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It is generally considered that hydrogen could accelerate the corrosion fatigue process, however, the effective monitoring approach for the corrosion fatigue development in the hydrogen related environment is still missing. In this work, the hydrogen effect on phase angle shifts in electrochemical impedance spectroscopy during corrosion fatigue crack formation in drill pipe steel was in-situ studied. The results show that phase angle shifts as a function of time could be used to monitor the corrosion fatigue development in the presence of hydrogen. The permeated hydrogen leads to a lower peak intensity and shifts the peak to a higher frequency on the phase angle vs. frequency curve. These differences are due to the formation of a corrosion fatigue crack with a shorter length than in the absence of hydrogen. The phase angle shift reveals that the presence of hydrogen results in shortening crack initiation time and corrosion fatigue life of the drill pipe steel.

Aiming to solve the computational cost problem in the discrete element simulation for lunar soil drilling sampling, an equivalent boundary method was proposed. A high-accuracy DEM model of lunar soil was established firstly. As the novel alterable constitutive law, the accuracy of the model was verified to meet the performance of real lunar soil very much both in shear strength indices and elastic–plastic behavior. A common drill bit in the geological exploration field for sampling soil was chosen as the simulation object. In preanalysis, it was known that with the increase of drilling depth, the stress concentration area was always near the drill bit, while the affected area of the lunar soil was a cylindrical area around the drill pipe, which extended towards the drilling direction instead of extending around it. Then a big boundary drilling simulation scene was established to investigate the flow direction of lunar soil particles. The motion law of particles and the velocity field information were obtained, and a U-shape chain was described around the drill bit. Finally an equivalent boundary was set near the U-shaped chain, and the size was determined by comparing the soil stress in the fierce collision zone and around the reference boundary. This method could be a reference for other lunar soil drilling researches with other drills of different sizes.

The high efficiency of hole cleaning is essential and critical for drilling horizontal wells. In this study, the effects of four-lobed drill pipe on drill cuttings transport behaviors are examined using a coupled Computational Fluid Dynamics and Discrete Element Method approach. The drill cuttings concentration in annulus is used as the primary quantitative parameter, and the efficiency of hole cleaning is evaluated. Numerical results show that the curvature wall of four-lobed drill pipe by driving secondary motions and induces a local swirling flow, which promotes the transport of drill cuttings and significantly improves the hole cleaning performance. Compared with the conventional drill pipe, the hole cleaning efficiency of four-lobed drill pipe is improved by 89.7% on average, and the average kinetic energy of drill cuttings increases by one order of magnitude. These results are expected to provide a useful strategy for local hole cleaning when drilling horizontal wells.

Light-alloy drill pipes have many advantages over steel pipes, but also have several disadvantages. One of their main is their low wear resistance. A way to increase wear resistance is make a coating. This paper describes tests that allow us to assess the wear resistance of these coatings and determine the factors that affect it. Including tribological tests on a test bench simulatingreal processes of drilling.

Improving wear resistance of drill pipe sub thread is a vital task, and finding effective solution for it would much assist oil and gas companies to enhance well construction process. The report presents the results of comparative wear resistance tests for P147/147 and P133/133 subs of the top drive manufactured by OOO «NIGMASH» in Bashkortostan. The tests were performed by OOO «Tatburneft» holding company, a division of PAO «TATNEFT». Both, series and test subs were made from 40X2H4A steel. This report shows the results of metallographic studies and tests for improvement of the parts wear resistance, including the method of final electromechanical hardening (EMH) of the box and pin threads as compared with the conventional method of bulk heat treatment. The researches has developed the equipment, tools and technology for hardening of tool joint thread of drill pipe subs. The performed tests and studies aimed at enhancing efficiency of oil and gas well drilling. Their results are of much interest for oilfield operators, drilling and service contractors, as well as drilling subs manufacturers and repair companies.

Improving the efficiency of drilling oil and gas wells is impossible without increasing the durability of the drill pipe. The main reason for drill pipe tool joints to wear in the open hole is the presence of a hard layer in aggressive geological formations and wear due to friction with the inner wall of the casing. One of the effective methods for increasing the wear resistance of drill pipes is surfacing of the drill joint of the drill pipe with cored wire (hardbanding). Leading oil and gas companies, as well as specialized companies for drilling wells, widely use surfacing materials of various grades. To assess the quality of drill pipe tool joint surfacing, in accordance with the recommendations of the American Petroleum Institute (USA), two test tests were determined: ASTM G65 abrasion resistance degree and Casing Wear Test. Studies conducted to increase the wear resistance of drill pipe tool joints and casing with wear-resistant surfacing material DRM-150 (China) applied to the material in relation to the production tool joints material testify to the efficiency of surfacing. The results of metallographic studies indicate the formation in the deposited layer of gradient layers of metal with high hardness on the surface of 650 HV0.1 to a depth of 3.2 mm, a transition zone of hardness 350 HV0.1 and the starting metal 300 HV0.1. The wear resistance of the DRM-150 surfacing is almost three times higher compared to the wear of the material without surfacing (ASTM G65 test) and more than 5 times higher than the wear resistance of the initial samples without surfacing (Casing Wear Test).

A shear ram is of great significance to ensuring the safe operation of oil/gas well drilling and production, but the mechanical properties of the ram itself in the shearing process are rarely researched. Based on the basic motion law of the shear ram, combined its structural and operating parameters comprehensively, a model for solving the stress on the cutting edge was established corresponding to three stages (i.e., shear point contact, cutting and penetrating the drill pipe) according to the wedge stress theory. Then, based on the novel shear ram, the numerical simulation and indoor shear experiment were carried out on CT90 coiled tubing to understand the variation laws of ram stress and shear point stress in the shearing process. And the following research results were obtained. First, when the shear point doesn't contact with the CT90 coiled tubing, the stress at the V-shaped angular center of the ram is the largest, and that at the shear point is extremely small. Second, when the shear point just touches the CT90 coiled tubing, the phenomenon of stress concentration occurs in the vicinity of the shear point of the ram cutting edge. Third, when the shear point cuts into the CT90 coiled tubing, the stress on the shear point and on both wedge edges is the largest, reaching the strength limit of the ram (1050 MPa). Fourth, when the shear point enters the annulus after penetrating the CT90 coiled tubing, the ram stress on both sides of the junction between the cutting edge chamfer and the vertical plane is the largest. Fifth, After the CT90 coiled tubing is cut, crack damage occurs in the vicinity of the shear point of the ram cutting edge. In conclusion, the research results can better reflect the stress state of the ram cutting edge and its interaction with the drill pipe in the shearing process, and can provide an important reference for the design, manufacturing and the correct field application of shear rams. Keywords: Coiled tubing, Blowout preventer, Shear ram, CT90 coiled tubing, Ram stress, Shear point, Cutting edge chamfer, Stress test

Directional reaming while drilling is mainly used to optimize the casing program, improve cementing quality, and avoid drill pipe sticking caused by hole shrinkage. Under the condition of directional reaming while drilling, polycrystalline diamond compact (PDC) bits often suffer from serious failure modes such as balling, coring, and ring out. Based on the failure mechanism of reaming-while-drilling PDC bits in the Tahe oilfield and actual drilling needs, the optimized design of the reaming structure, crown profile, and cutter distribution of the PDC bit were analyzed, and a directional reaming-while-drilling PDC bit was developed. Specifically, the basic reaming structure is two-stage reaming, with the crown profile of the pilot bit being designed as a slightly raised structure and the cutters being distributed on the basis of the self-balancing principle. Field application in the Tahe oilfield shows that the bit achieves good performance in directional reaming while drilling, with the reaming diameter being larger than the required Φ 170 mm while the dogleg severity reaches 3.3°/10 m, which indicates that both the reaming and deflecting abilities of the bit can satisfy the engineering requirement. Moreover, the average footage of CK306B is 93 m and the rate of penetration of the bit is 1.24 m/h, which are, respectively, 90% and 47.6% higher than values from the first round of field application. The research results demonstrate the feasibility of novel directional reaming while drilling with a PDC bit in deep wells. In addition, the method can meet the requirements of trajectory control and directional reaming. The lateral imbalanced factor, which has a great influence on the reaming and drilling process of a directional reaming-while-drilling PDC bit, could be controlled within 5%, which can improve the stability of the bit as well as reduce bit failure, thus prolonging the life of the bit.

