Air Drilling Research Articles

The Geysers Is a Unique Geothermal Resource Presenting Equally Unique Challenges to Drillers

_ For drillers, The Geysers is a unique sort of hell. It is one of the only places on Earth where a shallow well can reach a highly fractured reservoir so hot that it only produces steam. That steam powers 18 power plants generating 835 MW of electricity, making this 45-square-mile area the world’s most prolific geothermal power producer. High drilling costs there also stand out. Drilling a well requires 60 days or so and generates a lot of damaged drill bits and drillpipe. The drilling rigs have the size and power of modern onshore rigs, but a close look reveals there’s no topdrive. Below the rig floor there is a rotary table, known as a Kelly drive because it can spin drilling pipe without being in the line of fire of the steam flowing out when running slotted casing into the steam-production zone. When they get to that zone, they switch from drilling fluid and mud to injecting a high-pressure stream of air because of the enormous fluid losses anticipated when they reach that highly fractured level. A drill bit that lasts 500 ft in this harsh, highly fractured rock has had a long run. And the rugged terrain—mountains to a Texan but hills to a Californian—makes this a hard place to move a rig. “The Geysers is its own animal, for sure,” said Sam Noynaert, a Texas A&M professor who was a key member of a team of drilling experts and scientists that drilled a well in The Geysers to test if faster drilling methods from the oil business could work there. The two upper sections went pretty well, considering. As they went deeper, they repeatedly had to deal with severe fluid losses. Still, they had shaved nearly 6 days off the average drilling time. But when they reached the highly fractured steam-producing payzone and their drilling method changed to air drilling, things got worse with drill bits failing after runs as short as 21 ft. As a Geysers drilling paper presented at the Stanford Geothermal Workshop earlier this year delicately put it: “The air section proved to be more challenging.” The Blob The Geysers has a long history. The heat source is “a large blob of silica-rich magma (which) forced its way through Earth’s crust beneath the Coast Range,” according to the description of an image from NASA. That flow about 1.3 million years ago from deep within the earth heated the overburden, making the rock brittle and prone to fracturing. Over time, water seeped into those hot fissures, creating hot springs that were awed by Native Americans and later attracted tourists to a nearby resort hotel. By the 1960s drillers were tapping the steam in those payzones for commercial power generation, which peaked at 2,000 MW in 1987. It declined from there as steam production depleted the reservoir. Eventually, the output was stabilized at its current level by injecting water from sewage-treatment plants into the production zone.

Acquisition Study of Downhole Explosion Limit in Air Drilling

Summary Downhole explosions adversely affect air drilling; however, the explosion limit can facilitate the adjustment of the flow rate to prevent downhole explosions. The downhole explosion limit, comprising lower and upper limits, can be determined through diverse methodologies. In this study, the interrelation between absolute enthalpy and adiabatic flame temperature (AFT) enabled the deduction of the lower explosion limit (LEL) prediction method, and an equilibrium between heat generation and heat transfer formed the basis for the upper explosion limit (UEL) prediction method. Additionally, a variable-volume apparatus was established to measure the explosion limit and adjust the pressure precisely without changing the amount of gas. The explosion limit of methane in the air was determined using both predicted and experimental methods, mirroring the scenarios of natural gas entering the wellbore during air drilling. The theoretical model exhibited the same reliability as the experimental results, and the prediction method for the explosion limit proved more efficient. Moreover, the effects of initial temperature and pressure on the explosion limit are discussed. The LEL decreased by an average of 15.5% when the initial pressure increased from 0.1 MPa to 2 MPa, while the UEL experienced a significant increase by an average of 152%. The UEL exhibited a logarithmic dependence on the initial pressure. The effect of the initial temperature on the explosion limit was noticeably less pronounced than that of the initial pressure. This study provides the essential theoretical basis and experimental results for avoiding downhole explosions during air drilling.

