Dynamic Response of Two-Degree-of-Freedom Riserless Drill String for Vortex-Induced Vibration Suppression and Enhancement

The mechanical behavior,dynamic evolution,and flow-field distribution of a two-degree-of-freedom riserless drill string were simulated numerically by using FLUENT fluid simulation software with the user-defined function embedded.The rotation angular velocities before and after the critical rotation angular velocity were used as independent variables,and the reduced velocity range was 3-14.Fluid-structure coupling was realized based on the dynamic overset grid and the SST k-ωturbulence model.Results reveal that the dynamic response of the riserless drill string was considerably affected by rotation and flow velocity,which are coupled with each other.The cross-flow average dimensionless displacement increased with the rotation angular velocity,and rotation considerably enhanced the in-line maximum average dimensionless displacement.However,the cross-flow amplitude caused by vortex-induced vibration was suppressed when the rotation angular velocity reached a certain value.The in-line and cross-flow frequencies were the same,thereby causing the trajectory to deviate from the standard'figure-eight'shape and become a closed circle shape.The vortex did not fall behind the cylinder at low reduced velocity with high-rotation angular velocity,and the structure of the near-wake vortex remained U-shaped.The wake of the cylinder was deflected along the cross-flow direction,thereby leading to vibration asymmetry and resulting in increased vibration instability and disordered vibration trajectories,especially at high-rotation angular velocities.

Influence of friction on buckling of a drill string in the circular channel of a bore hole

Enhancement of technology and techniques for drilling deep directed oil and gas bore hole is one of the most important problems of the current petroleum industry.Not infrequently, the drilling of these bore holes is attended by occurrence of extraordinary situations associated with technical accidents. Among these is the Eulerian loss of stability of a drill string in the channel of a curvilinear bore hole. Methods of computer simulation should play a dominant role in prediction of these states. In this paper, a new statement of the problem of critical buckling of the drill strings in 3D curvilinear bore holes is proposed. It is based on combined use of the theory of curvilinear elastic rods, Eulerian theory of stability, theory of channel surfaces, and methods of classical mechanics of systems with nonlinear constraints. It is noted that the stated problem is singularly perturbed and its solutions have the shapes of localized harmonic wavelets. The calculation results showed that the friction effects lead to essential redistribution of internal axial forces, as well as changing the eigenmode shapes and sites of their localization. These features make the buckling phenomena less predictable and raise the role of computer simulation of these effects.

Exploration and determination of the principles of rotary-percussive underground slimhole drilling

A possibility of the efficient use of rotary percussive drilling to provide drilling smaller diameter holes(40–70 mm) both in mining and prospecting is disclosed herein. A new construction designed for the nipple thread connection is described. The relative amplitude variation, change of power pulse time and energy in their propagation throughout the drilling tool are determined. A possibility of the efficient power pulse transfer along the drill string to the rock destruction tools with new nipple connections which allow automating the make-up and breakout system of drill pipe was supported by experiments.

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

Notwithstanding the fact that the problem of drill string buckling （Eulerian instability） inside the cylindrical cavity of an inclined bore-hole attracts attention of many specialists, it is far from completion. This peculiarity can be explained by the complexity of its mathematic model which is described by singularly perturbed equations. Their solutions （eigen modes） have the shapes of boundary effects or buckles （harmonic wavelets） localized in zones of the bore-hole that are not specified in advance. Therefore, the problem should be stated in the domain of entire length of the drill string or in some separated part including an expected zone of its buckling. In the paper, a mathematic model for computer analysis of incipient buckling of a drill string in cylindrical channel of an inclined bore-hole is elaborated. The constitutive equation is deduced with allowance made for action of gravity, contact, and friction forces. Computer simulation of the drill string buckling is performed for different values of the bore-hole inclination angle, its length, friction coefficient, and clearance. The eigen values （critical loads） are found and modes of stability loss are constructed. The numerical results for the case when the inclination angle equals friction angle coincide with ones obtained analytically.

