Down-the-hole Hammer Research Articles

Dynamic analysis and experimental study of Down-the-Hole hammer based on DEM-MBD method

Pneumatic DTH(Down-The-Hole) hammer impact-rotary-compaction drilling is a well-established technology widely used in foundation engineering. This technique combines the advantages of impact rotary drilling and compaction drilling, making its working mechanism and fracturing process more complex. First, the dynamic differential equations for the DTH hammer piston and the coupled longitudinal vibration partial differential control equations for the DTH hammer and the soil stratum were established. The dynamic working characteristic curve of the piston was then obtained using the finite difference method(FDM).Subsequently, the DEM-MBD method was employed to compare the drilling efficiency of three types of drill bits—single-helix, multi-helix, and stepped bits—across three diameter specifications (Φ108, Φ135, Φ216) in three distinct strata: clay, pebble, and silty sand. The drilling efficiency of the multi-spiral bit was on average 11% and 21% higher than that of the single-spiral and stepped bits. From a micromechanical perspective, the shear failure effect of the drill bit on the soil was analyzed. The axial force of the drill bit (Z-axis) remained essentially consistent. Using the Y-axis as an example, 6% of the shear force for the single-helix bit falls within the 300–500N range, while 31% of the shear force for the multi-helix bit lies within the same range. Field tests demonstrated that the drilling efficiency and penetration effects simulated using the DEM-MBD method aligned with the actual test results, confirming the accuracy of this method.

Anti-Vibration Method for the Near-Bit Measurement While Drilling of Pneumatic Down-the-Hole Hammer Drilling

Pneumatic down-the-hole (DTH) hammer drilling technology has been used extensively in the fields of heat reservoir exploitation and geological exploration owing to its advantages of high efficiency and low pollution. However, the vibration near the bit is up to 40 g while DTH hammer drilling, which significantly affects the performance and longevity of the near-bit measurement while drilling (MWD). To enhance the environmental adaptability of the near-bit MWD in pneumatic DTH operations, a design method for a vibration-damping system based on the parameter optimization of a non-dominated sorting genetic algorithm II (NSGA-II) is proposed in this study. First, the whole structure of the near-bit MWD is designed, including the MWD sub-shell, sensors, measurement circuits, batteries, and connecting structures (the circuit unit). Secondly, this study analyzes the vibration characteristics of the pneumatic DTH hammer near the bit. According to the damping structure, the vibration response model for the circuit unit and the damping model are established. Thirdly, NSGA-II is employed to optimize the parameters of the damping model in terms of the low-frequency, high-intensity vibration characteristics near the bit in pneumatic DTH operations, thereby devising a damping scheme tailored to the unique conditions of DTH hammer drilling. Finally, vibration experiments were conducted to verify the effectiveness of the vibration-damping device. The experimental results indicate that within the vibration frequency range of 5–20 Hz and vibration level of 10–40 g, the peak attenuation rate of the circuit unit is more than 86.446%, and the improvement rate of the vibration stability of the system is more than 75.214%; the anti-vibration performance of the near-bit MWD system in DTH hammer drilling is improved remarkably. This study provides strong technical support for the stability of MWD equipment under such special working conditions. It has broad engineering application prospects.

Down-the-hole drilling construction acoustic research

nd The Alaska Department of Transportation and Public Faculties (DOT&PF) is conducting research to characterize underwater sounds from down-the-hole (DTH) drilling activities. This method of drilling is commonly used to drill holes through hard or rock substrates to support piles or tensions anchors for piles. A pneumatic DTH hammer is driven by pressured air coming from an air compressor that provides the energy to power the percussion piston that hits the drill bit with a specific impact frequency and energy to break the rock and advanced the hole. This activity produces continuous and impulsive sounds that affect marine mammals. Pile installation in marine environments typically uses vibratory drivers and/or impact pile driving. Underwater sounds from these activities have been well documented in publications, for example, there are compendiums prepared by Caltrans, and the U.S. Navy, along with many project-specific compliance reports submitted to resource agencies. However, there is limited acoustical data available for DTH activities, as the first published measurements were only made recently. The National Marine Fisheries Services (NMFS) recognizes the acoustical issues with DTH noise and is encouraging the collection and dissemination of additional sound data. This paper describes the research conducted and available DTH acoustic data.

