Drilling Velocity Research Articles

Study on the impact of weaving patterns of vibrating screen mesh on the performance of fluid flow through moving screens

Screen is a core component of the linear vibrating screen and is closely linked to the efficiency of drilling fluid recovery. This study aims to analyze the impact of different vibration frequencies and amplitudes on the fluid flow performance through screen with different weaving patterns. Analysis reveals that when the motion direction of the screen is opposite to the flow direction of the drilling fluid, higher screen velocity corresponds to increased drilling fluid permeation velocity and reduced pressure. Plain weave screen exhibits the highest fluid permeation velocity, maintaining the lowest negative pressure. Vortices concentrate mainly around the screen wires at the back of the screen, with herringbone twill weave screen showing improved vortex distribution compared to plain weave screen. Increasing vibration amplitude and frequency enhances screen motion, amplifying variations in pressure and pressure drop coefficients during the motion cycle. With increased amplitude and frequency, the average pressure drop coefficient of the screen rises, making it more challenging for drilling fluid to permeate through the screen. Herringbone twill weave screen demonstrate lower pressure drop coefficients than plain and twill weave screen, indicating superior drilling fluid permeation performance. Field experiments confirm that, compared to plain weave screen, drilling fluid filtered through herringbone twill weave screen results in significantly lower water content in cuttings. The findings of this study provide theoretical insights for the analysis and design of linear vibrating screen meshes in drilling fluid applications.

Direct assessment of the hydraulic structure of the plate boundary at the toe of the Nankai accretionary prism

SUMMARY The Nankai Trough is a locus of slow slip, low-frequency earthquakes, and large magnitude (Mw > 8) earthquakes. It is usually assumed that high pore pressure contributes substantially to earthquake dynamics. Hence, a thorough understanding of the hydraulic regime of the Nankai accretionary prism is needed to understand this diversity of behaviours. We focus on the toe of the accretionary prism by studying data from Hole C0024A, part of the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) project, that intersected the décollement at 813 m below seafloor (mbsf) about 3 km away from the trench. We contribute to this understanding by innovatively integrating drilling and logging data to derive high-resolution hydraulic profiles along the borehole. A quantitative re-analysis of the variation in the downhole annular pressure monitored during drilling show localized fluid flow from the formation to the borehole in excess of 0.05 m3 s−1, especially in the damage zones at the footwall of the décollement. To validate the fluid flow profile, pore pressure was estimated independently from empirical relationships between pore pressure, porosity and P-wave velocity, obtained from consolidation experiments and Eaton-type methods based on drilling or sonic velocity data. The formation fluids are becoming significantly overpressurized with depth in the few hundred metres above décollement. The hydraulic profile suggests that the core of the décollement acts as a barrier inhibiting upward fluid convection, whereas the damage zone acts as an efficient longitudinal channel able to diffuse high pressure from the deeper part of the subduction.

Stick–Slip Vibration Characteristics Study of the Drill String Based on PID Controller

In order to address the issue of drill string stick–slip vibration, which leads to drill bit wear and reduces the drilling velocity, we conducted a study on the characteristics of stick–slip vibration using a proportional-integral-derivative (PID) controller. By applying the principles of rigid body mechanics, we established a two-degree-of-freedom torsional dynamics equation and derived the first-order differential dynamics equation for the drill string. Subsequently, we designed a PID controller and obtained an equation for the control of stick–slip vibration. The research findings indicate that variations in the difference between the static and dynamic friction coefficients directly impact the nature of the limit cycles in the phase plane. As this difference decreases, the limit cycle narrows and the stick–slip vibrations weaken progressively. When the static and dynamic friction coefficients are equalized, no stick–slip vibrations occur within the drill string. The implementation of PID control effectively manages stick–slip vibrations in the drill string, with greater efficiency observed in controlling the turntable velocity compared to the drill bit velocity. This research provides valuable insights for the development of control strategies aimed at mitigating stick–slip vibrations in drilling engineering applications, thereby facilitating the efficient and safe extraction of oil and gas resources.

