Percussive-rotary Drilling Research Articles

Effect of Carbon Fiber and Potassium Titanate Whisker on the Mechanical and Impact Tribological Properties of Fe-Based Impregnated Diamond Bit Matrix.

Various contents of carbon fibers (CFs) and potassium titanate whiskers (PTWs) were added to an Fe-based impregnated diamond bit (IDB) matrix to enhance its adaptability to percussive-rotary drilling. A series of mechanical tests were conducted successively to find the effects of the reinforcing materials on the properties of the Fe-based IDB samples. Then, the fracture surfaces of the samples were analyzed via scanning electron microscopy (SEM) and energy-dispersive spectroscopy, and the worn surfaces and abrasive debris of the samples were analyzed using a laser scanning confocal microscope and SEM. The results show that both the CF and PTW can effectively improve the hardness and bending strength of an Fe-based IDB matrix, and those parameters reached their maximum values at the additive amount of 1 wt%. However, the CF had a better enhancement effect than the PTW. Furthermore, the CF improved the impact wear resistance of the IDB matrix, with a minimum wear rate of 2.38 g/min at the additive amount of 2 wt%. However, the PTW continuously weakened the impact wear resistance of the IDB matrix with increases in its content. Moreover, the morphologies of the worn surfaces indicated that the minimum roughness of the CF-reinforced IDB matrix decreased significantly to as low as 4.91 μm, which was 46.16% lower than that without CF, whereas the minimum roughness of the PTW-reinforced samples decreased by 11.31%. Meanwhile, the abrasive debris of the CF-reinforced samples was more uniform and continuous compared to that of the PTW-reinforced samples. Overall, the appropriate addition of CF or PTWs can enhance the mechanical properties of Fe-based IDB matrices, which can be used on different formations based on their impact wear resistance.

Rock strength identification while drilling based on percussive rotary drilling

Rock strength identification while drilling based on percussive rotary drilling

Simulation and Analysis of a Split Drill Bit for Pneumatic DTH Hammer Percussive Rotary Drilling

Reverse circulation impact drilling has the advantages of high drilling efficiency and less dust, which can effectively form holes in hard rock and gravel layer. As integral reverse circulation drill bits used in the conventional down-the-hole (DTH) hammers are only suitable for specific formations, the whole set of DTH hammer needs to be replaced when drilling different formations. In this paper, several types of split drill bits for different drilling technologies are designed. The flow field characteristics of one of the split drill bits is analyzed based on the computational fluid dynamics (CFD) method, with four technic parameters considered, which are input flow rate, number of inlet holes, angle of injection exhaust holes, and diameter of injection exhaust holes, respectively. Three parameters are selected as indicators to evaluate the rationality and performance of the split drill bit, which are injection exhaust hole outlet mass flow rate, ratio of the mass flow rate out of injection exhaust holes to the whole inlet mass flow rate, and maximum pressure at the upper end of the split drill bit. According to the CFD analysis results, the above four technic parameters influence the flow rate and pressure in different rules. Considering the injection capacity, pressure loss, and bit strength, inlet holes of 10, injection exhaust holes with an angle of 50°, and injection exhaust holes with a diameter of 12 mm are recommended to obtain ideal reverse circulation. Different types of split drill bits were manufactured, and drilling experiments were carried out in unconsolidated formations. The maximum drilling rate can reach 1.5 m/min in the drilling experiments. The split drill bit proposed in this paper exhibits excellent adaptability for reverse circulation drilling in loose formations.

Digital monitoring of rotary-percussive drilling with down-the-hole hammer for profiling weathered granitic ground