METHOD OF EQUILIBRIUM DIFFERENTIAL EQUATION FOR ANALYSIS OF STRENGTH OF LARGE DEFLECTION DRILL STRING

To counter the strength problem of drill string in well of large curvature and small diameter, well axis was taken as datum mis. Based on description of deflection of well an's and on analysis of three dimensional forces of a small section of drill string, equilibrium differential equations of large deflection drill string were established. The internal forces were found by Longe-Kutta method. The stresses were found by using them and the strength prerequisite was established. Stresses of drill string in lateral horizontal well H767 were computed. The results are in agreement with those of finite element model and soft-rope rigidified model. But the method is simpler for computation than finite element model and is more perfect than soft-rope rigidified model. Curvature of the well is too large and there is stress concentration so that the fraction accident of drill string occurs.

Improved Methods for Acoustic Transmission along the Drill String and Other Periodic Media

Acoustic telemetry along the drill string helps to know the physical and chemical characteristics of the formation and drilling fluid.A time-domain algorithm is developed for the propagation of one-dimensional axial stress waves with the inner and outer viscous fluid.The algorithm simulates the passbands,stopbands and spikes due to the presence of the discontinuous boundaries of drill string.Then the effects of transmitted pulses and transceivers on acoustic transmission are analysed.The simulated results show that the raised cosine pulses and optimal placements of transceivers improve system performance.Moreover,dual PZT receivers can exclude signals propagating in a direction opposite to the transmitted signals. It is obvious that the uses of the available modeling and signal processing techniques can make the drill string as a waveguide for transmitting information at high data rates.

NEW METHOD FOR GEOMETRIC NONLINEAR ANALYSIS OF LARGE DISPLACEMENT DRILL STRINGS

Based on the actual measured well depth, azimuth and oblique angles, a novel interpolation method to obtain the well axis is developed. The initial stress of drill string at the reference state consistent with well axis can be obtained from the curvature and the tortuosity of well axis. By using the principle of virtual work, the formula to compute the equivalent load vector of the initial stress was derived. In the derivation,the natural （curvilinear） coordinate system was adopted since both the curvature and the tortuosity were generally not zero. A set of displacement functions fully reflecting the rigid body modes was used. Some basic concepts in the finite element analysis of drill string were clarified. It is hoped that the proposed method would offer a theoretical basis for handling the geometric nonlinear problem of the drill string in a 3-D larg edisplacement wellbore.

Numerical Characterization of the Annular Flow Behavior and Pressure Loss in Deepwater Drilling Riser

In drilling a deepwater well,the mud density window is narrow,which needs a precise pressure control to drill the well to its designed depth.Therefore,an accurate characterization of annular flow between the drilling riser and drilling string is critical in well control and drilling safety.Many other factors influencing the change of drilling pressure that should be but have not been studied sufficiently.We used numerical method to simulate the process of drill string rotation and vibration in the riser to show that the rotation and transverse vibration of drill string can increase the axial velocity in the annulus,which results in the improvement of the flow field in the annulus,and the effect on pressure loss and its fluctuation amplitude.In addition,there are also multiple secondary flow vortices in the riser annulus under certain eccentricity conditions,which is different from the phenomenon in an ordinary wellbore.The findings of this research are critical in safely controlling well drilling operation in the deepwater environment.

THREE-DIMENSIONAL NONLINEAR ANALYSIS OF DRILL STRING STRUCTURE IN ANNUI US

Three-dimensional nonlinear analysis of drill string structure in annulus of curvedwellbore is done by using the theory of finite element and Newton-Raphson method.According to the characteristics of its deformation,a method of the description andcomputation of taking different forms of elements for different parameters is advanced.The penalty function method is applied for finding the unknown boundary .the nonlinear effects of curvature of wellbore on the side forces on bit ae shown by thecomputation.

