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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 bit-formation 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. [ABSTRACT FROM AUTHOR]

A finite element model for analysing the sealing performance of three types of wellhead rotary blowout preventer rubber ring structures in use on site was established. By using this model, the stress, deformation and contact pressure distribution of the passive rubber ring during pre-tightening conditions were calculated when the inner annulus of the passive rubber ring passed through the 5-inch drill pipe body and the 7-inch joint. The distribution position, length, and magnitude of contact pressure on the contact surface between the three types of rubber rings and the outer wall of the drill string under different pressure penetration loads under rated working conditions were calculated. Overall, the sealing performance of the active rubber ring is the best while the sealing performance of the passive rubber ring is the worst. However, the passive rubber ring has a simple structure and does not require a hydraulic system, which makes it impossible to adjust the sealing strength of the rubber ring in real time based on the actual fluid pressure on site. On the other hand, the I-type rubber ring uses part of the rotating blowout preventer structure as the hydraulic chamber wall, which can thicken the rubber layer in contact with drill pipe. Therefore, passive rubber rings are more suitable for low fluid pressure drilling operations. When the fluid pressure at the lower part of the rubber ring exceeds the rated maximum fluid pressure, it will lead to a sharp decrease in the sealing performance of the rubber ring. Therefore, stricter control of the use of the rubber ring is needed during on-site use, especially in drilling conditions with wellhead fluid pressure. The research methods and achievements in the article provide theoretical guidance for the safety evaluation of rotary blowout preventers used in ultra deep wells unbalanced drilling. [ABSTRACT FROM AUTHOR]

Slim hole drilling as an important technology is more and more used in developing deep oil and gas resources. In slim hole drilling, the much higher annular pressure losses impose a challenge to the annular pressure control. Accurate prediction of the annular pressure losses under the condition of eccentric rotation of drill string is an important theoretical and practical base for slim hole drilling. Conventional prediction models for this purpose have limited applicability and often omit the influences caused by the tool joints, thus cannot satisfy the requirements for accuracy in field operation. To solve this problem, a method of constructing empirical models with pressure loss correction factors is established based on the analyses of the effects of the tool joints on the flowfield and pressure losses in annular spaces using numerical simulation. The analyses show that the extra pressure losses produced by the tool joints are affected by the type of drilling fluid, rotary speed of drill pipe, eccentricity of drill pipe and annular flow velocity. Thus, when determining the pressure loss correction factor, the coupling of these effects should be taken into account. Using the result of numerical simulation of 152 sets of data, a model for predicting the annular pressure losses of the slim holes drilled in the Mahu oilfield in Xinjiang is established. The calculation using this model shows that there is a critical rotary speed at low drill pipe eccentricity, at which the annular pressure loss reaches maximum. At high drill pipe eccentricity, the annular pressure losses increase with rotary speed. The effects of the drill pipe eccentricity on the annular pressure losses will become complex because of the rotary speed. Using the annular pressure loss prediction model developed, the equivalent circulation density of the well MHHW-X in the Mahu oilfield was calculated and compared with the PWD data, the average error was only 1.18%, indicating that the model has high accuracy. The results of the study show that, the model established through numerical simulation for calculating annular pressure losses in slim holes, which takes into account the effects of tool joints, is able to satisfy the requirement of accuracy for field prediction of annular pressure losses, and to provide guidance to the annular pressure control in field operation. [ABSTRACT FROM AUTHOR]

In this paper, based on the non-linear mechanics theory of the drill pipe, a mechanical model of stick-slip vibration of the drill pipe has been established by considering the torsional properties of the drill pipe, kinetic energy and the motion law of the bit. The example calculations and sensitivity analysis of the parameters are carried out. The results show that increasing the rotational speed, viscous damping, length of the drill collar and de-creasing the weight of bit have the effect of suppressing the stick-slip vibration. [ABSTRACT FROM AUTHOR]

Currently, drilling of directional oil and gas wells under complex technical-technological and mining-geological conditions requires the use of drill pipes made of various materials. In turn, to choose rational modes of strengthening drill pipes and drill string layouts, information on the contact forces and friction forces of the drill string pipes on boreholes is necessary. Drill pipe curved sections friction with boreholes and drill bit resistance moment changes are the main causes of uneven rotation of a drill string during rotary or combined drilling methods and the occurrence of parametric oscillations. To reduce the cost of mechanical energy for well wiring, it is necessary to take into account the "drill string–borehole rocks" force interaction to estimate the magnitude of the frictional forces and their influence on the technological parameters of the drilling process. To solve this problem, mathematical models of "conventionally vertical and inclined drill string sections–borehole" were built. Based on the industrial data, an analysis of the force interaction of a deformed drill string composed of pipes made of different materials (aluminum, titanium, steel) was carried out. Analytical dependences were obtained for determining the contact forces and friction of the pipes on boreholes. A numerical study of the change of these power factors depending on the depth of the well under conditions of intensive vibration loading was carried out. The amplitude values of these forces, the frequency of their change for good sections, as well as the places for the most rational installation of drill pipes in the layout of the drill string were estimated. It was established that the intensity of contact and friction forces for steel drill pipes is greater than for titanium or aluminum ones. It is shown that the greater impact of a solid steel string on contact forces and frictional forces compared to a layout with sections of titanium or aluminum pipes in the range of vibration frequencies of 8–22 Hz corresponds to a bit rotation frequency of 70–80 rpm. The practical application of the obtained research results will contribute to the improvement of technical and economic indicators of the well drilling process. [ABSTRACT FROM AUTHOR]

