Percentage Drag Reduction Research Articles

Effects of Solids Loading on Drag Reduction in Polymeric Drilling Fluids Through Straight and Coiled Tubing

Abstract An experimental study has been conducted to evaluate the effects of solids on the drag reduction characteristics of polymeric drilling fluids, loaded with solids, through straight and coiled tubing. The polymers investigated were PHPA and XCD. These polymers were dissolved in brines which were prepared by mixing potassium chloride (KCl) and sodium formate (Naformate) in water. Various concentrations of polysaccharide gum (XCD) and partially hydrolyzed polyacrylamide (PHPA) polymers were dissolved in the KCl and Na-formate solutions. These fluids were pumped through straight pipes. Based on the results, it was established that the PHPA/KCl solution exhibited better drag reduction than PHPA/Na-formate, XCD/KCl, and XCD/Na-formate solutions in straight pipes. Thus, the PHPA/KCl solution was selected for further study. This polymer solution was then loaded with barite and bentonite to simulate solid cuttings. The fluid system was pumped through different sized coiled tubing and straight pipes. A correlation in terms of Fanning friction factor and generalized Reynolds number was developed, and percentage drag reduction was calculated. It was observed that, when clear polymeric solutions were loaded with solids, drag reduction decreases drastically. Finally, the effect of curvature on the flow of solidladen fluids was studied. It was observed that frictional losses in coiled tubing were almost twice those of frictional losses in straight tubing for the solid-laden polymeric fluids under investigation. Introduction In the past, various studies have been conducted on the flow of clean Newtonian and non-Newtonian fluids through straight pipes in turbulent flow. For the flow of Newtonian fluids through smooth pipes, von Karman(1), Nikuradse(2), and Prandtl(3) suggested correlations, but the most commonly used correlation was proposed by Drew et al.(4). Their correlation is valid for Reynolds numbers between 3,000 and 3,000,000. Similarly, for Newtonian fluids flowing through rough pipes in a turbulent flow regime, Moody(5), Nikuradse(2), Churchill(6), and Chen(7) developed correlations. Among these, Chen's correlation is the most widely used in the industry, as Chen's correlation is explicit for Fanning friction factor and correlates the Fanning friction factor, pipe roughness, pipe diameter, and Reynolds number. Although non- Newtonian fluids have not been studied as often as Newtonian fluids, they have been under intense examination for some time for flow effects through smooth and rough pipes. Dodge and Metzner(8), Melton and Malone(9), and Shah(10) presented extensive theoretical and experimental studies. Similarly for non- Newtonian fluids through rough pipes, Dodge(11) and Shah(10) correlations are widely used in the industry. As shown, numerous studies have been conducted in the past, especially in the case of Newtonian fluids. However, no study could be found in the literature regarding the effects of solids on the flow of non-Newtonian fluids through straight or coiled tubing. The objective of this project was to study the effects of solids loading on the drag reduction characteristics of commonly used polymeric drilling fluids flowing through straight and coiled tubing. This was achieved by first studying the polymeric fluids flowing through straight pipe without solids.

Experimental study on drag-reducing channel flow with surfactant additives––spatial structure of turbulence investigated by PIV system

The turbulent frictional drag of water can be reduced dramatically by adding small amounts of drag-reducing materials, such as polymers or surfactants. As a percentage drag reduction of 80% can easily be achieved, this technique is thought to be the most practical method of reducing turbulent frictional drag. In this work, a double pulse particle image velocimetry (PIV) system was used to clarify the spatial velocity distribution of surfactant solution flow in a two-dimensional channel. A type of cationic surfactant cetyltrimethyl ammonium chloride (C 16H 33N(CH 3) 3Cl) mixed with the same weight of counter-ion material NaSal (HOC 6H 4COONa) was used as a drag-reducing additive to water at a mass concentration of 40 ppm. Instantaneous velocity distribution taken by PIV was examined to clarify the effect of surfactant. It was found that the instantaneous velocity distribution taken in water flow exhibits penetration from the low-speed fluid region into the high-speed region, which is one of the important events of turbulence energy production and turbulent mixing. Although this structure is commonly observed in water flow, it was not found in drag-reducing flow under the same Reynolds number. The strong vorticity fluctuation near the wall also disappeared and the integral length scale in streamwise direction of turbulent fluctuation had a smaller value in surfactant solution flow.

