Buckling Of Drill Strings Research Articles

Dynamic Buckling Characteristics of Drill String in Horizontal Wells

Buckling may cause drill string damage or even drilling failure. For the 3[Formula: see text]000-m-long horizontal section drill string, a simplified analysis model of drill string in horizontal well is established, and the dynamic response results of axial displacement, angular displacement and contact force are obtained. When buckling, the closer the position of drill string is to the bottom, the later the buckling time, the smaller the buckling deformation degree, the slower the growth rate of axial displacement, and the smaller the attenuation degree of angular displacement and contact force amplitude. After buckling, drill string undergoes tensile deformation and eventually remains stable in the tensile state. After stabilization, from the top of drill string to the bottom of drill string, axial displacement increment increases first, then remains unchanged and then decreases, and the relative torsion angle between different positions gradually decreases. The drill string is always in horizontal contact with the wellbore, resulting in the same contact force values at different locations. The change of well inclination angle does not affect the change law of displacement and contact force. The absolute value of angular displacement is negatively correlated with the change of well inclination angle, and the value of axial displacement increment and contact force is positively correlated with the change of well deviation angle, but the value of contact force is quite close. The research results can provide reference for alleviating the buckling of drill string in horizontal wells.

Study on dynamic buckling characteristics of drill string in horizontal well based on stochastic model

The buckling of drill string will increase the difficulty of running casing and accelerate the damage of drill string. Many achievements have been made in the study of drill string buckling, but few studies consider the influence of randomness on it. Due to the irregularity of the horizontal wellbore, the contact collision and friction between drill string and wellbore are random. The simplified analysis model of drill string buckling, the probability distribution of radial clearance between drill string and wellbore and the stochastic model describing friction coefficient are established. Through numerical solution, axial displacement, angular displacement and contact force of drill string unit under the action of random parameters are obtained. Four kinds of response results are obtained by repeated simulation calculations of the buckling model, and the probability of occurrence is 75%, 5%, 5% and 15% respectively. Concerning the outcome with the highest probability (75%) of occurrence, parametric randomness has the least effect. The drill string used in this case should have a large torsional stiffness. Concerning the outcome with the lowest probability (5%) of occurrence, parametric randomness has the greatest effect. Therefore, the strength and stiffness of drill string used should be large enough. At the same time, in order to change the contact state and friction between drill string and wellbore, it is necessary to use anti-friction tools. What's more, the randomness of the parameters mainly affects the response results when drill string is buckling. After stabilization, axial displacement is almost unaffected, there is a 5% probability that contact force will be affected. Upper drill string has greater buckling degree, so the influence of parameter randomness is greater. Considering the influence of the randomness of the parameters on the buckling, more comprehensive stability evaluation results can be obtained, and it is also helpful for the risk assessment of drill string stability.

Lateral buckling of drill strings revisited: localised “snaking”

The classical lateral buckling of a straight drill string confined within an inclined cylindrical borehole is formulated as a singularly perturbed boundary-value problem which is subsequently explored using asymptotic techniques. In particular, the localised nature of the critical eigenmodes is discussed with the help of a special multiple-scale technique that yields simple and accurate approximations for the corresponding critical loads. The asymptotic formulae obtained capture the dependence of these loads on the magnitude of the frictional forces as well as the inclination angle of the confining borehole.

A dynamic method for post buckling analysis of drill string in vertical wells

In this paper, a dynamic method, which includes a coupled dynamic model of full-hole drill string and its numerical implementation approach, is developed to analyze the post buckling of drill string in vertical wells. The coupled dynamic model is established based on Lagrange's equations and finite difference method. Its numerical implementation approach is achieved by using the direct integration method and Rayleigh damping formula. Especially the developed dynamic method is able to consider the coupling of axial vibration, lateral vibration, torsional vibration and the effects of rotating speed, damping from the drilling fluid, the discontinuous contact and friction between drill string and borehole, which enable it to predict the post bucking behaviors of drill string in vertical wells more efficiently and accurately. The developed dynamic method is validated by the comparison with the static theoretical solution of drill string, and then it is used to calculate the dynamic post buckling of drill string in vertical wells. The calculation results show that the contact length increases with the increase of the friction coefficient when the weight on bit is stable. There are critical speeds to make the contact length take the extreme value, and the critical speeds vary with the change of weight on bit and drill string length. The increase of drill string length does not change the quasi-static contact length, but will make the dynamic contact length fluctuate greatly. The fluctuation of weight on bit and torque on bit make the contact length fluctuate near the quasi-static contact length under most weight on bit. This work provides important theoretical and technical support for the comprehensive analysis of the dynamic buckling characteristics of drill string in vertical wells.