The article presents an analytical model to study the deformation and mechanical behavior of the drill pipe during subsea production tree (SPT) installation. Lateral and axial loads were considered, including the ocean wave, ocean current, drill pipe size and SPT weight that might dominant the deformation and mechanical behavior of the pipe. And the finite difference method and Gauss-Jordan elimination method were used to solve the established nonlinear analysis model. The results indicate that the ocean current, water depth and drill pipe size are the main factors affecting the lateral displacement of the last node of drill pipe and mechanical behavior of the pipe at lift-off point and thus need to be considered when designing such installation process.

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.

Efficient cuttings transportation is a significant issue in wellbore drilling. The pulsed jet drilling technology is known to improve the rate of penetration (ROP), but lacks targeted research into its effect on cuttings transport. We presented a CFD model based on Eulerian-Eulerian method to investigate the cuttings transport characteristics in horizontal and directional wellbores injected with pulsed drilling fluid. Kinetic theory of granular flow was used to formulate the stress tensor of cuttings particles, and sliding mesh method was used to achieve the rotation of the drill pipe. The wave propagation of the flow of cuttings particles was analyzed from the variation of amplitude and frequency of the inlet velocities of pulsed drilling fluids. Effects of drilling fluid rheological properties and hole and pipe diameters on borehole cleaning in traditional and pulsed drilling were studied. Numerical results indicated that the pulsed drilling fluid contributes to borehole cleaning because it significantly reduces the cuttings concentration in the moving bed zone and increases the velocities of cuttings in the fixed bed zone. Increasing amplitude and frequency of the inlet velocity of pulsed drilling fluid also leads to a decrease of the height of cuttings bed. The pulsed drilling fluid produces higher turbulent kinetic energy and lower turbulent dissipation rate comparing with the case with a constant drilling fluid velocity. Furthermore, pulsed drilling was also proved to be universally applicable to the improvement of cuttings transport within a wide range of drilling fluid rheological parameters and hole and pipe diameters.

Field experience has shown that the inefficient transport of small cuttings is a main factor contributing to excessive drag and torque during the drilling of a deviated hole; however, very little is known about the transport behavior of small cuttings. This experimental study investigates the effect of different polypropylene bead concentrations in water-based mud (WBM) on hole cleaning, along with the effects of cutting size, drill pipe rotation, and hole inclination angle. A total of 160 runs were performed using an experimental rig consisting of a 13 ft (3.96 m) long casing with a 2 in (50.8 mm) Inner Diameter (ID) and a rotary inner pipe with a 0.8 in (20 mm) Outer Diameter (OD). Four cutting size ranges, namely, 0.5–1.0 mm, 1.0–1.4 mm, 1.4–1.7 mm, and 1.7–2.0 mm, with a density of 2400 kg/ m 3 were tested in WBM with varying polypropylene bead concentrations ranging from 0 to 8 ppb. The concentric annulus flow test section was changed to vertical and horizontal angles with pipe rotation from 0 to 150 rpm. The mud density and viscosity were maintained at 10 ppg and 16 cp, respectively, under a flow velocity of 3.48 m/s (Reynolds number of 6620). The results indicate that smaller cuttings are easier to transport at all pipe rotations and polypropylene bead concentrations in both vertical and horizontal holes. The optimal pipe rotational speed was found to be 60 rpm. In this study, polypropylene beads undeniably enhanced the mud carrying capacity by significantly increasing the cutting transport ratio (CTR) by up to 16.57% in vertical holes and 15.73% in horizontal holes.

Ultrasonic monitoring of gas kick in risers is an effective method for early gas kick detection in deepwater drilling operations. At present, the research on the ultrasonic propagation in gas-liquid two-phase flow within the risers and the response rules of ultrasonic signals under actual working conditions is not deep enough. In this paper, the numerical simulation method that can accurately control parameters such as the distribution and size of bubbles was introduced, and its effectiveness and accuracy were verified by experimental means. Through the analysis of the effective sensitivity fields under different gas-fraction conditions, the key monitoring parameters (emission frequency and receiving probe position) were optimized first. On this basis, the characteristic parameters of ultrasonic signals were optimized and their applicable conditions were also analyzed: The response law of coda wave velocity to the gas fraction was gained by using the coda wave interference method and it is suitable for the condition of small gas fraction (less than 0.42%); The response rule of main frequency on gas fraction was obtained through frequency domain analysis; The arrival time of head wave was relatively sensitive to the gas fraction of 2–8%. Finally, the conditions of the eccentricity of drill pipe and the non-uniform distribution of bubbles were discussed. The influence of drill pipe eccentricity on ultrasonic propagation under different frequencies was noted, and the monitoring solution under the condition of non-uniform distribution of bubbles was proposed based on the effective sensitivity of different receiving positions. This study not only optimized the key parameters of ultrasonic monitoring method, but also explored its applicable conditions and the influence rules of actual working conditions on the ultrasonic propagation.

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.

Fatigue and corrosion fatigue (CF) tests were carried out to investigate the behaviors of G105 and S135 low carbon high−strength drill pipe steels under different stress amplitudes in air as well as simulated H2S contained drilling environment. The regression analysis method was applied to obtain empirical equations governing the fatigue and CF lives of drill pipe steels in different environmental conditions. Results revealed that there exist fatigue limits for G105 and S135 drill pipe steels in air, and the fatigue life equations for G105 and S135 are N f = 3.28 × 10 8 ( S eqv − 406.1 ) − 2 and N f = 3.81 × 10 8 ( S eqv − 472.5 ) − 2 respectively. For both types of pipe steels, quasi−cleavage and cleavage fracture was identified as the main feature in the fatigue source zone of the two steels, while fatigue striations were the main feature in the stable crack growth zone. However, in H2S solution, no obvious fatigue limits were found for G105 and S135, and the corresponding CF life equations are N f = 3.58 × 10 8 ( S eqv − 143.7 ) − 2 and N f = 2.91 × 10 8 ( S eqv − 119.6 ) − 2 . The CF sensitivity levels of G105 and S135 in H2S solution are high (64.6% and 74.7%, respectively), but S135 displays a higher sensitivity (74.7%) than G105 (64.6%). Further, no apparent plastic deformation appeared on the fracture surface in H2S solution, and the fatigue cracks sprout from the surface and expand into the specimen with radiation pattern.