Transportation of cuttings by drilling mud in horizontal wells. Part 2. Numerical results of drilling at optimal rheological properties of mud

The relevance. Ensuring technological equipment operation efficiency when drilling wells with an arbitrary orientation of their wellbores. In particular, the search for productive hydrocarbon reservoirs requires drilling deeper wells with extended horizontal sections, for which the removal of the cuttings bed is the key problem of modern drilling. The aim. Study the features and establish the patterns of cuttings movement through the annulus eccentric space formed by a drill string and well walls under various modes (in-situ) and drilling conditions within the framework of modern mathematical models of hydrodynamics, numerical algorithms and approaches implemented in ANSYS CFD. Optimize the parameters that determine drilling, such as an inclination angle, mass-average velocity and morphology of the inlet rheologically complex viscous flow to form the maximum allowable drilling velocity for various combinations of mud effective viscosity and mixture flow rate. Give practical recommendations for engineers to reduce time, costs and material resources for maintenance and optimization of well cleaning. The object. A well with an eccentric core and an extended horizontal section operating in modes and conditions close to real drilling. The methods. Complex of physical and mathematical analysis and numerical modeling of hydrodynamics and mass transfer in homogeneous and heterogeneous continuous media. The media were widely tested on the class of internal rheological complex flows, the verification of which was carried out under appropriate conditions, performed by other authors when solving problems of drilling and cleaning wells. The results. The paper presents the results of a numerical study of hydrodynamics of a dispersed flow of a rheological complex viscous mixture of a drilling fluid with the properties of a Herschel–Bulkley type fluid and sand particles in wells with an arbitrary generatrix of its wellbore in an eccentric space. The results are required to clarify the features that accompany direct-flow and swirling flow (the moving wall method), identify the patterns in such modes, accounting for which allows for effective cleaning of the annulus. The calculations were performed within the framework of modern mathematical models of the RANS-method and the Euler–Lagrangian approach to describing the motion of heterogeneous media, implemented in the ANSYS CFD software and efficient numerical algorithms for determining intra- and interfacial processes of mass and momentum transfer in mixtures. The authors have determined that when drilling a vertical section, the most effective parameter in terms of cleaning control is the effective viscosity of the mud; the most problematic configurations for cleaning are wells with sloping sections at angles close to the vertical. When drilling a horizontal section, the eccentricity of the drill string creates “the dead” zone of flow and complicates cleaning. This zone should be removed by creating swirling flow conditions through relatively weak rotation of a drill string (30–60 rpm). When drilling inclined sections, it is necessary to reduce a solution viscosity (preferably to the level of fresh water) and increase the flow rate (in this case, to 2 m/s or higher). When drilling a horizontal section, a mud with a viscosity close to fresh water is recommended at flow rates of about 2 m/s (or 640 gpm) at the well inlet and a maximum drilling velocity of 9 m/h.

Numerical study of temperature and pressure effects of a yield-power law fluid flow on frictional pressure losses for laminar and turbulent regimes

The effective determination of pressure losses depends on accurate knowledge of the drilling fluid rheology. As the fluid circulates deeper around the wellbore, its rheological behavior undergoes significant alterations due to the variations in downhole conditions encountered. The present study investigates the effects of the rheological properties of Yield-power law fluid at various pressures and temperatures on annular pressure losses and velocity profiles. Simulations were performed using Computational Fluid Dynamics to examine the fluid flow in turbulent and laminar regimes. Comparison between numerical, experimental and slot approximation model results showed a good agreement. Results indicated that pressure losses have reduced in both regimes with increasing temperature, at a constant pressure. However the pressure has the opposite effect at a constant temperature. For a drilling fluid flow velocity of 1 m/s, the elevation of temperature from 25 °C to 90 °C, decreases the pressure drop gradient by (31% to 48%) at low and high- pressure conditions respectively. Whereas, the influence of increasing pressure on pressure losses is more apparent at 25 °C. Earlier transition from laminar to turbulent is observed with temperature rise. Therefore, the temperature effect on pressure losses in the turbulent region; is shown for different Generalized Reynolds numbers.