A Numerical Simulation of the Coal Dust Migration Law in Directional Air Drilling in a Broken Soft Coal Seam

Abundant industrial experiences have shown that directional air drilling technology is effective for gas drainage when drilling broken and soft coal seams. In this paper, the Eulerian–Eulerian model was used to simulate the gas–solid two-phase flow behavior of compressed air transporting coal dust in broken soft coal seams. The relationship between the degree of coal dust deposition, annular air pressure law, transportation of coal dust, aforementioned factors of rotational speed, particle size, and air volume could be determined. The results indicate that the particle size plays a significant role in the transport capacity of coal dust. Smaller particle sizes and a higher airflow result in a lower deposition degree of coal dust. When the particle size of coal dust is 1.69 mm and the airflow is 300 m3/h, in the case of coal dust generation at a rate of 0.24 m3/h, the deflection angle of the coal dust collection zone is increased by 130% as the rotational speed of the drill rod is increased from 0 to 120 rpm. Similarly, the deflection angle of the coal dust collection zone is increased by 12.8% in a 500 m3/h airflow under the same condition. Additionally, fine particle-sized coal dust is transported in a spiral line. The coal dust with larger particle sizes tends to be in the middle and lower parts of the hole and move along a specific trajectory. Industrial experiences of medium-air-pressure drilling confirm that a rotary drilling speed between 80 and 120 rpm, with a minimum air volume of 400 m3/h and preferably 500 m3/h, can promote a smooth hole drilling effect and enhance the construction safety in the gas drainage process.

A novel method for wireless telemetry during air drilling based on air pressure pulses

Utilization of air drilling and horizontal well drilling is theorized to be one of the most effective methods for drilling in tight sandstone reservoirs. However, only a few horizontal wells were successfully drilled with air over the decades. One major setback is the lack of an effective downhole wireless telemetry technique. This study offered an innovative solution to wireless telemetry in air drilling, which is called as air pressure pulse telemetry, wherein the downhole decoded information is transmitted via air pressure pulses signals. For the method to work, an air pulse generator was designed to create sufficiently strong positive pulses at the bottom of the well for telemetry. The generator can totally cut off air flow when closed. Theoretically, pressure pulses of any intensity can be generated on demand. Unipolar return to zero (Unipolar RZ) modulation was applied herein for signal modulation. Baseband filter and differential processing technique were used to cancel the noise and enlarge the weak signals, and a method of threshold line is used to decode the signals. To evaluate the performance of the method, a laboratory experimental set was built, and all the sub-methods, such as air pulses generator, signal modulation, noise cancellation, data decoding methods, were tested. The results show that the pulse generator can create sufficiently strong pressure pulses on demand, while signals can be successfully captured and decoded after transmission 2000 m. The experimental results have confirmed the functionality of the novel method of air pressure pulse telemetry. Increasing operating pressure can both create stronger pressure pulses and reduce the attenuation of pulse signals. Reducing the time slot can improve the transmission rate, but it can also cause severe signal attenuation, ultimately leading to telemetry failure. Based on our results, it is recommended that the time slot be no less than 4 s. The proposed method provides a new pathway to achieving reliable wireless telemetry in air drilling. The method was compared with the existing wireless telemetry, and some potential challenges and future research directions were also discussed.

Mechanical Strength Enhanced Excitations of Downhole Microwave Communication for Air Drilling

Mechanical Strength Enhanced Excitations of Downhole Microwave Communication for Air Drilling

Design and numerical study of active cooling system of measurement while drilling for high temperature based on supersonic

Measurement while drilling (MWD) plays an important role in controlling well trajectory, improving drilling efficiency and saving drilling cost. In recent years, a large number of high-temperature wells have appeared, which makes the traditional MWD instruments no longer applicable. So far, no active cooling method has been successfully applied to MWD instruments for high-temperature oil and gas wells. This paper presents a new active cooling method for air drilling by utilizing the throttling and cooling of drilling gas, and the cooling system is designed. An axisymmetric numerical model of internal fluid is established, and different drilling gas flow channel design methods are discussed. The research results indicate that the wall temperature of the cooling section is much higher than the center fluid temperature, but lower than the ambient temperature, and can be used for active cooling of downhole drilling instruments. Compared with other design methods, the supersonic nozzle designed using the Bezier method has better parallelism of the gas in cooling section. The diffusion capability of straight wall diffuser is better than that of curved wall diffuser, and it can withstand greater back pressure. For straight wall diffuser, increasing the throat length and reducing the contraction and expansion angle can improve the diffusion capacity, but they also lead to a longer diffuser.

