Non-rotating Pipe Research Articles

Dynamic evolution of Strouhal number in flexible pipes coupling rotation

The dynamic response evolution mechanism of the rotating and non-rotating pipe (RP-NRP) system remains inadequately explored, and there is a lack of a precise Strouhal-Reynolds (St-Re) model to effectively characterize the rotational and interference effects. To address this research gap, hydrodynamic experiments were conducted on flexible RP-NRP systems with varying spacing and angles. The spacing ratios ranged from 4-12 times the diameter, and the angle ranged from 0° to 270°. The experimental results reveal that St numbers in tandem systems are lower than those of the isolated pipe due to wake feedback inhibition and shadowing effect. Conversely, St numbers in side-by-side systems consistently exceed those of the isolated pipe due to the side-wall effect. Notably, the staggered systems exhibit fluctuations in St numbers, which are highly sensitive to the incident angle. A novel St-Re model accounting for rotation and interference effects was proposed based on the experimental data. The proposed model (Strms= 9.4 × 10−10Re2-2.05 × 10−5Re+0.26) demonstrates a "dumbbell-shaped" pattern, which can be categorized into regions of interference enhancement and attenuation based on the StRms curve. Furthermore, the critical Reynolds number of 6400 identifies the strong regions of interference enhancement and attenuation. Within these regions, 45.18 % of St numbers fell into the enhanced area of interference while 54.82 % in the weakened area. The St numbers of flexible pipes, accounting for rotation and interference effects, are lower than those of fixed cylinders and non-rotating vibrating flexible pipe systems. Additionally, the dominant frequencies are weakened in the 0°, 180°, and 135 – 180° RP-NRP systems, these angles could guide the layout of the riserless drill string and drilling fluid recovery riser.

Self-Attenuation of Drillstring Torsional Vibrations Using Distributed Dampers

Summary During drilling operations, drillstring vibrations cause many downhole dysfunctions, resulting in underperformance, equipment failure, and possibly wellbore damage. Current drillstring vibration mitigation solutions are generally located at a single site, either at the topdrive or close to the bit. However, because the sources of vibration excitation are distributed along the whole drillstring, these single-point vibration damping solutions do not succeed in removing all vibration modes. A distributed vibration damping solution is investigated, wherein damping subs are placed at intervals along the drillstring. The drillpipe rotates on bearings inside the damping subs, thereby reducing mechanical torque. The damping sub has a slightly larger diameter than the neighboring tool joints, lifting the drillstring off the borehole wall and thus eliminating most of the mechanical friction between the damping subs. Viscous friction is introduced in the form of rotary eddy current brakes within the damping subs, which cause the damping of torsional oscillations. The damping sub moves axially on spur wheels supported by bearings, thereby reducing drag forces. The decoupling of rotary and axial movement is a key element for removing a source of excitation. Simulations made with a 4n degree-of-freedom (DOF) transient torque and drag model confirm the expected results. The results of simulations for a use case based on a complex 3D trajectory are presented. With damping subs every 30 m and a damping coefficient of 20 N·s/rd, the topdrive torque is reduced to 40% of that of a plain drillstring, and torsional stability is obtained across the topdrive speed range of 60 to 180 rev/min. By comparison, conventional nonrotating pipe protectors (NRPPs) would have reduced the topdrive torque to 30%, but torsional stability would have not been achieved because the expected damping coefficient was less than 0.02 N·s/rd. The design of the damping sub relies on readily available technological components that can sustain very high pressures and temperatures. The damping subs are therefore compatible with high-pressure/high-temperature applications, including geothermal drilling.