Overpressure characteristics and geological origin of the paleogene in Baiyun Sag, Pearl River Mouth Basin

The accurate understanding of the origin of overpressure is the basis of formation pressure research and the core work of determining the distribution of formation pore pressure in drilling design. The deep water area of Baiyun Sag in the Pearl River Mouth Basin in the northern margin of the South China Sea has been proved to be a hydrocarbon rich depression. In recent years, overpressure has been encountered in the middle and deep layers, but the geological origin of the overpressure in the deep water area are still unclear. Therefore, the pore pressure profile of the Baiyun Sag was evaluated using the data of drilling and seismic velocity, and the relationship between overpressure and the generation mechanism was established. Most of the surrounding and shallow strata of Baiyun Sag show normal pressure, while the middle and deep strata generally show overpressure, with the maximum pressure coefficient up to 1.55. The overpressure zone mainly develops from the middle of Zhujiang Formation to the upper member of Enping Formation. The mudstone resistivity and density values of the two typical Wells deviated from the normal trend. The density showed a constant trend with the increase of depth, while the resistivity showed a certain degree of reversal. The upper layer of the overpressure zone showed abnormally high resistivity values, corresponding to the overgland and transition zone formed by high carbonate content. There is no obvious increase of porosity in the overpressured sandstone strata of Baiyun sag, which does not have the characteristics of undercompaction. The velocity in the overpressure section of the two Wells varies greatly, and the density is basically unchanged or slightly decreased. It is concluded that the overpressure is caused by fluid expansion from hydrocarbon-generation. The large-scale and long-term fluid expansion caused by hydrocarbon generation and expulsion of source rocks provides the power source for the formation of overpressure in Baiyun sag. The distribution of effective source rocks has a controlling effect on the distribution range of overpressure. The tight sandstone strata in the Zhuhai, Wenchang and Enping formations become the cover layer of the overpressure system in the longitudinal direction.

Suppressing stick–slip oscillations in drill-strings by Modified Integral Resonant Control

This paper presents development of a novel control scheme for suppressing stick–slip oscillations of drill-strings. This scheme utilises a Modified Integral Resonant Control (MIRC) with tracking in order to meet a desired drilling velocity. A low-dimensional two degrees-of-freedom drill-string model incorporating bit-rock interactions adopted for an open-loop control, clearly demonstrate presence of unwanted stick–slip responses. Next a detailed design of the MIRC-based damping scheme (without tracking) capable of eliminating this undesired behaviour is presented. Then in order to enhance efficacy, the MIRC-based scheme is combined with an integral tracking controller to show that this combined damping and integral tracking control scheme is not only capable of eliminating stick–slip oscillations but also maintaining the desired drill-bit angular velocity. To highlight the benefits of the proposed combined scheme, it is compared with the recently proposed Sliding-Mode Controller (SMC). Its inherent simplicity, robustness to parameter uncertainty and excellent performance of the proposed combined scheme propels it to be a leading candidate for stick–slip mitigation in drill-strings. To further showcase the efficacy of the proposed control scheme, its closed-loop performance when implemented on an 8-DOF system, has also been discussed.

Effect of mass variation on vibration properties of the tooth in drilling operation

Dental cavity represent one of the widespread illness of the tooth. Method for treating of the tooth is to drill the cavity and to fill the hole with suitable material. Measurements show that during drilling the tooth vibrates with increasing mass that causes unpleasant feeling for patient. The aim of the paper is to give the theoretical explanation for this phenomena and to give suggestion for vibration elimination. During drilling, mass of the tooth is decreasing and the so called ‘reactive force’ occurs. Drilling and reactive force cause tooth vibration. The system is modeled as a nonlinear time variable system. An analytical procedure for solving of the equation of vibration is developed. The solution is assumed in the form of the generalized trigonometric function with time variable amplitude and phase. It is obtained that not only the amplitude but also the frequency of tooth vibration in drilling are increased. In addition to reactive force the drilling velocity, diameter of the drill tool and spindle speed affect the vibration level. The appropriate values of these parameters would eliminate or decrease the patient bad feeling.