Reducing the taper and the heat-affected zone of CFRP plate by Micro fluid assisted laser induced plasma micro-drilling

Carbon Fiber Reinforced Plastics (CFRP) with superior mechanical properties are widely used in aerospace, automotive, and medical fields. The characteristics of CFRP with anisotropy and inhomogeneous result in poor machining performances by conventional drilling techniques. Laser drilling is a non-contact high precision machining technique without tool wear but leads to a large heat-affected zone (HAZ) and taper. Although underwater laser drilling could reduce thermal damage on CFRP surface, bubbles produced in the machining process severely affect the machining stability and surface quality. In this study, a micro fluid-assisted laser-induced plasma drilling (MFA-LIPMD) method was proposed to relieve the negative effect of bubbles as well as reduce the taper and HAZ. A comprehensive analysis of hole surface quality, HAZ, taper, and mechanical properties was conducted, and MFA-LIPMD performed more advantages over laser in the air (LIA) and laser-induced plasma drilling (LIPMD). It was found that the taper of micro-holes was reduced by 42.8%–51.78%, and the thermal damage rate of micro holes processed by the MFA-LIPMD process was reduced by 65.3%–68.1% compared with the LIPMD process, and the maximum tensile load of samples was increased by about 7.68%. Therefore, MFA-LIPMD has great potential for machining high-quality micro holes of CFRP plates.

Rheological effects of air drilling fluids on cuttings transportation in underbalanced drilling

This research investigates factors influencing cuttings transport efficiency in air drilling operations, aiming to understand the underlying mechanisms, identify critical factors, and optimize drilling parameters for enhanced performance. The methodology includes a literature review, computational fluid dynamics (CFD) simulations, and sensitivity analysis of air velocity, drilling fluid properties, cuttings size, and outlet pressure. CFD simulations were employed to model the multi-phase flow in the annulus during air drilling, examining the effects of varying air velocities, cuttings sizes, and outlet pressures on cuttings transport and hole cleaning efficiency. Results show that increased air velocity improves cuttings transport and hole cleaning but may cause higher pressure drops and borehole erosion. Air drilling fluids' unique rheological properties significantly impact cuttings transportation, requiring careful consideration of factors like air velocity, aerodynamic lift, hole cleaning efficiency, annular pressure losses, and potential cuttings accumulation. The study reveals that cuttings size is crucial for transport efficiency, with larger cuttings necessitating higher air velocities for effective transport and being more prone to settling and accumulation. Moreover, the research demonstrates that increasing outlet pressure typically enhances cuttings transport efficiency in horizontal wells. In conclusion, this study offers valuable insights into factors affecting cuttings transport efficiency in air drilling operations, providing recommendations for optimizing drilling parameters to balance efficient cuttings removal, hole cleaning, and minimal pressure drop. The findings hold practical implications for air drilling operations' design and execution, with the potential to improve drilling performance and reduce operational risks.

Axial-torsional nonlinear vibration of bottom hole assembly in the air drilling technology

The safety and efficiency of drilling engineering are greatly impeded by destructive vibrations of drill string in air drilling, such as stick-slip, bit-bounce and their coupled vibrations. To avoid or suppress these vibrations improving the stability of drilling operations, revealing the occurrence mechanisms of abovementioned harmful vibrations are indispensable by investigating dynamics characteristics of drill string system. In this paper, an axial-torsional coupled dynamics model that can capture the motion behaviors of bottom hole assembly (BHA) is established adopting the lumped parameter method. Subsequently, a rate of penetration (ROP) model appropriating for air drilling is obtained firstly by linear fitting means. Meanwhile, a novel discontinuous support model is established to describe the bit-formation interactions. Then, BHA dynamics are discussed using numerical simulations under different vibration scenarios: normal operation; stick-slip; bit-bounce; bit-bounce and stick-slip combination. Subsequently, in two drilling modes: the continuous and intermittent drilling, the vibration mitigation strategies and dynamics sensibility study of BHA are carried out based on the parametric analysis. The results show that increasing torsional stiffness of drill-pipes, appropriately adjusting rotation speed of top driven system and dynamic weight on bit (WOB) are deemed as an effective strategy suppressing or eliminating stick-slip and bit-bounce vibrations of BHA. Suggest that the rotation speed of top driven system and dynamic WOB are 5 rad/s and 3.5 kN, respectively. Finally, the constructed probability maps allow to driller to choose reasonable mechanical parameters, thereby realizing smooth drilling operation in the air drilling.

