Ordinary Drilling Research Articles

Research and application of PDC coring bit in marine drilling

Abstract The coring exploration and analysis of geological rock debris is an important part of offshore oil exploration engineering. The existing drilling coring technology has problems such as low drilling efficiency and the need for drilling operations, which increases the cost of offshore drilling. In order to improve the efficiency of offshore oil drilling and reduce drilling costs, a micro coring Polycrystalline Diamond Compact bit (PDC) has been developed, which can continuously obtain micro cores during the drilling process. Through mechanical analysis of the core teeth, the relationship between the back inclination angle of the core teeth and the rock shear failure angle was obtained. The analysis conclusion shows that the larger the back inclination angle, the more favorable it is for micro core formation. As the back inclination angle increases, the force on the core teeth increases, which affects the service life of the core teeth. Based on the rock core forming effect and the force analysis of the core teeth, the back inclination angle of the core teeth is determined to be 20 °. An analysis was conducted on the application of the micro coring PDC drill bit in three offshore drilling operations, including drilling speed, drilling efficiency, drill bit exit, and the quantity and quality of core samples obtained. The results showed that the drilling speed of the micro coring PDC drill bit was significantly improved compared to ordinary drill bits during offshore drilling, and a large number of block shaped cores and a few cylindrical cores were obtained. The application results of micro coring drill bits in offshore drilling show that this technology is beneficial for improving drilling speed and efficiency. It has the advantages of large core acquisition volume, high acquisition efficiency, and low cost in obtaining micro cores. To address the issue of low formation rate of rock cores obtained during offshore drilling applications, optimization can be achieved by adjusting the diameter of the core hole, arranging the core teeth, and adding seismic mitigation measures for rock core formation.

Research on the Effective Extraction radius of Directional Long Boreholes for Coalbed Methane Extraction Based on Gas Extraction Quantity Measurement

In order to solve the problems of low utilization rate of coalbed methane and difficult gas control in the working face caused by the difficulty of ordinary drilling construction for gas extraction in a high gas mine, a study was conducted on the effective extraction of coalbed methane using directional long drilling in the 2212 working face of a certain coal mine. Through on-site experimental investigation and theoretical analysis, the effective extraction radius of directional long boreholes in the working face was calculated under different pre extraction times, providing a scientific basis for the rational design of directional long boreholes for coalbed methane extraction.

Experimental Study on Gas Drainage Through Long-distance Bedding Directional Borehole

In order to solve the problem of gas exceeding the limit in the No.3 coal seam excavation face of Huoerxinhe coalmine, the gas outburst control measure was adopted to pre-evacuate the gas by the long-distance bedding directional borehole. The results show that after 25 days of gas drainage by long-distance bedding directional borehole, the gas content of test point decreased from 13.81m3/t to 7.81m3/t, and the gas pre-pumping rate was about 43.30%. The driving speed of the main transport roadway was 1.48 times that of the traditional ordinary drilling drainage measures, and the tunneling efficiency indicators had not exceeded the standard. Through the application of this measure, it is confirmed that the long-distance bedding directional borehole can effectively reduce the drilling hole construction amount and increase the gas extraction rate, and effectively eliminate the danger of protruding, and realize the safe and rapid excavation of the coal mine roadway.

Research and application of pressure relief and permeability improvement in high gas outburst mines by directional drilling and hydraulic jet

Efficient gas extraction technology is an important topic for low permeability and high gas outburst coal seam. Based on the engineering background of Hudi Coal Mine with the soft and hard coal seams and the existing hydraulic permeability enhancement technology, a new construction process to improve coal seam permeability was proposed to effectively reduce coal seam gas content and the risk of coal and gas outburst. In this measure, the roadway in floor was replaced with a directional main borehole, directional branch boreholes were used to replace crossing holes, and soft coal was mined along soft sub layers via the directional drilling machine and directional hydraulic jet. Main boreholes are drilled parallel to the seam in the coal seam floor, and branch boreholes are drilled through the floor and coal seam. The numerical simulation was used to study the permeability improvement effect of different mining diameters by the proposed measure. The result showed that, as the mining diameter increased from 2 m to 4 m, the average influence diameter of coal seam porosity increased from 15.44 m to 19.65 m, and the average influence diameter of the permeability increased from 15.75 m to 20.07 m, which is three times the influence range of the ordinary borehole. The application of the proposed measure and its supporting equipment was carried out under the special coal seam and gas conditions of Hudi Coal Mine. Results show that the soft coal was mined efficiently along the soft sub layer using the main borehole, branch boreholes, and directional hydraulic jet. Compared the traditional hydraulic flushing in the borehole with the ordinary drilling machine, the average speed of mining soft sub layers increased from 0.5 t/h to 3.6 t/h, the equivalent mining diameter of soft sub layers increased from 1.2 m to 7.6 m, and the average flow of gas extraction increased from 0.41 m3/d to 6.25 m3/d. The conclusions obtained in this study can provide a reference for coal mine gas extraction with similar coal seam conditions.