Corrosion fatigue crack propagation (CFCP) tests were employed to investigate the behavior of S135 low carbon high−strength drill pipe steel under different strain rates in a simulated H2S containing drilling environment. Results revealed that the CFCP rate curve of the S135 steel has the characteristics of stress corrosion and corrosion fatigue (CF), which can be divided into near threshold, platform and rapid propagation zone. H2S has an obvious acceleration effect on the CFCP rate of S135 steel, the propagation rate of S135 steel in H2S solution is about 10 times more than that of in air. The stress ratio R has different effects on rapid propagation and near threshold zone. In the rapid propagation zone, the order of CFCP rate from high to low is R = 0.1 > R = 0.3 > R = 0.5, while the order of near threshold zone just shows the opposite. In the near threshold zone, the CFCP rate increases with the increasing of the stress ratio R. Based on the proposed Corrosion–Passivation–Fracture model and elastic fracture mechanics, the CFCP rate expression of S135 steel in H2S solution is d a d N cf = 1.927 × 10 ‐ 9 Δ K − 6.15 1 − R 0.59 2 , which can be used to predict the CFCP life in practical engineering. Fracture analysis results shows that the CFCP of S135 steel in H2S solution is mainly controlled by anodic dissolution and hydrogen embrittlement.

The effect of orbital motion of drill pipe on the transport of non-Newtonian fluid and cuttings is simulated by means of the two-fluid model in combination with the kinetic theory of granular flow in the horizontal wellbore annulus. The drill pipe self-rotates around its own axis while pursuing a circular orbit around the axis of the wellbore annulus, in which the orbital radius is the eccentric distance of the drill pipe from the axis of the wellbore. The embedded sliding mesh method is adopted to achieve the effect of the orbital movement of the drill pipe wall on the liquid-solid mixture. The cuttings transport ratio (CTR) which is defined as the ratio of the concentration of injected cuttings to the concentration of cuttings retained in the annulus is chosen as the measurement to evaluate hole cleaning. Cuttings transport behaviors in the annuli with the four motion states of drill pipe are investigated respectively. Simulations indicate that if the drill pipe is not concentric, there must be the fluid force that causes the lateral movement of drill pipe when it rotates. The orbital motion of drill pipe improves cuttings transport ratio in the annulus due to the periodical stirring and entrainment effect on cutting particles. The tangential flow within the annulus is dominated by the orbital motion of drill pipe rather than the self-rotation. The secondary flow appears especially when the self-rotation and orbital motion of drill pipe are in the opposite direction. With the increase of the orbital radius, the cuttings transport ratio is improved and the pressure drop is reduced because of the agitation of the drill string against the flow field. Increasing the rotating speed of the drill pipe contributes to a better wellbore cleaning, while an excessive rotating speed causes a higher pressure drop. Although the orbital motion of the drill pipe improves the hole cleaning, it also greatly increases the resistance and resultant moment exerted by the liquid-solid mixture, especially at high rotation speeds and eccentricity ratios.

Field experience revealed that a whirling drill string in the wellbore would make severe impact and rubbing against the casing and lead to uneven and random wear of casing. The casing wear due to vibrational impacts of the drill string was also one of the major causes for casing failure, but it was always ignored in the previous studies on casing wear. This work aimed at modelling and intuitively displaying the rub-impact characteristics of drill string and the induced wear on casing. Taking into consideration of the damping of drilling fluid, bit-rock interaction together with the geometric and contact nonlinearity, a drill string dynamic finite element model was established and then solved with the node iteration and the Newmark method. The whirl orbit, whirl velocity and collision characteristics of the drill string were then obtained. Based on these results, a three-dimensional visualization method was established to describe the dynamic features of drill string. The results indicate that the drill string presents a strong nonlinear dynamic behavior and makes frequent impacts against the wellbore, which appears mainly in the low side of borehole and is more serious in the hole section where BHA is located. The hole curvature and surface rotary speed have important influence on the casing wear induced by impact-rub action. A large hole curvature will lead to more serious rub-impact action of the drill pipe on the casing, and a rotary speed closer to the natural frequency of BHA will obviously increase the wear risk of casing.

This paper presents a series of empirical expressions to correct the total natural gamma ray log due to well environmental factors. This correction is focussed on improving the quantification of 40 K, given its application in the computation of the clay content of the different layers crossed during drilling. To date, there are no analytical relationships that make this correction and continuously consider the different diameters of the many existing sondes. There are also no functions that continuously take into account the different combinations of media interspersed between the well walls and the sonde (casing, drill pipe, gravel pack, cement, etc.) for different measurement modes and systems, such as wireline, while drilling. To solve these shortcomings, the relationships developed in this work have cited, in addition to the different well diameters and mud densities, the diameter of the sonde and the environmental parameters as variables with any value and in any possible combination. The obvious advantage of these parametric equations is that they can easily be entered as a subroutine into any code. Unlike the existing correction methods, i.e., empirical charts and curves obtained by simulation codes based on the Monte Carlo method, the relationships developed take into account the variation of the build-up effect that the radiation undergoes as it travels from layers with a certain radioactive emission to the sonde. In addition, another difference is that the relationships generated in this work include the internal diameter of the sonde between its outer walls and the cylindrical radiation detector glass. Starting from the general relationships that consider the attenuation and build-up effects of gamma radiation when passing through a medium, the methodology consisted of establishing an effective distance for the cylindrical geometry in which the source is the well wall, particularized for each effect and each type of tool (centred and eccentred). The resulting correction factors have been contrasted with the most recognized experimental charts in the field of well logging, obtaining a very high correlation and an average deviation of around 1.5%.

The reasons for the drill pipes failure as a result of interaction with formation water and killing fluids were analyzed. It was determined that the aggressiveness of killing fluids increases as a result of acid treatment of wells, which causes severe pitting corrosion. The main corrosive components of the killing fluids from the exploited wells determined by chemical analysis were chlorides. The determined residual life-time of the G105 drill pipe in the acidic killing fluid was only 16.65 days, indicating that their usage in acidic, highly mineralized killing fluids is unacceptable.