Mechanical characterization of bottom hole assembly in air drilling engineering

To study the mechanism and control of well deviation in air drilling, a mechanical model of bottom hole assembly (BHA) with double stabilizer is established by using the beam-column method. The mathematical model related to side force of BHA and deviating force of strata are derived by analyzing the characteristics of gravel strata in the practical engineering. The effects of weight on bit (WOB), expansion ratio of borehole diameter (ERBD), angle of well inclination, diameter of drill collar and strata bending moment on side force of BHA are explored. Then, the superposition of bit side force and deviating force of strata is obtained. The results display that side force of BHA is obviously influenced by ERBD, angle of well inclination, diameter of drill collar and strata bending moment; and the deviation force and azimuth force of gravel strata are significantly affected by comprehensive cutting anisotropy index, angle of well inclination and dip angle of strata. Finally, the variation tendency of inclination angle and azimuth angle in field measurement is consistent with the theoretical and numerical researches. The present work can provide theoretical guidance to control the well deviation in the practical air drilling.

Vibration-collision mechanism of dual-stabilizer bottom hole assembly system in vertical wellbore trajectory

The lateral vibration of drill string causes well deviation and the collision between drill collar and sidewall, and severe lateral vibration even affects the drilling safety or reliability. In view of the problems above, the lateral vibration characteristics of drill string need to be analyzed. Therefore, a newly vibration-collision model of BHA (bottom hole assembly) with random collision characteristics is proposed in this paper. Firstly, the dynamic model of drill collar with double stabilizer is presented by utilizing the Lagrange equations. Secondly, the dynamic characteristics of drill collar in air and mud drilling is analyzed with different collision frequencies. Subsequently, the displacement and motion trajectory of drill collar under different structure parameters of BHA and mechanical parameters of system are investigated by numerical simulation. Finally, the influence of rotation speed of BHA and length of drill collar on lateral vibration of drill collar is discussed. The results indicate that the lateral vibration of drill collar in air drilling is more serious than that in mud drilling; and the higher the collision frequency, the more severe the lateral vibration. Improving rotation speed of BHA, length of drill collar and WOB (weight on bit) have promoting influence on lateral vibration of drill collar; however, increasing stabilizer diameter has suppressing influence on lateral vibration of drill collar. The research findings give reasonable guidance for structure design of BHA and selection of mechanical parameters of system.

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 Analysis and Structural Optimization of Air Hammer Drill Teeth Based on ANSYS /LS_DYNA

Air drilling is a prevailing technology of oil and gas energy industry in today’s world, it can solve problems when drilling in complex layer that can not be done by conventional drilling way. At the same time, some failures of dill bit teeth in air hammer drilling like teeth falling, breaking and severe abrasion seriously affect the drilling efficiency. Thus this paper intended to investigate rock breaking criteria and damage constitutive model, establish a finite element simulation model of single tooth rock breaking and use the impact of dynamic finite element software ANSYS/LS-DYNA to analysis characteristics of rock crushing under confining pressure, which includes fragmentation process, drilling tooth impact and the crush volume of rock broken. The study found that the tapered tooth has the highest efficiency in rock breaking under the same conditions and with edge teeth at 25°angle that increases the rock crushing volume significantly. In addition, the configuration of tooth surface was examined, which showed that the pattern of “spherical teeth in the middle and tapered teeth in the peripheral” has highest rock breaking efficiency.

Mechanical Analysis and Structural Optimization of Air Hammer Drill Teeth Based on ANSYS /LS_DYNA

Air drilling is a prevailing technology of oil and gas energy industry in today’s world, it can solve problems when drilling in complex layer that can not be done by conventional drilling way. At the same time, some failures of dill bit teeth in air hammer drilling like teeth falling, breaking and severe abrasion seriously affect the drilling efficiency. Thus this paper intended to investigate rock breaking criteria and damage constitutive model, establish a finite element simulation model of single tooth rock breaking and use the impact of dynamic finite element software ANSYS/LS-DYNA to analysis characteristics of rock crushing under confining pressure, which includes fragmentation process, drilling tooth impact and the crush volume of rock broken. The study found that the tapered tooth has the highest efficiency in rock breaking under the same conditions and with edge teeth at 25°angle that increases the rock crushing volume significantly. In addition, the configuration of tooth surface was examined, which showed that the pattern of “spherical teeth in the middle and tapered teeth in the peripheral” has highest rock breaking efficiency.

