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International audience; The drilling operations for oil or geothermic extraction use a slender structure introduced inside the drill well, hanging from a derrick and driven by a rotary table at the surface. The drilling structure consists in a series of drill-pipes and some heavy pipes at the well bottom. The drilling process involves nonlinear dynamic phenomena such as bit-bounce, stick-slip due to the well-drillstring multi-contacts and the pulsating mud flow. The drillstring vibrations may yield, the rate of penetration decrease, the premature wears and damages of drilling equipment. Many numerical models have been proposed to study the dynamics of drillstring to improve the reliability of drilling operations. However, the numerical models of drilling structures representing several kilometers length require a huge amount of computer memory storage and yield a too long computational time. The reduction technique proposed by Craig-Bampton (CB) has been developed for modelling the nonlinear dynamics of rotating machines to save the computational time but still limited in the context of rotordynamics. The paper focuses on the implementation of the CB method in the case of long drillstring assembly modelled by beam finite elements. The pre-loaded states of the drillstring due to the well curvature, well-structure contacts and fluid-structure interactions are determined and taken into account in the dynamic computation. The drillstring transient dynamics is simulated and the orbital motion of several nodes are analyzed. The result convergence and the reduction of computational time obtained by the CB method are investigated and discussed.

In rotary drilling, a drillstring is an assembly of slender pipes. It is used to transmit the driving torque of a motor at the drilling surface to the drill bit at the bottom hole of a 3D well. Numerous vibratory phenomena are induced during the drilling: whirling, stick-slip, bit-bouncing, lateral instability, inducing in particular reduction of the rate of penetration and mean time between failures. For the rotordynamics prediction of such a structure, the drillpipes are modelled with Timoshenko beam elements, containing 12° of freedom, equipped with distributed radial stop-ends. The rotary motion is assumed to have a constant speed of rotation imposed at the top of the drillstring. The drilling mud is taken into account by using a fluid-structure interaction model. The numerical simulations concern a real 3D-borehole and a parametric analysis is carried out for determining the role of the mud density and of the flows rate on the drillstring dynamics. It is shown that increasing the flow rate and densifying the drilling fluid reduce the fluid damping effect that increases drillstring lateral vibrations.

The drilling operations use a rotary slender structure introduced inside the drill well. The nonlinear dynamics with bit-bouncing, stick-slip phenomena, and pulsating mud flow may yield the premature wear and damage of drilling equipment and should be investigated to improve the reliability of drilling operations. This work presents the beam element formulation to model the drilling nonlinear dynamics. The well-pipe contacts are modeled by the radial elastic stops. The fluid–structure interactions are considered. The first step consists in computing the static position of structure to determine the contact points and calculate the preloaded state. These results are then considered to calculate the Campbell diagram. The potentially unstable speeds of rotation are identified. The results show that the modal coupling phenomena strongly occur for the three-dimensional well. The well-pipe contacts modify the modes in rotation, and the rotating fluid induces a strong deviation of the flexural mode curves.

International audience; The orthovanadate DyVO3 crystal, known to exhibit multiple structural, spin-, and orbital-ordering transitions, is presently investigated on the basis of magnetization, heat capacity, resistivity, dielectric, and polarization measurements. Our main result is experimental evidence for the existence of multiferroicity below a high TC of 108 K over a wide temperature range including different spin-orbital-ordered states. The onset of ferroelectricity is found to coincide with the antiferromagnetic C-type spin-ordering transition taking place at 108 K, which indicates that DyVO3 belongs to type-II multiferroics exhibiting a coupling between magnetism and ferroelectricity. Some anomalies detected on the temperature dependence of electric polarization are discussed with respect to the nature of the spin-orbital-ordered states of the V sublattice and the degree of spin alignment in the Dy sublattice. The orthovanadates RVO3 (R= rare earth or Y) form an important new category for searching for high−TC multiferroics.

International audience

International audience; A new drill pipe buckling model provided excellent predictions for each full-scale buckling test performed, not only in terms of deformed buckling shape but also in terms of weight transfer. Existing models, on the other hand, failed to predict observed drill pipe buckling behavior. This is the first time in the drilling industry that a buckling model was successfully validated in the field, and this model can predict realistically the onset and severity of buckling for any 3D trajectory.