The Jeribe–Kirkuk reservoir is one of the major pay zones in the Halfaya Oilfield, Iraq, and its overlying 500 m thick Lower Fars anhydrite salt layer with a formation pressure coefficient of 2.25 acts as the caprock sealing. That's just why the first Jeribe–Kirkuk directional well experienced multiple drill pipe stickings and two side trackings, and the first horizontal well had to be completed with casing ahead of the schedule. Obviously, the drilling in the Lower Fars high-pressure anhydrite salt layer is faced with severe challenges. In this paper, the Lower Fars anhydrite salt layer was analyzed from the aspects of mechanical property, pore pressure, ground stress and rock mineral characteristics. Then, a mathematical model and criterion rules were established for borehole stability and wellbore deformation in the Lower Fars formations with different lithologies and the wellbore deformation in the process of well drilling was simulated. Finally, the high-density saturated salt water drilling fluid was specially developed for directional drilling in anhydrite salt layers, and the well trajectory and drilling program of directional wells were optimized. The following results were obtained. First, the most unstable zone in the Lower Fars anhydrite salt layer is composed of mudstones. As to the main reason for drill pipe sticking, the increase of rheological property after mudstone hydration leads to tight holes, so the neighboring anhydrites and salt rocks are pulled to collapse, which ultimately results in drill pipe sticking. Second, borehole deformation and instability in the Lower Fars layer intensify with the increase of inclination angle and wellbore opening time, and the risk of borehole instability increases sharply with the increase of wellbore opening time. Third, polyamine inhibitor BZ-HIB and polymer thinner JNJ are selected to optimize the formula of the high-density saturated salt drilling fluid, thus making its inhibition and rheology during the drilling in anhydrite salt layer improved effectively. Fourth, the kick off point of the Jeribe–Kirkuk directional well is moved upward to Upper Fars from Lower Fars. Specifically, the buildup section is in Upper Fars, the angle holding section is in Lower Fars, and the inclination angle and directional section length in Lower Fars are decreased, so the risk of drill pipe sticking is reduced. So far, it has been practically applied to 22 wells, showing that the drilling complexities in Ø311.2 mm hole have been effectively controlled. In 2016, the average drilling cycle was 35.8 days, 52.8% shorter than that in 2015, and the average ROP was increased by 122% from 3.3 m/h to 7.33 m/h. In conclusion, technological optimization has achieved good application results. Keywords: Halfaya oilfield, Iraq, High-pressure anhydrite salt layer, Wellbore deformation, Drill pipe sticking, Directional drilling, High-density saturated salt drilling fluid, Well trajectory

Coal and gas outburst accidents occurring in underground coal mines generally cause great casualties and economic losses, especially in construction areas of coal seams where the outburst risks are not accurately evaluated. Therefore, accurately identifying the outburst risks of coal seams is necessary and critical to prevent and control outbursts. In order to improve the prediction accuracy for outbursts in working faces of coal roadways, a self-designed drilling device that can simulate the in-situ outburst prediction of coal roadways was used in this study. We used the coal samples with different coal ranks to adsorb CO 2 and N 2 with different pressures in the laboratory, so as to simulate the coal seams with different outburst risks. Finally, boreholes for predicting the outburst risk were drilled in the simulated coal seams to study the correlation between common dynamic phenomena (e.g. gas and coal being ejected from the borehole (GCEB) and drill pipe being stuck by coal mass in the borehole (DPSC)) and outburst risks. The results show that the greater the outburst risks of coal seams, the more frequent the occurrence of GCEB and DPSC is. The GCEB phenomenon for outburst prediction is attributed to small-sized coal and gas outbursts in boreholes, while the occurrence of DPSC phenomenon does not affirm that there definitely are outburst risks on working faces. The DPSC phenomenon indicating outburst risks is generally accompanied with GCEB, which form a linkage system and are triggered successively.

In the process of underbalanced pressure drilling, the drill pipe body and its joint repeatedly pass though the sealing rubber core of the rotating blowout preventer (RBOP), making the rubber core susceptible to alternating cyclic load, and prone to fatigue failure. Under the premise of effective sealing realized by the rubber core, to increase its service life, first the Yeoh constitutive model and constitutive parameters describing the material of rubber core were determined by uniaxial tensile and compression tests, and the finite element governing equation of the nonlinear large deformation of the rubber core was obtained according to the principle of virtual work; then a three-dimensional finite element model of the rubber core was established by ABAQUS software to simulate the dynamic sealing process, contact pressure and Mises stress distribution and variation on the sealing surface were analyzed, and the accuracy of the finite element analysis results was verified by comparing the existing test results; subsequently, the influence of structural parameters such as inner angle, outer angle and inner diameter on the sealing surface stress was studied, and these parameters were optimized through Taguchi experiment. The optimal combination of structural parameters was obtained as inner angle 29°, outer angle 69° and inner diameter 84mm. The maximum Mises stress was reduced by 2.48MPa and the Mises stress amplitude by 42% after optimization. Finally, the suitable conditions of the optimized rubber core were selected based on the applicability analysis to conduct the field application and result shows that the rubber core has good sealing performance and significantly increased fatigue life after optimization.

Directional drilling has become popular in recent decades in both onshore and offshore operations due to reduced drilling costs and improved recovery. In a directional well drilling operation, drill cuttings tend to settle down at the lower side of the inclined annular section. If the generated cuttings are not removed from the hole section properly, it causes a cuttings bed formation in the annular section. Different drilling related problem such as poor rate of penetration, excessive torque and drag, increase differential sticking often associated with a poor hole cleaning which eventually lead to increase in non-productive time (NPT). Therefore, the success of inclined well drilling operation largely depends on effective cleaning of drill cuttings from the annular section. A variety of parameters, including the fluid rheology, mud velocity, cuttings size, drill pipe rotation and drill pipe inclination generally influence the cuttings transport performance. Optimization of these drilling parameters is crucial to ensure proper hole cleaning. In this study, a Computational Fluid Dynamics (CFD) model for the inclined well section is used to investigate the cuttings transport efficiency (CTE). An Eulerian-Eulerian multiphase flow model is proposed and validated with lab scale experimental data. The experiments were performed in a 6.16-m-long annular test section having an outer pipe diameter of 4.5-inch and an inner pipe diameter of 2.5-inch. The setup is equipped with Electrical Resistance Tomography (ERT) system to measure the instantaneous solid volume fraction and a visualization section. A non-Newtonian Heschel-Bulkley (HB) fluid was used as drilling mud and solid glass beads of 2.50 mm–3.00 mm were used as cuttings in the experiment. This study shows a good agreement in visualization of mechanistic three-layer model of cuttings transport in terms of ERT data from experiment and CFD simulation. The validated CFD model is used to perform 5- Factors factorial design and analysis of variance (ANOVA) study. ANOVA shows that the interaction effects of mud velocity-cuttings size, mud velocity-inclination are statistically significant. Finally, this study proposed a statistical model to estimate the CTE of an inclined well considering the two factor and three factor interactions among the variables. Also, the model shows that drill pipe rotation has negligible effect in improving cuttings transport efficiency in the inclined well. The proposed model also reveals that cuttings size and fluid velocity account for 78% contribution in the transport efficiency for an inclined well. Furthermore, an Artificial Neural Network (ANN) method is used to verify the contribution of lower order interaction in the statistical model. Though empirical model shows few lower order two factor interactions (fluid rheology -cuttings size, fluid rheology-inclination), and three factor interactions (velocity-cuttings size-inclination, fluid rheology-cuttings size-inclination); ANN model shows that lower order interaction are significant in model prediction and should not be ignored. The findings of this study can help in better understanding the interaction behaviour among drilling parameters and optimized cuttings transport efficiency in the inclined drilling operation for a wide variety drilling parameters.

This paper studies the rheology and annular flow of a smart lost circulation material (LCM) at 160 °C, using a high-temperature flow loop. The smart LCM is a shape memory polymer (SMP) that activates at high temperatures, and its particle size increases to seal fractures in geothermal formations. SMP was mixed with the base fluid in two different concentrations, 1.0 and 3.0 wt%, to study rheology, wellbore hydraulics, activation process, and settling behavior under different testing conditions. The results of this study showed that the SMP could be activated at high temperatures. An increase of 80–100% in the particle size was observed at 160 °C. The mud samples showed a high shear-thinning behavior at the two concentrations with a Power-law flow index (n) ranging between 0.025 and 0.101. No additional frictional pressure losses were observed when SMP was added to the base fluid. SMP particles showed an excellent suspension at 1.0 wt% while, at 3.0 wt%, a bed was formed at a low flow rate and without pipe rotation. Increasing the drill pipe rotational speed or flow rate effectively removed the bed and homogeneously dispersed the SMP particles, ensuring a better sealing efficiency. SMP particle dispersion in inclined wells was better than in horizontal wells. Moreover, the findings of this study help optimize the lost circulation treatment by considering a wide range of operating parameters that can further be extended to different systems and geometries.