Experimental Investigation on the Impacts of Fracture Roughness and Fluid Composition on the Formation of Bubble Bridges through the Microbubble Fluid Flow.

The colloidal gas Aphron (CGA) drilling fluids are an alternative to ordinary drilling mud to minimize formation damage by blocking rock pores with microbubbles in low-pressure or depleted reservoirs. Fractured formations usually have different characteristics and behavior in contrast to conventional ones and need to be investigated for Aphron applications. In this research, a series of core flood tests were conducted to understand the factors controlling the pore-blocking mechanisms of microbubbles in fractured formations. For the first time, a synthetic metal plug was used to simulate the fracture walls and eliminate the formation matrix effect. This study analyzed the effects of three fluid compositions, considering the polymer and surfactant concentrations at reservoir conditions, including temperature and overburden pressure. Additionally, fracture surface roughness as one of the parameters affecting the microbubble fluid penetration through the fracture path and bubble blockage were studied. The results indicated that microbubble fluid composition would not affect the bubble size or blockage probability. The different stable microbubble fluids resulted in the same pattern and conditions. Besides, fluid penetration would be more challenging if the fracture roughness decreased. Due to the accumulation of bubbles and the fact that some of them were trapped in the fracture's rough surface, the blockage possibility increased. According to the range of roughness for the steel core in previous studies and compared with the roughness of carbonate reservoir rocks, the roughness of fractured reservoir rocks is much higher than that of the steel surface. Accordingly, the observed trend in the experiments showed that when it is possible to form a bubble bridge in steel cores, then in carbonate rocks, we will definitely see blockage with any roughness, provided that other parameters are acceptable.

BTA Deep Hole Vibration Drilling for Nickel-Based Alloys: Cooling Patterns and Cutter Tooth Wear Mechanisms.

The high cutting temperature and poor thermal diffusion efficiency of nickel-based alloys during deep hole machining have become technical challenges in the hole machining field. In this paper, a finite element simulation model of Inconel-718 BTA ordinary drilling and vibration drilling processes was established by using Deform-3D finite element simulation software. The variations in the temperatures of the tool teeth and the workpiece at different positions of the nickel-based alloy under ordinary drilling and vibration drilling were investigated. Additionally, the wear pattern of each tool tooth under the two drilling methods was further analyzed by building an experimental platform for workpiece temperature detection, which reveals the wear and cooling mechanism of nickel-based alloy BTA deep hole drilling. The results show that the average temperatures of the external, intermediate, and central teeth were reduced by 18.1%, 21.1%, and 17.8%, respectively, during vibration drilling. In addition, the workpiece hole wall and hole bottom temperatures were reduced by 5.7% and 4.6%, respectively. To conclude, the experimental tests were consistent with the simulated temperature trends. BTA vibration drilling optimizes the heat exchange conditions between the cutter teeth and the workpiece during the drilling of nickel-based alloys, which effectively reduces the cutting temperature and, thus, improves the wear resistance of the cutter teeth.

Analysis and Research on Bit Rigidity of Carbon Fiber Composite Vibration Drilling

To explore the effect of vibration drilling on bit rigidity, the motion characteristics of the bit during vibration drilling were analyzed theoretically. According to the change of the minimum cutting thickness hmin, the bit rigidity theory was deduced, and the bit rigidity theory was verified by the drilling test of Carbon fiber reinforced polymer/aluminum alloy laminated structure. The experimental results show that; Compared with ordinary drilling, the machining accuracy of upper and lower aperture in vibration drilling is increased by 46.6% and 28.5% respectively, which makes the bit rigid and improves the stability and drilling accuracy.