Water‐soluble polymers. LXXXII. Shear degradation effects on drag reduction behavior of dilute polymer solutions

AbstractDrag reduction measurements were conducted on extensively characterized poly(ethylene oxide) and poly(acrylamide) utilizing a fully automated rotating disk rheometer equipped with an optical tachometer, torque transducer, and software allowing real‐time data acquisition. The instrument sensitivity allowed the study of concentrations as low as 0.1 ppm. In addition, previously immeasurable concentration‐ and time‐dependent shear degradation effects were readily observed. A power law equation was shown to adequately correlate the percentage of drag reduction and the volume fraction for each polymer. Furthermore, an empirical shift factor was utilized to superimpose data from all the systems that were studied. By conducting measurements in the proper concentration and time domains, it was possible to extract the minimal concentration for the maximum drag reduction efficiency in the absence of shear degradation. The resulting values were significantly higher than those previously reported by our laboratories for poly(ethylene oxide) and poly(acrylamide). © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1211–1221, 2001

Universal drag reduction characteristics of saline water-soluble poly(ethylene oxide) in a rotating disk apparatus

Polymer-induced turbulent drag reduction in a rotating disk apparatus was investigated using nonionic poly(ethylene oxide) (PEO) in a synthetic saline solution with novel application to ocean thermal energy conversion technology. A maximum total (skin friction plus form) drag reduction of 30% was obtained with 50 wppm of PEO with molecular weight 5.0 × 106. The concentration dependence of the percentage drag reduction for the PEO/saline solution system is found to fit Virk's empirical correlation, and a universal correlation for various molecular weights and Reynolds numbers is also presented. Furthermore, hydrodynamic volume fraction was introduced to correlate drag reduction efficiency with molecular parameters in this PEO/saline solution system.

The effect of drag-reducing polymer additives on wall-pressure fluctuations in turbulent channel flows

The present paper is concerned with the experimental study of the influence of Toms' phenomenon on the convective part of the hydrodynamic turbulent wall-pressure field. The experiments were carried out in a water tunnel, at flow velocities of 2.3, 3.3 and 4.3 m/s, where amounts of drag reduction up to 40% were obtained by injecting dilute polymer solutions. An investigation of the spectral feature of the wall-pressure frequency spectrum and the wall-pressure frequency cross-spectrum was achieved from data taken using pinhole transducers. The scaling laws for the mid- and high-frequency regions of the spectrum were examined both for the water flow and the drag-reducing flow. The use of a noise cancellation procedure allowed observation of the maximum of the spectrum in the mid-frequency range at an approximately reduced frequency ωδ u τ of 80 for the water flow. This maximum is shifted towards a higher value of the reduced frequency in the presence of Toms' effect. From cross-spectral data obtained over separation distances ranging from 0.4 δ to 2.8 δ, the effect of drag reduction was estimated on the coherence functions as well as the convection velocity. These data show a correlated shift of the threshold which delineates the low wave number group identified as the large-scale turbulence contributor in the outer region of the flow and the high wave number group associated with turbulent sources in the log-region. The effect of drag reduction on the convection velocity data supports the fact that the contributions to the different wave number groups should be attributable to activity in the outer and inner regions, respectively. In addition, a computation of the root mean square pressure was achieved from the wall-pressure frequency spectrum. When expressed as functions of the percentage of drag reduction, the rms pressures related to the wall shear stress are found to increase monotonicaly. The equivalent ratio obtained by scaling the rms pressures using the dynamic pressure is found to decrease in the drag-reducing flow. Finally, an estimation of the probability density distribution showed that the skin friction reduction affects predominantly the occurrence of higher pressure amplitudes as well as very low pressure amplitudes. This confirms the important contribution of the large pressure peak events to the overall features of the wall-pressure.

Drag reduction in two‐phase gas‐liquid flows

A considerable amount of drag reduction is observed in various flow regimes for two-phase gas-liquid flow of drag reducing fluids. Various attempts have been made to correlate the amount of drag reduction, but comparison with single phase flow of drag reducing fluids has not been done in a satisfactory manner. It is well known that single phase flow of drag reducing fluids exhibits a diameter effect. In order to account for this, a plot of percent drag reduction versus friction velocity, ..mu../sup */, in the absence of a polymer additive gives a simple method of estimating the amount of drag reduction for a given flow rate and pipe diameter. For two-phase flow no such comparison has been made.