Effect of Annular Gas-Liquid Two-Phase Flow on Dynamic Characteristics of Drill String

Natural gas hydrate (NGH) is a kind of new type green energy source with giant reserves which has been thought of highly by energy explorers in the world. However, NGH breaks down to produce some natural gas that enters the annulus and flows together with the drilling fluid. The gas-liquid two-phase flow can have an impact on the work of the drill string. Therefore, it is important to study gas-liquid two-phase flow in the annulus on the dynamic characteristics of the drill string. In this article, taking a single drill string as the research object, a fluid-structure coupled finite element mathematical model of two-phase flow in the annulus and drill string is established based on computational fluid dynamics and computational structural dynamics theory. The finite element numerical simulation method is used to analyze the influence of drilling fluid and natural gas in the annulus on the dynamic characteristics of the drill string. The simulation analysis shows the following: (1) The motion of drilling fluid or natural gas in the annulus will reduce the natural frequency of the drill string, and the drilling fluid has a greater impact on the natural frequency of the drill string. (2) When single-phase drilling fluid flows in the annulus, the displacement peak in different directions, maximum equivalent stress, and strain of the drill string increase with the increase of the drilling fluid flow velocity or pressure, and the drilling fluid pressure has a more significant effect. (3) When the gas-liquid two-phase fluid flows in the annulus, the displacement peak, maximum equivalent stress, velocity amplitude, and acceleration amplitude of the drill string all increase with the natural gas flow velocity and natural gas content increase, and the natural gas flow velocity has a more significant effect.

The influence of extremely abrasive rock on the drilling velocity and tool wear in bored piles

The significance of the excavatability for the successful completion of constructional projects has been recognized in recent years, but little attention has been paid specifically to rotary pile boring. Given the quantity of geological parameters alone which need to be taken into account, it is apparent that the estimation of the drilling rate is difficult. Based on a case study in extremely abrasive tertiary silcretes (quartzite), the engineering geological influences on the drillability are examined. A minutely detailed documentation of the drilling process was produced, and laboratory testing was conducted to gain a better understanding of the correlation between significant rock properties and wear on drilling tools. The examined silcretes (quartzite) show CERCHAR abrasivity indices (CAI) up to a value of more than 6. It comes as no surprise that this highly abrasive rock causes extensive wear on piling equipment and an extremely high consumption of wear parts. In combination with the drilling velocity of both the drill tools and the casing shoe remaining well below 10 cm/min, it is obvious that the drilling performance is significantly impacted in more than one way. A correlation between the lifespan of the wear parts and the net drilling velocity is developed, allowing for a more reliable performance prediction for bored piles.

Analysis of critical whirling velocity of drill string

ABSTRACT During the drilling process, the whirling motion often occurs, which will cause the drill string to vibrate violently, accelerate the fatigue damage of the drill string, and eventually cause the bottom hole assembly to fail. But the existing research rarely focuses on the critical whirling velocity of drill string. To solve this problem, the whirl differential equation of drill string was set up based on the D’Alembert principle, and the critical whirling speed equation of drill string was deduced according to separation variable method. Reference to actual downhole conditions, the influence of drill stem wall thickness, tension, drilling depth, drilling fluid flow rate, and other factors on the critical whirling speed of drill string are considered. Research results indicate that when n ≤ 8324, drill string has a critical whirling speed, and when n > 8324, there is no critical whirling speed. And under different orders, as drill string wall thickness and drilling depth increase, the critical whirling velocity decreases. In general, the drill string rotation rate is 0–150 rad/min. When the drilling depth is 0–500 m, the critical speed is not considered. However, as drilling depth exceeds 500 m, the critical whirling velocity is within the general range of drill string speed. Therefore, drill string velocity should be chosen reasonably to avoid resonance. When the tension increases, critical whirling velocity increases. As the drilling fluid flow rate increases, the critical whirling velocity of drill string decreases. But when drilling fluid velocity is close to 120 L·s−1, increasing the drilling fluid velocity hardly affects the critical whirling velocity of drill string. In a word, research results of this paper have certain guiding significance to drilling engineering.

