely depends on its ability to lift water. Sometimes, it is necessary to engage artificial lift to dewater the well. Accurate forecasting of gas well deliverability requires accurate predictions of pressure loss and gas and liquid inflow performance to select and design the appropriate artificial lift method. Most often, two-phase flow correlations are employed to determine flow rate and pressure loss in gas wells. Those methods are generally adequate for wells completed in homogeneous reservoirs that exhibit steady-state flow. But these correlations typically fail in reservoirs with a high degree of heterogeneity, such as fractures, due to the unsteady-state flow behaviour from the reservoir to the wellbore. The modelling calculation presented in this paper outlines a method using wellhead measurements to calculate sandface pressure and flow rate in order to design artificial lift systems to manage water loading problems and improve production and ultimate recovery. An example of the application of this method for a gas lift design is included in this paper. Theoretical Development Gas flows intermittently with water from a fractured formation with free water influx. The intermittent flow is maintained in the reservoir into the wellbore. By studying gas-water unsteady-state flow in the tubing, it is possible to estimate fluctuations along the entire flow path from the sandface to the wellhead. The production of gas and water at the wellhead is not synchronized with the sandface. This is primarily due to wellbore storage effects. The slippage between water and gas under unsteady-state flow conditions causes time dependent flow rate changes to the gas and liquid phases as the gas arrives at the wellhead.

A Simple Model for Annular Two-Phase Flow in Wellbores

Summary Annular flow is associated with production from both gas-condensate and geothermal wells. Oil wells also experience it during high-gas-to-oil-ratio (high-GOR) production. The current semimechanistic modeling approach requires estimation of film thickness before computing frictional pressure drop as gas flows past the wavy-liquid film surrounding the pipe wall. This study intends to investigate this film thickness and its impact on pressure-drop computation in wellbores producing steam-water, gas-condensate, and gas-oil mixtures. Computational results show that this dimensionless liquid-film thickness is most likely less than 0.06 in annular flow. For such values of thin-film thickness, the computed friction factor is only slightly higher than that estimated with a smooth-channel assumption. When the homogeneous model is used to compute pressure gradient by ignoring the wavy-liquid film on frictional pressure drop, good agreement is achieved with field data and with the predictions of a semimechanistic model.

Wellbore Two-Phase Flow and Heat Transfer During Transient Testing

Summary This paper presents a comprehensive wellbore/reservoir simulator to study pressure-transient behavior during two-phase flow in a vertical or deviated wellbore. We adapted a hybrid approach by modeling the wellbore numerically in which mass, momentum, and energy of the fluids are conserved, while treating the reservoir fluid flow analytically. Conductive heat transport occurs through the tubulars, cement sheaths, and formation. Both conductive and convective heat transport mechanisms are operative for the annular fluid, however. For an offshore well, convective heat transfer through seawater and air are also considered. The simulator can be run in two modes. In forward simulation, transient pressure and temperature can be computed at any point in the wellbore, given the reservoir and completion parameters. Conversely, in a reverse simulation, bottomhole pressures (BHP's) can be computed given the pressure and temperature measurements at any other point in the borehole, including at the wellhead. However, the quality of reverse simulation derived solution is likely to suffer with increasing gas/oil ratio (GOR). Field data were used to show both features of the simulator. Computational results show that the effect of heat loss through seawater is marginal for most offshore wells with a short submerged section (<500 ft) because of the fluids’ short residence time. However, for wells with long submerged tubulars (>2,000 ft), heat loss to the seawater becomes significant. Similarly, a deviated well loses more heat to the formation than its vertical counterpart because of increased residence time. Among major variables, thermal conductivity of the annular fluid plays a key role in heat retention and, therefore, in the wellhead temperature (WHT).

A Comprehensive Mechanistic Model for Upward Two-Phase Flow in Wellbores

Summary 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.