Drill String Fatigue Research Articles

Influential mechanism of operational parameters on internal resonance of drill strings by numerical simulations

Abstract Drill string vibration is highly conductive to drill string fatigue and component failure. In this study, a finite element model of a drill string with bottom hole assembly (BHA) is constructed to investigate the effect of different operational parameters, such as different string length, density, pressure, and velocity of drilling fluid on drill string natural frequencies, and thus internal resonance by considering fluid-structure interaction (FSI) in ANSYS. Numerical simulations demonstrate that the natural frequencies decrease as the length of the drill string increases, which is especially true for the axial mode. The condition of 1:1 internal resonance between the axial and torsional modes only occurs when the length of drill string is sufficiently high. Nevertheless, this resonance fades away in the presence of fluid. The increment of fluid density slightly increases the natural frequency in lateral mode, whereas decreases that in axial mode. On the other hand, this effect of density is negligible in the torsional mode. The natural frequencies for axial, torsional and lateral modes decrease as the fluid velocity increases, and the impact of fluid pressure on natural frequency is almost not observable. The numerical results for the case without drill fluid are in qualitative agreement with analytical solutions. when considing the effect of drill length on natural frequency.

Fatigue life prognosis of an oil well drill string using cascaded dynamic models

Early estimation of the fatigue life of an oil well drill string reduces the risk associated with drill string fatigue failures. In this study, a low-order computationally efficient bond graph model of a vertical well drill string and a component-level higher-order finite element model of a drill pipe threaded connection are employed to predict the fatigue damage of a given drill pipe. The bond graph is a 3D lumped segment model developed using the Newton–Euler formulation and body fixed coordinates. It is parameterized using finite element modelling simulations. The stress history from the top-level model is applied to the component-level model that contains details such as threaded geometry. Then, a multi-axial, non-proportional, and variable amplitude (MNV) fatigue estimation is performed using an open-source finite element analysis code. The fatigue prognosis approach is then demonstrated in a drill string design case study that optimizes the placement of vibration stabilizers in the wellbore to avoid severe vibrations while minimizing fatigue damage. Optimal placement of stabilizers predicts a 200% increase in fatigue life of the most vulnerable component with reference to the worst-case scenario.

Drillstring Failure: Analytical and Experimental Approach

Drilling is one of the costliest activities in oil and gas industry due to the complexity of interactions with downhole rock formation. Under such conditions, the uncertainty of drillstring behaviour increase and hence it becomes difficult to predict the causes, occurrences, and types of failures. Lateral and torsional vibrations often cause failure of Bottom Hole Assembly (BHA), drillstring failure, drill bit and wall borehole damages. In this work, a model is presented to determine the impact of lateral and torsional vibrations on a drillstring during the drilling operation. The model aims to mimic real drillstring behaviour inside a wellbore with regards to its dynamic movements due to multiple real situations such as eccentricity of collars, drill pipe sections, and stick-slip phenomena occurring due to the interaction of the bit and the drillstring with the well formation. The work aims to develop a basis for determining critical operating speeds and design parameters to provide safe drilling procedures and reduce drill string fatigue failure. Lagrangian approach is used in this study to attain drillstring lateral and torsional vibration coupling equations. The nonlinear equations are solved numerically to obtain the response of the system. In this work, we also present a brief description of an in-house constructed experimental setup. The setup has the capability to imitate the downhole lateral and torsional vibration modes. Parameters from the experimental investigations are incorporated for validation of the mathematical models and for prediction of the drillstring fatigue life. Such investigations are essential for oil and gas industries as they provide solutions and recommendations about operational speed, lateral and torsional amplitudes measurements and corrections, and the conditions for avoiding occurrence of natural frequencies of the system.