Performance of a hybrid heating system based on enhanced deep borehole heat exchanger and solar energy

Deep borehole heat exchanger (DBHE) is a closed loop system without the problem of fluid losses, scale formation and corrosion; however, low rock thermal conductivity limits its performance. Enlightened by drilling mud loss in oil and gas industry, here an enhanced DBHE (EDBHE) is proposed by filling materials with much higher thermal conductivity into leakage formation or depleted gas and oil reservoir to enhance the thermal conductivity performance of rock. Solar thermal energy is stored into EDBHE during the non-heating season to replenish the loss of heat energy extracted during the heating season. The results show that average heat mining rate for 20 years operations is, respectively, 3686.5 and 26,384.4 kW for EDBHE filled by ordinary drilling mud and by composite materials with high thermal conductivity. The percentage reduction of heat mining rate for 20 years operations for EDBHE and the hybrid system of geothermal and solar energy are, respectively, 16.1 and 5.8%, indicating that the hybrid system can make the heat mining rate more stable.

Study on Crack Penetration Induced by Fatigue Damage of Low Permeability Coal Seam under Cyclic Loading

For low permeability coal seam permeability is weak, low degree of gas migration, prone to gas accidents and other issues. In this paper, a numerical model is established to simulate the process of hydraulic fracturing under monotonic loading and cyclic loading, and a method of increasing permeability of coal seam by cyclic loading hydraulic fracturing technology is proposed. Combined with similar experiments, the influence of cyclic load and cyclic load applied parameters on the fracturing effect of coal and rock mass was analyzed by applying a cyclic load with a pulse pump. The effect of cyclic load pressure technology on coal seam drainage was analyzed by application in 20915 gas control roadways of a coal mine in Guizhou. The results show that after fracturing, the fracture extends along the weak plane of the prefabricated fracture, the pore pressure in the fracture is high pressure, and the pore pressure around the fracture decreases step by step. Due to the compression of the crack, the energy is transferred to the two ends of the crack. The pore pressure has an irregular oval distribution, and there is stress concentration. The pressure value reaches 41.48 MPa. After the cyclic load was applied to the model, the pressure reached the maximum value of 27.64 MPa at 3.37 s. Compared with the monotonic load, the pressure value was reduced by 46.27%. Through pressure and ringing analysis, the fatigue damage of specimens can be realized under cyclic loading. In the experiment, the unconstrained initiation pressure was 2.48 MPa, but after the constraint was applied, the initiation pressure increased to 4.58 MPa, and the pressure increase reached about 55%. After multiple loading and unloading, the peak pressure of the specimen can be reduced and the number of cracks can be increased. In the experiment, the gas extraction rate of ordinary drilling was maintained at about 0.019 m3/min, and the gas extraction rate of ordinary fracturing drilling fluctuated at 0.025 m3/min after 21 days of gas extraction. The pumping capacity of 15 Hz and 20 Hz cyclic loading fracturing boreholes tended to be stable after 15 days, which were about 0.041 m3/min and 0.062 m3/min, respectively. Cyclic loading hydraulic fracturing is better than monotonic loading hydraulic fracturing, and the lower the cyclic loading frequency, the better the fracturing effect.

New Technology of Mechanical Cavitation in a Coal Seam to Promote Gas Extraction.

Realizing efficient gas drainage in low permeability coal seams has always been a difficult problem for coal miners. Based on this, this paper proposes a new technology of large-diameter mechanical cave-making to promote gas extraction in a coal seam. This technology mainly uses the pressure of a water injection pump to control the automatic opening and closing of a mechanical reaming device to realize mechanical cavitation, and the hole diameter can reach up to 500 mm. The gas drainage effect of mechanical cavitation drilling is analyzed by a numerical simulation, which shows that under the condition of the same drainage time, the larger the cavitation radius is, the larger the effective influence radius of gas drainage is. According to the field test results, the time of single cave-making is about 5 min, and the speed of cave-making is fast. The coal output of a single cave is 0.42 t/m, and the pressure relief effect is obvious. Compared with ordinary drilling, the gas drainage concentration of mechanical cavitation drilling is increased by 2 times and the net amount of drainage is increased by 1.8 times. Large-diameter mechanical cavitation technology can better improve the gas drainage effect of outburst coal seams with low permeability and has a good application prospect.