Experimental and Numerical Simulation Study on the Mechanism of Fracture-Increasing and Permeability-Increasing in Granite Pore Walls by the Air DTH Hammer Percussion Drilling

Air DTH (Down-The-Hole) hammer percussion drilling (vibration percussion drilling) has proven to be a highly efficient geothermal drilling technique, and percussion fractures near the wellbore benefit geothermal energy development in many ways (such as hydraulic fracturing, perforation, etc.). However, no research has been done on the mechanism of fracture-increasing and permeation-increasing in granite pore walls by air DTH hammer percussion drilling. This article: (1) using an air drilling test device, an air DTH hammer whole bit impact rock fragmentation test was conducted on granite in an atmospheric environment; (2) dyeing experiments, CT scanning, and 3D reconstruction modeling were used to characterize and identify wellbore cracks; (3) research the strength, porosity, and permeability changes of granite wellbore through mechanical and permeability testing experiments; and (4) numerical simulation of impact stress waves using particle flow code (PFC) 6.0 software to demonstrate the rationality of impact experimental results. The results show that the air DTH hammer impact can induce micro-cracks in the wellbore, and the distribution of cracks is regionalized, mainly due to the attenuation of the impact stress wave. The numerical results are consistent with the experimental results. The average strength of granite decreased by 16.5%, the average porosity increased by 9.5%, the average permeability increased by 63.3%, the porosity increased from 0.0025% to 0.03%, and the porosity increased by about 12 times under the air DTH Hammer percussion drilling. The above results provide the theoretical basis and experimental proof for the ability of air DTH hammer drilling to produce wellbore cracks and improve wellbore permeability. The presented experimental results can be a useful reference for building numerical models.

Structure optimization of DTH hammer piston based on RBF neural network and WSO algorithm

To address the issue of piston fracture due to insufficient strength in the Down-The-Hole (DTH) hammer. The effect of the pressure state of the gas chamber on the piston motion is considered. A piston motion model is established based on the steady flow energy equation and the working principle of the piston. The finite element method is used to analyze the dynamic response of the piston during the impact of the drill bit. RBF neural network is employed to construct a surrogate model for the relationship between piston structural parameters (front-end diameter, front-end length, and center bore) and piston strength and performance (impact energy, frequency, and gas consumption). By combining this model with the white shark optimization search algorithm, the design of the DTH hammer’s piston structure parameters is optimized. The minimum piston mass is the objective function. Impact energy, frequency, air consumption and stress are constraint factors. The effect of piston life is considered while meeting rock drilling efficiency. The optimization results show that the stresses in the optimized piston structure are reduced by 13%. The proposed RBF performance prediction model combined with the optimal search algorithm can significantly improve the optimization efficiency.

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.

Experimental investigation and CFD simulation of multiphase flow behavior in air reverse circulation drilling

In reverse circulation (RC) down-the-hole hammer (DTH) drilling, hole cleaning has a great impact on reducing accidents and improving efficiency. There is a technical difficulty in RC drilling to select the minimum air influx while keeping cuttings discharged smoothly according to different water invasion conditions. A novel experimental device was used to study the physics of multiphase flow associated with the cleaning process. Air influx required for cuttings transport was measured under different conditions in Rate of Penetration (ROP), cuttings diameter, and water yield, and influence among three factors were revealed. Furthermore, the computational fluid dynamic (CFD) method simulated and analyzed multiphase flow behavior. The results show that factors of ROP, cuttings diameter, and water yield obviously impact minimum air influx during the cuttings transport process. The accuracy and credibility of CFD method have been confirmed on account of reasonable agreement with experimental data (a relative error of less than 14% is achieved). The CFD simulation of multiphase transport reveals that cuttings velocity and pressure drop could be influenced by ROP, cuttings diameter, and water yield. Therefore, these factors should be carefully characterized during air RC drilling and hole cleaning to maximize the efficiency of cuttings transport.