Rock and geotechnical engineering investigations involve drilling holes in ground with or without retrieving soil and rock samples to construct the subsurface ground profile. On the basis of an actual soil nailing drilling for a slope stability project in Hong Kong, this paper further develops the drilling process monitoring (DPM) method for digitally profiling the subsurface geomaterials of weathered granitic rocks using a compressed airflow driven percussive-rotary drilling machine with down-the-hole (DTH) hammer. Seven transducers are installed on the drilling machine and record the chuck displacement, DTH rotational speed, and five pressures from five compressed airflows in real-time series. The mechanism and operations of the drilling machine are elaborated in detail, which is essential for understanding and evaluating the drilling data. A MATLAB program is developed to automatically filter the recorded drilling data in time series and classify them into different drilling processes in sub-time series. These processes include penetration, push-in with or without rod, pull-back with or without rod, rod-tightening and rod-untightening. The drilling data are further reconstructed to plot the curve of drill-bit depth versus the net drilling time along each of the six drillholes. Each curve is found to contain multiple linear segments with a constant penetration rate, which implies a zone of homogenous geomaterial with different weathering grades. The effect from fluctuation of the applied pressures is evaluated quantitatively. Detailed analyses are presented for accurately assess and verify the underground profiling and strength in weathered granitic rock, which provided the basis of using DPM method to confidently assess drilling measurements to interpret the subsurface profile in real time.

Application of Percussive-Rotary Drilling Technology in Petroleum Drilling

Application of Percussive-Rotary Drilling Technology in Petroleum Drilling

Rock breaking mechanism in percussive drilling with the effect of high frequency torsional vibration

ABSTRACT High-frequency torsional vibration percussive drilling is considered a promising approach to improve drilling performance in deep hard formations, so studying its rock breaking mechanism and effect is the essential and basic issue. Compared with percussive-rotary drilling and high-pressure jet drilling, it can increase the service life of drilling tools and reduce drilling cost significantly. In this paper, based on elastic mechanics and principles of mechanical vibration, the cutting mechanism model of PDC (polycrystalline diamond compact) drill bit cutter and the amplitude–frequency characteristic model of steady-state vibration response of rock system are established, as well as the response characteristics of the rock system are also pointed out. Based on elastic–plastic mechanics and rock mechanics, Drucker–Prager criterion is adopted as the constitutive equation of rock, and plastic strain is used as the criterion of rock failure. Moreover, the model of rock damage failure is also established. The effect of exciting frequency on ROP (rate of penetration) has been studied by carrying out rock breaking test using high-frequency torsional vibration percussive drilling of PDC drill bit along with analyzing and handling test data. The study results show that when torsional vibration percussive frequency is approximately equal to inherent frequency of the rock, rock resonates with cutter, the plastic strain and ROP reach maximum, and drilling efficiency is the highest. The research results can help to deepen the understanding of the percussive drilling with high-frequency torsion vibration and provide useful insight into the design, application, and optimization of this new type of downhole tools in drilling engineering.

Multi-fractured stimulation technique of hydraulic fracturing assisted by the DTH-hammer-induced impact fractures

Hydraulic fracturing is one of the key technologies in geothermal development of hot-dry-rock (HDR) geothermal energy. How to reduce the fracturing pressure and enhance the fractures connectivity of HDR has become a hot issue. In this paper, we propose to use a down-the-hole (DTH) hammer to impact granite, which assist to create new artificial fractures similar to natural fractures or widen the existing fractures near the wellbore, consequently enhancing the connectivity of fractures during hydraulic fracturing. A series of experiments were conducted to verify the feasibility of this stimulation technique, including the observation and quantification of impact fractures, and the determination of fracturing pressure. In addition, numerical simulation of impact stress wave was carried out to explain the distribution of fractures. The results showed that the granite rock mass damage caused by percussive rotary drilling was about 5–7 times larger than that caused by diamond rotary drilling. Meanwhile, the distribution of fractures was characterized by regionalization, which was mainly attributed to the attenuation of impact stress wave, and the numerical results were consistent with the experimental observations. Laboratory experiment results of hydraulic fracturing indicated that the fracturing pressure of granite samples near the wellbore after percussive drilling had been greatly reduced, which was nearly 50% lower than that of conventional drilling. It indicates that the proposed multi-fractured stimulation technique of hydraulic fracturing assisted by the impact fractures induced by a DTH hammer can be a potential solution to solve the problems of hydraulic fracturing.