International audience; A new drill pipe buckling model provided excellent predictions for each full-scale buckling test performed, not only in terms of deformed buckling shape but also in terms of weight transfer. Existing models, on the other hand, failed to predict observed drill pipe buckling behavior. This is the first time in the drilling industry that a buckling model was successfully validated in the field, and this model can predict realistically the onset and severity of buckling for any 3D trajectory. Many articles discuss buckling inside a wellbore but an increasing number of field observations suggest that existing buckling theories fail to predict buckling phenomenon such as lockup. Indeed, existing buckling theories generally assume that the wellbore is idealistically perfect without any doglegs. Recent advancements in drillstring mechanics modeling have demonstrated that doglegs, friction, and rotation affect greatly the buckling phenomenon. This article compares results of full-scale buckling tests with a new buckling model that takes into account actual wellbore tortuosity.

Thin films of Pr0.5Sr0.5MnO3 have been deposited on [100]-LaAlO3 using laser ablation. In contrast to the bulk compounds, such films do not exhibit any structural and magnetotransport transitions versus temperature; more particularly the A-type antiferromagnetic phase with the Fmmm structure which exists in the bulk below TN=135 K is suppressed, and the film is an insulator in the absence of a magnetic field. However a colossal magnetoresistance effect is observed, with resistance ratios much larger than in the bulk. These differences with respect to the bulk, are explained by the presence of substrate-induced strains.

Axial force transfer is an issue in deviated wells where friction and buckling phenomenon take place. The general perception of the industry is that once drill pipe exceeds conventional buckling criteria, such as Paslay-Dawson, axial force cannot be transferred down-hole anymore. This paper shows that, even though buckling criteria are exceeded, axial force transfer could be still good if drill pipe is in rotation. On the contrary, there exists sliding operations where lockup is observed, due to buckling, even though standard buckling criteria are not exceeded. This paper is intended to show and explain how axial force is transferred down-hole in many simulated field conditions: sliding, rotating, with or without dog legs. These new results have been obtained from an advanced model dedicated to drill string mechanics successfully validated with laboratory tests. This paper will show applicable results for practical well operations where axial force transfer is an issue. These results will enable to give some guidelines to help the drilling engineer to select cases where conventional buckling criteria should be used cautiously. Indeed, simultaneous torque-drag-buckling calculations show that tubular can tolerate significant levels of compression, enabling to provide weight transfer to the drill bit, even though drill pipe is buckled. Others examples, in contrast, show that standard buckling criteria cannot predict the occurrence of buckling that may cause tubular lockup while tripping in the hole. The applications of these results are numerous for all deviated wells such as horizontal or extended reach drilling wells. This paper should contribute to reduce unpredictable lock-up situations and improve axial load transfer performance.

Buckling of tubulars inside wellbores has been the subject of many researches and articles in the past. However, these conservative theories have always followed the same assumptions: the wellbore has a perfect and unrealistic geometry (vertical, horizontal, deviated, curved), the friction and rotation effects are ignored, conditions relatively far from actual field conditions. How do tubulars buckle in actual field conditions, that is, in a naturally tortuous wellbore with friction and rotation ? Can we apply theories developed for perfect well conditions (no tortuosity, no friction, no rotation) to actual well conditions ? For the first time, this paper presents how the drillstring rotation affects the critical buckling load in actual field conditions. These new results have been obtained from an advanced model dedicated to drillstring mechanics successfully validated with laboratory tests. Firstly, this paper presents the new developments integrated in a recently advanced model for drillstring mechanics that enables to take into account the buckling phenomenon in any actual well trajectory. Indeed, some simultaneous torque-drag-buckling calculations are presented and allow to properly take into account the additional contact force generated in a post-buckling configuration, and as a consequence the additional torque at surface. Secondly, this paper shows the influence of friction and rotation on buckling loads for some practical and critical cases met in the drilling industry. These friction and rotation effects are demonstrated with an experimental set up that enables to confirm theoretical features. Lastly, this paper shows that using standard buckling criteria may lead to too conservative solutions, and that under specific circumstances, the drilling and completion engineer could safely operate in a buckling mode for a given time. These new results presented in this paper should improve significantly well planning and operational procedures to drill and operate more and more complex wells.