In recent years, aluminum alloy drill pipe are used more and more frequently in the exploration and development of the deep wells, ultra-deep wells and sour gas wells due to the high strength, light weight and corrosion resistance to H2S and CO2. However, the pitting and fracture failure sometimes occurred, resulting in giant economic losses and fatal disaster. In this study, the failure analysis of aluminum alloy drill pipe was addressed and the formation cause of the pits and parallel transvers cracks was investigated. Results show that the chemical composition and the regular mechanical properties (including tensile and impact properties) meet ISO 15546:2011 standard requirements. But the tensile strength of samples immersed in the mud environment is lower than that of ISO 15546:2011 standard requirements. Metallographic analysis results show intermittent ribbon Al6(MnFe) solid solution, S (CuMgAl2) phase and AlFeSi phase distributed on α solid solution. The failure cause of aluminum alloy drill pipe is mainly attributed to the brittleness sensitivity of intermittent banded second phase and inclusions to corrosive media from mud environment. Cracks and pits are prone to generate here. XRD and EDS analysis results of corrosion products and the pits bottom show that the main corrosion products are Al2O3, Al2S3, AlPO4, BaSO4 and CaCl5. S and Cl are from environment media. The microscopic morphology analysis results of the tensile and impact specimens fracture show that the fracture is the brittle fracture caused by the environmental medium.

In some situations while drilling through severe doglegs, drill strings are inevitably touching the inner wall of casing, which may wear casing harshly. For instance, this is a frequent problem in wells drilled in Bohai Bay basin in East China. In large dogleg sections of the well, casing is subjected to a dual-wear accumulation contributed by the tool joint and drill pipe (alternate wearing). Nonplanar geometry of the hole and complex geometry of the rotating drill pipe may add to the complexity of the wear process. Here, we propose a mathematical model to calculate the loss of wall thickness of the casing due to the dual wear. A finite element model is developed to incorporate wearing of the casing alternating between the tool joint and the drill pipe. Arbitrary Lagrange-Eulerian (ALE) adaptive meshing and remapping technique is utilized to specify the ablation velocity vectors at the inner casing surface. Our numerical results show that the dual wear contributions and ever changing contact geometry in alternate wearing intensifies the rate of the casing wear 150% faster than that of the single wear models. Additionally, the curvature at point with maximum wear depth has been found to significantly impact the maximum stress of worn casing. This paper provides an accumulative wear model for accurate prediction of the casing wear and its residual strength before running the casing through the dogleg section.

A hydraulic top drive is a high-power gyrator used in oil or scientific drilling rigs, whose shaft is connected to drill pipe when it drives drilling tools to excavate well. The output speed of top drive determines the speed of drill bit directly. Load acting on the top drive shaft fluctuates randomly, which will cause top drive output speed hard to be in consistent with the setting value. This paper presents a main transmission system of a hydraulic top drive designed for deep continental scientific drilling, which was built with a multi-stage mechanical structure and a closed circuit hydraulic system with variable displacement pumps and motors. Electro-hydraulic proportional control was applied to vary the speed of the hydraulic top drive. A theoretical model is detailed for the hydraulic top drive main transmission system. Among the new techniques proposed in this paper is a simulation model for studying the performance of hydraulic top drive and capturing speed characteristics under fluctuant load. A drilling experiment of the hydraulic top drive was performed on the CRUST-I drilling rig in CCSD-SK-II well site. This paper concludes by comparing the results of the simulation model with theoretical results and drilling experimental data gathered in the hydraulic top drive possessing the same architecture, components, and control methods used within the simulation model. The drilling experiment and the analysis result showed that the hydraulic top drive could meet the requirements of deep continental scientific drilling and that the speed could be output according to the setting speed with very small oscillation. The simulation model can be used for several applications such as hydraulic top drive design and performance analysis of various drilling conditions.

Well intervention in long lateral-reach wells, i.e., wells with laterals 10,000-ft or longer, is predicted to become more common within the current low price oil environment. During drilling, the drill pipe can be rotated, significantly reducing its friction in the long lateral-reach wells comparing to coiled tubing (CT) that can only slide linearly. The CT industry's trend to transfer more weights-on-bit (WOBs) to the bottom hole assembly (BHA) has been to increase the CT size to 2- or 2 ⅜-, 2 ⅝-, or even 2 ⅞-in. However, without specialized friction-reduction technologies, these typically larger CT sizes still don't have enough rigidity to reach the bottom of the long lateral wells. As currently there is no economically practical technology to rotate the CT, entirely or partially, and the larger CT sizes bring significant operational challenges, the only available CT friction-reduction technologies are chemical (i.e., lubricants) and mechanical or hydraulic (i.e., vibratory tools and tractors) that are traditionally used to extend the CT reach. However, the field performance of these CT friction-reducing technologies is usually less optimistic than that observed in laboratory. In addition, the field experience with the vibratory and tractor tools, in particular, is usually unpredictable and unreliable, depending on unknown or unexpected downhole conditions. In the first part of this critical review study, the most important aspects related to the CT lubricants, including their laboratory and field performance and the current understanding of their predictability and reliability within the CT industry, were discussed. In this second part, the same aspects for CT vibratory tools and tractors are discussed for the first time, focusing on the challenges and limitations encountered in the field. It is shown that field performance studies regarding vibratory tools and tractors are mostly anecdotal or proprietary. Given their importance for well intervention operations in extended-reach wells, it is hoped that this critical review will trigger further research and development of CT vibratory tools and tractors and best field practices to improve their predictability and reliability in the field.

Hydraulic slotting in a gas drainage borehole is an effective method of enhancing gas drainage performance. However, it frequently occurs that a large amount of slotting products (mainly the coal slurry and gas) intensely spurt out of the borehole during the slotting, which adversely affects the slotting efficiency. Despite extensive previous investigations on the mechanism and prevention-device design of the spurt during ordinary borehole drilling, a very few studies has focused on the spurt in the slotting process. The slotting spurt is mainly caused by two reasons: the coal and gas outburst in the borehole and the borehole deslagging blockage. This paper focuses on the second reason, and investigates the hydraulic deslagging flow patterns in the annular space between the drill pipe and borehole wall. Results show that there are six deslagging flow patterns when the drill pipe is still: pure slurry flow, pure gas flow, bubble flow, intermittent flow, layering flow and annular flow. When the drill pipe rotates, each of those six flow patterns changes due to the Taylor vortex effect. Outcomes of this study could help to better understand the slotting-spurt mechanism and provide guidance on the anti-spurt strategies through eliminating the borehole deslagging blockage. Keywords: Coal hydraulic slotting, Cross-measure borehole, Borehole spurt, Deslagging flow pattern

Offshore drilling with ultra-long drill strings (i.e., longer than 10,000 m) creates a new class of technical challenges, such as dynamic variation of weight on bit (WOB). This article investigates observational data obtained from a drilling program conducted by the scientific drilling vessel Chikyu using an 8000 m drill string, which is first of their kind to be recorded. The data exhibited longitudinal oscillation of the drill pipe at frequencies higher than that of heave motion. To identify the cause of such oscillation, one-dimensional dynamic simulation to model drill string's behavior was carried out. The key component of this model is the detailed modeling of the heave compensator. Numerical experiments revealed that longitudinal natural vibration was excited in the ultra-long drill pipe, and the excitation modes corresponded to the behavior of a string with both ends fixed, indicating the possible influence of friction in the heave compensator. We named this class of phenomena compensator-induced vibration (CIV). In addition, longitudinal elasticity leads to divergence of the tension variation near surface and downhole WOB, which calls for the need to directly measure the downhole WOB behavior.