Performance of large-diameter pneumatic down-the-hole (DTH) hammers: A focus on influences of the hammer structure

Pneumatic down-the-hole (DTH) hammer has been extensively used in air drillings through hard and ultra-hard geological formations. Numerical modeling can offer close observation on the working behaviors by visualizing internal pressure status as well as provide reliable performance predictions for large-diameter DTH hammers to which conventional empirical and experimental approaches cannot be applied. In this study, CFD simulations coupled with dynamic meshing are utilized to simulate the air flow and piston movement inside the large-diameter DTH hammers. The numerical modeling scheme is verified against a theoretical model published in literature. Effects of structural parameters on hammer performance, including piston mass, piston upper-end diameter, piston groove diameter, and lengths of intake and exhaust stroke in both front and rear chambers, are analyzed in detail by virtue of sets of numerical simulations. The simulations suggest that changing the intake stroke of front chamber has a negligible influence on hammer performance while increasing the piston groove would lower all the four indicators of hammer performance, including impact energy, impact frequency, maximum stroke, and air consumption rate. Changing the other structural parameters demonstrates mixed effects on the performance indicators. Based on the numerical simulations, a large GQ-400 DTH hammer has been designed for reduced air consumption rate and tested in a field drilling practice. The air drilling test with the designed hammer provided a penetration rate 1.7 times faster than that of conventional mud drilling.

Mechanical Response of Stress Wave Attenuator With Layered Structure Under Impact Load: Experimental and Numerical Studies

Abstract The fluidic down-the-hole (DTH) hammer drilling is generally regarded as one of the best means for hot dry rock (HDR) drilling. The fluid oscillator, as the core part of the fluidic DTH hammer, is prone to fracture when subjected to impact loads due to its brittle characteristics. Therefore, a steel-layered structure with different contact areas is developed as a stress wave attenuator to protect the fluid oscillator for the DTH hammer under high-temperature drilling conditions. In this paper, the stress wave attenuation performance with different steel-layered structures is analyzed based on the split Hopkinson pressure bar (SHPB) technique. The effects of contact area ratio, the orientation of contact surfaces, and number of layers on the stress wave attenuation are investigated by numerical simulations and laboratory tests. It is found that the attenuation ratios in stress amplitude and impact energy gradually increased with the increase of the contact area ratio. Besides, the orientation of contact surfaces has a significant influence on the attenuation effect. For the layered structure with a two-layer object part, the maximum attenuation ratios of stress amplitude and impact energy are 62.4% and 79.6%, respectively, when the included angle between the two convex structures is increased to 90 deg. Additionally, the attenuation ratio of the layered structure can be improved by increasing the number of layers. The results demonstrate that the stress wave attenuator with layered structures has great potential for brittle materials protection against impact loads.

On the switching mechanisms and output response of an output-fed fluidic oscillator for fluidic hammer over full stroke

Owing to the complex interaction between the output-fed fluidic oscillator and the moving part of the fluidic down-the-hole (DTH) hammer, the jet switching mechanisms and output response are not clear. Focusing on an output-fed fluidic oscillator, we systematically analyzed the switching mechanisms and output response based on a newly designed fluidic DTH hammer over full stroke. The results show that the oscillation frequency depends on the load characteristic and varies more or less in direct proportion with the Reynolds number. The impact feedback is optional rather than necessary for the switching of the main jet in the output-fed fluidic oscillator. When the partial stroke disappears, the output-fed fluidic oscillator operates under a constant Strouhal number.