International audience

International audience

International audience

Interbedded formations hard/soft or soft/hard are a major cause of borehole tortuosity. Cases history have demonstrated that this tortuosity induces a higher torque and drag, running tubular problems, stabilizers wear, pipe damage and trajectory controlling problems. In some fields, shale formations have a tendency to cause wellbore deviations to undesired directions. The formation anisotropy modifies the rock-bit and the bit-string interactions. Those interactions have to be fully understood in order to eliminate the phenomena of tortuosity. To do so, an experimental drilling program has been carried out on a full-scale bench using various polycrystalline diamond compact (PDC) drilling bits (different gauges, profiles) in different formations (hard/soft, soft/hard with different interface angles). Some directional tests have been also carried out in anisotropic shale at several dip angles. Coupling a 3D bit-rock model with a 3D bottomhole assembly (BHA) model enables to predict the occurrence of tortuosity (due to the anisotropy) at small and large scales (micro and macro-tortuosity) and to evaluate feet by feet the response of all directional drilling systems (rotary, steerable motors or rotary steerable systems). Deviations caused by formation anisotropy are separated into two phenomena. An initial deviation is caused by the rock-bit interaction. The experimental and theoretical results explain how the gauge length, bit profile, and dip angle, can affect the amplitude of this deviation. A second deviation is generated when the different stabilizers are sliding through the initial one. They can be amplified or attenuated according to the drilling system used. The number of stabilizers and their positions, BHA characteristics and bit steerability have a considerable effect on these deviations. A post analysis of some real drilling cases showed that, for a given drilling conditions including the formations anisotropies, it is possible to select the best drilling system minimizing the well tortuosity.

SummaryWith the emergence of rotary steerable systems (RSSs), the technical issue concerning bit design for a specific directional application has reappeared. Today, a bit must be specifically designed for use with a particular directional system: rotary bottomhole assembly (BHA), steerable mud motor, or RSS. The reason is that the bit must have the ability to respond properly and rapidly to a side force applied by the steering system to initiate a deviation. To do so, the bit must have a predetermined steerability compatible with the directional system to provide the optimum dogleg potential.The new generation of directional-drilling systems differentiates "pointing the bit" from "pushing the bit." As a consequence, the bit's directional response is a key factor that operators and directional drillers need to know to make a good adaptation between the bit and the BHA. However, at the moment there is no standard method for classifying bits by steerability and walking tendency.On the basis of a comprehensive analysis of the directional behavior of polycrystalline diamond compact (PDC) bits (numerical simulation and pilot and field tests), a simple methodology has been developed that defines and evaluates their steerability and walking tendency. This methodology is used to classify the PDC bits defined with their IADC bit profile codes.Because PDC bit steerability is mainly a function of the bit profile, the gauge cutters, and the gauge pad, some design recommendations are given concerning these three parts. For each IADC bit profile code, the bit steerability and walking tendency are estimated through some formulas linking only the heights and lengths of the cutting profile. Some guidelines are also given about the gauge-pad length and gauge-cutter characteristics to achieve improved steerability.This simple method based on geometrical criteria allows quick estimation of not only the PDC bit steerability but also the maximum dogleg potential achievable by the bit when it is coupled with the steering system.

Summary The importance of wellbore deviation is well recognized by the drilling industry. An analysis of a drilling system's directional behavior must include the directional characteristics of the drill bit. This paper presents a comprehensive analysis of the directional behavior of polycrystalline diamond compact (PDC) bits, including the effect of bit profile, gauge cutters, and gauge length. Numerical simulations as well as laboratory tests have been carried out to better understand the mechanisms of PDC bit deviation and to evaluate the most important parameters affecting the directional behavior of PDC bits. The analysis presented in this paper shows that each part of the PDC bit (profile and active and passive gauges) plays a major role in its walking tendency and steerability. A quantitative evaluation of how these factors contribute to well trajectory (inclination and azimuth) is given. For the first time, a full-scale directional-drilling bench was built to measure the walking tendency and steerability of PDC bits. The results obtained demonstrate that the bit profile, gauge cutters, and gauge length have a significant effect. A 3D theoretical rockbit interaction model was developed to reproduce the drilling test results.