Computational study of cutting transport by drilling fluids in directional wells

The paper presents the computation results of the cutting transport in directional wells. Two samples of oil-based muds were prepared. The rheological parameters, incorporated in the computation model, were measured. The geometry of the real well was used for the computation. Three well slopes equal to 15, 45, 75 degrees were studied. The sludge velocity profiles in the annular channels were obtained. The average volumetric value of the particle slip velocity was obtained (the difference between the drilling fluid velocity and the sludge velocity).

Predictability and controlling factors of overpressure in the North Alpine Foreland Basin, SE Germany: an interdisciplinary post-drill analysis of the Geretsried GEN-1 deep geothermal well

The North Alpine Foreland Basin in SE Germany is Germany’s most active deep geothermal province. However, in its southern and eastern part the basin is considerably overpressured, which is a significant challenge for drilling deep geothermal wells. In this study, we combine drilling data and velocity-based pore pressure analyses with 3D basin modeling to assess the predictability and controlling factors of overpressure in the sub-regional context (area of 80 km × 50 km) around the Geretsried GEN-1 well, a deep geothermal exploration well in the southern part of the North Alpine Foreland Basin in SE Germany. Drilling data and velocity-based pore pressure analyses indicate overpressure maxima in the Lower Oligocene (Rupelian and Schoeneck Formation) and up to mild overpressure in the Upper Oligocene (Chattian) and Upper Cretaceous, except for the hydrostatically pressured northwestern part of the study area. 3D basin modeling calibrated to four hydrocarbon wells surrounding the Geretsried GEN-1 well demonstrates the dominating role of disequilibrium compaction and low permeability units related to overpressure generation in the North Alpine Foreland Basin. However, secondary overpressure generation mechanisms are likely contributing. Also, the impact of Upper Cretaceous shales, which are eroded in the northwestern part of the study area, on overpressure maintenance is investigated. The calibrated basin model is tested against the drilling history and velocity (VSP) data-based pore pressure estimate of the Geretsried GEN-1 well and reveals that pore pressure prediction is generally possible using 3D basin modeling in the North Alpine Foreland Basin, but should be improved with more detailed analysis of lateral drainage systems and facies variations in the future. The results of the study are of relevance to future well planning and drilling as well as to geomechanical modeling of subsurface stresses and deep geothermal production in the North Alpine Foreland Basin.

Influence of Rotation Speed and Air Pressure on the Down the Hole Drilling Velocity for Borehole Heat Exchanger Installation

The relation between rotation speed, air pressure and the velocity of air-rotary drilling using the down the hole method is determined in an empirical manner. For the study, velocity measurements are obtained for combinations of the aforementioned parameters during fieldwork for the installation of borehole heat exchangers near Lublin, Poland. The tests consider three drill bit diameters—110, 127 and 140 mm; three rotational speeds—20, 40 and 60 1/min; and three air pressures—16, 20 and 24 bar. The borehole heat exchangers need 100 m deep wells. The lithology consists mainly of loess and clays to 24 m, sand and carbonate rocks to 36 m, and marls and limestone to 100 m. It is found that the highest drilling velocity is achieved when the greatest pressure is applied, while the lowest drilling velocity is connected to the lowest pressure. However, the relation between rotation speed and drilling velocity is more complex, as drilling velocity seems to be more affected by depth. Therefore, lithology can be a major factor. The results may find direct use in drilling, and provide a basis for further studies on the optimization of drilling technology.