Titanium drill pipe have promising application prospects in ultra-deep drilling, but the nonlinear dynamic characteristics of composite drill strings are very complex. It is very important to use titanium drill pipe safely, economically, and effectively in the drilling process. In this paper, different schemes of the titanium/steel drill pipe composite drill string was designed, and the statics and dynamics characteristics of these composite drill strings were analyzed. The design scheme of titanium/steel composite drill strings were optimized by using whirling characteristics, dynamic stress and vibration acceleration. The results show that the titanium drill pipe can effectively improve the tensile allowance of the wellhead and reduce the whirling velocity, dynamic stress and vibration acceleration of the drill string. By comparing and analyzing the dynamic characteristics of 3 kinds of composite drill strings, the use of titanium drill pipe for the lower 2000 m of the 4′′ drill pipe have the smaller dynamic stress and lateral vibration, and less collision with the wellbore. Based on the analysis of vibration and dynamic characteristics, an optimal scheme of drilling operation parameters for the titanium/steel composite drill string was formed finally, which can provide guidance for the use of the drill string composed of titanium/steel drill pipe in natural gas drilling of ultra-deep well. [ABSTRACT FROM AUTHOR]

The object of research is the drill string bottom structure using the correcting devices of drilling modes to control the dynamics of the drill string. The work is aimed at the study of longitudinal, torsional and transverse oscillations when adjusting the axial load on the bit by using a drilling shock absorber with a two-link characteristic. A dynamic model of the drill string during the drilling process is presented, which is a concentrated-continuous nonlinear system that interacts with the ball bit and the downhole engine as a source of energy. It is shown that elastic oscillations of all types affect the interaction of the bit with the outcrop rock. In order to evaluate drilling performance, it is necessary to take into account not only longitudinal, torsional and transverse oscillations, but also parametric oscillations, which are associated with the deformation of the weighted drill pipe under axial loads and during its rotation in the process of deepening the hole. It was found that transverse vibrations of weighted drill pipes, as a flexible element, during the drilling process are, as a rule, parametric in nature. They lead to the appearance of additional stresses in the elements of the column and, as a result, to the acceleration of their destruction and accelerated wear of the bit arms and rolling bearings. It is proved that in the future, for the development of dynamic models, it is necessary to take into account their hydrodynamics and the type, design and parameters of the applied punching elements. The obtained research results can be applied in practice in the process of designing the structure of the drill string bottom structure (DSBS) using correcting devices of drilling modes to control the dynamics of the drill string, by using a drilling shock absorber with a two-link characteristic in order to correct the axial load on the bit. [ABSTRACT FROM AUTHOR]

Experimentation is a common method to reveal the stick–slip vibration characteristics of horizontal well drill string system. Three different diameters of mini bits and an experimental bench of horizontal well drillstring system are innovatively designed to simulate the interaction between the bit and rock and the interaction between the drill pipe and well wall, which are the two boundary conditions that generate stick–slip vibration. The effects of bit type, drill pipe stiffness, rotational speed, and (ROP) Rate of Penetration on stick–slip vibration are investigated using rock-breaking experiments. The experimental results show that as the rotational speed increases from 9 to 45 r/min, (SSVI) stick–slip vibration intensity decreases. When the rotational speed is 9 r/min, the SSVI of the bit with higher cutter density drilling rock is lower than that of the bit with lower cutter density drilling rock. When the rotation speed is 45 r/min, the SSVI of the three bits is equal. The SSVI of drill pipe with smaller stiffness is greater than that of drill pipe with larger stiffness. The SSVI increases as the ROP increase from 0.36 to 1.26 m/h. The experimental findings aid in our understanding of the causes of stick–slip vibration. It lays the groundwork for the next step in reducing the harm caused by stick–slip vibration. [ABSTRACT FROM AUTHOR]

Copyright of Iraqi Journal of Chemical & Petroleum Engineering is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Dual-layer pipe dual-gradient drilling technology is an emerging technology for solving the problem of the narrow safety density window in deepwater drilling. The unstable spacer fluid interface in this technology directly affects the dual-gradient pressure system in the annulus, causing changes in the drilling mud performance and affecting the control of bottom hole pressure and rock removal with drilling mud. Therefore, the key to the stable operation of dual-layer pipe dual-gradient drilling technology is to maintain the stability of the spacer fluid interface. Based on this, a seawater-spacer fluid-drilling mud annular flow model was established in this study, with a bottom hole pressure control step of 0.2 MPa, and the spacer fluid height after a single control was used as the evaluation index to study the influence of annular flow velocity, the spacer fluid properties, and the drill string rotation speed on the stability of the spacer fluid interface. The results show that in the determined conditions of the seawater and drilling mud system, the annular fluid flow rate and the physical parameters of the spacer fluid are the main factors affecting the stability of the spacer fluid interface. When the annular fluid flow rate increased within the range of 0.04~0.2 m/s, the liquidity index of the spacer fluid increased between 0.5 and 0.9, the consistency coefficient increased in the range of 0.6 to 1.4 P a ⋅ s n , and the stability of the spacer fluid interface decreased. However, the stability of the spacer fluid interface increased with the increase in its density in the range of 1100~1500 kg/m3. The results obtained in this study can provide a reference for selecting the operating parameters to ensure the stable operation of dual-gradient pressure systems. [ABSTRACT FROM AUTHOR]