Effect of control flow on main jet switching for single and double feedback channels fluidic oscillator

The fluidic down-the-hole (DTH) hammer controlled by the single feedback channel fluidic oscillator (SFO) has been to be effective in hard rock drilling. However, the unstable motion of the piston limits the performance of the fluidic DTH hammer in some cases. In this paper, a double feedback channels fluidic oscillator (DFO) is proposed to improve the smoothness of the piston motion, and the relationship between the control flow and main jet is observed through numerical simulation. The results show that the flow rate and symmetry of the control flow are the main factors affecting the switching of the main jet and the smoothness of the piston motion. The elevation of the flow rate of control flow shortens the switching time of the main jet. The symmetrical control flow of DFO is beneficial to the stable growth of the vortex and the wall attachment of the main jet. Compared with the SFO, the flow rate at the control nozzle of DFO is increased by 15.8%, and the switching time of the main jet is reduced by 25%. The bench test results show that the pause time is decreased by 61.4% and the impact frequency is raised by 38%.

Underwater sound characteristics from down-the-hole pile drilling for a coastal construction activity

Sound generated by pile installation using a down-the-hole (DTH) hammer is not well documented and differs in character from sound generated using conventional impact or vibratory hammers. This study describes underwater acoustic characteristics from DTH pile drilling during the installation of 0.84-m shafts within 1.22-m steel piles associated with a cruise ship terminal construction in Ward Cove, Alaska. The median single-strike sound exposure levels measured at 10 m were 138 and 142 dB re 1 μPa2s for each of the two piles, with cumulative sound exposure levels of 188 and 193 dB re 1 μPa2s at 10 m, respectively. The sound levels measured in this study were significantly lower than previous measurements of DTH pile driving, and the sound is determined to be less impulsive in this study as compared previous studies. These differences likely result from fact that the DTH hammer used at Wade Cove did not make direct contact with the pile, as had been the case in previous studies. Further research is needed to investigate DTH piling techniques and associated sound-generating mechanisms and to differentiate the various impulsive structures from anthropogenic underwater noise in general.

Design optimization and feasibility analysis of pneumatic DTH Hammer with self-rotation bit

This paper presents a novel pneumatic Down-The-Hole (DTH) hammer with self-rotation bit used for rock drilling, and the mechanical structure and working principle are mainly covered. A unique mechanism with ratchet and pawl incorporated in pneumatic DTH hammer is proposed for percussion-rotation drilling to break rock. The drill bit can rotate while the drill pipe stays still because of the structure design and reduces the friction between the drill pipe and borehole. Firstly, the rationality of mechanical invention is verified via the finite-element software ANSYS and the numerical simulation of impact dynamics. Moreover, the energy transfer regulation is revealed in the impact process under differential final impact velocity, which can help practical experience in mechanical design. Finally, based on the experimental study on the novel hammer, we found that its function can satisfy the requirement, as well as overall performance, was improved.

Acoustic characteristics from an in-water down-the-hole pile drilling activity.

Sound generated by pile installation using a down-the-hole (DTH) hammer is not well documented and differs in character from sound generated by conventional impact and vibratory pile driving. This paper describes underwater acoustic characteristics from DTH pile drilling during the installation of 0.84-m shafts within 1.22-m steel piles in Ketchikan, Alaska. The median single-strike sound exposure levels were 138 and 142 dB re 1 μPa2s at 10 m for each of the two piles, with cumulative sound exposure levels of 185 and 193 dB re 1 μPa2s at 10 m, respectively. The sound levels measured at Ketchikan were significantly lower than previous studies, and the sound was determined to be non-impulsive in this study as compared to impulsive in previous studies. These differences likely result from the DTH hammer not making direct contact with the pile, as had been the case in previous studies. Therefore, we suggest using the term DTH pile drilling to distinguish from DTH pile driving when the hammer strikes the pile. Further research is needed to investigate DTH piling techniques and associated sound-generating mechanisms and to differentiate the various types of sound emitted, which has important implications for the underwater sound regulatory community.