High-strength S135 drill pipe is an important component in the oil and gas exploration and development of deep and ultradeep wells under complicated environments. It is of great significance to the study on the corrosion fatigue fracture of high-strength steel S135 in complex environments. In this paper, two samples of smooth and unilateral notch were used to conduct fatigue in air, pre-corrosion fatigue and corrosion fatigue at different temperatures, respectively, to study the corrosion fatigue behavior of high-strength steel S135 under the complex environments of the notch, corrosion medium, temperature and alternating stress. The experimental results indicated that the influences of coupling multiple factors (notch, temperature, corrosion medium and alternating stress) on the corrosion fatigue of S135 steel were greater than that of single factor, and the more factors indicated the greater influence on fatigue. The influence of three kinds of coupling factors, such as the notch, corrosion medium and temperature, was the most significant (80.8%). In single factor, the impact of notch on fatigue was the largest (49.9%), followed by corrosion (41.6%) and temperature (34.4%). Obviously, the notch was the dominant factor of fatigue fracture, and the temperature had a significant influence on corrosion fatigue. It was found that the influence of coupling-factor on fatigue was less than of the superposition of single factor, so the relationship among multiple factors was not superposed but competitive and synergistic relationship. This can be attributed to the fact that the crack was always initiated from the corrosion pits at the notch root under coupling multi-factor in complex environments and the initiation was the combined action of stress concentration, anodic dissolution and temperature. The stress concentration at the notch was the main factor of crack initiation, and the electrochemical activity of at the notch root was the highest under the action of cyclic stress and this place gave priority to corrosive pitting, made the increase of local stress concentration and promoted the initiation of crack. And the temperature provided the energy to the corrosion electrochemical reaction and accelerated the evolution of the corrosion pits, so crack initiation was accelerated. Besides, article established the testing method of rotating bending fatigue in complex environments, revealed the relationship of fatigue fracture as well as the mechanisms of crack initiation and propagation of high-strength S135 steel under coupling multiple factors in complex environment.

The cuttings transport was numerically simulated based on kinetic theory of granular flow in combination with sliding mesh for drill pipe rotation in the horizontal well. The Herschel-Bulkley (H-B) model was implemented to describe the rheological behavior of drilling mud. Three distinguishable flow regions of cuttings and swaying phenomenon of cuttings distribution along the direction of drill pipe rotation were observed. The granular temperature of cuttings is high near the wall of drill pipes, which indicates that the energy from the rotating drill pipe is transferred to cuttings. Effects of three rheological parameters (τ0, KHB and n) on the flow behavior of cuttings and H B fluid were analyzed. With the increase of Herschel-Bulkley fluid rheological parameters, the height of cuttings bed decreases, and the axial flow of cuttings at the lower side is significantly enhanced, but the pressure drop through the annulus is increased. When the value of consistency coefficient and flow behavior index of H-B fluid is low, the cuttings transportation in the wellbore is unstable with the pulsation of cuttings volume fraction in the annulus. Among the three rheological parameters, the flow behavior index plays the most significant role in pressure drop through the annulus.

The external environment in deep water is quite complicated, during the installation process of subsea cluster manifolds by the drill pipe, the safety and precise localization need to be addressed desperately. In this paper, based on small deformation theory, basic theoretical model on the drill pipe installation of subsea manifolds is proposed and OrcaFlex software is used to make a simulation on setting up the corresponding numerical model in which the installation process is divided into three main phases. Its main purpose is to make a simulation research in guiding for engineers before the practical installation. The displacement and stress state of drill pipe are simulated and their curves in the different phases are obtained. In the different phases of lowering subsea cluster manifold, three factors: current velocity, wave height and manifold weight have an evident impact on tension, bent moment, Mises stress of drill pipe and displacement of subsea manifold, which are quite useful for actual installation in deep water.

The cuttings transport during well drilling was numerically simulated based on kinetic theory of granular flow in combination with sliding mesh for drill pipe rotation. The power-law model was implemented to describe the rheological behavior of drilling fluid. Numerical results were compared with available experimental data in the literature to validate the algorithm, and good agreement was found. Three distinguishable regions of cuttings flow pattern and swaying phenomenon of cuttings distribution were observed along the direction of drill pipe rotation. Increasing the fluid velocity results in a reduction in the height of cuttings bed and weakening of the swaying phenomenon. Higher apparent viscosity of drilling fluid contributes to a good performance of cuttings transport at a low annular velocity, but rising in pressure loss. There is critical inclination angle of the well θctr for cuttings transport ratio and θdp for pressure drop through the annulus. The most difficult of cuttings transport occurs in the well inclinations around 35°–65°. There is no additional contribution of drill pipe rotation to cuttings transport after reaching a critical rotation speed. Increasing the cutting size leads to a reduction in the cuttings transport ratio and an increase in pressure drop.

In drilling industry, barite particles settling and barite sag as a major problem can potentially impose significant operational issues. Static conditions, in which well undergoes an extended shut-in period, could occur during different drilling and completion operations such fishing operation, tripping, and logging. Despite its importance, such phenomenon is not well understood yet. To avoid issues related to barite settlement and barite sag, a good understanding of the impact of different drilling parameters on barite settlement and sag phenomenon is required. Recently, the mathematical formulation and modeling of settlement and sag processes have gained more attention. In order to better design the drilling fluids and to optimize the operational conditions such as flow rate and drill pipe rotation speed, as well as drilling well trajectory design to avoid barite settlement, the mathematical formulation and modeling of such physical phenomena is required. This study is aimed at mathematically describing and analyzing the settling of barite particles in annular concentric space without axial flow by the means of computational fluid dynamic (CFD) simulation. The modeling approach consists of two main steps: a) simple vertical annular domain and b) complex three dimensional barite settlement process in a deviated well with rotational drill pipe. The current work is based on Eulerian two phase model. The settling of the single particle and the hindering effect of other particles on settling velocity have been investigated. Based on single particle model, the rate of barite settlement and fluid pressure reduction have been modeled. However, the single particle model cannot describe the particle to particle interactions and their impacts on settlement such as particle shearing viscosity, kinetic particle viscosity, and collisional effects. In this study, the accurate and comprehensive modeling of barite settlement has been done by applying the Eulerian-Eulerian approach. The models have been validated against available published experimental data in the literature. In addition, in order to further validate the model presented here, drill pipe rotation, fluid rheology, and inclination angle impacts have been experimental investigation and compared with results of the proposed model. The results indicate that the model based on using Eulerian-Eulerian approach accurately predicts the experimental data results. Afterward, the sensitivity analyses were carried out to show the impact of inclination angle, inner pipe rotation, fluid rheology, and barite content on the rate of settlement. This study showed that drag forces induced resuspension plays a vital role in barite settlement inside a deviated well. The results reveal that the settling rate is decreased with increasing the inner pipe rotation and the vortex effect created by inner pipe rotational, play a major role in the reduction of barite settlement. The results also show that the maximum settlement rate accrues at the deviation angles between of 45–60°.