Dynamics characteristics of axial–torsional–lateral drill string system under wellbore constraints

The combination of air and liquid drilling technologies is usually used for increasing rate of penetration (ROP) and protecting reservoir in drilling engineering. Meanwhile, dynamics characteristics of drill string system are closely relevant to drilling safety and well trajectory quality in the practical drilling engineering. Hence, in this paper, dynamics characteristics of axial–torsional–lateral coupled drill string system under wellbore constraints are emphatically concerned in the air and liquid drilling process. Firstly, a rotor dynamics model for revealing the dynamics characteristics of bottom hole assembly (BHA) with single stabilizer is established by the lumped parameter method. Moreover, two novel contact models for describing real-time interactions of BHA-sidewall and bit-formation are established through Hertzian contact theory and discontinuous support model, respectively. Then normal, stick–slip and bit-bounce modes of BHA are discussed on basis of coupling vibrations of drilling string in lateral, axial, torsional and whirling motion. Meanwhile, the dynamics responses of the BHA in the processes of air and liquid drilling are conducted by contrast analysis. Subsequently, dynamics behaviors of the BHA at different hardness formations are further revealed through numerical computations. The results indicate that the lateral, axial and torsional vibrations of BHA in the air drilling process are obviously stronger than the liquid drilling process in the same operation conditions. When drill bit suddenly encounters hard formation, especially in air drilling process, the dynamics characteristics of drill string system are easily disturbed, and the coexistence motion of stick–slip and bit-bounce is appeared in BHA, thereby leading to severe whirling and lateral impact of drilling string. Besides, when the BHA is out of contact with the sidewall, only the forward whirling of BHA is implemented; when the sidewall is frequently impacted by the BHA, forward and backward whirling of drilling string are easily happened; when the BHA is contact with the sidewall, the backward whirling of drilling string is easily appeared. Therefore, the proposed model in this paper may offer a comprehensive understanding for dynamics of BHA, and is expected to further develop dynamics studies of the BHA with double or multiple stabilizers.

Three dimensional wellbore feature of air drilling hole and its influence on bit side force

In existing drill string mechanics analysis, smooth and regular wellbore is assumed and makes the calculated results sometimes differ greatly from the actual situation. In this study, based on measured data, the well characteristics of air drilling are shown from static and dynamic aspects, which proves the irrationality of this assumption. A six-arm calliper logging tool was applied to measure the wellbore data, and a cubic spline function was firstly adopted to reconstruct the wellbore. Then a 3D dynamic visualization description of the wellbore was realized based on the visualization toolkit. The results indicate that the 3D dynamic wellbore view can intuitively describe the characteristics of a high ovality and notable axial irregularity of the cross section of the wellbore drilled with BHA with an air hammer (AH-BHA), while the wellbore drilled with a pre-bent pendulum bottom hole assembly(PBP-BHA) exhibits low ovality and a smooth and regular shape along the axial direction. This can explain why it is difficult to run casing in a hole section drilled with AH-BHA. The FEM calculation example shows that the regularity of wellbore has a great influence on the bit side force. The BHA, which generates a bit side force that would reduce wellbore deviation in regular wellbore, may even produce a bit side force that increases wellbore inclination in severely irregular wellbore, and can be used to reveal the deviation mechanism in the air/gas drilling process. Importantly, this result indicates that the assumption of irregular wellbore should sometimes be taken seriously in drill string mechanical analysis.