Study on exit damage characteristics of ultrasonic vibration assisted drilling of CFRP

In order to solve the disadvantage of tearing and burr damage in axial drilling of carbon fiber reinforced plastics (CFRP), the stiffness at the exit is increased by applying different drilling speed in ultrasonic vibration assisted drilling (UVAD) Firstly, compared with conventional drilling (CD), ultrasonic assisted vibration drilling can realize the separation of axial tool and tool/chip; Secondly, the cutting speed characteristics of ultrasonic assisted drilling at different speeds are analyzed, and the change of cutting speed characteristics of ultrasonic assisted drilling at low speed is obvious; Finally, the change trend of contact rate at different speeds is analyzed. The experimental results show that the stiffness of ultrasonic assisted vibration drilling is significant. Taking the speed of n = 100 r/min as an example, the stiffness of ultrasonic assisted drilling is about twice as high as that of rotary speed n = 2400 r/min, which is about 8% higher than that of ordinary drilling when n = 100 r/min; Hole exit quality of low-speed drilling: compared with CD, the tearing factor of ultrasonic assisted vibration drilling is lower. Therefore, this method provides a way to improve the hole quality of CFRP.

Experimental Research on Longitudinal Ultrasonic Assisted Vibration Drilling of 0Cr17Ni4Cu4Nb

In the present study, by adding ultrasonic vibration in the longitudinal direction to assist the drill bit to drill on 0Cr17Ni4Cu4Nb stainless steel, in order to obtain high-quality deep small holes and prolong the service life of the drill bit. By establishing the movement mathematical model of the drill bit under ordinary drilling and longitudinal vibration drilling, the movement trajectory of the main cutting edge of the drill bit in two different drilling methods is compared and analyzed, and the anti-friction mechanism of longitudinal vibration drilling is analyzed. The conventional drilling and longitudinal ultrasonic drilling of 0Cr17Ni4Cu4Nb stainless steel are carried out on a longitudinal ultrasonic vibration drilling device. After drilling test, the wear morphology of the drill bit, the surface roughness of the hole wall and the chip morphology are observed and analyzed by the detection equipment. The result shows: the wear degree of the drill bit after longitudinal ultrasonic vibration drilling is lower than that of conventional drilling, which can prolong the service life of the drill bit. The surface roughness of the hole wall is reduced, and the drilling chips are more finely divided and easier to discharge.

Research and Optimization of Gas Extraction by Crossing-Seam Boreholes from Floor Roadway

Deep coal seams are characterized by large stress, high gas pressure, and low permeability. The gas disaster threatens the safe production of coal mine seriously. Gas extraction by crossing-seam boreholes from floor roadway (GECMBFR) can reduce the pressure and content of coal seam gas, which is the main measure to prevent gas disaster. Considering the Klinkenberg effect, governing equations of gas adsorption/desorption-diffusion, gas seepage, and stress fields within the coal seam are established to form the seepage-stress coupling model. The governing equations are embodied into a finite element driven software to numerically simulate gas migration and fluid-solid coupling law in coal seam. On this basis, the process of gas extraction under different borehole spacings and diameters is simulated. The effects of these two key parameters on coal seam gas pressure, gas content, and gas permeability were analyzed. The borehole spacing and diameter were determined to be 5 m and 0.09 m, respectively. Combined with the actual situation of a mine, the process of gas extraction from floor roadway with different cross-sectional schemes, ordinary drilling boreholes and punching combined drilling boreholes, is comparatively analyzed. The results show that the gas extraction effect by ordinary drilling boreholes is lower than that of the punching combined drilling boreholes, and the extraction is uneven and makes it difficult to meet the standard. Hydraulic punching was carried out, and coal was washed out of the borehole, which expanded the contact area between the borehole wall and coal seam. The coal seam around the punching borehole is unloaded, which improves coal permeability and accelerates gas migration towards the borehole, thus promoting the efficiency of gas extraction. It is more reasonable to use punching combined drilling borehole scheme when implementing the GECMBFR technology.

