Siamack A. Shirazi

A CFD Based Correlation for Erosion Factor for Long-Radius Elbows and Bends

A model for predicting sand erosion in 90 degree elbows and bends has been developed based on computational fluid dynamics (CFD), particle tracking and erosion data. After the flow field was obtained from the flow (CFD) model, particles were introduced into the flow and particle trajectories were computed using a Lagrangian approach. A model was also implemented that accounts for the interaction between the particles and the target material. Based on predicted particle impingement velocities, erosion rates and penetration rates were predicted using the empirical equations for erosion ratio. The predicted penetration rates are compared with available experimental data for several different elbows. The agreement between the predicted penetration rates and the experimental data is good. In addition, based on many predictions and erosion rate results, a new CFD based correlation is developed that can be used for an approximate engineering calculation to account for effects of elbow radius on erosion in long-radius elbows. This equation is for computing the ratio of the wall thickness loss (or the penetration rate) in a long-radius elbow to the penetration rate of a standard (short-radius) elbow. The results from the correlation agree well with the trend of available data in the literature.

Modeling Solid Particle Erosion in Elbows and Plugged Tees

Predicted erosion patterns on the surface of a pipe fitting can now be obtained using a technique implemented into a computational fluid dynamics (CFD) code. This comprehensive erosion prediction procedure consists of 1) generation of a flow field simulation, 2) computation of a large number of particle trajectories inside the flow field, and 3) erosion model equations applied as particles impinge the walls of the geometry. Other quantities related to erosion, namely the particle deposition rate as well as local average impingement angle and velocity components, are also stored in the procedure. All predicted quantities (flow solution, particle trajectories, and erosion profiles) are analyzed using a three-dimensional visualization tool that was also developed. The current work focuses on two pipe fittings commonly used in the oil and gas production industry: elbows and plugged tees. First, the flow field and erosion predictions are evaluated through comparisons with experimental data. Erosion predictions yield trends and locations of maximum wear that are consistent with experimental observations. Next, two 90-deg pipe elbows with centerline curvature-to-diameter ratios of 1.5 and 5.0 are analyzed under prescribed erosive conditions. Predicted erosion results are presented in the form of surface contours. Finally, a simulated plugged tee geometry placed under erosive conditions is studied and erosion rates are compared to that of the two elbow test cases.

A Comprehensive Procedure to Estimate Erosion in Elbows for Gas/Liquid/Sand Multiphase Flow

A comprehensive procedure that combines mechanistic analysis and numerical simulation approaches is proposed to estimate the erosion in elbows for gas/liquid/sand particle multiphase flow systems. The erosion problem in multiphase flow is approximately transferred to one in single-phase flow by introducing the effective sand mass ratio and a representative single-phase flow to which a single-phase computational-fluid-dynamics-based erosion-prediction model can be applied. Erosion in elbows is calculated for various multiphase flow patterns and compared to experimental data in the literature. Reasonable agreement between the simulations and the literature data is observed. The proposed approach is an effective tool to estimate the erosion in multiphase flow.

An Alternate Method to API RP 14E for Predicting Solids Erosion in Multiphase Flow

One commonly used method for determining oil and gas production velocities is to limit production rates based on the American Petroleum Institute Recommended Practice 14E (API RP 14E). This guideline contains an equation to calculate an erosional or a threshold velocity, presumably a flow velocity that is safe to operate. The equation only considers one factor, the density of the medium, and does not consider many other factors that can contribute to erosion in multiphase flow pipelines. Thus, factors such as fluid properties, flow geometry, type of metal, sand production rate and size distribution, and flow composition are not accounted for. In the present paper, a method is presented that has been developed with the goal of improving the procedure by accounting for many of the physical variables including fluid properties, sand production rate and size, and flowstream composition that affect sand erosion. The results from the model are compared with several experimental results provided in the literature. Additionally, the method is applied to calculate threshold flowstream velocities for sand erosion and the results are compared with API RP 14E. The results indicate that the form of the equation that is provided by the API RP 14E is not suitable for predicting a production flowstream velocity when sand is present.

Hydrodynamics of Two-Phase Flow in Gas-Liquid Cylindrical Cyclone Separators

This paper presents new experimental data and an improved mechanistic model for the Gas-Liquid Cylindrical Cyclone (GLCC) separator. The data were acquired utilizing a 3” ID laboratory-scale GLCC, and are presented along with a limited number of field data. The data include measurements of several parameters of the flow behavior and the operational envelope of the GLCC. The operational envelope defines the conditions for which there will be no liquid carry-over or gas carry-under. The developed model enables the prediction of the hydrodynamic flow behavior in the GLCC, including the operational envelope, equilibrium liquid level, vortex shape, velocity and holdup distributions and pressure drop across the GLCC. The predictions of the model are compared with the experimental data. These provide the state-of-the-art for the design of GLCC’s for the industry.