With the emergence of rotary steerable systems, the technical issue concerning the bit design for a specific directional application has reappeared. Today, a bit must be specifically designed for use with a particular directional system: rotary bottom hole assembly (BHA), steerable mud motor or rotary steerable system (RSS). The reason is that the bit must have the ability to respond properly and rapidly to a side force applied by the steering system in order to initiate a deviation as requested. To do so, the bit must have a predetermined steerability compatible with the directional system in order to provide the optimum dog leg potential. The new generation of directional drilling systems differentiates "pointing the bit" from "pushing the bit". As a consequence, the bit directional response is a key factor that operators and directional drillers need to know to make the good adaptation between the bit and the BHA. However at the moment, there is no standard method that can propose a way to classify bits according to their steerability and walking tendency. Based on a comprehensive analysis of the directional behavior of polycrystalline diamond compact (PDC) bits (numerical simulation, pilot and field tests), a simple methodology has been developed in order to define and evaluate the steerability and the walking tendency of PDC bits. This methodology is used to classify the PDC bits defined with their IADC bit profile codes. As the PDC bit steerability is mainly a function of the bit profile, the gage cutters and the gage pad, some design recommendations are given concerning these three parts. For each IADC bit profile code, the bit steerability and the walking tendency is estimated through some formulas linking only the heights and lengths of the cutting profile. Some guidelines are also given about the gage pad length and gage cutters characteristics in order to achieve improved steerability. This simple method based on geometrical criteria enables to estimate quickly not only the PDC bit steerability, but also the maximum dog leg potential achievable by the PDC bit, when coupled with the steering system.

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International audience

The importance of wellbore deviation is well recognized by the drilling industry. An analysis of the directional behaviour of a drilling system must include the directional characteristics of the drilling bit. A comprehensive analysis of the directional behaviour of PDC bits is presented in this paper, including the effect of bit profile, gage cutters and gage length. Numerical simulations as well as laboratory tests have been carried out in order to better understand the mechanisms of PDC bits deviation and to evaluate the most important parameters affecting the directional behaviour of PDC Bits. The analysis of the directional behaviour of PDC bits presented in this paper shows that each part of the PDC bit (bit profile, active and passive gages) plays a major role on the walking tendency and steerability of the bit. A quantitative evaluation of the contribution of these factors on the well trajectory (inclination and azimuth) is given. A full-scale directional drilling bench was built to measure, for the first time, the walking tendency and the steerability of PDC bits. The results obtained demonstrate that the bit profile, the gage cutters and the gage length have a significant effect on the walking tendency and on the steerability of the PDC bits. A 3D theoretical rock-bit interaction model was developed to reproduce the drilling tests results.

Recent developments in PDC bit modelling and single cutter analysis have enabled to design a new generation of cutting structures – based on the optimization of a specific interactive cutting mode – that generates, by the mere drilling action of the cutters, an axial force oriented in the drilling direction: a negative weight on bit. This paper presents the application of this new PDC bit design and shows that WOB can be significantly reduced in a wide range of formations. A monobloc 8″1/2 PDC bit was designed, tested in laboratory, and self penetration was clearly achieved in field conditions. A full PDC bit design methodology using a new PDC cutters geometry optimized for a maximum thrust effect, along with specific manufacturing procedures for high-level precision in cutter positioning, were developed for this specific new bit generation. Laboratory tests showed that it was possible to drill without WOB at a high rate of penetration and with a small increase in specific energy. Preliminary field tests in cement demonstrated that self penetration – drilling with the neutral point just above the bit – was possible with specific surface control, and a first operational application was conducted by Total E&P Angola. This new bit technology has the potential to increase bit performance, specifically in operating conditions where power is available but WOB is limited due to friction, buckling or reduced vertical depth. The ability to drill with reduced WOB – or even without any WOB – should extend the potential of existing drilling technologies such as Extended Reach Drilling, Coiled Tubing or Steerable Motor in sliding mode and reduce axial vibration, thus increasing the MTBF of downhole tools.