Computational analysis of the particle size effect on the pressure profiles and type of flow regimes of TiO2 microparticles in a fluidized bed

The effect of particle size on the pressure profiles and flow regimes of the bed containing TiO2 microparticles (MPs) was investigated in a fluidized bed. The fluidization behavior of particles with mean diameters, d p , of 170, 200, 225, and 300 μm at different gas velocities, U g , was investigated both experimental and computational viewpoints. A computational fluid dynamic (CFD) model was developed by the Eulerian–Eulerian approach to evaluate the sensitivity of the Syamlal–O’Brien, and Gidaspow drag models on the predicted results of the bed pressure profiles. The results showed that with increasing particle size, the amplitude of pressure fluctuations increases and the type of flow regime in the bed tended from bubbling to slugging flow regime. The error analysis showed that the use of the Gidaspow model led to more accurate results than the Syamlal–O’Brien model in predicting the bed pressure drop and pressure fluctuations in the slugging flow regime. However, the Syamlal–O’Brien model was more suitable for predicting the pressure profiles in the bubbling flow regime. The results were more suitable for the bed containing particles of 300 μm than the beds with d p ≤ 225 μm. The highest and lowest deviations between the experimental data and simulation outputs were obtained at U g of 0.295 and 0.650 m/s, respectively. The findings confirmed that the mutual effects existed between the d p pressure profiles, and the type of flow regimes in the bed.

Buoyancy Force on a Plain or Perforated Portion of a Pipe

Summary Torque and drag models have been used for several decades to calculate tension and torque profiles along drillstrings, casing strings, and liner strings. Buoyancy forces contribute to the loads acting on the pipe and affect its interaction with the borehole wall. Torque and drag calculations account for these localized effects, as well as the material internal forces, torques, and moments on each side of the contact. When the analysis is applied to a discrete length of pipe, the cross sections at each end do not contribute to the buoyancy forces because they are not in contact with the fluid, except where there is a change in diameter or at the end of the string of pipe. We argue that it is important to check that the models used for solid pipe torque and drag calculations remain valid for sand screens, in particular, the extent to which the buoyancy forces acting on a perforated tube might differ from those on a solid pipe. Because the buoyancy force is the result of the pressure gradient acting on the surface of the pipe, the presence of holes may also influence the buoyancy force. We propose that there are theoretical differences between local buoyancy forces acting on plain or perforated tubes. This paper describes how to calculate the local buoyancy force on a portion of a drillstem by the application of Gauss’ theorem and accounting for the necessary corrections arising from the cross sections not being exposed to the fluid. We built an experimental setup to verify that the tension inside a pipe subject to buoyancy behaves in accordance with the derived mathematical analysis. With complex well construction operations, for instance during extended-reach drilling or when drilling very shallow wells with high buildup rates, the slightest error in torques and drag calculations may end up jeopardizing the chances of success of the drilling operation. It is therefore important to check that the basis of design calculations remain valid in those contexts and that, for instance, sand screens or slotted liners may be run in hole safely after a successful drilling operation.

Drag model validation of slurry pipeline using CFD

A number of drag models have been suggested for the interaction of fluid particles in slurry flow over the previous centuries. It is necessary to examine the correctness and applicability of these models in the slurry transportation. Based on this concept, a comparative analysis of the different drag models is performed for the 0.0549 m diameter slurry pipeline. The research is carried out by using three drag models: Syamlal-obrien, Schiller-naumann and Gidaspow due to their accessibility in the Fluent commercial software. The simulation is performed at mean flow velocity range, Vm= 2–5 ms-1 and solid concentration range, Cvf = 10– 20% (by volume) using computational drag models. The simulated outcomes for solid particle size 440 μm having density 2470 kg/m3 are recorded using Eulerian two-phase model with selected drag models in the computational domain. It has been found that the Eulerian two-phase model with Syamlal O’brien drag model gives the accurate and meticulous results with the published data in the literature. Finally, the simulated outcomes of solid concentration contours, solid concentration profiles and pressure drop are predicted at distinct velocity and solid concentration range for chosen drag models.

A Comparative Study of Soft String Vs Stiff String Models Application in Torque and Drag Analysis

Torque and drag models estimate downhole forces, torques and moments acting in wellbores and drillstring elements during drilling and completion operations. A comparison was made between soft string and stiff string torque and drag model using conventional survey data. Survey data needed for torque and drag modeling are provided by field surveys. Field survey can be conventional survey or continuous survey. Conventional survey is carried out every 90 to 100ft interval or more and only gives a partial representation of the actual wellpath, micro-doglegs and micro-tortuosities may not be fully captured with this survey. Continuous survey is carried out between 1 to 5ft intervals of the wellbore using high resolution survey tools and captures more the micro-doglegs and micro-tortuosities but more expensive than the conventional survey. Torque and drag simulations were performed using both Soft and Stiff String models for comparison using a novel software package. Data provided includes deviational survey data from conventional survey, drillstring/BHA data, and fluid rheological data. The torque and drag simulation produced results for hook loads and buckling while running-in-hole (RIH) and pulling-out-of-hole (POOH). Results from this study show that prior to buckling, results from soft string and stiff string model are almost identical with minimal differences within the range of 0.8% to 1.6% and these were achieved as open-hole friction factors (CHFF) from 0.1 to 0.25. High buckling risk was detected for OHFF of 0.3. When buckling occurs, the differences in results between the two models become very apparent. This paper showed that in order to use stiff string torque and drag model for a more realistic, representative and more accurate pre-buckling and post-buckling operations in a highly deviated well, a high resolution continuous survey is needed; this will capture more readily, the micro-doglegs and micro-tortuosities in the wellbore paths.

On the drag force closures for multiphase flow modeling

Drag force models are one of the most important factors that can affect TFM and CFD-DEM simulation results of two-phase systems. This article investigates the accuracies, implementation issues and limitations of the majority of the drag models for spherical, non-spherical and systems with size distribution and evaluates their performance in various simulations. Around 1888 data points were collected from 19 different sources to evaluate the drag force closures on mono-dispersed spherical particles. The Reynolds number and fluid volume fraction ranges were between 0.01 and 10,000 and between 0.33 and 1, respectively. In addition, 776 data points were collected from seven different sources to evaluate the drag force closures on poly-dispersed spherical particles. The Reynolds numbers were between 0.01 and 500, fluid volume fractions between 0.33 and 0.9, and diameter ratios up to 10. A comprehensive discussion on the accuracy and application of these models is given in the article.