Objective The post-accident analysis of major hazards is a very complicated research work in oil field drilling site. The key parameters of the accident and its influence rule are studied by numerical simulation. Methods The fuzzy boundary condition is solved by the boundary condition hypothesis and trial calculation method on the premise that the specific parameters cannot be obtained. This paper mainly uses the well loss calculation model and field data to invert the well loss process to determine the leading parameters required for kick simulation, and studies the change law of bottom hole pressure when the string is falling. Results The downhole drilling string of a certain well is 4 500 meters long, generating more than 20 MPa surge pressure, and the cumulative loss for 7-8 minutes can reach more than 20 m³, which has a great impact on field operations and a short response time. The falling of short drill pipe produces less surge pressure and lower risk. The results show that under the condition of large fracture (more than 10 mm), the large surge pressure can instantly produce more than tens of cubic meters of leakage, which can not be controlled. In the case of narrow fracture (1 mm), the accumulated leakage amount reaches 20 m³ in about 6 minutes. In the case of micro-fracture (0.25 mm), the accumulated loss in 10 hours is only 20 m³. Conclusions The long drill string drop produces a larger surge pressure, which is the main sensitive parameter of loss and the main reason of blowout. The well shut-in measures should be taken as soon as possible. [ABSTRACT FROM AUTHOR]

This paper deals with the development of a novel mesoscopic model of polycrystalline diamond compact (PDC) drill bits that can be implemented in complex drill string models for simulations to analyse the influence of rock inhomogeneities or the impact of anti-whirl bits on drill string dynamics. In contrast to existing modelling approaches, the model is developed at a mesoscopic level, where the basic bit–rock interaction is taken from the macroscopic bit model and the cutting characteristics are summarised at a microscopic cutting level into a simplified configuration via cutting blades. This model can therefore effectively describe asymmetries and thus interactions between the torsional and lateral dynamics of the drill bit, and is particularly suitable for investigating the effects of drilling into rock inhomogeneities and fault zones on drilling dynamics. By integration into a complex drill string model, simulation studies of drilling through a sandwich formation were carried out. The simulation results allow detailed stability statements and show the influence of formation properties and bit design on torsional and lateral drill string dynamics. [ABSTRACT FROM AUTHOR]

• Stress–strain curves of S135 drill pipe steel at temperatures ranging from 20 to 800 °C were obtained through high-temperature tensile experiments. Determined the m and D5 values for the Johnson-Cook model. • The Johnson-Cook model was used for simulation to model the drill pipe containing fusion cuts, and the accuracy of the Johnson-Cook intrinsic model and failure model was verified. • Tensile loads have a better destructive effect on drill pipe than compressive loads; changes in loading rate have a smaller effect on the amount of tensile force required to destroy drill pipe. • Depth of cut, high temperature pairs can significantly reduce the external loads needed to break drill pipe. High-temperature melt cutting is an important technology for fast cutting and unjamming of downhole jammed tubular rods, but due to the well depth and mud environment, it cannot completely cut through the large wall thickness tubular rods such as weighted drill pipe, and it needs to be damaged by external load applied by drilling rig. The shape of the drill pipe kerf after the melt cutting operation is not the same, so the size of the applied external load needs to be further investigated. To address this problem, firstly, this paper establishes the Johnson-Cook ontology and failure model of S135 steel grade drilling tools based on the high temperature tensile test; secondly, according to the characteristics of the weighted drill pipe melt-cutting notch, a finite element model for mechanical damage failure analysis of weighted drill pipe with melt-cutting notch is established, and the reliability of the model is verified; lastly, the influence of high temperature and different notch characteristics (melt-cutting depth, circumferential cutting angle, Finally, the effects of high temperature and different notch characteristics (depth of cut, circumferential cutting angle, number of perforations) on the mechanical failure capacity of weighted drill pipe with fusion notch are analysed. The results show that the errors of the maximum stresses and strains of the samples obtained from the tensile fracture simulations at 20 °C and 400 °C and the maximum stresses and fracture strains obtained from the experiments are within 9 %, which verifies the accuracy of the model. Tensile loading was more effective than compressive loading in destroying the drill pipe; the change in loading speed had a small effect of 4.1 % on the tensile force required to destroy the drill pipe. The damage load of the drill pipe and the pressure acting on the cross-section of the fusion cut decreases with the increase of the fusion cutting depth; the damage load required decreases with the increase of the circumferential cutting angle and the number of openings, but the pressure acting on the cross-section of the fusion cut does not decrease. The softening effect of high temperature on the drill pipe is very obvious, and the tensile capacity of the drill pipe is attenuated by 80.6 % at a temperature of 800 °C. The research work can improve the operation process of cutting and unjamming thick-walled drilling tools in deep wells and guide the field operation to achieve the purpose of rapid unjamming. [ABSTRACT FROM AUTHOR]

An axial‐mode helical antenna with a spiral strip arm excites circularly polarized plane waves propagating along the axis of a drill string bore. This antenna extends the transmission distance of downhole signals in drill strings, thereby increasing the depth of possible measurements. The half‐power lobe width and directivity of the axial‐mode helical antenna matched the microwave channel of the drill string bore. The helical radiator in the antenna was optimized to ensure that center frequency was within the optimal operating frequency band of microwaves in the drill string bore. The reflector in the antenna was optimized through the creation of gas vents, which reduced its cross‐sectional area. The axial‐mode helical antenna reduced the effects of drill string twisting on the microwave channel, reduced reflection in the walls of the drill pipe, and reduced the loss of microwave signals. Compared to linear antennas, the axial‐mode helical antenna had superior performance because S21 increased to about 45 dB in the 2.4 GHz frequency band. The use of axial‐mode helical antennas in drill string bores during microwave measurement while drilling (MMWD) helped in monitoring downhole safety risks and expanding the scope of gas drilling. Therefore, axial‐mode helical antennas have practical applications and require further research. [ABSTRACT FROM AUTHOR]

