Drilling Technology Research Articles

Deep Well and Ultra-Deep Well Drilling and Completion Technology Optimization and Application of Kuche Piedmont Area

In recent years, the exploration and development of China's Tarim Basin has moved towards ultra-deep and complex areas. With the increase in well depth and the influence of the geological characteristics of the Kuche Piedmont area, a series of drilling problems for 8000m-level ultra-deep wells in this area have been caused. As a result, a series of new drilling and completion technologies have been formed: ①Based on the tower standard I type well structure, the improved tower standard II-B\II-C type well structure is used to solve the drilling of two sets of salt formations. Difficulties; ②Optimizing UDM-2 oil-based drilling fluid, achieving an average hole diameter expansion rate of only 6.82%, reducing lost circulation and other complications; ③Designing and optimizing a new type of multi-edge PDC bit to significantly increase the average ROP; ④Application The industry-leading pre-measurement resistivity technology successfully predicts the salt bottom; ⑤The application of fine controlled pressure cementing technology to achieve effective sealing of high-pressure saline formations. In recent years, the Kuche Piedmont Block in the Tarim Basin has continued to tackle key problems in the application of ultra-deep well drilling and completion technologies, and has successfully reached a new level of 8000m, which has played an important role in supporting the development of deep oil and gas exploration and development business.

Structural Optimization Design of Modular Double Drill Pipe

Aiming at many drilling blocks with pore pressure coefficient ≦1.05 in China (shale gas surface layers in Tarim Basin and Sichuan Basin, depletion of reservoirs and gas reservoirs in developed oil and gas fields in China), the narrow window of drilling fluid density in such blocks will directly lead to wellbore instability, difficulty in carrying rock debris and serious formation losses. In order to control the fluctuation range of formation pressure, on the basis of conventional managed pressure drilling technology, gas lift positive circulation drilling technology and Marine double gradient drilling technology are integrated to form gas lift positive circulation drilling technology. The double drill pipe is one of the key equipment to realize the above drilling technology. Under this background, a double drill pipe for gas lift positive circulation drilling technology is designed. In this paper, the key equipment of gas lift positive circulation drilling technology is analyzed and its structure is optimized.

Technical advances in well type and drilling & completion for high-efficient development of coalbed methane in China

Compared with the United States, Australia, Canada, and other countries, China's coalbed methane reservoir is featured by low formation pressure, low permeability, low gas saturation, and strong heterogeneity, which not only increases the difficulty of reservoir stimulation but also restricts the single well production and the recovery efficiency of coalbed methane (CBM). In view of this, the research and application of horizontal drilling and completion technology of CBM at home and abroad are reviewed to provide references and theoretical supports for the advancement of the horizontal well engineering technology of CBM in China. This paper introduces a series of horizontal drilling and completion technologies (e.g., the well type design, well structure optimization, well trajectory control, wellbore stability, completion optimization, reservoir protection, etc.). The advanced technologies and their adaptability, including screen pipe completion and stimulation with dual-layer tubular strings, radial horizontal well screen pipe completion and magnetic steering drilling, are dialectically discussed in this paper. In addition, a novel integrated engineering mode for the efficient and green development of deep CBM and coal through the underground “well factory” is proposed. The conclusions are as follows: (1) In view of the geological conditions and surface environment of the coal seam in China, the horizontal drilling and completion technologies of high rank coalbed methane should be further refined, and an integrated development for the coal measure gas is required; (2) More efforts should be made to strengthen the innovative research on horizontal drilling & completion technology for low-medium rank coals and the broken coal, so as to identify the efficient development mode for the complex coalbed methane reservoir; (3) When encountering major technical challenges during the green and efficient development of unconventional coal mines such as deep coal mines, low grade coal mines and thin coal seams in China, it is necessary to explore the development mode via in-situ conversion process based on underground “well factory” to realize the integrated green and efficient development of deep CBM and coal; (4) The high quality transformation with low-carbon and green energy in China will not only ensure national energy security, but also achieve the goal of “carbon peaking and carbon neutrality”.