Case Study Examines Safely Exceeding Buckling Loads in Long Horizontal Wells

This article, written by Editorial Manager Adam Wilson, contains highlights of paper SPE 163518, ’Safely Exceeding Buckling Loads in Long Horizontal Wells: Case Study in Shale Plays,’ by S. Menand, SPE, DrillScan, and D. C-K Chen, SPE, Hess, prepared for the 2013 SPE/IADC Drilling Conference and Exhibition, Amsterdam, 5-7 March. The paper has not been peer reviewed. The general industry perception is that, when drillings or casing strings exceed conventional helical-buckling criteria, they cannot be operated safely in the hole because the risk of failure or lockup is too high. However, some theoretical, experimental, and field case studies have shown that a tubular may be run in the hole even in a buckling state within safe limits. Introduction Buckling occurs when the compressive load in a tubular exceeds a critical value, beyond which the tubular is no longer stable and deforms into a sinusoidal or helical shape. Sinusoidal buckling corresponds to a tube that snaps into a sinusoidal shape, and it is sometimes called lateral buckling, snaking, or two-dimensional buckling. Helical buckling corresponds to a tube that snaps into a helical (spiral) shape. Recent studies have shown that the conventional sinusoidal- and helical-buckling criteria are accurate only in a perfect wellbore geometry because wellbore tortuosity and doglegs play a great role in the buckling phenomenon. An example is illustrated in Fig. 1, which shows that sinusoidal and helical buckling take place simultaneously despite the same compression; doglegs and tortuosity play an important role in the onset of buckling. Compression on the drillpipe is maximal when tripping in, running casing/liner, or performing slide drilling. Buckling may also occur when drilling with a rotary assembly with a large weight on bit (WOB). The critical helical-buckling load for a rotating pipe may be approximately 50% less than that obtained for a non-rotating pipe. The helical-buckling load is generally the load used in drillstring or casing design to define the limit upon which the tubular might be fully buckled, with the risk of getting stuck or with the risk of large bending stresses that may lead to failure. During well planning, if the compression in the drillstring exceeds the critical helical-buckling load, drilling engineers usually modify the drillstring design until this buckling does not occur. It is widely recognized that sinusoidal buckling is not harmful to a tubular, but helical buckling is generally perceived as a dangerous situation.

Turbulent heat transfer characteristics of water flow in a rotating pipe

Large-Eddy-Simulation of turbulent heat transfer for water flow in rotating pipe is performed, for various rotation ratios (0 ≤ N ≤ 14). The value of the Reynolds number, based on the bulk velocity and pipe diameter, is Re = 5,500. The aim of this study is to examine the effect of the rotating pipe on the turbulent heat transfer for water flow, as well as the reliability of the LES approach for predicting turbulent heat transfer in water flow. Some predictions for the case of non-rotating pipe are compared to the available results of literature for validation. To depict the influence of the rotation ratio on turbulent heat transfer, many statistical quantities are analyzed (distributions of mean temperature, rms of fluctuating temperature, turbulent heat fluxes, higher-order statistics). Some contours of instantaneous temperature fluctuations are examined.

Direct numerical simulation of the motion of particles in rotating pipe flow

In this paper the motion of particles in rotating pipe flow is studied for various flow cases by means of direct numerical simulation. Compared to flow in a non-rotating pipe, the Navier–Stokes equation contains as only extra term the Coriolis force when the equation is considered in a rotating frame of reference. Particles in the flow also experience a centrifugal force, which drives them to one side of the wall of the pipe. The flow is characterized by two Reynolds numbers for the mean axial velocity and the rotation rate, respectively. Among the cases studied are one in which the flow without rotation would be laminar and rotation leads to turbulence and another one for which Poiseuille flow is unstable but instead of transition to a turbulent state, a time-dependent laminar flow results. In all cases studied a counter-rotating vortex is present. The simulation results are used to calculate the collection efficiency of the rotational phase separator (RPS) under turbulent flow conditions. The RPS is a device to separate liquid or solid particles from a lighter or heavier fluid by means of centrifugation in a bundle of channels which rotate around a common axis. The results show that, compared to Poiseuille flow, the collection efficiency for larger particles decreases due to the combined action of the vortex and turbulent velocity fluctuations, while it is unchanged for smaller particles.

A friction factor bound for transitional pipe flow

An upper bound λmax on the friction factor λ is found for transitional pipe flow up to Reynolds numbers of Re=4000. This bound corresponds to the laminar Hagen–Poiseuille value until the energy stability point of Re=81.52 (where λmax=0.7851) after which it decreases monotonically to approach a viscosity-independent asymptote of 0.27±0.01 as Re→∞. Comparison is made with the friction factors associated with recently discovered, finite-amplitude traveling waves in rotating and nonrotating pipe flow as well as experimental data.

Direct simulations of turbulent flow in a pipe rotating about its axis

Flow in a circular pipe rotating about its axis, at low Reynolds number, is investigated. The simulation is performed by a finite difference scheme, second-order accurate in space and in time. A non-uniform grid in the radial direction yields accurate solutions with a reasonable number of grid points. The numerical method has been tested for the non-rotating pipe in the limit ν→0 to prove the energy conservation properties. In the viscous case a grid refinement check has been performed and some conclusions about drag reduction have been reached. The mean and turbulent quantities have been compared with the numerical and experimental non-rotating pipe data of Eggels et al. (1994a, b). When the pipe rotates, a degree of drag reduction is achieved in the numerical simulations just as in the experiments. Through the visualization of the vorticity field the drag reduction has been related to the modification of the vortical structures near the wall. A comparison between the vorticity in the non-rotating and in the high rotation case has shown a spiral motion leading to the transport of streamwise vorticity far from the wall.