Reasonable Scope of Kilometer Drilling in Lower Layer of Extrathick Coal Seam: A Case Study of Tingnan Coal Mine, China

When stratified mining is adopted in high-gas and extrathick coal seam, a large amount of pressure-relief gas of the lower layer flows into the upper layer goaf along the cracks in the layer, resulting in upper layer working face to frequently exceed the gas limit. And ordinary drilling can no longer meet the requirements of the pressure-relief gas drainage of the lower layer. The 205 working face of Tingnan Coal Mine is taken as the test background in this paper, and based on the “pressure-relief and flow-increase” effect of the lower layer under the action of mining stress during the upper layer mining, the gas drainage of kilometer directional drilling in lower layer is studied. According to the distribution characteristics of support pressure before and after the working face, the pressure-relief principle, fracture development characteristics, and gas migration law of the lower layered coal body are analyzed in the process of advancing the upper layered working face in the extrathick coal seam with high gas. The maximum depth of goaf damage is calculated theoretically, and the Flac3D numerical simulation of the failure deformation of the 205 working face floor is carried out. It is found that the maximum depth of plastic failure of the lower layer is about 13 m. According to the plastic deformation of the lower layer under different vertical depths and the movement of coal and rock mass, it is determined that the reasonable range of kilometer directional drilling in the lower layer is 6–9 m below the floor vertical depth. From 15 m to 45 m in the two parallel grooves, there is no fracture failure with a sharp increase or decrease in the displacement in the local range. Meanwhile, in this part, the roof falling behind is not easy to compaction, and the displacement of the floor is large, which does not cause plastic damage. The degree of pressure relief is more sufficient, and the permeability of the lower layer is good. Therefore, drilling should be arranged as much as possible along the working face in this tendency range. The determination of reasonable arrangement range of kilometer directional drilling in extrathick coal seam provides reference index and theoretical guidance for industrial test of working face and also provides new ideas for gas control of stratified mining face in high-gas and extrathick coal seam.

Experimental study on ultra high pressure hydraulic cutting seam pressure relief and permeability enhancement of strip drilling along seam in C19 coal seam of Shiping No.1 Coal Mine

In view of the low permeability of C19 coal seam in Shiping No.1 coal mine, the large amount of drilling work and the long time of reaching the standard of extraction, which seriously restricts the replacement of mining, the ultra-high pressure hydraulic cutting technology is adopted to improve the permeability of coal seam. After using ultra-high pressure hydraulic slotting, the average single hole chip removal is 3.31t, the average chip removal per cutter is 0.38t, the width of slotting slot is 4cm, and the equivalent radius of slotting slot is 1.59m. The field test results show that the pressure relief and permeability enhancement effect of 11719 lifting machine roadway (East) in Shiping No.1 mine is significantly improved under this parameter condition. The single hole drainage pure quantity of slotted drilling is 7.8 times that of ordinary drilling, the concentration is increased by 2-2.4 times, the drilling construction quantity is reduced by 30.6%, the drilling drainage time is shortened by 80.7%, and the drilling gas drainage efficiency is greatly improved.

Numerical simulation study on gas drainage by interval hydraulic flushing in coal seam working face

In order to solve the problem of difficult gas extraction in coal mine, a method of gas extraction from coal seam by interval hydraulic flushing is put forward. Based on the coal seam gas occurrence conditions of 7609 working face in Wuyang Coal Mine, the numerical simulation research on gas drainage by ordinary drilling and hydraulic flushing drilling was carried out by using COMSOL numerical simulation software. The results show that with the increase of hydraulic flushing coal quantity, the effective gas drainage radius also increases. The effective extraction radius of ordinary drilling is 0.5 m, and the effective extraction radius is 1.0 m, 1.2 m and 1.3 m respectively when the coal flushing quantity is 0.5t/m, 1.0t/m and 1.5t/m. As multiple boreholes are drained at the same time, the boreholes will affect each other, which will reduce the gas pressure and increase the effective drainage radius, the spacing between boreholes can be greater than twice the effective drainage radius of a single borehole when arranging boreholes. And the smaller the flushing interval, the more uniform the gas pressure reduction area. According to the numerical simulation results, the ordinary drilling and 1.0t/m interval hydraulic flushing test were carried out in the field. Through observation and analysis, the gas concentration of the interval hydraulic flushing drilling module was increased by 31.2% and the drainage purity was increased by 5.77 times compared with the ordinary drilling module. It shows that the interval hydraulic flushing drilling can effectively improve the gas drainage effect.