Horizontal well drills are difficult to operate and require high borehole cleaning operations. The impact of cuttings accumulation on friction and torque cannot be ignored. In the process of horizontal well drilling, it is very easy to form a cuttings bed in the highly inclined eccentric annulus. The formation of the cuttings bed will not only increase the friction torque but also have a greater impact on the annulus flow. Based on the application of gas drilling in horizontal wells, this paper uses laboratory experiments to study the influence of cuttings with different particle sizes and lithology on the friction coefficient between the drill string and the borehole wall of the horizontal well section. In addition, in view of the difficulty in the migration of cuttings in gas drilling horizontal wells and the formation of cuttings deposits, this paper carries out an experimental study on the effect of the cuttings bed on drill pipe coating height and cuttings bed thickness on friction coefficient. Experimental results show that the friction coefficient of gas drilling horizontal wells is about 0.44–0.58. When the coating height of the cuttings on the drill pipe exceeds a certain value (26 mm), the friction coefficient tends to be stable, but its value is as high as about 0.55. When the thickness of the accumulation of cuttings exceeds a certain value (10 mm), the subsidence hindering effect between the particles in the cuttings bed is weakened, so the friction coefficient of the casing section and the open hole section tends to be stable, about 0.53. [ABSTRACT FROM AUTHOR]

Accurate prediction of extension limit of extended-reach well is of great significance for safe drilling. Hydraulic extension limit is an important part of the extended reach wells design. In this paper, the borehole size, the inner and outer diameter of the drill string are first normalized; Then, based on the definition of hydraulic extension limit, the minimum pressure loss gradient and the maximum hydraulic limit of the drilling section are established by using the inner and outer pressure loss of the drill string. A well X in Bohai Oilfield is taken as a case study to calculate the hydraulic limit before and after optimization of the drill string size under different pump pressures and mudflow rate. Finally, the hydraulic extension limit distance of X well with different optimized sizes are calculated and compared with the corresponding limit computed with API drill string size dimension under the same range of pump pressure and mudflow rate.The results showed that the optimized drill string size can increase the hydraulic limit of the designed well. When the pump pressure is 22 MPa and the mud flow rate is 40 L/s, the optimized horizontal section increased by 50.61% while the hydraulic limit of the well enhanced by 20.30%. For a pump pressure ranging from 12 to 26 MPa and a mudflow rate between 30 and 65 L/s the growth rate of hydraulic extension limit after drilling string optimization ranged between 18.47 and 22.69%. Equally, the pressure loss of the upper section and the pressure loss gradient of the drilling section should be considered in the whole drilling process, and the optimal drill string of different well sections should be selected according to the hydraulic energy distribution. Under the same conditions, the optimal drill string can maximize the hydraulic extension limit of the well. On the basis of case analysis, the optimum size of drill collar and drill pipe for hydraulic extension is recommended for drilling different hole sizes in Bohai Sea. The research results can provide theoretical guidance for Bottom Hole Assembly (BHA) design, drilling assembly optimization, extension limit enhancement, and safe drilling in extended reach wells drilling process. [ABSTRACT FROM AUTHOR]

Copyright of Oil Drilling & Production Technology / Shiyou Zuancai Gongyi is the property of Shiyou Zuancai Gongyi Bianjibu and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The dynamic model of the drill string is very useful for studying its motion to improve the drilling speed. The rock breaking efficiency of the drill bit is a crucial factor influencing overall drilling efficiency. Traditional dynamic models face a bottleneck in the development of drill string dynamics, as they cannot simultaneously consider the rock-breaking process of the drill bit and motion of drill pipes spanning hundreds to thousands of meters. Hence, this paper develops an integrated model including the drill string, drill bit, formation, and wellbore. The drill string model is established with the lumped mass method (LMM) and the other parts of the integrated model are established using the discrete element method (DEM). A simulation of the motion of the bottom hole assembly (BHA) in a vertical well is conducted, yielding results that closely aligns with laboratory experiments. This alignment confirms the reliability of the established drill string model. The drilling simulation results conducted with the integrated model under different ground rotational speeds (GRSs) and weight-on-bits (WOBs) demonstrate that the developed model can be effectively used to investigate rock-breaking of drill bit and drill string motion simultaneously. And the proposed model establishes the relationship between drill string motion and drill bit rock breaking. [ABSTRACT FROM AUTHOR]

• The coupling model of riser string and drill string is established by using Euler-Bernoulli beam model. • The dynamic characteristics of drill string are compared with those under the condition of fixed riser string. • The kinematic characteristics of drill string in "pipe in pipe" structure were obtained. The deepwater drilling string system consists of riser and drill string, forming a "pipe in pipe" structure with the riser as the outer pipe and the drill string as the inner pipe, thereby increasing the complexity of simulation and analyzing the dynamic characteristics of the string system. In this paper, a coupling model of the riser string and drill string is established by using Euler-Bernoulli beam model. Based on obtaining the dynamics of drill string, considering the influence of riser vibration, the dynamic characteristics of drill string are compared with those under the condition of fixed riser string. The kinematic characteristics of drill string in the "pipe in pipe" structure are analyzed as well. The distribution of contact forces between the drill string and the inner wall of riser is also studied. The results indicate that the vibration of the riser string has a significant influence on the dynamic characteristics of the inner drill string, and there is a high risk of failure due to serious contact wear between the riser and the drill string near the underwater wellhead. This observation is consistent with practical observations. [ABSTRACT FROM AUTHOR]