Совершенствование организационно- технологических схем обращения с отходами бурения

In the article the relevance is substantiated related to improving the organizational and technological schemes for handling of drilled cuttings of hydrocarbons of a polycomponent composition from the standpoint of improving the environmental safety of territories during the development and operation of oil and gas fields, as well as ensuring the industrial safety. Analysis of the existing drilled cuttings management systems is carried out, and the classification of their storage facilities is presented depending on the time, their location and on the waste management scheme to prevent flooding and waste spills due to emergencies. The requirements are given concerning the construction of temporary accumulators and sludge pits, as well as the conditions for classifying the waste management system as a pitless drilling method. The recommendations are proposed for choosing an accident-free organizational and technological scheme for handling of drilled cuttings, and measures to reduce the negative effect on the components of the environment during the accumulation and disposal of drilled cuttings. The features of accumulative drilling technology are considered, which provide for the accumulation of generated drilled cuttings in the temporary storage facilities with their subsequent processing, neutralization and (or) disposal without removal from the territory of the well construction/reconstruction site. The causes and consequences of emergency situations are presented. The implemented organizational and technological scheme of drilling waste management is presented using a logical and information model. Recommendations are given on the choice of an organizational and technological scheme for handling of drilled cuttings when improving the systems for managing the flow of drilled cuttings from the wells of hydrocarbons of the multicomponent composition, depending on the hazard class of drilled cuttings generated by the subsurface users, as well as the territories with environmental restrictions.

Meniscus-Induced Directional Self-Transport of Submerged Bubbles on a Slippery Oil-Infused Pillar Array with Height-Gradient.

Directional manipulation of submerged bubbles is fundamental for both theoretical research and industrial production. However, most current strategies are limited to the upward motion direction, complex surface topography, and additional apparatuses. Here, we report a meniscus-induced self-transport platform, namely, a slippery oil-infused pillar array with height-gradient (SOPAH) by combining femtosecond laser drilling and replica mold technology. Owing to the unbalanced capillary force and Laplace pressure difference, bubbles on SOPAH tend to spontaneously transport along the meniscus gradient toward a higher elevation. The self-transport performances of bubbles near the pillars depend on the complex meniscus shape. Significantly, to understand the underlying transport mechanism, the 3D meniscus profile is simulated by solving the Young-Laplace equation. It is found that the concave valleys formed between the adjacent pillars can change the gradient direction of the meniscus and lead to the varied transport performances. Finally, by taking advantage of a water electrolysis system, the assembled SOPAH serving as a bubble-collecting device is successfully deployed. This work should not only bring new insights into the meniscus-induced self-transport dynamics but also benefit potential applications in the field of intelligent bubble manipulation.

Research on Deep Coalbed Methane Localized Spotting and Efficient Permeability Enhancement Technology

To solve the bottleneck problem of low deep coal seam permeability and difficult coalbed methane (CBM) mining. Combining hydraulic splitting technology and directional drilling technology, a directional hydraulic splitting enhancement method of deep CBM mining was proposed. The selection equation for the directional hydraulic splitting of deep coalbed was constructed. The numerical simulation reveals the variation in coal fractures around different split angles. The split angle under the maximum coal damage effect was obtained. It was found that the combined effect of the double crack damage disturbance region led to reciprocal stress fluctuations during crack development and, eventually, the formation of a zigzag fracture. The larger the splitting angle, the larger the fissure development length and the larger the coal-damaged area. A double crack takes 25% less time to complete propagation than a single crack. When the splitting angle is 90°, the disturbed area occupies 2/3 of the area around the borehole, and the overall fracturing effect is the best. In the application process, the new directional hydraulic splitting technology can increase CBM mining by 5.08%, greatly improve CBM mining efficiency, and reduce the coal mining risk, which is of great significance to the project.

Failure mechanism of continuous large deformation and a novel pressure relief control technology on the two sides of deep coal roadway

Traditional intensive drilling (or grooving) technology in a roadway destroys the rock mass and supporting structure in the shallow anchoring area while implementing pressure relief. In Dongpang coal mine, it is difficult to avoid the failure of the supporting system and continuous large deformations of the deep roadways influenced by disturbance, despite the application of strong bolt (cable) supporting systems and grouting reinforcements. Therefore, this study proposes a novel “anchoring and pressure relief” synergistic supporting technique to eliminate the dilemma among the anchoring supporting and pressure relief. With strong anchoring supporting in the shallow surrounding rock, this novel technology realizes pressure relief by excavating large-diameter holes in the deep peak stress area, to enable active regulation of the move of the peak stress area to the deep surrounding rock without impairing the shallow anchoring area. The path of coal body rheology and stress move is cut off by large-diameter holes using this novel technology, achieving the purpose of absorbing energy and deformation, decreasing the stress applied on the supporting structure in the anchoring area. The novel technology effectively solves the control problems of continuous large deformation in deep roadway and has a good engineering application prospect. This study findings will add scientific value for the improvement of surrounding rock control of deep roadway.