Study of Complex Helical Drill with a “S” Type Chisel Edge Tip Orient to Carbon Fiber Reinforced Plastics

In this paper, a complex helicoids’ drill tip of “S” type chisel edge grinded with a three‐parallel universal CNC grinding machine tool is carefully studied to obtain the optimum drill bit tip geometry parameters. The effects of experimental parameters, such as apex angle, chisel edge incline angle, and structure circumference rear angle, on the quality of the drilling hole and the machining force were studied from the orthogonal experiment compared with the ordinary drill bit. The range of technological parameters are confirmed which should be used during the drilling process of carbon fiber reinforced plastics (CFRP) in order to realize the reduction of cutting defects such as cutting force and spurs. The effect of spindle speed and feed on the drilling behaviour of the experiment using optimum complex helicoids’ drill tip is also analyzed. It is found that the feed has a great influence on the drilling axial force and the spindle speed has little influence on axial force, but great influence on torque.

Research and Application of Hydraulic Punching Pressure Relief Antireflection Mechanism in Deep “Three‐Soft” Outburst Coal Seam

To solve the problems of gas predrainage in deep seams with “three softs” and low‐air permeability, hydraulic punching pressure relief antireflection technology is proposed on the basis of the research background of gas predrainage technology in Lugou Mine to alleviate technical problems, such as low gas drainage efficiency, in this mine. Through the analysis of the mechanism of hydraulic punching and coal breaking, combined with FLAC3D software, a hydraulic punching pressure relief antireflection model is established. Then, the fracture radii of coal rock are simulated and calculated. The results show that, under hydraulic punching with a water pressure of 10 MPa and coal outputs of 3 m3, 6 m3, 9 m3, and 12 m3, the fracture radii of coal and rock are 3.4 m, 4.8 m, 5.5 m, and 5.9 m, respectively. Using the software to fit the relationship between coal output V and hydraulic punching fracture radius R under the same water pressure, R = 2.32479 V0.3839 is obtained. The field test is carried out in the bottom drainage roadway of 32141 in Lugou Mine. The application effect is as follows: the gas concentration of hydraulic punching with a coal output of 3 m3 is twice that of ordinary drilling, and the coal output of hydraulic punching with a coal output of 6 m3 is four times that of ordinary drilling. The extraction concentration is four times that of ordinary drilling, and the extraction concentration of hydraulic punching with a coal output of 9 m3 is 6.4 times that of ordinary drilling. Combining the results of the numerical simulation and taking into account the actual construction situation on site, the coal output of water jetting from the borehole is 9 m3, and the fracture radius is 5.5 m. This outcome means that the effective half radius is 5.5 m, and the borehole spacing is 7.7 m. These values are the construction parameters for large‐scale applications. This proposal provides effective technology and equipment for gas drainage in the deep three‐soft coal seam. Consequently, it has promotion and reference significance for gas drainage in coal seam of the same geological type.

Research on gas pre-drainage in coal roadway strips by combined ordinary drilling and directional drilling

Research on gas pre-drainage in coal roadway strips by combined ordinary drilling and directional drilling

Modeling and experimental investigation of drilling force for low-frequency axial vibration-assisted BTA deep hole drilling

The ability to form regular chips and evacuate them smoothly is crucial for deep hole drilling. In this work, an eccentric cam mechanism is used to apply low-frequency axial vibration at the end of the drill tube for boring and trepanning association (BTA) deep hole machining, and the instantaneous cutting thickness equation of low-frequency axial vibration assisted drilling is derived, which can actively control the length of the chip and achieve a good chip removal effect. Considering the variable geometric parameters and the scale effect of teeth cutting, a new analytical model is established to obtain the instantaneous drilling force of staggered teeth BTA deep hole drill assisted by low-frequency axial vibration. The relevant parameters in drilling force model are identified, and the distribution laws of the normal friction angle, normal shear angle, and shear stress with instantaneous cutting layer thickness and drilling radius values are achieved. The influence of the vibration drilling process parameters, including feed, speed, amplitude, and frequency ratio, on the drilling force is investigated experimentally, and the validity of the drilling force model is verified. These results show that the drilling force model is reliable, and the thrust and torque of the low-frequency axial vibration assisted drilling relative to ordinary drilling are reduced by 21.63% and 13.74%, respectively.