Critical helical buckling load assessment of coiled tubing under axial force by use of the explicit finite-element method

Previous theoretical formulations for helical buckling of drill strings vary significantly and are mostly proposed for the linear questions. But there are a little no-linear questions in the mechanical behaviour of tubulars. Explicit finite element analysis (FEA)method has the ability to consider geometric details and nonlinearities. This paper builds an explicit FEA model to describe the behaviors of comprehensive buckling and transmission of axial force for coiled tubing (CT) with residual bending in a horizontal well. The calculational results show that the CT with residual bending is easier to buckle than a straight CT. For the CT with an initial sinusoidal shape, the parameters of initial amplitude and initial pitch are inversely proportional to the helical buckling force, and the outer diameter (OD) is proportional to the helical buckling force. In the process of axial force transmission, the parameters of initial amplitude and frictional coefficient are inversely proportional to the axial force, the OD and initial pitch are proportional to axial force. Residual curvature in coiled tubing appears to have only a small effect on its downhole performance, based on FEA modeling of CT with sinusoidal curvature.

Helical Buckling of Drill-Strings

This paper presents experimental and numerical investigations of the complex drill-string vibration, with particular attention to the helical buckling of drill-strings and its influence on the system dynamics. The analysis is conducted using a novel experimental drilling rig, capable of exhibiting of all major types of drill-string vibration, including torsional, axial and lateral modes, which utilizes real industrial drill-bits and rock samples. A good qualitative and quantitative agreement between the experiments and numerical model is demonstrated.

Global analysis of drill string buckling in the channel of a curvilinear bore-hole

Currently, with advent of new techniques of drilling deep and curvilinear bore-holes, the conditions of their drivage become more drastic and severe. In these cases, redistribution of gravity, contact and friction forces acting on a drill string can give rise to emergency situations, one of which is the loss of its equilibrium stability and buckling. This phenomenon has been studied comprehensively as applied to the inclined rectilinear holes, but it is still understood incompletely if the drill string buckles in the channel of a curvilinear hole. In this paper, a new formulation of the problem on critical buckling of drill strings in inclined holes with variable geometry is devised through the use of the theory of curvilinear flexible rods. The stated eigen value problem is demonstrated to be singularly perturbed, that is the reason why its solutions have the shapes of localized harmonic wavelets. The computation results testify that the buckling phenomenon manifestation is determined by the relation between the influences of gravity and friction forces dictated by the angle of the bore-hole inclination. The peculiarities of the drill string behavior associated with the values of critical loads, pitches of the buckling wavelets, their widths and places of their localization in the rectilinear and curvilinear inclined bore-holes are discussed.

Experimental Investigation and Analysis of Dynamic Buckling of Drill String in Horizontal Well

Buckling of tubulars has been the subject of many researches in the past. However, the models in previous research always followed the same assumptions: the friction and rotation effects are ignored. The assumptions are relatively far from the reality. This paper focuses on the rotational drill string in horizontal well. The differential equation of the dynamic buckling is established considering some various factors, including friction, the drill string-borehole interaction, and rotation, and the equations of the critical load of the sinusoidal buckling and the spiral buckling are derived. Furthermore, the friction curve of the drill string and the critical load of the dynamic buckling during rotation are obtained. In addition, the influence of the rotational speed on the dynamic buckling and the axis orbit of the dynamic buckling are also gained. The results show that the critical load of the sinusoidal buckling has nothing to do with the rotational speed while the amplitude and the frequency of the dynamic buckling become larger with the increase of the rotational speed, and the dynamic buckling presents a completely different state with the development of the axial load at different speed ranges.

Critical Buckling of Drill Strings in Cylindrical Cavities of Inclined Bore-Holes

Critical Buckling of Drill Strings in Cylindrical Cavities of Inclined Bore-Holes

Experimental and numerical study of drill string dynamics in gas drilling of horizontal wells

The combination of gas drilling and horizontal well has been considered as an effective technique for the exploitation of low permeability reservoirs to protect reservoir, enlarge drainage area and increase production. Given the currently inadequate understanding about drill string dynamic characteristics in gas drilling of horizontal wells, a theoretical model of drill string dynamics is established in this paper. The nonlinear dynamics equations are derived to study the motion state of drill string. Meanwhile, an experimental apparatus is developed according to similarity principle, and the kinetic characteristic of drill string is investigated based on the simulation experiment. Particular attention is focused on the lateral vibration which results from the impact and frictional interaction with wellbore constraint. The effect of weight on bit and rotary speed on drill string motion pattern is also discussed based on experimental results. Finally, the buckling and contact of drill string are analyzed through finite element simulation study. The results indicates that the contact force between wellbore and drill string is relatively large and helical buckling of drill string can be caused without the lubrication and damping effects of drilling fluid in gas drilling. The work presented in this paper can provide theoretical foundation and technological basis for drill string dynamics analysis and drilling parameter optimization in horizontal wells drilled with gas.