Drill String Fatigue Failure and Lockup Risks Assessment in Tortuous Trajectory Well in Algeria

Drill String Fatigue Failure and Lockup Risks Assessment in Tortuous Trajectory Well in Algeria

Fatigue crack growth analysis of drill pipes during rotary drilling operations by the multiple reference state weight function approach

Abstract Drill-string fatigue failures are the most common and costly type of failures in Oil & Gas and Geothermal drilling operations. However, the drilling industry currently does not have a means of quantitatively evaluating drill-pipe fatigue fife. The aim of the present study is to fill this gap, providing a rapid and easy means of accurately obtaining drill-pipe fatigue life estimates. The geometry considered is the passage of a drill-pipe through a dogleg. It is characterised by a load combination of tension and bending while undergoing rotation. This load–geometry combination is taken as representative of the present-day drilling. The Stress Intensity Factors along the crack front of a semi-elliptical internal crack in a drill-pipe are obtained by means of Multiple Reference States Weight Function approach that is then implemented in a developed MATLAB code. The developed computer code is validated by comparison with data available in the literature and then applied to the geometry of interest. The Stress Intensity Factors thus obtained are then inserted in the Paris Fatigue Crack Growth Model to quantitatively evaluate the drill-pipe fatigue life. Finally, a parametric study is performed in order to identify the influence of load magnitudes, dogleg, crack shape and geometrical parameters on the fatigue life. A detailed discussion of all these effects concludes the paper. It is the contention of the authors that the method can be easily, rapidly and successfully extended to other oilfield tubulars.

Dynamic Model for Stiff-String Torque and Drag

SummaryA dynamic stiff-string torque-and-drag (T&D) model is presented that assumes steady-state motion of the drillstring as its basis for calculations. Results are compared with previously published T&D models that are based on static equilibrium. The novelty of the new dynamic model is the ability to solve T&D operations of the entire drillstring from bit to topdrive in reasonable time by use of standard engineering computers.The new approach is modeled after a 3D dynamic model of drillstring and bottomhole assembly in an elastic borehole. It considers bending stiffness, torsional stiffness, contact forces, and friction with localization of contact points. A numerical method is described that has proved to have excellent convergence. Complete governing equations are provided, and the method is described in detail to permit readers to replicate results.The dynamic model is compared with two static stiff-string models. Comparisons are also provided for three conventional soft-string models, including the Lubinski-Paslay-Cernocky bending-stress-magnification factor. Four field case studies are presented for horizontal wells. One well is short radius with dogleg severity greater than 50°/100 ft, and three wells are unconventional shale wells with doglegs up to 15°/100 ft. Predictions for surface T&D up/down for the new dynamic stiff-string model are compared with the static stiff- and soft-string models. In many situations modeled, the top-level results for surface T&D up/down are close enough for all six models to be within the uncertainty range associated with the commonly used, lumped-parameter friction factor. However, some major differences in hookload for sliding and slackoff operations are observed, which are shown to be caused by differences in location and magnitude of contact force between the drillstring and wellbore. Further, significantly lower surface torque is predicted by the new dynamic stiff-string model compared with other models for one case history because of lower contact forces in the vertical section of the well. In fact, the key finding of this paper is that major differences are observed for contact forces for the new dynamic stiff-string model compared with all five other models, including the two static stiff-string models. These differences in contact forces are most significant when the drillstring has helically buckled or when doglegs in the wellbore are high. Contact forces have a large impact on local stress behavior, which is important for predictions of casing and drillpipe wear, drillstring fatigue, and failure points in the drillstring.Although several previous papers have published stiff-string models, there is no industry-standard formulation. The main problem holding back the development of an industry-standard stiff-string model is perhaps the complexity of the numerical algorithm and substantial running time. To address this problem, some previous stiff-string models account for bending stiffness of the drillstring but not for radial clearance, whereas others appear to model only portions of the drillstring as stiff. The new stiff-string model accounts for bending stiffness and radial clearance for the entire drillstring while still giving reasonable computational times. For stiff-string models, the advantage of the use of a dynamic approach to solve the steady-state position of the drillstring is mainly related to superior convergence of the numerical algorithm compared with static stiff-string models because the calculation of contact points is faster.