Recovery of Microbes from Subsurface Europa Analog Environments: An Efficient Mechanical-Thermal Probe for Collecting Biological Samples from the Subsurface of Icy Moons.

The ultra-low temperatures (<173K) and ultra-low pressures (<0.1 Pa) that exist on the surface of icy moons present a formidable challenge for collecting biological samples. Standard drilling technology is not efficient in these conditions, where conduction of thermal energy leads to the possibility of freezing in place and shear forces impart a strenuous test on microbial viability. If microbes exist within the first few meters of the surface, an extraction process must be gentle enough to recover them intact. This report describes a substantial improvement from the study by Davis in 2017, who presented a concave conical thermal probe capable of penetrating -65°C ice in 1000 Pa pressure. The current report describes a mechanical-thermal device for penetrating ≤ -150°C ice in 10 Pa pressure, which is analogous to the physical conditions on the surface of icy moons. The mechanism has an efficiency of >68% with -65°C ice and >61% with -150°C ice, which is well above the expected 10-15% for a Philberth-type probe. In addition, the probe can harvest a sensitive bacterium (Escherichia coli) from under a layer of acidified peroxide ice (pH 1.1), which is analogous to the expected surface chemical composition of the icy moon Europa. In field tests at -20°C air and -6°C ice temperatures, multiple organisms were extracted in a viable state, and chemical analysis indicated high-resolution separation of stratified layers. Finally, attaching the thermal tip to a telescopic mechanism allowed the probe to penetrate through 1.0 m of -65°C ice, which is well below the depth of harmful radiation expected at the subsurface of Europa. The current work opens the door for a lander vehicle to penetrate the upper subsurface of Europa and analyze biologically active samples.

Micromotion-based balanced drilling technology to increase near cortical strain

ObjectiveA micromotion-based balanced drilling system was designed based on a locking plate (LP) and far cortical locking (FCL) concept to maintain the balance of micromotions of the cortex on both sides of a fracture region. The system was tested by axial compression test.MethodsThe fracture gap was set to 2 cm, and locking screws with a diameter of 5 mm and a locking plate were used to fix it. The diameters of the two sections of the stepping drill were 3.5 mm and 5.0 mm, respectively. One of the matching drilling sleeves was a standard sleeve (eccentricity, 0 mm) and the other was an eccentric sleeve (proximal eccentricity, 1 mm). A model of the fixed locking plate (AO/ASIF 33-A3) for distal femoral fractures with a gap of 2 cm was established based on data from 42 artificial femurs (SAWBONE). According to the shape of the screw holes on the cortex, the fixed fracture models were divided into a control group (standard screw hole group X126, six cases) and an experimental group (elliptical screw hole group N, 36 cases). The experimental group was further divided into six subgroups with six cases in each (N126, N136, N1256, N1356, N12356, N123456), based on the number and distribution of the screws on the proximal fracture segment. The control, N126, and N136 groups were subjected to an axial load of 500 N, and the other groups were subjected to an axial load of 1000 N. The displacements of the kinetic head, far cortex, and near cortex were measured. The integral structural stiffness of the model and the near cortical strain were calculated. The data of each group were analyzed by using a paired t-test.ResultsWhen the far cortical strains were 2%, 5%, and 10%, the near cortical strains in group N126 were 0.96%, 2.35%, and 4.62%, respectively, significantly higher than those in the control group (X126) (p < 0.05). For a different distribution of the screws, when the far cortical strains were 2%, 5%, and 10%, the near cortical strains in group N126 were significantly higher than those in group N136 (p < 0.05). However, there was no significant difference between the near cortical strains in the two groups with four screws (p > 0.05). For different numbers of screws, the near cortical strains in the three-screw groups were significantly higher than those in the four-screw groups (p < 0.05), and there was no significant difference in near cortical strains among the four-, five-, and six-screw groups (p > 0.05).ConclusionThe proposed drill and matching sleeves enabled a conventional locking compression plate to be transformed into an internal fixation system to improve the balanced motion of the near and far cortices. Thus, strain on a fracture site could be controlled by adjusting the diameter of the drill and the eccentricity of the sleeve.