Critical buckling of drill strings in curvilinear channels of directed bore-holes

Abstract The problem about theoretic modeling incipient stage of a drill string (DS) buckling in a curvilinear channel of a deep directed bore-hole is stated. On the basis of the theory of curvilinear flexible rods, non-linear differential equations describing elastic bending of the DS inside the bore-hole cavity are deduced. The effects of the DS curvature, its axial non-uniform prestressing, action of torque, and interaction between the DS and the bore-hole surface are taken into consideration. Owing to the use of curvilinear coordinates in the constraining channel surface and a specially chosen concomitant reference frame, it became possible to separate the desired variables and to reduce the total order of the equations system. With the aim to analyze critical states of the DS equilibrium and to construct modes of its stability loss, these equations are linearized in the vicinity of the considered state and eigen-value problem is formulated. Techniques for its numerical solution are proposed. Via its use the critical loads and shapes of buckling DSs are found for their different locations inside the bore-hole with circular trajectory. It is shown that the buckling proceeds with generation of irregular harmonic wavelets localized inside the well or in the neighborhood of its boundaries. Influence of boundary conditions, torque, clearance value, and channel axis curvature on the buckling process is analyzed. The presented results illustrate the applicability of the method proposed for the regimes of drilling and the drill string lowering and raising.

The buckling of a drill string in a curvilinear borehole with axial line imperfections

The problem of the elastic buckling of drill strings in the channels of deep curved boreholes with geometric axial line imperfections is formulated. Imperfections in the form of localized helices are considered. The relation between the forces resisting the motion of the string and the amplitudes, pitches and sites of localization of the imperfections is analysed. The distributed forces of contact and friction interaction between the drill string and the borehole surface are found and the effects of seizure of the drill string are established. It is shown that the resistive forces and their moments increase as the amplitudes of the imperfections increase, and as their pitches and the displacement of the zones where they are relocated from the lower most distorted parts to the upper least distorted parts, decrease.

Stability of drill strings in controlled directional wells

We formulate the problem of theoretical simulation of the bifurcation buckling of drill strings in deep directional and horizontal oil and gas wells, and propose the procedure for its solution. The analysis is made of the critical states in drill strings for various values of the well inclination, axial velocities of drill string motion and rotation. The buckling modes of the bifurcation drilling are constructed.

Helical Collapse of a Whirling Elastic Rod Forced to Lie on a Cylinder

Helical Collapse of a Whirling Elastic Rod Forced to Lie on a Cylinder

Spatially complex localisation in twisted elastic rods constrained to a cylinder

Abstract We consider the problem of a long thin weightless rod constrained to lie on a cylinder while being held by end tension and twisting moment. Applications of this problem are found, for instance, in the buckling of drill strings inside a cylindrical hole. In a previous paper the general geometrically exact formulation was given and the case of a rod of isotropic cross-section analysed in detail. It was shown that in that case the static equilibrium equations are completely integrable and can be reduced to those of a one-degree-of-freedom oscillator whose non-trivial fixed points correspond to helical solutions of the rod. A critical load was found where the rod coils up into a helix. Here the anisotropic case is studied. It is shown that the equations are no longer integrable and give rise to spatial chaos with infinitely many multi-loop localised solutions. Helices become slightly modulated. We study the bifurcations of the simplest single-loop solution and a representative multi-loop as the aspect ratio of the rod's cross-section is varied. It is shown how the anisotropy unfolds the `coiling bifurcation'. The resulting post-buckling behaviour is of the softening–hardening–softening type typically seen in the cellular buckling of long structures, and can be interpreted in terms of a so-called Maxwell effective failure load.

The static deformation of a twisted elastic rod constrained to lie on a cylinder

The Cosserat director theory is used to formulate the problem of a long thin weightless rod constrained, by suitable distributed forces, to lie on a cylinder while being held by end tension and twisting moment. Applications of this problem are found, for instance, in the buckling of drill strings inside a cylindrical hole. In the case of a rod of isotropic cross‐section the equilibrium equations can be reduced to those of a one‐degree‐of‐freedom oscillator in terms of the angle that the local tangent to the rod makes with the axis of the cylinder. Depending on the radius of the cylinder and the applied load, the oscillator has several fixed points, each of which corresponds to a different helical solution of the rod. More complicated shapes are also possible, and special attention is given to localized configurations described by homoclinic orbits of the oscillator. Heteroclinic saddle connections are found to play an important role in the post‐buckling behaviour by defining critical loads at which a straight rod may coil up into a helix.