Torsional vibration analysis of push-the-bit rotary steerable drilling system

Ordinary drillstring torsional vibration is a very common phenomenon that has been attracted great interesting. Through Measurement data, a series of studies and analysis of torsional vibration characteristics of the bottom hole assembly (BHA) have been developed. However, for rotary steerable system (RSS), especially push-the-bit mode, its drill torsional vibration phenomenon will demonstrate the new properties, because that the underground implementing agencies will generate cycle torque and drag to the BHA in the orientation process. This process is completely different to the previous. A set of “strap-down” measurement system was developed in this paper, and the triaxial accelerometer and triaxial fluxgate were installed near the bit. Proposed a method of solver drill bit rotation speed using real-time downhole measurement data (sampling frequency 100 Hz), and the torsional vibration mathematical model of push-the-bit RSS was established. We found that the torsional vibration phenomenon of push-the-bit RSS is more serious than the ordinary drilling system by downhole measurement data analysis, even in most cases manifested as stick-slip. The torsional vibration was divided into five different modes, which showing different statistical regularities. Corresponding analysis of the angular displacement and speed, we found that the drill bit always appears low-speed in the position of oriented. This is a strong proof of that the RSS implementing agencies pushing the BHA caused the drill bit torsional vibration more serious. This work is supplemented and development of the drill string torsional vibration studies. Contribute to the better understanding of the dynamics of the push-the-bit RSS. Put forward a new way of analysis the rotary steerable drillstring fatigue damage predicted, steering ability and the torsional vibration control.

Fatigue Analysis of Wenchuan Scientific Drilling BHA under Complex Conditions

Longmenshan earthquake fault zone has experienced several earthquakes in history, the formation is extremely broken and contains some very loose and strong water-sensitive shale formation. Due to the complexity of engineering of geological conditions, drilling accident-prone. In this paper, for example WFSD-4 well, and use of ANSYS Workbench to establish a simplified of fracture accident of WFSD-4 well drill collars, analysis stress and fatigue damage of BHA model. The results showed that the maximum stress occurs at the bottom of the drill string, the first position of fatigue failure is in the drill string at the bottom of the drill bit, the entire drill string fatigue life is 1.66 × 10e9 cycles, and through the analysis to guide the design, manufacture and use of BHA.

Longitudinal Harmonic Response Analysis of Drill String in Deep Well by Using ANSYS

With energy consumption and the development of exploitation technology of oil and gas underground, the drilling engineering has developed toward the direction of deep well, even ultra-deep well. The problem of fatigue of drill string has a great effect to drilling engineering. Strong vibration is one of the main reasons that induce drill string fatigue. In this study drill string of deep well is object being studied. The models about longitudinal vibration is set up. First, modal vibrations of drill string are studied. Then, harmonic response analysis of drill string vibration is studied. Rules of all kinds of free frequency are obtained by drilling instance. This study can offer basic method for optimizing drilling tool of deep well and drilling parameter for the purpose of reducing drill string failure.

Fatigue Life Prediction of Buckling String with Cracks in Horizontal Wells of Mining Engineering

Fatigue damage in the rotating drill pipe in the horizontal well of mining engineering is usually resulted from cyclic bending stresses caused by the rotation of the pipe especially when it is passing through curved sections or horizontal sections. This paper studies fatigue life prediction method of rotating drill pipe which is considering initial crack in horizontal well of mining engineering. Forman fatigue life prediction model which considering stress ratio is used to predict drill string fatigue life and the corresponding software has been written. The program can be used to calculate the stress of down hole assembly, can predict stress and alternating load in the process of rotating-on bottom. Therefore, establishing buckling string fatigue life prediction model with cracks can be a good reference to both operation and monitor of the drill pipe for mining engineering.

Stress Analysis on Drilling String Vibration in Gas Drilling

Using the finite element method, attempting to solve the serious drilling tools failure in gas drilling, this paper modelled the transient response of string vibration, and worked out the distribution regularity of the transient stress at two different drilling states: gas and mud drilling. Research shows that the stress fluctuation in gas drilling is greater than that in mud drilling; the alternate stress under such two drilling conditions has the same value relationship as those of stress fluctuation. The string vibration level is gradually increasing from the head to the bottom of the well Thus it is easier to cause the drill string fatigue failure. Such mechanism analysis, which explains the cause of string tools failure, provides guidance in drilling string design optimization.