Delineation of Coal Bed Geometry using High Resolution Seismic Reflection Data for Uninterrupted Directional Drilling Exploration

Abstract The utilization of innovative technology by the coal mine industry requires proper guidance of sub-surface information so that it can provide uninterrupted exploration with less time and minimum cost. Sufficient knowledge about the coal beds that is variation of thickness, depth, and associated structures will facilitate the mine engineer to run machinery systematically. Conventional geological reports based on borehole data may not sufficient to adopt state-of-the-art drilling technology. To address these issues, high-resolution seismic survey (HRSS) was conducted to delineate the thickness of coal seams and mapping of structural features which are associated with coal seams. An effort was made to demonstrate the high-resolution seismic reflection study for picking of minor faults locations and thickness of coal seams in the central part of the Sohagpur, Gondwana basin that occurs at the junction of the Mahanadi and Son-Narmada rift systems in central India. The study reveals thick Barakar Formation and coal seams at a depth range of 300 to 550 meters. The thickness of coal seams and the location of minor faults were interpreted with the help of attribute analysis from the seismic sections. The obtained results from the seismic survey were useful for the selection of potential target zones which are favourable for drilling.

Drilling fluid for stabilizing the wellbore in compound-salt formation based on multiple-synergism-method

The complex features of the compound-salt formation result in wellbore instability during drilling operations. The mechanism of wellbore instability in compound-salt formation is studied by the analysis of mineral compositions, microstructures, physical-chemical properties, and interface mechanical properties of compound salts from different areas. The results show that the existing micro-scale pores and fractures, creep and dissolution of salt, hydration of gypsum-mudstones are the key causes of wellbore instability in compound-salt formation. In order to stabilize the wellbore in compound-salt, we propose the drilling strategies based on the synergism of multiple methods of strengthening the wellbore by the sealing and consolidating effect of drilling fluid, inhibiting the dissolution of salt and the hydration of gypsum-mudstones, balancing the water activity between rocks and drilling fluid, providing effective stress to support the wellbore. Based on the effect of water activity on the shale hydration swelling and dispersion properties, the design basis of the safe window of water activity for drilling fluids is determined. According to the wellbore instability problems when drilling in compound-salt formations in M Oil Field in the Middle East, H-S Oil Field of Uzbekistan, and Xinjiang Uygur Autonomous Region of China, the drilling fluids are designed respectively based on the proposed wellbore stabilizing technology. The field applications show that the drilling fluid technology greatly improves the wellbore stability in compound salt formations and reduces downhole problems, thereby improving drilling efficiency.

Novel Water-Based Drilling and Completion Fluid Technology to Improve Wellbore Quality During Drilling and Protect Unconventional Reservoirs

The efficient exploration and development of unconventional oil and gas are critical for increasing the self-sufficiency of oil and gas supplies in China. However, such operations continue to face serious problems (e.g., borehole collapse, loss, and high friction), and associated formation damage can severely impact well completion rates, increase costs, and reduce efficiencies. Water-based drilling fluids possess certain advantages over oil-based drilling fluids and may offer lasting solutions to resolve the aforementioned issues. However, a significant breakthrough with this material has not yet been made, and major technical problems continue to hinder the economic and large-scale development of unconventional oil and gas. Here, the international frontier external method, which only improves drilling fluid inhibition and lubricity, is expanded into an internal-external technique that improves the overall wellbore quality during drilling. Bionic technologies are introduced into the chemical material synthesis process to imitate the activity of life. A novel drilling and completion fluid technique was developed to improve wellbore quality during drilling and safeguard formation integrity. Macroscopic and microscopic analyses indicated that in terms of wellbore stability, lubricity, and formation protection, this approach could outperform methods that use typical oil-based drilling fluids. The proposed method also achieves a classification upgrade from environmentally protective drilling fluid to an ecologically friendly drilling fluid. The developed technology was verified in more than 1000 unconventional oil and gas wells in China, and the results indicate significant alleviation of the formation damage attributed to borehole collapse, loss, and high friction. It has been recognized as an effective core technology for exploiting unconventional oil and gas resources. This study introduces a novel research direction for formation protection technology and demonstrates that observations and learning from the natural world can provide an inexhaustible source of ideas and inspire the creation of original materials, technologies, and theories for petroleum engineering.