To ensure an effective drilling operation of an explored well, the associated hydraulics program should be established carefully based on the correct prediction of a drilling fluid's pressure drop and velocity field. For that, the impact of the drill string orbital motion should be considered by drilling engineers since it has an important influence on the flow of drilling fluid and cuttings transport process. In the present investigation, the finite volume method coupled with the sliding mesh approach is used to analyze the influence of the inner cylinder orbital motion on the flow of a power-law fluid (Ostwald-de Waele) in an annular geometry. The findings indicate that the orbital motion positively affects the homogeneity of the power-law axial velocity through the entire eccentric annulus; however, this impact diminishes as the diameter ratio increases. In addition, higher torque is induced when the orbital motion occurs, especially for high values of eccentricity and diameter ratio; nonetheless, a slight decrease in torque is recorded when the fluid velocity increases. [ABSTRACT FROM AUTHOR]

Stick-slip vibration is one of the main factors that contribute greatly to reducing the service life of drill string equipment and decreasing the efficiency of the overall drilling system. Thus, it would be very desirable to overcome the challenge of stick-slip vibration via an effective control strategy. This paper proposes a new robust active controller based on the fuzzy sliding mode approach to suppress stick-slip vibration and to maintain the angular velocity of the drill components at the desired references. A discontinuous lumped parameter torsional model of a vertical drill string based on four degrees of freedom is used in this study. In addition to the drill bit and rotary table, the drill pipes and drill collars are included in the model. Moreover, nonlinear interactions between the drill bit and the rocks, including friction torque and the mud drilling effect, are considered. The proposed hybrid controller is based on a combination of artificial intelligence and a discontinuous first-order sliding mode control approach. A comprehensive numerical analysis was conducted by means of MATLAB and Simulink software. Real-time implementation of the system was conducted using dSPACE control board. The proposed controller has been tested under severe weight on bit variation and at different angular velocities. The results of the simulation and the real-time implementation are presented to demonstrate the good performance and feasibility of the proposed controller. [ABSTRACT FROM AUTHOR]

This paper presents a novel controller for drill string systems based on a super-twisting sliding mode theory. The aim is to eliminate the stick-slip vibration and maintain a constant drill string velocity at the desired reference value. The proposed controller inherently attenuates the torsional vibration while ensuring the stability and high efficiency of the drill string. A discontinuous lumped-parameter torsional model of vertical drill strings based on four components (rotary table, drill pipes, drill collars, and drill bit) is considered. The Karnopp friction model is adopted to simulate the nonlinear bit-rock interaction phenomena. In order to provide a more accurate evaluation, the proposed drill string controller is implemented with the induction motor, a variable frequency drive, and a gearbox to closely mirror the real environment of oil well drill strings. The increasing demand for prototyping and testing high-power plants in realistic and safe environments has led to the advancement of new types of experimental investigations without hurting the real system or building a small-scale prototype for testing. The dynamic performance of the proposed controller has been investigated with MATLAB software and in a novel hardware-in-the-loop (HIL) testing platform. A power plant is modeled and implemented in the real-time simulator OPAL-RT 5600, whereas the controllers are implemented in the dSPACE 1103 control board. The results obtained through simulatiosn and HIL testing demonstrate the feasibility and high performance of the proposed controller. [ABSTRACT FROM AUTHOR]

In this paper, the process of crack propagation is investigated using the extended finite element method at the mesoscale to study the drill pipe fracture mechanism. Firstly, the property of the S135 drill pipe was analyzed through physical and chemical experiments and the scanning electron microscope method. After that, a grain distribution model of the drill pipe material at the mesoscale was established by the Python scripting language on ABAQUS platform. Furthermore, the extended finite element method was applied to study crack dynamic propagation. And the distribution of stress and strain during the crack propagation were obtained at the mesoscale grain model. Finally, by the mesomechanics "homogenization" method, the stress and strain of the crack propagation model at different times were analyzed, and the influence of crack propagation on drill pipe material was obtained. Simulation results show that, although drill pipe material at the macroscopic scale is in the elastic stage, plastic zone and micro-crack propagation may also exist at the mesoscale. The proposed method in this paper studied the stress distribution in the crack tip during the propagation, which is a benefit for exploring the fracture mechanism of drill pipe. [ABSTRACT FROM AUTHOR]

Accurate pressure drop estimation is important for drill string and bit nozzles design and optimized fluid circulations as well as identifying the drilling problems such as bit nozzle(s) washout or plugging. In this study, the Bingham Plastic model has been modified by applying a coefficient to its turbulent pressure loss calculations. This coefficient encompasses the effects of the drill pipe tool joints and other effects in estimation of pressure losses. The range of the coefficient was determined in field applications for different hole sizes and mud types. The results showed that applying a correction coefficient of 1.08–1.12 to turbulent pressure loss equations (depending on borehole size and mud type) improves the pressure loss estimation. By applying this coefficient, the estimated pressure losses are increased to compensate the under-estimation of the Bingham Plastic model. This is considered a significant contribution to accurate calculation of borehole hydraulics and in-time detection and identification of borehole problems and reduction of invisible lost time. The findings also showed that this enhanced effect is independent of the mud type. The use of this coefficient removes the necessity of using rather complex mud rheological models such as the Herschel–Bulkley model. [ABSTRACT FROM AUTHOR]