Experimental study of the dynamic indentation damage in thermally shocked granite

This paper presents an experimental procedure to study the effects of pre-existing cracks and damage on the rock behavior under dynamic indentation. To gain better understanding on the mechanism involved in percussive-rotary drilling procedure, a modified Split Hopkinson Pressure Bar device was used to carry out dynamic indentation tests, where rock drill buttons were impacted on rock samples with dimensions of 30 cm × 30 cm × 30 cm. Before the mechanical testing, the samples were thermally shocked using a plasma spray gun for periods of 3, 4, and 6 seconds. The plasma gun produces a powerful heat shocks on the rock sample, and even short exposures can change the surface structure of the samples and provide samples with different crack patterns and surface roughness for experimental testing. The effects of the heat shock damage on the dynamic indentation behavior of the rock were characterized with single- and triple-button indentation tests. The specific destruction work was used to characterize the effects of heat shocks on the material removal during dynamic indentation. The results show that the force-displacement response of the rock does not change much even if the rock surface is severely damaged by the heat shock, however, the destruction work decreases significantly. This means that the same loading removes more volume if the material surface is pre-damaged, and that the efficiency of the indentation process cannot be evaluated from the bit-rock interaction forces alone. The presented experimental framework can be a useful tool for the verification of numerical models where the rock microstructure and especially the microcracks are essential.

3D Numerical Simulation and Experiment Validation of Dynamic Damage Characteristics of Anisotropic Shale for Percussive-Rotary Drilling with a Full-Scale PDC Bit

The lower rate of penetration (ROP) is one of the key technical difficulties during drilling of shale reservoirs. Percussive-rotary drilling (PRD) is crucial for increasing ROP. One of the core problems of ROP optimization for PRD are the dynamic damage characteristics of rock fragmentation. By considering the dynamic drilling parameters, a new model for estimating the PRD with a full-scale polycrystalline diamond compact (PDC) bit is established. The mechanical parameters of shale are measured by a wave velocity method. Rock damage characteristics are simulated by using the finite element method. The numerical simulation model is verified by the actual drilling case in LMX shale reservoir in Sichuan (China). The results indicate that rock element damage occurs along the direction of maximum principal stress. The order of decreasing rock damage rate is impact-static load, static load and impact load. When the impact load has the same peak value, and the rock elements in contact with the cutters obtain more energy with load frequency increasing. The rock fragmentation efficiency under a sine wave is higher than rectangular and pulse waves. The rock can obtain more energy to be broken with the increasing impact load duration and peak values. When the impact-static load goes over the rock damage threshold value, the higher the peak value of the impact load is, the more energy the rock will obtain. The higher the lateral vibration amplitude of the drill bit, the lower the efficiency of rock fragmentation. Repetitions of drill bit axial vibration at one indentation point will reduce the ROP, and the axial vibration energy of the drill bit is consumed. Therefore, a small lateral movement and reasonable axial vibration frequency increase the rock breaking efficiency. The ROP was increased through the suppression of drill string and the application of vibration. The study results can be used in the optimization designs of bit trajectory and ROP for PRD tools.

On the mutual relations of drill monitoring variables and the drill control system in tunneling operations

The mutual relation between Measurement While Drilling (MWD) parameters in percussive-rotary drilling is investigated in order to limit the number of MWD variables, and to select the more significant ones, that are required for a sound rock mass characterization. Cross-correlation of the MWD signals is used to determine their relations, the analysis of which brings a thorough understanding of the way that the rig control system governs the different parameters. Data recorded from six drilling machines, working in semi-automatic and manual mode, on three different rock types with different logging interval, have been analyzed. The results point out the feed pressure as the lead parameter that drives the adjustment of the other variables to optimize the drilling, thus being the upfront response to variations in the rock mass. Control parameters that limit this adjustment to minimize disturbances during the operation are also discussed. Finally, the influence of the rock mass condition on the MWD parameters response is studied.