Laser-Doppler anemometer measurements of turbulent structure in drag-reducing fibre suspensions

A laser-Doppler anemometer (LDA) was used to measure turbulent velocities in drag-reducing fibre suspensions. Measurements of streamwise velocities (and, in one case, the circumferential velocity as well) were made in flow through a straight pipe at x/d = 190, and at Reynolds numbers in the range 1.4 × 104–5.3 × 104. The fibres used were chrysotile asbestos of high aspect ratio (∼ 106), at a concentration of 300 w.p.p.m. They were dispersed in an aqueous solution of a surfactant (0.5% by weight Aerosol OT). In some experiments, the fibre suspensions were supplemented by a drag-reducing polymer (Separan AP30) at a concentration of 150 w.p.p.m. A complete experiment involved passing a quantity of fibre suspension through the apparatus a number of times (at a given Reynolds number) and measuring the velocity distribution across the pipe during each pass. As the amount of drag reduction generally declined with the number of passes (i.e. due to fibre degradation), this provided a convenient way of varying the percentage drag reduction as an experimental parameter. Results were obtained for mean velocity and intensity profiles, autocorrelations, and one-dimensional energy spectra. The mean period of turbulent bursts was determined by measuring autocorrelations with short sampling times.At the lowest Reynolds number (Re = 1.4 × 104), drag reductions of about 70% were obtained during the first two passes. This was accompanied by a reduction in the streamwise intensity below the level obtained in the surfactant solution alone. (Note: The opposite behaviour is found in drag-reducing polymer solutions, where intensity levels are larger than those in the solvent alone.) A measurement of the r.m.s. circumferential velocity showed an increased level (relative to surfactant alone) during this part of the experiment. During further passes, there was a transition to ‘polymer-like’ behaviour, with increased streamwise intensity, which subsequently declined with pass number (and hence drag reduction) towards the result for surfactant alone. This effect had previously been found in preliminary experiments at Re = 9 × 103 (McComb & Chan 1979). Repetition of the experiment a Re = 1.4 × 104, with the addition of Separan AP30, confirmed the existence of this transition from ‘fibre-like’ to ‘polymer-like’ drag reduction. In this case, the drag reduction was smaller (at about 60%), but the mixed suspension was much more resistant to degradation, with transition occurring at the ninth pass. However, such behaviour was not found at higher Reynolds numbers (Re = 3.2 × 104 and 5.3 × 104), in fibre suspensions where increased streamwise intensities occurred, even at high levels of drag reduction (about 70%).Anomalous streamwise autocorrelations were found during ‘fibre-like’ drag reduction but in the ‘polymer-like’ regime they were very similar to those measured in polymer solution, and showed characteristically increased lengthscales. On the other hand, energy spectra were found to be anomalous in all cases and showed an energy deficit at lengthscales of the same order as the fibre length. Finally, mean bursting periods were found to be much increased, with the increases being about the same as those in polymer solutions at the same Reynolds number and percentage drag reduction.

Flow Increase in the Trans Alaska Pipeline Through Use of a Polymeric Drag-Reducing Additive

Summary The first commercial use of a polymeric drag-reducing additive to increase the flow rate in a crude oil pipeline began during 1979 in the Trans Alaska Pipeline System (TAPS). This paper discusses the details of the two drag-reduction experiments conducted in TAPS that ultimately led to the decision for full-scale additive use. The logistics pertaining to and the benefits resulting from the current application also are discussed. Introduction Drag reduction is a well-known phenomenon first observed in the laboratory almost 35 years ago.1 Although extensive experimental studies of drag reduction are continuing, the mechanism of drag reduction is not well understood. In spite of this limitation, there is a wide potential application for drag reduction in the oil industry in both production and transportation operations. Drag reduction, as defined by Savins,2 is the increase in pumpability of a fluid caused by the addition of small amounts of an additive to the fluid. The effectiveness of a drag reducer is normally expressed in terms of percent drag reduction. At a given flow rate, percent drag reduction (DR) is defined asEquation 1 where ?p is the base pressure drop of the untreated fluid and ?pp is the pressure drop of the fluid containing drag-reducing polymer. Percent drag reduction is a measure of drag-reducing additive performance, but it does not reflect the primary end use of drag reducers. Normally, the increased pumpability is used to increase flow rate without exceeding the safe pressure limits within the flow system. The relationship between percent drag reduction and percent throughput increase (TI) can be estimated using the following equation.3Equation 2 where %DR is the percent drag reduction as defined in Eq. 1. Eq. 2 assumes that pressure drop for both the treated and untreated fluid is proportional to flow rate raised to the 1.8 power. The volumetric capacity and/or horsepower of the existing pumps may limit the amount of throughput increase. The installations of additional pump capacity may be necessary to obtain the full benefits of drag reducer use. The use of drag reducers in the oil industry has been limited primarily to hydraulic fracturing operations.4 Water-soluble polymers have been effective in reducing hydraulic horsepower requirements and/or increasing pump rates during fracturing treatments. Many water gels used to improve the sand-carrying capacity of the fracture fluid have excellent drag-reduction properties. Oil-soluble polymers have been used to a lesser extent in hydraulic fracturing with oil-base fluids. Drag reducers have not been used routinely in standard crude oil pipeline operations.