Improvements of Particle Near-Wall Velocity and Erosion Predictions Using a Commercial CFD Code

The determination of a representative particle impacting velocity is an important component in calculating solid particle erosion inside pipe geometry. Currently, most commercial computational fluid dynamics (CFD) codes allow the user to calculate particle trajectories using a Lagrangian approach. Additionally, the CFD codes calculate particle impact velocities with the pipe walls. However, these commercial CFD codes normally use a wall function to simulate the turbulent velocity field in the near-wall region. This wall-function velocity field near the wall can affect the small particle motion in the near-wall region. Furthermore, the CFD codes assume that particles have zero volume when particle impact information is being calculated. In this investigation, particle motions that are simulated using a commercially available CFD code are examined in the near-wall region. Calculated solid particle erosion patterns are compared with experimental data to investigate the accuracy of the models that are being used to calculate particle impacting velocities. While not considered in particle tracking routines in most CFD codes, the turbulent velocity profile in the near-wall region is taken into account in this investigation, and the effect on particle impact velocity is investigated. The simulation results show that the particle impact velocity is affected significantly when near-wall velocity profile is implemented. In addition, the effects of particle size are investigated in the near-wall region of a turbulent flow in a 90 deg sharp bend. A CFD code is modified to account for particle size effects in the near-wall region before and after the particle impact. It is found from the simulations that accounting for the rebound at the particle radius helps avoid nonphysical impacts and reduces the number of impacts by more than one order-of-magnitude for small particles (25 μm) due to turbulent velocity fluctuations. For large particles (256 μm), however, nonphysical impacts are not observed in the simulations. Solid particle erosion is predicted before and after introducing these modifications, and the results are compared with experimental data. It is shown that the near-wall modification and turbulent particle interactions significantly affect the simulation results. Modifications can significantly improve the current CFD-based solid particle erosion modeling.

STATE-OF-THE-ART CUTTINGS TRANSPORT IN HORIZONTAL WELLBORES

In the ever-growing use of, directional and horizontal drilling, hole cleaning is a common and costly problem. It can become particularly critical in the case of extended reach drilling where larger and longer wellbores are drilled. During the past two decades, especially in recent years, many laboratory studies as well as field observations have been directed towards addressing the cuttings transport problem. This has resulted in better understanding of the subject and some remedies to the problems. Several correlation/models have also been developed that give the field engineer a tool to better specify the hydraulic requirements in cleaning the hole. However, because of the complexity of the subject, a comprehensive and proven model, which does not exist at this time, requires much more laboratory research and field studies.

Erosion-Corrosion of a Carbon Steel Elbow in a Carbon Dioxide Environment

Abstract For many conditions, erosion-corrosion can produce higher wall penetration rates than erosion or corrosion alone. While flow velocity generally is believed to be an important factor, more ...

Generalization of the API RP 14E Guideline for Erosive Services

The commonly used practice for controlling sand erosion in gas and oil producing wells is to limit production velocities following the provisions of American Petroleum Inst. (API) RP14E. This guideline contains a procedure to calculate a threshold velocity, the flow velocity below which an allowable amount of erosion occurs. While providing the advantage of computational ease, the approach has some disadvantages. One is that, while many factors influence the erosion rate, APE RP14E includes only one factor, the density of the medium. Thus, such factors as flow geometry, type of metal, sand size, and Reynolds number are not accounted for. In this paper, the method is applied to calculate threshold velocities. The computational procedure allows an allowable amount of erosion to be specified in mils per year for elbows, tees, and direct impingement geometries. Threshold flow-stream velocities are calculated for carrier fluids of crude oil, water, and methane at elevated pressure. Resulting threshold velocities are presented for a range of sand sizes, pipe diameters, sand production rates, and methane pressures. Results show that threshold velocities for single-phase gas flows are much lower than those for single-phase liquid flows.

Prediction of Erosion-Corrosion Penetration Rate in a Carbon Dioxide Environment with Sand

Abstract In oil and gas wells producing carbon dioxide (CO2) with saturated water, carbon steel piping can corrode rapidly depending upon the nature of the hydrocarbon phases produced and on flow and environmental parameters. In some CO2 environments, a protective iron carbonate (FeCO3) scale can form on carbon steel piping walls and reduce corrosion rates to within acceptable design limits. If sand also is being produced, protective scales can be removed or prevented from forming on piping walls at points where sand particles entrained in the flow stream impinge the walls. When this happens, bare metal corrosion is enabled at these impingement points, and corrosion rates again reach high levels. This process involves both erosion and corrosion mechanisms and often is referred to as “erosion-corrosion.” In some cases, pitting occurs at impingement points, resulting in extremely high penetration rates. In the present work, a laboratory flow loop circulating a CO2-saturated sodium chloride (NaCl) solution a...