Fracture mechanism of air percussive rotary bit matrix based on impact stress wave theory

An air percussive rotary bit is a key component of air percussive rotary drilling technology, and its fracture failure seriously affects the safe operation and economic efficiency of drilling. This paper presents (1) theoretical analysis of the impact stress wave propagating in the air percussive rotary bit and effect of the stress wave on bit fracture and (2) finite element simulation study based on the stress wave theory which builds a model of the air hammer piston, drill and rock, defines material parameters, meshes and defines boundary conditions, clarifies propagation characteristics of the impact stress wave, analyzes stress characteristics of the bit matrix under different conditions (same drilling pressure and same piston speed, different drilling pressure and same piston speed and same drilling pressure and different piston speed) and determines the main factors of bit matrix fracture. The correctness of the theoretical analysis was verified with simulation results and fundamental ways of preventing bit fracture failure were proposed to provide a theoretical basis for the structural optimization design of a new bit. The results show that a bit section mutation is the root cause for the shock of the impact wave and the change in nature of the wave during propagation. The tensile wave is the root cause for bit matrix fracture, and a breakage is the most serious at stomatal interchanges. With increasing drilling pressure and piston speed, the rate of increase in the peak stress of the bit matrix increases, leading to early fatigue fracture of the bit matrix. The fracture of the bit matrix can be reduced, and the bit life can be extended by rationally designing the bit sectional structure parameters, ensuring that the bit withstands the effects of the compression wave so as to reduce the formation of a tensile wave, and rationally choosing drilling process parameters (such as drilling pressure and air pressure).

Design and analysis of a new down‐the‐hole electromagnetic hammer driven by tube linear motor

Percussive-rotary drilling is an effective method for the hard rock drilling. As hydraulic and pneumatic hammers have many problems especially in the deep core drilling, a new electromagnetic hammer driven by a tube linear motor is introduced in this study. The study mainly covers the mechanical structure and electromagnetic design of the hammer, respectively. Due to the direct use of electric power, the electromagnetic hammer has the advantage of high efficiency while it must meet the minimal percussive energy requirement under the limitation of drill pipe diameter. In this study, the validity of electromagnetic design is verified through the finite-element analysis software Ansoft/Maxwell 2D and numerical calculation of electromagnetic force. The working temperature in deep down-hole is relatively high, the influence of high temperature in deep hole on the electromagnetic thrust of the linear motor is then analysed. A motion model of linear motor hammer is established to calculate and analyse the impact power and frequency under different conditions. The results show that the performance of linear motor hammer can reach or even exceed the one of same diameter hydraulic hammer, especially in the low-frequency range. The prototype test also confirms the validity of the design.

Combined Percussive-Rotary Drilling to Increase Rate of Penetration and Life of Drill Bit in Drilling Hard Rock Formation

It is generally recognized that stick-slip motion of polycrystalline diamond compact (PDC) bits is responsible for the low rate of penetration (ROP) and premature wearing of drill bits while drilling hard rock formations. An innovative tool designated combined percussion jet (CPJ) was developed in this work to solve the problem. Because the tool generates both axial and torsional percussion, drilling with CPJ is referred as combined percussion-rotary drilling approach (CPRDA). The results of dynamics modeling and stress computation showed that the CPRDA induces more shear stresses in rock formations compared to axial percussion drilling and axial percussion-rotary drilling. The CPRDA was tested on two wells drilled in hard rock formation. The results demonstrated that the CPRDA increased ROP by 56.1-60.4% and extended drill bit life. However, for solving the high stress problem, the tool needs to be optimized further.

Stress-transfer in concrete encased and filled tube square columns employed in top-down construction

Top-down construction is a construction technique in which pit excavation and structure construction are conducted simultaneously. Reducing construction time and minimizing noise and vibration which affect neighboring structures, the technique is widely employed in constructing downtown structures. While H-steel columns have been commonly used as core columns, concrete filled steel tube (CFT) columns are at the center of attention because the latter have less axial directionality and greater cross-sectional efficiency than the former. When compared with circular CFT columns, square CFT columns are more easily connected to the floor structure and the area of percussion rotary drilling (PRD) is smaller. For this reason, square CFT columns are used as core columns of concrete encased and filled square (CET) columns in underground floors. However, studies on the structural behavior and concrete stress transfer of CET columns have not been conducted. Since concrete is cast according to construction sequence, checking the stress of concrete inside the core columns and the stress of covering concrete is essential. This paper presents the results of structural tests and analyses conducted to evaluate the usability and safety of CET columns in top-down construction where CFT columns are used as core columns. Parameters in the tests are loading condition, concrete strength and covering depth. The compressive load capacity and failure behavior of specimens are evaluated. In addition, 2 cases of field application of CET columns in underground floors are analyzed.