The telemetry drill string transmits the measured drilling and formation parameters near the bit to the ground at high speed through the transmission line in the wired drill pipe and the inductive coupler formed by the coil embedded in the drill pipe joint. The voltage transfer function of the inductive coupler seriously affects the signal transmission characteristics of the telemetry drill string. Present research methods cannot accurately and quantitatively describe the influence of the electromagnetic parameters of the inductive coupler on its voltage transfer function. This paper quantitatively analyzes the effects of the electromagnetic parameters of the inductive coupler on signal transmission through reasonable high-frequency circuit modeling. The generation mechanism of eddy current in the magnetic core and the interaction mechanism between eddy current and coupling coils are studied using the electromagnetic detection analysis method of nondestructive testing (NDT) technology. Then, the high-frequency circuit model of the coupler containing eddy current loss is established. The mathematical model of input impedance and signal transmission characteristics of the inductive coupler is established through circuit analysis. The influence of the electromagnetic parameters of the magnetic core and the load resistance of the coupler on the voltage transmission characteristics and power transmission characteristics of the coupler is studied. The research results show that the relative permeability of the magnetic core, load resistance of the coupler, and signal frequency seriously affect the signal voltage transmission. When the relative permeability of the magnetic core material reaches 50, the voltage transmission of the inductive coupler is effectively improved. The electromagnetic simulation results are consistent with the theoretical analysis of the circuit model, which proves the correctness of the circuit model. This paper provides theoretical guidance for the electromagnetic design of inductive couplers and the improvement of signal transmission characteristics of telemetry drill string. [ABSTRACT FROM AUTHOR]

Using drilling fluids with optimum density is one of the most important approaches to stabilize the pressure of the bottom formation and prevent blowout through the drilling process. One of the common methods for this purpose is adding some additives with high specific gravity to the drilling fluid to tune its density. Among the possible chemicals, barite and hematite with the density of 4.2 and 5.2 g/cc are the most common additives. Unfortunately, although the application of these additives is advantageous, they have some drawbacks which the most important one is separation and settlement of solid phase called barite sag. The barite sag comes from barite, or other dense materials particles deposition resulted in undesired density fluctuations in drilling fluid can lead to mud loss, well control problems, poorly cementing and even pipe sticking which occurs in severe cases. With respect to these concerns, the current investigation is concentrated to obtain the relation between the dynamic conditions such as flow rate (0.308 and 0.19 l/s) and deviation angles of 30°,45°,60° and 90° and barite sag phenomenon through a flow loop equipment. Besides, the effect of drilling string rotational speed (70 rpm) on the barite deposition is investigated. The results not only indicate that increasing the flow rate from 0.19 l/s to 0.308 l/s can reduce the deposition rate, but also increasing the deviation angle from 45 to 60 o enhance the barite deposition to its maximum value. [ABSTRACT FROM AUTHOR]

A telemetry drill string system consists of a string of wired drill pipes, and high-frequency signals pass the adjacent drill pipes through inductive couplers. Such a system is used to upload downhole information at high data transmission rates for measurements while drilling (MWD). Since the signal energy attenuates greatly in the system, many repeaters must be provided to ensure signal transmission. A reduction in the signal transmission in a telemetry drill string can extend the relay distance and improve the reliability of the transmission system. In this study, the transmission characteristic of the rod of the wired drill pipe is studied using transmission line theory, and the transmission characteristic of the inductive coupler is studied using high-frequency circuit theory. Using impedance matching between the transmission line of the rod and the inductive coupler, external impedance compensation elements, including a capacitor and a resistor, are recommended, and the electromagnetic parameters of the wired drill pipe are determined. Based on the determined electromagnetic parameters, certain changes in the external impedance compensation capacitance and resistance can lead to impedance mismatch between the transmission line and the inductive coupler. This will generate a reflected signal at the transmission line, and the vector superposes with the transmitted signal. The terminal reflection coefficient of the transmission line is controlled by increasing the compensation resistance value to enhance the signal amplitude, which can compensate the transmission loss when passing through the inductive coupler to a certain extent. Thus, the signal transmission capability of the telemetry drill string can be improved, allowing for long-distance signal transmission or drastically extending the relay distance, while maintaining a certain channel bandwidth. [ABSTRACT FROM AUTHOR]

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Copyright of Natural Gas Industry is the property of Natural Gas Industry Journal Agency and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Wellbore instability happens mostly in the shale formation. Early researches have studied thoroughly on the physicochemical and mechanical mechanism that causes instability. However, only a few works have considered the influence of field drilling operations, such as drill pipe rotation. In this paper, a true triaxial cell is used to simulate the downhole field situations, and a drill pipe rotation device is innovatively designed and implemented into the true triaxial cell. Using this facility, the influence of drill pipe rotation on shale instability has been performed. Different rotation speed, weight on bit, drilling fluid pressure, and microcracks on borehole have been considered. The enlargement of the wellbore is quantitatively plotted and compared. Results show that the drill pipe rotation contributes to a more enlargement of the wellbore, and a higher rotation speed causes a more severe collapse. The drill string weight on bit also contributes to the enlargement of the wellbore, with a larger weight on bit induces a larger diameter of the collapsed wellbore. Compared with the rotation speed and weight on bit, the influence of drilling fluid density is relatively less significant. However, the influence of microcracks caused by hitting of drilling tools is profound. For a cracked shale formation, the wellbore diameter can be enlarged for more than 40%. Then, the variation of borehole collapse with time and depth under drill pipe rotation influence is analyzed. In all of these four factors, the significant sequence is microcracks > weight on bit > rotation speed > drilling fluid pressure. In all the collapse phenomena, the collapse is more severe in the minimum horizontal stress direction. This is explained by the analysis of the stress distribution in the whole circumferential angle (360°) of the wellbore. Overall, this work fills the gap of the influence of drilling operations on wellbore instability. [ABSTRACT FROM AUTHOR]