Drill string dynamic characteristics simulation for the ultra-deep well drilling on the south margins of Junggar Basin

Improper drilling parameters may cause severe vibration of drill string which leads to reduce the rate of penetration and drilling tool premature failure accidents in the drilling process of ultra-deep well.The study on dynamic characteristics of drill string plays an important role in increasing the safety of drilling tool and optimizing the drilling parameters.Considering the influences of real borehole trajectory,interaction between bit and formation,contact between drill string and borehole wall,stiction of drilling fluid and other factors,a comprehensive drill string dynamic model was established to simulate the changes of wellhead hook load,torque,equivalent stress of drill string and BHA(bottomhole assembly)section acceleration and motion trajectory with time at different WOBs(weights on bit)and rotary speeds.The safety factor and overpull margin of wellhead drill string were calculated and the strength of drilling tool in ultra-deep well was checked using the fourth strength theory.The analysis results show that,in the drilling process of ultra-deep well,the transverse motion amplitude of the drill string near the wellhead is relatively small and vibration of drill string mainly occurs in the lower well section.As the rotary speed increases,the number of collision between lower drilling tool and borehole wall increases,wellhead transverse stress increases,change in torque is not large and change in wellhead equivalent stress is relatively small.As the WOB increases,wellhead torque will increase,axial load and equivalent stress will decrease and vibration acceleration of BHA will increase sharply.Wellhead overpull margin and safety factor will decrease with the increase of rotary speed and increase with the increase of WOB.Wellhead safety factor of S135 drilling tool in an F190.5 mm ultra-deep well on the south margins of Junggar basin changes around 1.8.The drilling tool is safe and has relatively sufficient ability to deal with the downhole accidents if a large size high steel grade drill string(F139.7 mm S135)is used.However,in view of BHA safety,neither rotary speed shall be too high nor WOB shall be too large.

Axial-torsional nonlinear vibration of bottom hole assembly in the air drilling technology

The safety and efficiency of drilling engineering are greatly impeded by destructive vibrations of drill string in air drilling,such as stick-slip,bit-bounce and their coupled vibrations.To avoid or suppress these vibrations improving the stability of drilling operations,revealing the occurrence mechanisms of abovementioned harmful vibrations are indispensable by investigating dynamics characteristics of drill string system.In this paper,an axial-torsional coupled dynamics model that can capture the motion behaviors of bottom hole assembly(BHA)is established adopting the lumped parameter method.Subsequently,a rate of penetration(ROP)model appropriating for air drilling is obtained firstly by linear fitting means.Meanwhile,a novel discontinuous support model is established to describe the bitformation interactions.Then,BHA dynamics are discussed using numerical simulations under different vibration scenarios:normal operation;stick-slip;bit-bounce;bit-bounce and stick-slip combination.Subsequently,in two drilling modes:the continuous and intermittent drilling,the vibration mitigation strategies and dynamics sensibility study of BHA are carried out based on the parametric analysis.The results show that increasing torsional stiffness of drill-pipes,appropriately adjusting rotation speed of top driven system and dynamic weight on bit(WOB)are deemed as an effective strategy suppressing or eliminating stick-slip and bit-bounce vibrations of BHA.Suggest that the rotation speed of top driven system and dynamic WOB are 5 rad/s and 3.5 kN,respectively.Finally,the constructed probability maps allow to driller to choose reasonable mechanical parameters,thereby realizing smooth drilling operation in the air drilling.

Method of suspender line trajectory design

Based on the mechanical model of an elastic rod,a new trajectory design method was established.The advantages of the suspender line trajectory in reducing drag and torsion were compared,and the main controlling factors of drag and torque and their influence rules were analyzed.Research shows that the suspender line trajectory reduces drag and torque more effectively than the conventional trajectory in a certain parameter interval and has more controllable parameters than that of the catenary trajectory.The main factors affecting the drag reduction and torque reduction of the suspender line trajectory include the friction coefficient,vertical distance,horizontal distance,and deviation angle at the initial point in the suspended section.The larger the friction coefficient and deviation angle,the less the drag reduction and torque reduction.The suspender line trajectory has the best drag reduction effect when the horizontal and vertical distances are more than 3000 m and the ratio is close to 1.5.The drag in sliding drilling can be reduced up to 60%,and the torque in rotary drilling can be reduced by a maximum of 40%.Therefore,the trajectory design of the suspender line has unique application prospects in deep extended-reach wells.