Peculiarities of drilling hard rocks using hydraulic shock technology

Purpose. To test the theoretical provisions for calculating the geometric and gas-dynamic parameters of a hydropulse apparatus for strikers using core pipes. Methodology. The research methodology is based on the tests carried out. The tests were conducted between January 6, 2021, and April 28, 2021. The type of test is laboratory bench trials. In the course of the study, methods of synthesis and analysis of information were applied. Finding. The basic design parameters of a hydro-pulse generator capable of operating efficiently with impact machines were obtained during the bench research. The optimal scheme of air flow distribution at the exhaust of the hydraulic hammer has been established. The optimal value of the pressure drop in the operating and blocking modes of operation of the generator is determined. In addition, the optimal value of the ejection coefficient in these two modes of operation of the generator was determined. Originality. The article investigated the technologies of drilling hard rocks in order to optimise the basic geometric parameters of the hydraulic pulse generator, to distribute the working flow in front of the jet blower, to measure the value of the ejection coefficient and pressure drop to clarify the composition and methodology of experiments in borehole conditions. Practical value. The presented study can be used to optimise the drilling technology as well as a basis for training specialists in the field of hard rock drilling using hydraulic percussion technology.

Review of high-temperature geothermal drilling and exploitation technologies

Global warming induced by excessive carbon dioxide emission generated from fossil fuels consumption is becoming increasingly severe. Development and utilization of clean and renewable energy is a significant measure to contribute for the carbon neutrality. Geothermal resource is an important clean and renewable energy, because of its advantages of abundant reserves, exploitation without restrictions from the climate and season. Extracting heat from the high temperature geothermal reservoir requires well drilling, completion and fracturing. However, due to some particular conditions in geothermal development, such as high temperature, erosion, leakage, and hard rocks, traditional petroleum well drilling and completion technologies are not well applicable in the geothermal industry. In this paper, the state-of-the-art geothermal drilling, and completion technologies as well as several fracturing methods, such as foam drilling, air hammer drilling, hydrothermal jet drilling, expansion casing technology, high temperature resistant drilling fluid and cement, chemical stimulation and thermal stimulation are comprehensively reviewed. Besides, heat extraction performances of water and CO2 as working fluids in the geothermal system are discussed. A few novel heat extraction methods including closed loop, open loop, enhanced geothermal systems are compared and analyzed. This review is expected to provide suggestions for research fields worthy of study for geothermal drilling and exploitation.

The thermoporoelastic coupling analysis of wellbore stability in shale formation under supercritical CO2 drilling conditions

Supercritical carbon dioxide (ScCO2) drilling can effectively protect shale formation from hydration damage and improve drilling rate comparing to conventional drilling technology. The wellbore stability of shale formation is one considerable issue under ScCO2 drilling conditions. In this study, the numerical simulations are performed to calculate collapse cycling time of shale formation under ScCO2 drilling conditions based on thermoporoelastic coupling model. The results show that comparing to water seepage condition, the variation of formation temperature is larger, pore pressure and stress are lower for ScCO2 seepage condition without adsorption effect, the comparison between water and ScCO2 seepage conditions verifies the thermoporoelastic coupling model. For ScCO2 drilling conditions, if adsorption‒induced strain is ignored, the risk of wellbore collapse will be slightly underestimated comparing to the results with adsorption effect. When adsorption‒enhanced elastic modulus is ignored, the risk of wellbore collapse will be significantly underestimated comparing to the results with adsorption effect. The wellbore collapse may occur with the increasing well depth for ScCO2 drilling conditions. This study can provide the theoretical guidance for exploiting shale reservoirs using ScCO2.

Influence Factors on EGS Geothermal Reservoir Extraction Performance

The heat extraction performance of the enhanced geothermal system is simulated by using COMSOL software. The effects of six factors, such as the thermal conductivity of heat reservoir, matrix permeability, fracture width, injection temperature, injection flow rate, and the number of wells, on the heat extraction performance of EGS heat reservoir for 40 years are analyzed. The results show that the matrix permeability and injection flow are the main factors affecting the heat production performance of the EGS geothermal reservoir, while the thermal conductivity, fracture width, and injection temperature have little effect on the heat production performance of the EGS geothermal reservoir. Although increasing the number of production wells can improve the uneven distribution of the flow field to improve the system heat performance, taking into account the existing drilling technology and cost, the cost is higher, and the two-well system is still the basic form of absorbing rock heat.