Finding velocity of roller-bit and rotary-percussive drilling using the energy conservation law

Velocity of roller-bit and rotary-percussive drilling depends on many factors distributed in 4 groups in technical literature: rock properties, bit parameters, bit-rock interaction conditions and drilling modes. Literature sources present some very complex formulas which need finding empirical coefficients before determining drilling velocity, i.e. the formulas are difficult to use. Moreover, the formulas neglect jointing of rock masses. At the same time, mathematical relations connecting drilling velocity, drilling mode and drillability of jointed rocks will make it possible to rate drilling processes and adjust blasting parameters. These studies aim to determine velocity of roller-bit and rotary-percussive drilling using the energy conservation law. The used method of mathematical modeling allowed obtaining formulas for rock drilling velocity with regard to drilling modes, bit parameters, factor of rock hardness (strength) and rock mass jointing. The validity of the relations of the roller-bit and rotary-percussive drilling velocity is proved. The reliability of the drilling velocity formulas can be determined by means of investigations performed in open pit mines, with recording of all parameters and with mathematical processing of the data. The mathematical relations connecting drilling velocity, drilling modes, drill bit parameters and drillability of jointed rocks will enable rating of drilling and adjustment of blasting patterns.

Central tube erosion investigation of torque impactor in the deep shale gas formation

ABSTRACT To figure out erosion mechanism of the torque impactor and optimize the structure of such tools, CFD (computational fluid dynamics) simulation model of the central tube is established. Results show that the location of the most serious erosion and the maximum erosion rate (4.80 × 10−4 (kg/(m2·s)) are consistent with the actual situation. Solid particles retained in the central tube are distributed unevenly. When drilling fluid velocity increases from 26 to 32 m/s, the maximum erosion rate of the central tube increases from 3.89 × 10−4 to 6.60 × 10−4 (kg/(m2·s)). As the mass flow rate of the solid particles increases from 0.2 to 0.8 kg/s, the maximum erosion rate increases from 5 × 10−4 to 28 × 10−4 (kg/(m2·s)). With increasing of particle diameter from 0.2 to 1.2 mm, the maximum erosion rate increases from 5.98 × 10−4 to 48 × 10−4 (kg/(m2·s)) and shows different upward trend in different intervals of particle diameters. As the solid particle shape coefficient increases from 0.4 to 1, the maximum erosion rate decreases from 14 × 10−4 to 1 × 10−4 (kg/(m2·s)). Grey correlation coefficient method indicates that the most relevant to the erosion rate is the drilling fluid velocity, followed by the particle shape coefficient, the particle diameter, and the solid particle mass flow rate.

Numerical analysis and Experimental Investigation of Lateral vibration on Drill String under Axial Load Constrained with Horizontal Pipe

Horizontal well technology is an important means to improve drilling efficiency and oil and gas production, but it is easy to generate the lateral vibration of the drill string. This strong lateral vibration of the drill string will further lead to the whirl of the drill string, which will accelerate the wear of the drill string and further lead to the failure of the drill string. According to the rotor dynamics theory and fluid dynamics, the whirling equation of the drill string in horizontal wells is established. The effects of the weight of the drill string, wall friction, internal and external drilling fluid flow velocity and fluid resistance on the whirling of the drill string are studied. The mechanism of inducing the whirling of the horizontal drill string and the boundary conditions for judging the whirling are analyzed. Based on the existing dynamic simulation test equipment of the horizontal drill string in the laboratory, the experimental research on the whirling characteristics of the horizontal drill string is carried out, and the influence laws of the weight on bit and the rotation speed on the whirling of the drill string are studied. The results show that with the development of axial load, the intense of lateral vibration of drill string increases.