Vertical section construction of wells at Kuyumbinsky oil field via percussive-rotary drilling with DTH hammer.

The article presents the analysis of sequential use of mobile percussive-rotary drilling sets with DTH hammer and bottom-hole cleaning by foam mud in construction of vertical sections along with at Kuyumbinsky oil field. On the basis of the analysis, an engineering solution is proposed to prevent disastrous mud loss that is the key factor of efficiency in implementation of resource-saving technologies.

Prospects for directional drilling in hard rocks

The study is focused on the existing methods of long directional borehole drilling in hard rocks in high-viscous oil and natural bitumen field development. The authors suggest improving the hard rock mass drilling process by combining percussion–rotary drilling and positioning systems.

Design and feasibility analysis of a fluidic jet oscillator with application to horizontal directional well drilling

The drilling problems on how to reduce the drag and torque in horizontal directional drilling process have become the focused issues for the directional drilling researches. With regard to the heavy drag and torque of drilling tool, low drilling efficiency and high occurrence of drilling accidents, a fluidic jet oscillator is novelly proposed and designed on basis of the combination between percussive rotary drilling and friction reduction technology. In order to avoid the stand pipe pressure while drilling, the feasibility and pressure loss of the oscillator have been acquired by numerical simulations and experimental tests in condition of various pumped volumetric flow rates. In conclusion, the numerical simulation results agreed well with the corresponding experimental tests. The pressure loss of fluidic jet oscillator is almost exponentially varying with the input flow rates. The minimum pressure loss of fluidic jet oscillator is 1.7 MPa while pumped volumetric flow rate is 10 L/s, and the maximum pressure is 5.65 MPa while the flow rates is 18 L/s, which is permissible in horizontal directional well drilling. Allowing for the limitation of pressure loss in directional drilling, the design of fluidic jet oscillator is feasible to horizontal directional drilling to reduce friction and drag torque, which contributes to improving the penetration rate and reservoir development capacity in oil and natural gas well drilling.

Drilling bits in percussive-rotary drilling technology (down the hole DTH)

Drilling bits in percussive-rotary drilling technology (down the hole DTH)

Friction-driven vibro-impact system for percussive-rotary drilling: A numerical study of the system dynamics

Stick—slip-induced vibration in drilling has a detrimental effect on the drilling system and may lead to the failure of the drill string. This study is a further development of a friction-driven vibro-impact system which was investigated previously. The system used the stick—slip properties to generate a vibratory motion of a hammer that collides with the bit. The previous study focused on the influence of the friction on the response of the system without impacts. This paper investigates the full dynamic response of the model including friction and impact. Numerical bifurcation analysis of the system is undertaken to establish various motions and dynamical changes. This study focuses on the system performance outside the stable interval identified in the earlier investigation. The response of the system is illustrated along with the phase portraits.

Numerical bifurcation analysis of a friction-driven vibro-impact system

The dynamic response of a friction-driven vibro-impact system is presented. The system has two degrees-of-freedom with discontinuous nonlinear forces applied (dry friction and impact). This new self-exciting system tends to self-synchronisation with a potential industrial application in the field of percussive-rotary drilling. Friction-induced vibration is used as the source of excitation of impacts, which in turn influences the parameters of stick–slip motion. The friction force is defined as a nonlinear function of the drive velocity and allows for self-excitation. The dynamic coupling of vibro-impact action with the stick–slip process provides entirely new adaptive features important for practical application. The self-exciting process (stick–slip) depends on the mechanical properties of the medium interacting with the device. In this paper, which is the initial stage of a series of investigations into the full dynamic response of the system for scientific and engineering interests, the dynamic behaviour of the system motion without impact is presented. The equations of motion are solved numerically and the analysis is focused on the effects that discontinuity induced bifurcations have on the system. Within the scope of the assumptions made, a bifurcation diagram provides a further understanding of the system dynamic behaviour. Self-excitation and self-synchronisation using a single drive has some advantages that can be exploited in oil drilling applications.