Helicity fluctuations and turbulent energy production in rotating and non-rotating pipes

In this paper finite-difference second-order accurate direct simulations have been used to investigate how the helicity density fluctuations change when a turbulent pipe rotates about its axis. In this case the rotation axis is parallel to the near wall vortical structures which play a fundamental role on the wall friction and turbulence production. The helicity density is the trace of the tensor γij′=〈vi′ωj′〉 whose elements form the components of v′×ω′. When the momentum equations are written in rotational form the turbulence energy production term splits into two parts, one related to the convection of the large scales and the other related to the energy cascade to the small scales. From data of direct simulations the changes of the turbulent production term profile with the rotation have been explained by the pdf of the v′×ω′ components. The links between the changes on the pdf of the v′×ω′ and the modifications of the vortical structures have been also investigated. The joint pdf of the dissipation with the helicity density has shown that the dissipation is highly correlated with regions of very low helicity density in the non-rotating pipe. When the pipe rotates the helicity density increases and the dissipation decreases. Since a drag reduction is one of the results of the background rotation, in this paper, it has been speculated that the alignment between velocity and vorticity could be a common feature in drag reducing flows.

Nonlinear spiral waves in rotating pipe flow

A numerical investigation of finite-amplitude, non-axisymmetric disturbances, in the form of travelling spiral waves, is made in pipe flow with superimposed solid-body rotation. Rotating pipe flow is found to be supercritically unstable both in the rapid and slow-rotation regimes. Earlier weakly nonlinear calculations, suggesting subcritical instability in the slow-rotation limit, are shown to be in error. Bifurcating neutral waves are calculated for various axial and azimuthal Reynolds numbers and wavenumbers. For fixed axial mean pressure gradient, the axial mean flow induced by these waves gives rise to a significant flux defect, in certain cases as large as 40-50% of the undisturbed mass flux; the possible relevance of this finding to the phenomenon of vortex breakdown is pointed out. In non-rotating pipe flow, no neutral disturbances in the assumed form of spiral waves are found for moderate Reynolds numbers; this indicates that previous conjectures, regarding a possible connection between nonlinear spiral waves in slowly rotating pipe flow and the asymptotic neutral states of Smith & Bodonyi (1982) in non-rotating pipe flow, are not valid.

The dynamic instability of a non-rotating pipe in a high speed rotor filled with liquid.

An investigation is made into the dynamic instability of a non-rotating elastic pipe in a high speed hollow cylindrical rotor filled with a viscous liquid. The system considered simulates a liquid cooled rotor mechanism. Assuming a small circular whirling motion of the pipe, perturbed motions of the liquid-pipe system are analyzed. The theory shows that the forward self-excited whirling motions of the pipe can be induced at rotor speeds somewhat higher than the natural frequency of the pipe. the lower bound of the unstable region mainly depends on the bulk density of the pipe relative to the liquid density. Hence, the most effective way to stabilize the system is to introduce a pipe lighter in bulk density than the surrounding liquid. Experiments are carried out to verify the theory. some interesting results of the dynamic behavior of the pipe are also obtained in the experiments.

Turbulence in Helically Corrugated Pipe Flow

Results are reported of experimental measurements of friction factor, mean and turbulent velocities, and Reynolds stresses in fully developed flow through a helically corrugated pipe. Helical corrugations induce a strong rotational component in the mean flow near the wall but this decreases rapidly toward the pipe axis. Turbulence intensities and axial shear are generally smaller in this flow than in nonrotating pipe flow and the reduction is attributed to rotation. Reynolds stress measurements extrapolated to the wall are in agreement with pressure drop measurements. Both show that pipe friction factor is less in helically corrugated pipe than in normally corrugated pipe, other factors being the same. The axial component of the mean flow is well fitted by the two-dimensional semilogarithmic law-of-the-wall for rough pipes. It is also fitted by the defect law but the numerical parameters of the latter behave as in an adverse pressure gradient boundary layer, indicating less shear stress than in nonrotating pipe flows. This is consistent with reduced friction factor.

Stability of Hagen-Poiseuille flow with superimposed rigid rotation

The linear stability of Hagen-Poiseuille flow (Poiseuille pipe flow) with superimposed rigid rotation against small three-dimensional disturbances is examined at finite and infinite axial Reynolds numbers. The neutral curve, which is obtained by numerical solution of the system of perturbation equations (derived from the Navier-Stokes equations), has been confirmed for finite axial Reynolds numbers by a few simple experiments. The results suggest that, at high axial Reynolds numbers, the amount of rotation required for destabilization could be small enough to have escaped notice in experiments on the transition to turbulence in (nominally) non-rotating pipe flow.