Study on the response of the Steel / Poly-ether-ether-ketone layered protective structure for a fluidic DTH hammer

The impedance-graded material (IGM) systems can be used as a protective structure to attenuate the stress. Due to the fluidic oscillator of the down-the-hole (DTH) hammer made by cemented carbide was broken during the test, it is urgent to design a protective structure to decay the stress transferred to the fluidic oscillator. This paper studied the stress attenuation effect of Steel-Poly-ether-ether-ketone (PEEK) -layered-protective-structure (SPLPS) subjected to low-velocity impact loadings. The contact state of samples is measured by pressure-sensitive test paper. The experiments were carried out by the split Hopkinson pressure bar (SHPB) method. The stress attenuation effect of 5-layer SPLPS was tested at the different impact velocities. A three-dimensional numerical simulation model is established to simulate the SHPB experiments with the same boundary conditions. The stress attenuation effect of different layers of SPLPS is compared by numerical simulation. Besides, the influence of the thickness of steel-sheet and PEEK-sheet is investigated. And the SPLPS made for the DTH hammer has been tested in the hot dry rock drilling field. The results show that the data of numerical simulation are consistent with the SHPB experimental results. It is found that the different impact velocities do not change the contact state of the sample's end face. The stress attenuation ratio of 5-layer SPLPS in numerical simulation and experiment is 77%. The attenuation ratio increases rapidly when the number of SPLPS layers changes from 1 to 4. When the number of SPLPS layers exceed 4, the attenuation ratio does not increase significantly. Additionally, the thickness of 6 mm and 8 mm are suitable parameters for the SPLPS. The field test has proved that the SPLPS could protect the fluidic oscillator effectively. • A Steel-Poly-ether-ether-ketone (PEEK) layered protective structure (SPLPS) is designed for a fluidic DTH hammer. • The stress attenuation ratio of the 5-layer SPLPS is up to 77% under the low-velocity impact. • The SPLPS have the advantages of simple structure, high service life and low cost for engineering application.

Acoustic characteristics from an in-water down-the-hole pile drilling activity

Sound generated by pile installation using a down-the-hole (DTH) hammer is not well documented and differs in character from sound generated by conventional impact and vibratory pile driving. This paper describes underwater acoustic characteristics from DTH pile drilling during the installation of 0.84-m shafts within 1.22-m steel piles in Ketchikan, Alaska. The median single-strike sound exposure levels measured at 10 m were 138 and 142 dB re 1 μPa2 s for each of the two piles, with cumulative sound exposure levels of 188 and 193 dB re 1 μPa2 s at 10 m, respectively. The sound levels measured at Ketchikan were significantly lower than previous studies, and the sound is determined to be non-impulsive in this study as compared to impulsive in the previous studies. These differences likely result from fact that the DTH hammer used at Ketchikan did not make direct contact with the pile, as had been the case in previous studies. Further research is needed to investigate DTH piling techniques and associated sound-generating mechanisms, and to differentiate the various types of sound emitted.

Numerical and Experimental Study on the Effects of Rheological Behavior of Drilling Fluid on the Performance of the Fluidic Down-the-Hole Hammer

Summary In the field of oil and gas exploration, the fluidic down-the-hole (DTH) hammer has frequently been used to solve the challenges associated with hard rock drilling and excessive friction along the drillstring. Appropriate performance prediction for drilling tools is particularly important for the drilling operation. Previous experiments showed that the performance prediction scheme determined by the water was not accurate for fluidic DTH hammer driven by mud, which is a typical pseudoplastic power-law fluid. Based on the results, compared with water, the rheological behavior of the pseudoplastic power-law fluid can be significant for the flow behavior in the fluidic oscillator with a lower supply flow rate. However, for a normal or higher level of supply flow rate, because of the shear diluting effect of the pseudoplastic power-law fluid, the influence of rheology behavior of drilling mud on the performance of fluidic DTH hammer was not apparent. The temperature of the drilling fluid and barite weighting agent can also affect the performance of the fluidic DTH hammer by affecting the rheological properties of the drilling mud. In this paper, numerical simulation and experiments are used for qualitative discussion and conclusion verification, respectively.