Prediction of Cuttings Transport Behavior under Drill String Rotation Conditions in High-Inclination Section

Cuttings are likely to accumulate and eventually form a cuttings bed in the highly-deviated section, which usually lead to high friction and torque, slower rate of penetration, pipe stuck and other problems. It is therefore necessary to study cuttings transport mechanism and improve hole cleaning efficiency. In this study, the cuttings-transport behaviors with pipe rotation under turbulent flow conditions in the highly deviated eccentric section were numerically simulated based on Euler solid–fluid model and Realizable [Formula: see text]–[Formula: see text] model. The resulted numerical results were compared with available experimental data in reported literature to validate the algorithm, and good agreement was found. Under the conditions of drill string rotation, cuttings bed surface tilts in the direction of rotation and distributes asymmetrically in annulus. Drill string rotation, drilling fluid flow rate, cuttings diameter, cuttings injection concentration and drilling fluid viscosity affect the axial velocity of drilling fluid; whereas drilling fluid tangential velocity is mainly controlled by the rotational speed of drill string. Increase in value of drill string rotation, drilling fluid flow rate or hole inclination will increase cuttings migration velocity. Notably, drill string rotation reduces cuttings concentration and solid–fluid pressure loss, and their variations are dependent on inclination, cuttings injection concentration, cuttings diameter, drilling fluid velocity and viscosity. However, when a critical rotation speed is reached, no additional contribution is observed. The results can provide theoretical support for optimizing hole cleaning and realizing safety drilling of horizontal wells and extended reach wells.

Simulations of deep drilling of metals by continuous wave lasers using combined smoothed particle hydrodynamics and ray-tracing methods

A robust numerical method based on smoothed particle hydrodynamics (SPH) is used to investigate the melt pool expulsion mechanism during high-aspect ratio laser drilling of two different materials: aluminum and 316L stainless steel. The computational model is validated with previously published results which show extremely close matches. The ray-tracing method is combined with SPH method which makes the model capable of taking into account the multiple reflections of laser radiations from the keyhole wall. The drilling velocity is found to be a non-linear function of time, which is dependent on the shape of the heated surface. For a flat surface, the drilling velocity is small, but after the cavity is formed and multiple reflections of laser radiations become significant, the drilling velocity strongly increases. The main driving force of melt expulsion is the repulsive force produced by vapor pressure. The Marangoni stresses are found to provide marginal effect on melt expulsion during deep drilling.

Experimental research on the influence of working parameters on the drilling efficiency

Rock drills are usually applied in petroleum engineering applications, tunnel excavation, and hard rock mining. The rock drills directly impacted the rock through the hydraulic impact power mechanism and are controlled by propulsion force and torque. However, there still exists the most serious problem in impact drilling which is low efficiency during the process of impact drilling, and thus the orthogonal experiment using Taguchi method L25 (56) is conducted to analyse the influence of the working parameters, including impact power, propulsion force, rotation speed and bit type, on the rock drilling efficiency. Unconfined compressive strength tests and Brazilian splitting tests are conducted first to present the bluestone characteristics. The drilling efficiency including drilling velocity and specific energy is the evaluating indicators for orthogonal experiments under different drilling conditions. The results demonstrate that the factor order affecting drilling efficiency is impact power, rotation speed, propulsion force and bit type. In addition, the impact power has a highly appreciable influence on the drilling efficiency, whereas the influence of rotation speed, propulsion force and bit type on that in their level range is slight. However, the influencing parameters of impact power, rotation speed, propulsion force and bit type in terms of percentage contribution on drilling velocity and specific energy is 38.54%, 20%, 20%, 20% and 35.307%, 20%, 20%, 20%, respectively. Moreover, the optimum combination in view of drilling velocity and specific energy are 6.4 kW, 240 r/min, 3800 N and 7-button for impact power, rotation speed, propulsion force, and bit type respectively. Based on the regression analysis of the main working parameters which affect drilling velocity, the relationship between drilling velocity and working parameters is obtained and verified, thus it easily provides a basis about equipment selection, optimal working parameters, equipment improvement and progress prediction.