In this paper, an integrated model is presented to study the axial–torsional dynamics of a distributed drill string. The coupled axial and torsional drill string dynamics typically lead to severe phenomena such as bit-bounce and stick–slip, which are the main causes of failure and efficiency reduction. The top-drive dynamics and the Bottom Hole Assembly (BHA) dynamics are interconnected through the drill pipes. In order to preserve the infinite-dimensional feature of the drill pipes in the mathematical modeling, a distributed model in terms of Delay Differential Algebraic Equations (DDAE) is proposed to represent the dynamics of the drill string. The bit-rock interaction, which consists of the cutting and the frictional components, is responsible for the coupling between the axial and torsional dynamics. A rate-independent bit-rock interaction law is employed for both cutting and frictional components. In order to capture the global bit motion, including multiple regenerative effects, the well-bottom depth function is used to determine the depth of cut. The well-bottom pattern evolution is formulated through algebraic equations rather than Partial Differential Equations (PDEs). A new formulation for the linearized drill string system in terms of Neutral-type Delay Differential Integral Equations (NDDIEs) is proposed to investigate the initiation of the oscillations around the nominal operation. By this formulation, the local stability of the distributed system is studied by determining the right-most eigenvalue of the linearized dynamics. A simulation-based case study reflecting real-life scenarios is presented to investigate the dynamical behavior of the system under different operating conditions. • Delay Differential Algebraic Equations (DDAEs) for the distributed drill-string. • Neutral-type Delay Differential Integral Equations for the linearized dynamics. • A new comprehensive approach for determining the depth of cut. • Investigating the effect of different time-delays on the stability characteristics. [ABSTRACT FROM AUTHOR]

In drilling engineering, it is extremely challenging to drill a prescribed wellbore over several thousand meters. One of the main difficulties arises from accurately predicting and controlling the directional drilling performance, caused by the complex nonlinear dynamics of the slender drilling assembly and its interactions with the surrounding rocks. Nowadays, the simplified analytical geometry method, which has been adopted as the industry standard, can merely offer a rough estimation of the drilling direction, while the high-accuracy finite element method is computationally inefficient. This study is intended to provide a straightforward prediction of the drilling direction for a long drilling distance accurately and efficiently by proposing a dynamical simulation method based on the flexible multibody approach. Three techniques were adopted to achieve the critical objective of the paper. First, an Arbitrary Lagrangian–Eulerian formulation was used to provide a new approach to balance the efficiency and accuracy. Additionally, it can perfectly simulate the realistic drilling operation that drill pipes are continuously added to the drill string one by one through dynamically inserting new beam elements into the existing model. Second, the whole drill string and its interaction with the wellbore were all considered to carry out a high-fidelity simulation. Finally, the bit–rock interaction model was introduced to offer a straightforward way of evaluating the steerability of drilling assemblies. The presented method and model were validated by the consistency between the simulated wellbore trajectory and the in-field experimental data and are ready to be applied in drilling tools design, real-time drilling simulation, and drilling direction control. [ABSTRACT FROM AUTHOR]

For many years, a critical factor while drilling deep wells in Algeria oil fields has been the fatigue loads in drill strings used in high tortuosity sections. One solution is the use of drill pipes made of alternative lighter materials instead of conventional steel. A thorough study of superficially (ST) treated 2024 aluminum alloy joined to steel drill pipes in crooked well trajectories is presented in this article. This work discusses several limiting loads exerted on the drill pipes that affect the drilling operation such as axial, twisting and bending forces, which lead to combined cyclic loads. This study is aimed to determine whether it is possible to extend the drilling operation by joining ST 2024 aluminum alloy drill pipes into the drilling string, without losing drilling stability or reliability. It is established that the ST 2024 aluminum alloy drill pipe exerts significant influence on the allowable combined load, but affects to a larger extent the critical load at which loss of drilling string stability occurs, along with improved resistance to wear and corrosion, even at high temperature. • Surface treated 2024 aluminum alloy drill pipe has a lower friction coefficient compared to steel drill pipe. • Surface treated 2024 aluminum alloy drill pipe has significantly good fatigue resistance even in severe doglegs. • The side force in a dog leg region is reduced in aluminum alloy drill string. • The mixed drill string assembly provides a balance strength regarding both tensile and bending forces as well as compression during axial loading. [ABSTRACT FROM AUTHOR]

Abstract This paper studies the vibration characteristics of a drill string in gas drilling under gas-structure interactions, and affected by the combined effects of several parameters including the spinning motion, the weight on bit, the hydrodynamic force, the damping force of drilling fluid and the stabilizer. Based on the Hamilton's principle, the dynamic equations of the spinning drill string subjected to the weight on bit and gas-structure interaction are established and solved by using the Galerkin's method. The exact solutions of the i -th natural frequencies of the drill string with uniform section are derived considering the gas-structure interaction and the spinning motion, and the characteristic curves of the non-dimensional natural frequencies versus different parameters are obtained respectively. The results show that the spinning angular speed, the weight on bit, the flow velocity, the viscous damping force of drilling fluid, the ratio of the external diameter of drill pipe to that of the drill collar and different installation positions of the stabilizer have significant influences on the dynamic characteristics of the drill string. In addition, the effects of the gas drilling fluid and the mud drilling fluid on the system vibration characteristics are discussed and compared, which reveal that natural frequencies of the drill string in gas drilling are higher than that in mud drilling. [ABSTRACT FROM AUTHOR]