A New Mechanical Specific Energy Model for Composite Impact Drilling

Composite impact drilling technology is one of the important techniques to increase drilling speeds in deep hard formations. In order to evaluate the efficiency of drilling with a composite impactor in real time and effectively, and to further improve the drilling speed in deep formations, the mechanical specific energy (MSE) model of drilling with a composite impactor was studied. Based on previous theoretical studies on MSE, and considering the effect of the composite impactor on the axial and torsional impact of the drill bit during operation, a new MSE model for composite percussion drilling was established. The results show that the evaluation of the drilling efficiency by MSE obtained by this calculation model is consistent with the actual situation of a Lufeng X well. It can be more widely used in wells drilled with composite impact tools and meet the needs of field operations.

Research on goaf treatment and geothermal comprehensive utilization technology in coal mining subsidence area

Goaf treatment and comprehensive utilization of geothermal energy are great significance to the restoration of land resources and sustainable development of energy in coal mining subsidence areas. In this paper, goaf treatment technology and geothermal energy development technology are reviewed in detail. Among them, the goaf treatment technology mainly includes: caving treatment method, filling treatment method, support method, closed isolation method and joint treatment method. Geothermal development technology mainly includes: shallow ground source heat pump technology, coaxial casing development technology, pumping and reinjection technology, directional drilling technology, U-type precision docking drilling technology. The systematic idea of filling treatment and geothermal comprehensive utilization in coal mining subsidence area is proposed, and the technology is described in detail through three cases. The research results can provide innovative inspiration for subsidence control and comprehensive utilization of geothermal energy in coal mining subsidence area, and has broad application prospects.

Application of models for directional drilling technology

The aim of this study is to develop a program to compare directional survey models and select the most accurate. When drilling a directional well, the actual route of the well must be regularly checked to ensure that it is in agreement with the planned route. This is done by measuring the position of the well at constant intervals. A program was established to be used for the five methods (Minimum Curvature, Tangential, Angle Averaging, Balanced Tangential, and Radius of Curvature) for well path design. The directional survey extents are assumed in terms of inclination, azimuth, and 3D coordinates. Comparing the result from the program developed which was used for the different methods it was observed that this new method is faster and more reliable. T-Test statistical method to compare the values gotten for the vertical section from the plan with that of the actual survey was used. The results obtained using the average angle, minimum curvature, balanced tangential, and radius of curvature are very small hence any of the methods can be used for calculating the well trajectory but the Tangential shows considerable error and is highly strayed from the plan in the build section hence it should not be used in directional survey calculation. The conclusion drawn from the t-test carried out, therefore, is that there is no significant difference in the vertical section values between the plan and the fives methods considered.

Experimental study on dynamic characteristics of axial-torsional coupled percussive drilling

Axial-torsional coupled percussive drilling is a novel technology to enhance the rate of penetration (ROP), which takes advantage of both axial and torsional percussive drilling technologies. Our paper focuses on experimental investigations on coupled percussive drilling. A novel experiment setup, using a rock breaking tester, was developed to carry out dynamic drilling tests on granite specimens under different impact modes, weight on bit (WOB), rotation rates, and lithologies. Based on the optimization analysis of window functions, by combining the fast Fourier transform (FFT) and short-time Fourier transform (STFT) processing methods, the spectrum and 3D time-frequency-amplitude evolution characteristics of coupling impact response signals were demonstrated. According to experimental results, a high-frequency and high-amplitude rotational rate and lower torque are produced in coupling impact. The agglomeration of the cutting force is alleviated and the occurrence of “stick-slip effect” is slowed down. Compared with axial impact, the penetration depth and ROP are increased by 173.38% and 182.74% in coupling impact, respectively. As the WOB increases, a stable-high frequency and high amplitude rock breaking torque is generated, which increases the cutting force and ROP. There is an optimal ratio between the rotation rate controlled by the axial rotator and the torsional impact frequency, which takes advantage of axial and torsional percussion for a bit and obtains the optimal speed-raising effect. The variation of rock mechanical properties has a significant influence on the amplitude of time domain signals in coupling impact. Our results in this paper are of great value for future studies of axial-torsional coupled percussive drilling.