Design Optimization and Performance Analysis of the Pneumatic DTH Hammer with Self-Propelled Round Bit

Although pneumatic down-the-hole (DTH) hammers have good performance of high penetration rate and minimal deviation tendency in the vertical section of oil and gas wells, they have not been successfully used in directional drilling due to drill tool wear and wellbore disturbance. Herein, we developed a novel type of pneumatic DTH hammer with a self-propelled round bit to overcome the technical difficulties of directional drilling. Nonlinear dynamic modeling developed by the authors was used to analyze the working principle and performance of the novel DTH hammer. The kinematics and dynamics simulation of this hammer were carried out using MATLAB language, and the motion law of the piston was revealed. The performance of the novel hammer was numerically simulated and evaluated by considering fluctuations of the front and rear chamber pressure, impact energy, acceleration, and frequency. The results show that our novel DTH hammer’s working principle is feasible and has an adequate structural design. The simulation results demonstrate reasonable design parameters. Compared to the numerical results for conventional DTH hammers, the velocity and acceleration of the piston of the novel hammer changed smoothly. The frequency was slightly higher than that of conventional hammers, while other parameters were nearly equal. The novel DTH hammer can be used in directional drilling, trenchless drilling, and seabed sampling drilling.

Drill rig with a down-the-hole hammer for regulating the drilling rate by changing the air flow

At present, a lack of efficiency of the rotary drilling intensification can be observed at mining enterprises that employ drill rigs. Due to this, we propose to enhance the rotary drilling using shock loads by installing a down-the-hole (DTH) hammer into the drill string of the rig for roller drilling, for instance, SBSh-250. The paper discusses the issue related to an increase in the drilling rate using a drill rig with DTH hammer and adjustable valve that regulates the air flow. The paper considers different types of drilling in engineering and geological surveys. Rocks were sampled for various types of drilling. The physical and mechanical properties of rocks, which affect the drilling process, were considered. The study focuses on a significant increase in the drilling rate through an increase in the impact power. As part of the study, an improved drill rig with a down-the-hole hammer controlled by a radio receiver was developed. When analyzing the physical and mechanical properties, it was shown that the control of DTH hammer operation enables fast drilling of complex rocks without reducing the drilling rate. An increase in the drilling rate of self-propelled equipment using DTH hammers installed above the drill bit will reduce the cost of drilling and extend the service life of the working tool.

Influence of water-based drilling fluids on the performance of the fluidic down-the-hole hammer

Fluidic down-the-hole (DTH) hammer is a recently explored percussion drilling tool for the production of boreholes in hard rock. It has been proven efficient for exploration core drilling, geothermal drilling, and oil and gas drilling. Previous studies of this hammer have concentrated on its performance operating with clear water rather than water-based drilling fluids with additives. As the first step to filling the gap of knowledge in this area, this study was designed to explore only the performance of an SC86–H fluidic DTH hammer driven by water-based drilling fluids with various temperatures and different contents of bentonite and barite. Such performance was characterized in terms of output power, motion characteristic and operating pressure drop, and compared with that driven by water. The results showed that the output power of the SC86–H type hammer driven by drilling fluids with bentonite content <3% was better than that driven by water thanks to the lubrication effect in the fit clearance, whereas with bentonite content ≥3%, its output power was in the range or below that driven by water due to the elevation of the hydraulic losses and the frictional drag. Its operating pressure drop is only insignificantly influenced by the bentonite content. As the weighting agents in the drilling fluids, the barite particles impeded the smooth motion of the piston. However, the increased impact energy and output power can entirely offset the disadvantage mentioned above. Temperature affects the performance of the SC86–H type hammer by influencing the viscosity and density of the drilling fluids. Some optimal schemes are suggested for the rational design and application of the fluidic DTH hammer in practice. In summary, the SC86–H type hammer operated well in the drilling fluids with realistic fluid power levels. It means that the fluidic DTH hammer has good adaptation and robustness, which is favorable to practical application.