Analysis of wellbore stability of gas underbalanced drilling technology

Gas underbalanced drilling technology has the advantages of high ROP and little damage to oil and gas reservoirs. In recent years, it has been widely used in the exploration and development of oil and gas fields in China. Under normal air drilling conditions, the pore pressure is basically zero, so it is necessary to establish the wellbore stability model under the condition of zero pore pressure to provide theoretical support for the wellbore stability analysis of air drilling. However, gas underbalanced drilling also has wellbore instability, more sand deposition at the bottom of the well, and even the malignant accident of sticking. Firstly, through the analysis of the traditional wellbore stability model, the influence of pore pressure is removed, and the wellbore stability model suitable for air drilling is obtained. At the same time, it is proposed that the sand deposition is mainly caused by the collapse material when the collapse ellipse is formed on the shaft wall, and the formation of the collapse ellipse is conducive to maintaining the stability of the shaft wall. For large and medium-sized gravel layers, the influence of cementation strength on wellbore stability should be considered.

Theory and application of gas drilling technology

Gas drilling began in the 1950s. The drilling process is implemented by injecting a mixture of air and water into the well with an air compressor. Field experiments have gradually proved that air drilling in hard rock can improve the ROP by 2 ∼ 3 times, especially in reservoir protection. In this paper, the gas drilling technology is analyzed and discussed. The test results of gas drilling technology show that the drilling time is reduced and the mechanical ROP is greatly improved. Compared with mud drilling, the mechanical ROP of gas drilling in the same structure and well section is generally increased by 2 ∼ 10 times, the production of oil and gas wells is relatively high and the economic benefit is remarkable.

Evaluation of deep geothermal exploration drillings in the crystalline basement of the Fennoscandian Shield Border Zone in south Sweden

The 3.1- and 3.7-km-deep FFC-1 and DGE-1 geothermal explorations wells drilled into the Precambrian crystalline basement on the southern margin of the Fennoscandian Shield are evaluated regarding experiences from drilling, geological conditions, and thermal properties. Both wells penetrate an approximately 2-km-thick succession of sedimentary strata before entering the crystalline basement, dominated by orthogneiss, metabasite and amphibolite of the (1.1–0.9 Ga) Eastern Interior Sveconorwegian Province. The upper c. 400 m of the basement is in FFC-1 severely fractured and water-bearing which disqualified the use of percussion air drilling and conventional rotary drilling was, therefore, performed for the rest of the borehole. The evaluation of the rotary drillings in FFC-1 and DGE-1 showed that the average bit life was very similar, 62 m and 68 m, respectively. Similarly, the average ROP varied between 2 and 4 m/h without any preferences regarding bit-type (PDC or TCI) or geology. A bottomhole temperature of 84.1 °C was measured in FFC-1 borehole with gradients varying between 17.4 and 23.5 °C/km for the main part of the borehole. The calculated heat flow varies between 51 and 66 mW/m2 and the average heat production is 3.0 µW/m3. The basement in FFC-1 is, overall, depleted in uranium and thorium in comparison to DGE-1 where the heat productivity is overall higher with an average of 5.8 µW/m3. The spatial distribution of fractures was successfully mapped using borehole imaging logs in FFC-1 and shows a dominance of N–S oriented open fractures, a fracture frequency varying between 0.85 and 2.49 frac/m and a fracture volumetric density between 1.68 and 3.39 m2/m3. The evaluation of the two boreholes provides insight and new empirical data on the thermal properties and fracturing of the concealed crystalline basement in the Fennoscandian Shield Border Zone that, previously, had only been assessed by assumptions and modelling. The outcome of the drilling operation has also provided insight regarding the drilling performance in the basement and statistical data on various drill bits used. The knowledge gained is important in feasibility studies of deep geothermal projects in the crystalline basement in south Sweden.

Construction technology and parameter calculation of air drilling with raise boring machine

Based on the characteristics of raise boring technology and air drilling technology, the construction equipment and process of raise boring with air as circulating medium are studied. Raise air drilling equipment includes the hydraulic control system, the air-cooled cooler and the air compressor. The drilling process is that the bit is cooled by the high-pressure air, at the same time, the broken rock debris generated in the drilling process are discharged to the ground, and the high temperature hydraulic oil is cooled by the air-cooler cooler. By the study above, the problems are solved effectively such as heat dissipation, cooling and rock debris collection and discharge in the process of construction with raise boring machines without drilling fluids. Based on the basic assumption and the aerodynamic theory, the circulation system pressure of the raise air drilling is studied, the calculation method and formula of the annular pressure drop, bit pressure drop and rod pressure drop are presented. The research results can provide theoretical guidance and technical support for the application of raise air drilling technology.