Incidents such as borehole collapse, suction drill, and drill pipe drop resulting from borehole instability may occur in the process of drilling in loose coal bed sections for coal mine methane (CMM) drainage before mining. Grouting while drilling (GWD) is a technique used to reduce such incidents. Sodium Silicate used in GWD has the advantages of controllable consolidation-time, non-toxic material, non-pungent odor and relatively inexpensive. Although it will shrink after solidification, this could be used to connect gas channels. This paper presents the feasibility of using Sodium Silicate to make GWD slurry through results of laboratory experiments. The principal ingredients of the two Sodium Silicate grouting slurry formulae, namely 4% Glycerol Triacetate with 20–40% Sodium Silicate and 4% 1,4-Butyrolactone with 20–40% Sodium Silicate, were selected based on the requirements of GWD. The experimental results from a traditional test device revealed that coal cement stress is still low after 45 min thus limiting its field application. However, after 72 h, multiple cracks appear along the edge of the coal grains suggesting that the formulae can be used to connect gas channels naturally after hardening. If a PH stabilizer is not added, the optimal grouting time occurs within 20 min. In the process of GWD, the grouting slurry will not consolidate until it is injected into the borehole wall, which is enables the drill pipe to remain clean after grouting. Seepage grouting simulation experiments based on a self-developed device indicate that injecting certain slurry into pre-set positions of a drilling hole by circulation wind pressure is feasible to some extent when drilling in fractured, strongly fractured, and pulverized coal beds. In powder coal, however, it will close the gas channels, and thus cannot be applied.

A model based method for kick and loss detection and attenuation in Managed Pressure Drilling is presented. The drilling system is modeled as a distributed parameter system combined with a reservoir flow equation containing reservoir pressure and the so-called productivity index as uncertain parameters. A swapping-based design for state and parameter estimation utilizing bottom-hole pressure measurements available via wired drill pipe is combined with a closed loop controller for kick and loss attenuation. The performance of the proposed method is compared to earlier results on kick attenuation in a simulation, showing significant improvement. © 2018, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd.

The packing unit is the key part of a rotating blowout preventer (RBOP) and its sealing performance affects the operation of under-balanced drilling, but sealing failure often happens. This paper studies the influence of various parameters on its sealing performance and discusses the packing unit's failure mechanism. Firstly, the Yeoh constitutive model is chosen through a group of tensile tests of the packing unit material. Then, the finite element model of the packing unit is established, and the influence of well pressure, tripping and drilling speed, friction coefficient and five structural parameters on the contact stress between the packing unit and drill pipe are discussed. Finally, the failure mechanism of the packing unit is analyzed, and the structural parameters of the packing unit are optimized. The results show that during the tripping process, the contact stress is the largest when the drill pipe joint passes through the packing unit, and the contact stress of the packing unit increases with the increase of well pressure and friction coefficient. The tearing at the top of the packing unit is caused by shear stress. The failure mechanism of the packing unit at the inner angle is divided into two types, one is that excessive contact stress causes the tongue piece to fall off, the other is that alternating von Mises stress and shear stress cause lumpy to fall off. Alternating von Mises stress and CSHEAR 2 (Transverse friction shear stress) causes tearing at the inner lower angle. The drill pipe eccentricity causes the Y-shaped cracks at the side of the packing unit. The optimized parameters of the packing unit are as follows: The tripping and drilling speed is 0.15 m/s, the inner diameter of the primary sealing section is 107 mm, the outer angle is 154°, the inner angle is 150°, the inner lower angle is 135°, and the length of the primary sealing section is 107 mm. In this paper, the failure mechanism and various influencing factors of the packing unit were analyzed, and the reliability of the finite element model was verified, which has reference value for failure analysis and structural design of the packing unit.

Despite the grooved drill pipe (GDP) has been applied in the soft coal seam in recent years, it remains unclear of the cinders transport mechanism in the annulus of GDP. In this study, the cinders transport model of GDP was developed based on an improved method, combining the kinetic theory of granular flow and Eulerian-Eulerian two-phase flow model. The annular fluid field characteristics and cinders transport laws of GDP were studied in this model by considering drag force, lift force, and virtual mass force. Finally, the precision of this model was verified via the experimental data. The results show that the annular velocity and cinders distribution present periodic variations with the drill pipe pitch. A role of guiding and tangential force on fluid field by the helix grooves is found. The volume fraction of residual cinders is dramatically reduced from 0.144 to 0.085 as the inlet velocity increases from 0.6 m/s to 1.2 m/s. This indicates the performance of cinders transport can be improved by increasing inlet velocity of drilling fluid.

Efficient cuttings transport is important for achieving safe and successful drilling operations. However, poor hole cleaning is considered to be one of the main issues that happens frequently in horizontal and highly deviated wells. The selection of the drilling fluids with enhanced rheological properties is one of the effective methods to increase cuttings transportation efficiency. The major purpose of the present research is to investigate the application of silica (SiO2) nanoparticles in improving hole cleaning in extended reach drilling (ERD) operations. Nanocomposite drilling fluids were prepared by adding silica nanoparticles into water-based mud (WBM) at different weight percent concentrations (0.1–1.5 wt%). The flow loop experiments were performed on a sophisticated purpose-built flow rig by circulating the tested fluid samples into the test section in a horizontal position, considering the influence of drill pipe rotation, flow rates, cuttings sizes, mud density, and drill pipe eccentricity. In addition, the study covers the impacts of laminar, transition, and turbulent flow regimes. The goal of such variation in the operational parameters is to simulate real field conditions. The results indicated that the addition of the silica nanoparticles to WBM increases the colloidal interactions with cuttings, therefore leading to a substantial enhancement in cuttings removal efficiency especially with the higher concentration of silica nanoparticles. It was shown that nanoparticles in drilling fluid increase cuttings transport by 20.32%–32.75% for different nanocomposite water-based drilling fluids used in this study. The proposed investigation demonstrates the feasibility of using silica nanoparticles in WBM to enhance the capability of drilling fluids in transporting and circulating drilled cuttings out of the wellbore. Furthermore, the results of this project would provide a more reliable understanding of the relationship between drilling operation parameters and hole cleaning performance in ERD operations.

The rotation speed of the drill pipe is one of the key parameters for adjusting the drilling technology, so it needs to be monitored in real-time. Here, a self-powered rotation speed sensor for drill pipe based on the triboelectric-electromagnetic hybrid nanogenerators (NG) is proposed in this paper, and the triboelectric nanogenerator (TENG) and the electromagnetic generator (EMG) parts of the sensor can be used independently as the rotation speed sensor and generator, which shows high reliability. Test results show that when the TENG part is selected as the sensor, the measurement range is 0–1000 rpm,the sensitivity is 0.033 Hz/rpm, the measurement error is less than 3%, and the maximum output voltage, current and power are respectively 15.08 V, 1.05 uA and 3.4 u W. And when the EMG part is selected as the sensor, the measurement range is 0–1000 rpm, the sensitivity is 0.017 Hz/rpm, the measurement error is less than 5%, and the maximum output voltage, current and power are respectively 3.31 V, 43.25 mA, and 36.5 mW. In addition, the combined use of TENG and EMG increases the reliability of the sensor, and the output current can be connected in parallel to increase the output power, which is very suitable for the drilling environments.