We have proposed approaches to analytical assessment of the moment of inertia related to the curved rotary sections in a drill string. Research into rotation processes of the curvilinear sections in a drill string is associated at present with a particular difficulty, which arose because of the lack of precise expressions to evaluate the moments of inertia for a curved pipe based on the parameters of its deformation. Solution to such problems is important for the analysis of dynamic resistance of drill strings at rotor and rotor-turbine drilling techniques, when studying the stressed-strained state of its elements, refining the energy costs for rotation process of the curved sections in a well, as well as for analysis of critical rotation speeds. We have investigated the moment of inertia for a bent section in the rotating drill string using the models with concentrated and distributed masses. Based on the results, we have established the exact and asymptotic analytical dependences in order to determine inertial characteristics of the curvilinear sections in a drill string, as well as provided recommendations regarding the application of these dependences. A current trend in the development and modernization of drilling equipment is the use of drill pipes made of unconventional materials. Given the scientific and practical interest in the application of these materials, we calculated the moments of inertia for the curved sections of drill strings, which can be equipped with steel, aluminum, titanium, or glass-plastic drill pipes. Analytical estimation of the moment of inertia of curved sections refers to a different scale of the deformed state of a drill string. The formula for the moment of inertia, established for simple models, holds in cases when the curved section of a drill string executes large displacements. For the case of small displacements, it is necessary to apply the analytical result derived when using a model with distributed parameters. The established patterns are essential for analyzing the dynamics of a drill string in deep conditionally vertical, inclined-directional, or horizontal wells with a complex mining-geological profile. [ABSTRACT FROM AUTHOR]

In the process of air drilling, underground monitoring data can be transmitted by a microwave signal in the drill pipe. In this paper, we analyze the characteristics of the microwave transmission channel in a drill pipe, by regarding the drill pipe as an irregular lossy cylindrical waveguide. We use multipath transmission theory and an experimental statistical method to research the characteristics of the microwave channel and the attenuation law. The existing research results only focus on the dielectric loss of the drill stem; however, herein we point out that there are numerous reflective surfaces that can produce a great deal of reflected waves in the joint section of the drill pipe. Hence, the drill pipe has microwave multipath channel characteristics; consequently, multipath fading and delay are the main factors affecting the transmission quality. According to actual measurement results, the microwave channel composed of a drill pipe unit is in accordance with the ultra-wideband channel standard and has dual cluster multipath channel characteristics. The relative time delay between the two clusters is 51 ns, the mean square delay is 22.58 ns, and the maximum data rate in a drill pipe is about 7 Mb/s. [ABSTRACT FROM PUBLISHER]

Excessive drill stem (DS) vibration while rotary drilling of oil and gas wells causes damages to drill bits and bottom hole assemblies (BHAs). In an attempt to mitigate DS vibrations, theoretical modeling of DS dynamics is used to predict severe vibration conditions. To construct the model, decisions have to be made on which beam theory to be used, how to implement forces acting on the DS, and the geometry of the DS. The objective of this paper is to emphasize the effect of these assumptions on DS vibration behavior under different, yet realistic, drilling conditions. The nonlinear equations of motion were obtained using Hamilton's principle and discretized using the finite element method. The finite element formulations were verified with uncoupled analytical models. A parametric study showed that increasing the weight on bit (WOB) and the drill pipe (DP) length clearly decreases the DS frequencies. However, extending the drill collar length does not reveal a clear trend in the resulting lateral vibration frequency behavior. At normal operating conditions with a low operating rotational speed, less than 80 RPM, the nonlinear Euler-Bernoulli and Timoshenko models give comparable results. At higher rotational speeds, the models deliver different outcomes. Considering only the BHA overestimates the DS critical operating speed; thus, the entire DS has to be considered to determine the critical RPM values to be avoided. [ABSTRACT FROM AUTHOR]

Using the drill string in the wellbore as the information transmission channel and acoustic wave as the carrier of information transmission to realize the acoustic transmission of information in the well is an important means to realize the high-speed and accurate transmission of downhole information. However, the existence of noise in the drill string during the drilling process seriously affects the transmission rate and transmission accuracy of acoustic wave. In order to explore the characteristics of drilling noise in the drill string, the drilling noise under six different working conditions was measured on site. The results show that the frequency and intensity of drilling noise change with the change of drilling conditions and drilling parameters; During directional drilling, when drilling in normal formation, the noise frequency is mainly concentrated at 1000 Hz, when drilling in hard formation, the WOB increases, and the noise frequency will be concentrated at 6000 ∼ 8000 Hz; When combined drilling, the average intensity of low-frequency drilling noise can reach at 50 dB, while when the drilling is stopped and the pump is stopped, the intensity of low-frequency drilling noise is only 20 dB; The drilling noise is mainly concentrated in the low-frequency band of about 2000 Hz, and the strongest noise is concentrated in 800 ∼ 1200 Hz; Calculate and compare the noise intensity, select the condition of stopping drilling and pump as the best transmission condition, analyze and compare the noise frequency, and select 400 ∼ 600 Hz as the best acoustic carrier transmission frequency. • A noise testing device is designed, which mainly includes wireless acquisition equipment, terminal control equipment and test body. The field test shows that the equipment is feasible. • The test device is installed on the drill pipe to measure the noise in real time under different drilling conditions and transmit it wirelessly. • Through the measured data analysis, the operating conditions suitable for downhole information transmission by sound wave are selected, the noise frequency band distribution is analyzed, and the noise intensity is calculated to provide basis for efficient downhole information transmission. [ABSTRACT FROM AUTHOR]