Emerging the dual string drilling and dual coil tubing drilling technology in a geothermal well applications

The challenges found in geothermal well drilling have forced the industry to develop new significant cost effective,time saver technologies to go for deeper geothermal resources beyond their traditional limits.To overcome these challenges,the new Dual String Drilling(DSD)technology which is based on penetration pathway of drilling fluid and rock cuttings during drilling a well.The principle of DSD employs drilling fluid flows through the annulus of inner and outer string pipe while cutting from the bottom of the well through inner pipe.The paper describes the novel Dual String Drilling(DSD)technology,predicting their occurrence and advantages on drilling of geothermal well.The outcome shows that with DSD approach a lot of time will be saved to circulate the kick out of the well.Additionally,the characteristic response of DSD enables to improve the hole cleaning capacity,to prevent pipe stuck,better well stability,reduction in torque and drag,to remove the dynamic equivalent circulating density gradient in geothermal wells.Moreover,the paper also depicts the system and method for dual coil tubing drilling of horizontal well which follows the same principle as DSD.The comparison of DSD with conventional drilling assesses that the DSD technology is affordable and appropriate for geothermal well drilling.

New model for standpipe pressure prediction while drilling using Group Method of Data Handling

The continuous evaluation of the measured Stand Pipe Pressure(SPP)against a modeled SPP value in real-time involves the automatic detection of undesirable drilling events such as drill string washouts and mud pump failures.Numerous theoretical and experimental studies have been established to calculate the friction pressure losses using different rheological models and based on an extension of pipe flow correlations to an annular geometry.However,it would not be feasible to employ these models for real-time applications since they are limited to some conditions and intervals of application and require input parameters that might not be available in real-time on each rig.In this study,The Group Method of Data Handling(GMDH)is applied to develop a trustworthy model that can predict the SPP in real-time as a function of mud flow,well depth,RPM and the Fan VG viscometer reading at 600 and 300 rpm.In order to accomplish the modeling task,3351 data points were collected from two wells from Algerian fields.Graphical and statistical assessment criteria disclosed that the model predictions are in excellent agreement with the experimental data with a coefficient of determination of 0.9666 and an average percent relative error less than 2.401%.Furthermore,another dataset(1594 data points)from well-3 was employed to validate the developed correlation for SPP.The obtained results confirmed that the proposed GMDH-SPP model can be applied in real-time to estimate the SPP with high accuracy.Besides,it was found that the proposed GMDH correlation follows the physically expected trends with respect to the employed input parameters.Lastly,the findings of this study can help for the early detection of downhole problems such as drill string washout,pump failure,and bit balling.

On“Lump mass torsional vibration model”and helical deformation of drill string

This paper analyses the physical models in“Kapitaniak M,Hamaneh VV,Chavez JP,Nandakumar K,Wiercigroch M.Unveiling complexity of drillestring vibrations:experiments and modelling.International Journal of Mechanical Sciences 2015;101e102:324e327”.The results are that the physical models described in the original paper are clearly incorrect.For the physical model used to explain the axial vibration on a drill string,using a lumped mass-axial spring with damping to model a long slender drill string is not advisable.For the physical model used to explain the torsional vibration on a drill string,using a torsional spring-pendulum with damping to model a long slender drill string is not advisable.The drill string should be constrained in the well bore.As an example,appropriate physical and mathematical models of drill string axial and torsional vibrations are recommended.

On physical models in V.I.Gulyayev's three papers on drill string whirling and torsional vibrations

This paper introduces physical models of drill string whirling and torsional vibrations and analyses the physical models in V.I.Gulyayev's three papers on drill string whirling and torsional vibrations:“V.I.Gulyayev,L.V.Shevchuk,Drill string bit whirl simulation with the use of frictional and nonholonomic models,Journal of Vibration and Acoustics 138(1)(2016)011021”,“V.I.Gulyayev,L.V.Shevchuk,Nonholonomic dynamics of drill string bit whirling in a deep bore-hole,J Multi-body Dynamics 227(3)(2013)234–244”and“V.I.Gulyayev,SN Hudoliy,O.V.Glushakova,Simulation of torsion relaxation auto-oscillations of drill string bit with viscous and coulombic friction moment models,J Multi-body Dynamics 225(2011)139–152”.This work finds that the physical models described in these three papers are clearly incorrect.