In a horizontal well drilling operation, a part of generated drill cuttings tends to settle down at a lower annular section. Formation of sand bed causes several operational issues such as low rate of penetration and stuck drill pipe. In this study, a lab-scale experimental work is carried out to investigate hole cleaning in the extended reach and horizontal drilling operation. This work focuses on the visualization of the flow behaviour of drill cuttings in the horizontal annular section. A 6.16 m-long horizontal well test section with an outer diameter of 4.5 inch (11.43 cm) and an inner diameter of 2.5 inch (6.35 cm) is used in this study. Four non-Newtonian Herschel-Bulkley fluids are tested as the drilling mud. Solid glass beads of 2.5–3.0 mm with a density of 2650 kg/m3 are utilized as the drill cuttings with two different solid concentrations. The flow behaviour in the horizontal annular section is analyzed with a high-speed imaging technology at 2000 frames/second and electrical resistance tomography (ERT) technique. The effects of fluid rheology, fluid velocity, drill pipe rotation, and eccentricity on the cuttings transport are investigated. This study showed that an optimum drill pipe rotation of 80 RPM and a minimum transport performance number (TPN) of 70 is required for efficient hole cleaning in horizontal well section. This study also reveals that fluid rheology has a significant effect on the minimum transport velocity (MTV). A flow regime analysis revealed that a turbulent flow regime is required for effective hole cleaning without sand bed formation. The mechanistic three-layer model of cuttings transport is experimentally verified with high-speed visualization techniques. Furthermore, this study introduces the concept of estimating the instantaneous annular solid volume fraction by the ERT system as well as visualization of solid bed distribution in the annulus section.

The drilling for hydrocarbons from oil and gas wells requires efficient drilling fluid and cutting-edge drilling technology. Furthermore, the removal of rock cuttings from oil and gas wells while drilling is a vital task of the drilling fluid, particularly in large-angle wells and long-range drillings. The rock cuttings if not transported to the surface effectively can result in severe costly drilling problems of drag and torque, pipe sticking, faster bit damage, etc. This research suggests a new method that applies polypropylene beads (PP) and silica nanoparticle (NS) treated by sodium carbonate (Na2CO3) to enhance the cuttings transport efficiency (CTE) of water-based mud (WBM). Tests were carried out in laboratory-scale cuttings lifting rig simulator equipped with a 20-ft. Long annulus, a 2.75-in. ID outer acrylic pipe, and an inner drill pipe of 1.05-in. OD. Six different 10 ppg weighted mud samples were formulated and coded mud nos. 1–6 using PP beads and Na2CO3 treated NS concentrations. Four cuttings sizes in the range between 0.4 and 4.0 mm at various hole angles (0°, 30°, 60°, and 90°) without pipe rotation were evaluated using a constant flow rate of 5.13 L/s. The results of rheological characterization using Herschel-Buckley model showed that all the mud systems are shear-thinning as the flow behaviour index ranged between 0.50 and 0.60. The fluid consistency parameter of the WBM indicates that the addition of PP beads and NS concentrations decreases the viscosity of the WBM. Also, the viscosity, yield point, gel strength, and filtration parameters of the WBM were decreased when the PP beads and NS concentrations were introduced before and after thermal aging experiments. This interprets the thinning nature of the mud systems. However, when these products were applied to lift cuttings to the surface, the lifted cuttings increased. The optimum mud system using Bingham plastic expression was found at mud no. 6 (BM-PP8-NS1) containing apparent viscosity of 30.5 cP at a shear rate of 1022 s⁻1, plastic viscosity of 13 cP and a yield point of 35 lb/100 ft2 at 78 °F. Cuttings size and hole angles seem to wield significant influence on CTE as the smallest cuttings (0.4–1.4 mm) were easier to be lifted in the vertical hole (0° angle), while the largest ones (2.8–4.0 mm) were the most lifted in the horizontal section (90° angle). The findings of this study can help for a better understanding of the mud performance of PP beads and Na2CO3 dispersed NS mixture for cuttings transport in a wellbore.

Erosion of drill pipe caused by the rock particles in annular space is very serious in gas drilling. The aim of this paper is to study the erosion wear law of drill pipe by theoretical derivation and laboratory experiment. Based on the micro-cutting model of single rock particle, the erosion model of drill pipe is established to calculate the erosion wear loss. This model establishes the relationship between the erosion wear loss of drill pipe and drilling parameters, such as gas injection volume and rate of penetration (ROP). The laboratory experiment is carried out to verify and revise the erosion model, and the results show that when ROP is less than 20 m/h, the erosion wear loss of drill pipe is approximatively proportional to the square of gas injection volume and has positive correlation with ROP. However, it has negative correlation with ROP when ROP is faster than 20 m/h. In addition, it is also obtained that gas injection volume has more impact on drill pipe erosion compared to ROP based on the analysis of an engineering example, and high ROP will suppress the erosion wear of drill pipe. Therefore, under the premise of satisfying the drilling requirements, employing lower gas injection volume and higher ROP can reduce drill pipe erosion in gas drilling, which will save the drilling cost greatly.

Well interventions in long lateral-reach wells, i.e., wells with laterals 10,000-ft or longer, continues to challenge the oil and gas industry around the world. Without specialized friction reduction technologies, typical-size coiled tubing (CT), such as 2- or 2 ⅜-, 2 ⅝-, or even 2 ⅞-in., has enough rigidity to transfer weights-on-bit (WOBs) to the bottom hole assembly (BHA) in only a part of the current horizontal wells. For instance, 2-in. CT could effectively intervene in about the first half of the 5 ½-in. completed laterals. Increasing the CT diameter or rotating the CT, entirely or partially, remain theoretical options to improve reach. However, larger-diameter CT creates logistical challenges with onshore road transport and offshore crane-lifting/deck-loading limitations. Also, CT rotation, similar to drill pipe rotation, is not economically practical with current CT technologies. Technologies such as lubricants, vibratory and tractor tools are traditionally used to extend the CT reach. Although fluid hammer tools and tractors have extended the CT reasonable operational range significantly, they also increase circulating pressures and operational complexity. To reach a 10,000-ft lateral, metal-on-metal lubricants are required to work with the other friction reduction technologies. However, most of the lubricants currently used for well interventions perform worse in the field than at atmospheric conditions in the laboratory. In addition, field success can depend on factors besides the lubricant's friction reduction capability, such as its synergy with the other commonly circulated brines and fluid friction reducers or its regain permeability performance. Despite a broad use of the CT lubricants and their importance for the predictability and success of the well interventions in extended-reach wells, reliable and consistent field validation studies of their friction reduction capabilities are rare. Field performance data are mostly anecdotal or proprietary. In addition, there was no available literature review of the knowledge gained to date. Thus, a critical review of studies addressing the CT lubricants and scientific demonstrations of their field performance will indicate the challenges and limitations currently encountered in the field. This will hopefully trigger further research and development and best field practices for CT lubricants and well intervention operations in extended-reach wells.