Fatigue Analysis of the Drill String According to Multiaxial Stress

To find out the cause for fatigue failure of a drill string used in oil field drilling, and considering the actual working conditions, axial, radial and circumferential cyclic stresses borne by the drill string in borehole of oil and gas well, fatigue strength of drill string is analyzed based on multi-axial fatigue assessment method. Then the formula to calculate the mean stress of multi-axial load of the drill string is obtained, and the formula serves as a method to calculate multi-axial fatigue life of the drill string, which has been verified through field data. It is realized that multi-axial stress has significant influence on drill string fatigue. When on drill string fatigue, Soderberg equation shall be employed to calculate the stress amplitude of drill string fatigue.

Addressing BHA Whirl: The Culprit in Mobile Bay

Summary Lateral bottomhole assembly (BHA) vibration, more particularly BHA whirl, is known to be an extremely destructive downhole phenomenon, the occurrence of which is thought to be one of the primary contributing factors to drillstring failure in Mobile Bay. Unfortunately, indications that BHA whirl is occurring while drilling are rarely evident from conventional surface measurements, especially in deeper sections of wells. Without knowledge of the existence of a problem, avoidance is almost impossible. For the first time, the potential for the surface identification of BHA whirl is thought to be possible through the measurement of drillstring vibrations. We present data from a well in Mobile Bay where surface vibration measurement and monitoring was conducted while drilling the 12¼-in. hole section. Axial and torsional data demonstrate characteristics thought to be indicative of BHA whirl, which is shown to be associated with accelerated drillstring fatigue, as demonstrated by BHA failures. Various approaches were taken to eliminate the whirl once the phenomenon was recognized, with ultimate success in that the incidence of BHA failure was reduced. Prewell planning and improved drilling practices resulted in the use of fewer bits and reduced drilling time over the same section on wells previously drilled in the area.

A New Approach to the Analysis of Drillstring Fatigue Behavior

SummaryThis paper presents a method for determining the fatigue behavior of drillstring (DS) components under given environmental conditions. Over the past few years, field data for DS failures have been gathered from certain wells drilled in Italy and West and North Africa. Fatigue phenomena were identified as the main cause of most of such failures. Among the several factors that can affect DS-element fatigue resistance are tensile load, makeup torque, material properties, corrosive environment, abrasive wear, and so on. However, simply on the basis of the existing guidelines, it is difficult to define the real cause of a failure under given operating conditions. A comparative study of full-scale fatigue-test results and field data suggests a new approach for the analysis of some of the drilling technology factors that can affect the DS fatigue behavior.

Comparisons of Drill String Cyclic Loading Due to Vibration and Dog-Legs

This paper presents an investigation of the cyclic loading on oilfield drill strings due to longitudinal, torsional and lateral vibrations and compares this with the ‘statical’ cyclic loading caused by a deviated string at a dog-leg. Such cyclic loading is a principal contributor to drill string fatigue failures. The methodology of the paper uses numerical dynamic analyses of longitudinal and torsional vibrations together with quasi-static models for lateral vibration and dog-legs to compare the cyclic loading induced separately by each of these effects. A linear damage law (that is Miner's rule) is used to calculate the resultant fatigue damage from the cyclic loading. The results of this investigation show that longitudinal and torsional vibrations may induce significant cyclic loading comparable to that from typical dog-legs whereas the influence of lateral vibration is small. The longitudinal and torsional vibrations are strongly influenced by rotary speed and damping coefficients and can induce significant cyclic loading and rapid accumulation of fatigue damage on drill pipes and collars.

Inspection Interval Guidelines To Reduce Drillstring Failures

Summary Inspection interval guidelines were developed to reduce the occurrence of costly drillstring fatigue failures. The guidelines are based on a state-of-the-art fracture mechanics model and incorporate reliability data of commercial inspection services using conventional nondestructive testing techniques. On the basis of extensive full-scale testing, the model was found to predict fatigue-crack-growth behavior reliably. By establishing inspection intervals on the basis of fatigue-crack growth, inspection services are systematically and cost-effectively specified to achieve acceptable reliability (or risk). Simple equations and charts are presented in terms of practical drilling parameters to reduce typical downhole fatigue failures.