Influence of drag reducing polymers on turbulent mass transfer to a pipe wall

AbstractCompletely developed and entry region mass transfer rates in turbulent pipe flow of drag reducing polymer solutions were studied experimentally using electrochemical techniques. The percent change in the fully developed mass transfer rate at a given volumetric flow was found to be greater than the percent change in the pressure gradient. The data are interpreted by using the law of the wall, valid for Newtonian fluids at large Schmidt numbers, whereby K+ is related to Sc−0.74. The proportionality constant is correlated with percent drag reduction and is found to decrease with increasing drag reduction. The use of an analogy between momentum and mass transfer predicts a somewhat greater mass transfer reduction than was observed.

The drag reduction of poly(ethylene oxide)-carboxylate soap mixtures

The interaction of poly(ethylene oxide) with a homologous series of carboxylate soaps has been detected through measurements of drag reduction under turbulent flow conditions. The plots of percentage drag reduction at constant polymer concentration versus soap molarity are quite similar to literature data reported for the effect of several anionic surfactants on the reduced viscosity of a nonionic polypeptide. At low soap concentrations, the drag reduction of poly (ethylene oxide) is suppressed and falls to a minimum value. As the concentration is increased further the drag reduction rises above the value in pure water to one almost 75% greater in the stronger soap solutions. When the soap concentration corresponding to the minimum in the plot ( C M ) is plotted against the critical micelle concentration (cmc) the simple relation C M = 0.225 cmc is obtained. Such a result strongly suggests a cooperative micelle formed between soap and polymer at this point. Furthermore, the enhanced drag reduction obtained is consistent with the model of surfactant molecules hydrophobically bonded to the polymer chain in which repulsion between adjacent polar surfactant groups promotes expansion of the polymer coil.

Cavity-flow wall effects and correction rules

This paper is intended to evaluate the wall effects in the pure-drag case of plane cavity flow past an arbitrary body held in a closed tunnel, and to establish an accurate correction rule. The three theoretical models in common use, namely, the open-wake, Riabouchinsky and re-entrant-jet models, are employed to provide solutions in the form of some functional equations. From these theoretical solutions several different rules for the correction of wall effects are derived for symmetric wedges. These simple correction rules are found to be accurate, as compared with their corresponding exact numerical solutions, for all wedge angles and for small to moderate ‘tunnel-spacing ratio’ (the ratio of body frontal width to tunnel spacing). According to these correction rules, conversion of a drag coefficient, measured experimentally in a closed tunnel, to the corresponding unbounded flow case requires only the data of the conventional cavitation number and the tunnel-spacing ratio if based on the open-wake model, though using the Riabouchinsky model it requires an additional measurement of the minimum pressure along the tunnel wall.The numerical results for symmetric wedges show that the wall effects in-variably result in a lower drag coefficient than in an unbounded flow at the same cavitation number, and that this percentage drag reduction increases with decreasing wedge angle and/or with decreasing tunnel spacing relative to the body frontal width. This indicates that the wall effects axe generally more significant for thinner bodies in cavity flows, and they become exceedingly small for sufficiently blunt bodies. Physical explanations for these remarkable features of cavity-flow wall effects are sought; they are supported by the present experimental investigation of the pressure distribution on the wetted body surface as the flow parameters are varied. It is also found that the theoretical drag coefficient based on the Riabouchinsky model is smaller than that predicted by the open-wake model, all the flow parameters being equal, except when the flow approaches the choked state (with the cavity becoming infinitely long in a closed tunnel), which is the limiting case common to all theoretical models. This difference between the two flow models becomes especially pronounced for smaller wedge angles, shorter cavities, and with tunnel walls farther apart.In order to gauge the degree of accuracy of these theoretical models in approximating the real flows, and t o ascertain the validity of the correction rules, a series of definitive experiments was carefully designed to complement the theory, and then carried out in a high-speed water tunnel. The measurements on a series of fully cavitating wedges at zero incidence suggest that, of the theoretical models, that due to Riabouchinsky is superior throughout the range tested. The accuracy of the correction rule based on that model has also been firmly established. Although the experimental investigation has been limited to symmetric wedges only, this correction rule (equations (85), (86) of the text) is expected to possess a general validity, at least for symmetric bodies without too large curvatures, since the geometry of the body profile is only implicitly involved in the correction formula. This experimental study is perhaps one of a very few with the particular objective of scrutinizing various theoretical cavity-flow models.