Experimental and Numerical Simulation Study on the Mechanism of Fracture-Increasing and Permeability-Increasing in Granite Pore Walls by the Air DTH Hammer Percussion Drilling
Abstract
:1. Introduction
2. Experimental Methodology
2.1. Percussion Drilling Test
2.1.1. Granite Sample
2.1.2. Impact Specimen Processing
2.1.3. Percussion Drilling Equipment
2.1.4. Percussion Drilling Test Process
2.2. Percussion Crack Identification
2.2.1. Dyeing Experiment
2.2.2. CT Scan Recognition
2.3. Mechanical and Permeability Experiments
2.3.1. Mechanical Test
2.3.2. Permeability Measurement
3. Results and Discussion
3.1. Analysis of Fracture Distribution around the Wellbore
3.2. CT Analysis
- The three-dimensional length distribution of pores ranges from 0.06 to 2.38 mm, with pores smaller than 0.2 mm accounting for approximately 81% of the total number, and the number of pores shows a significant decreasing trend with the increase in three-dimensional length.
- The three-dimensional width distribution of pores ranges from 0.06 to 1.36 mm, with pores less than 0.15 mm accounting for about 93% of the total number, and the number of pores shows a significant decreasing trend with the increase of three-dimensional width.
- The equivalent diameter distribution of pores ranges from 0.06 to 0.91 mm, with pores ranging from 0.05 to 0.15 mm accounting for approximately 94% of the total number. The number of pores decreases significantly with the increase in equivalent diameter.
- The volume distribution of pores ranges from 0.00016 to 0.4 mm3, with pores with a volume less than 0.01 mm3 accounting for over 99%. Among pores with a volume greater than 0.015 m3, 85% are pores with a volume between 0.015 and 0.06 mm3. After a volume greater than 0.04 mm3, the number of pores decreases sharply.
- After drilling experiments, the porosity of the granite block increased from 0.0025% to 0.03%, and the porosity increased by about 12 times.
3.3. Analysis of Mechanical Test Results
3.3.1. Uniaxial Compression Test
3.3.2. Permeability Testing
3.4. Numerical Analysis of Impact Stress Waves
3.4.1. PFC3D-GBM Establishment Method Based on the Real Mineral Composition of Granite
3.4.2. Simulation Process
3.4.3. Simulation Result Analysis
4. Conclusions
- The dyeing test and CT results indicate that air DTH hammer drilling can increase wellbore cracks, and the distribution of cracks has a regional feature. Microcracks are distributed from near to far on the borehole wall and bottom, mainly related to the attenuation of impact stress waves. According to the analysis of the three-dimensional reconstruction results, the porosity of the granite block has increased from 0.0025% to 0.03%, and the porosity has increased by about 12 times.
- The results of mechanical and permeability testing experiments show that the air DTH hammer impact drilling process can reduce the strength of granite around the hole wall and increase porosity and permeability. The average strength of the granite has decreased by 16.5%, from 148.65 MPa to 124.81 MPa. The porosity has increased by 9.5%, from 1.127% to 1.234%. The permeability rate increased by 63.3%, from 0.0546 mD to 0.0891 mD. This further verifies the feasibility of this process for increasing permeability in geothermal mining.
- The numerical results are consistent with the experimental results. The results indicate that over time, the energy of stress waves decreases with the distance from the impact location, and the energy propagates faster along the impact direction compared to perpendicular to the impact direction. The failure of the rock mass also exhibits a regional pattern. The stress wave area in the simulation results agrees with the experimental crack distribution area, revealing the rationality of crack zoning distribution in the experiment.
- The next step is to study the air DTH hammer drilling mechanism to create fractures and increase permeability in thermal storage environments (high temperature and pressure). By changing the parameters of impact drilling, more impact fractures can be obtained to assist in developing and utilizing geothermal resources.
Author Contributions
Funding
Data Availability Statement
Conflicts of Interest
References
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Main Minerals | Quartz | Potassium Feldspar | Albite | Mica |
---|---|---|---|---|
Content | 28% | 36% | 31% | 5% |
Mechanical Properties | Values |
---|---|
Density, (kN/m3) | 26.3 |
Young’s modulus, E (GPa) | 35.6 |
0.23 | |
Tensile strength, σt (MPa) | 8.91 |
Uniaxial compressive strength, σc (MPa) | 148 |
Friction angle, Φ (deg) | 57 |
Porosity, % | 1.127 |
Permeability, (mD) | 0.0546 |
Drill Diameter (mm) | Edge Tooth Diameter (mm) | Minimum Wall Thickness (mm) | Minimum Side Length (mm) |
---|---|---|---|
140 | 18 | 44.82 | 229.64 |
Wellbore Diameter | Wellbore Depth | Weight of Bit | Weight of DTH | Pump Pressure | Input Flow | Rotation Rate | Rate of Penetration | Impact Energy | Impact Frequency |
---|---|---|---|---|---|---|---|---|---|
140 mm | 260 mm | 15.3 kg | 70 kg | 1.0 MPa | 7000 L/min | 30 r/min | 10.4 m/h | 4546.52 J | 30 Hz |
Location of Rock Samples | Sample Number | Length (cm) | Diameter (cm) | Average Compressive Strength (MPa) |
---|---|---|---|---|
Original rock sample | A1–A10 | 100 | 50 | 148.653 |
Near-borehole wall rock sample | B1–B10 | 100 | 50 | 129.680 |
Distant-borehole wall rock sample | C1–C10 | 100 | 50 | 142.027 |
Orifice rock sample | D1–D8 | 100 | 50 | 118.990 |
Borehole bottom rock sample | F1–F8 | 100 | 50 | 108.525 |
Location of Rock Samples | Sample Number | Length (cm) | Diameter (cm) | Average Porosity (%) | Average Permeability (Md) |
---|---|---|---|---|---|
Original rock sample | A1–A3 | 4.999 | 2.457 | 1.127 | 0.0546 |
Near-borehole wall rock sample | G1–G3 | 4.989 | 2.445 | 1.218 | 0.0911 |
Distant-borehole wall rock sample | H1–H3 | 4.990 | 2.465 | 1.156 | 0.0589 |
Orifice rock sample | J1–J3 | 5.491 | 2.450 | 1.191 | 0.1107 |
Borehole rock sample | K1–K3 | 4.987 | 2.460 | 1.370 | 0.0716 |
Micro-Parameters | Value | |||
---|---|---|---|---|
Mineral Properties | Quartz | Potassium Feldspar | Albite | Mica |
Content | 28% | 36% | 31% | 5% |
Minimum particle radius, mm | 0.06 | 0.06 | 0.06 | 0.06 |
Particle-size ratio | 1.66 | 1.66 | 1.66 | 1.66 |
Particle density, kN/m3 | 26.3 | 26.3 | 26.3 | 26.3 |
Contact normal to shear Stiffness ratio (kn/ks) | 1.5 | 1.5 | 1.5 | 1.5 |
Particle–particle contact modulus, GPa | 49 | 39 | 29 | 19 |
Particle friction coefficient | 1.2 | 1.2 | 1.2 | 1.2 |
Radius multiplier | 1.5 | 1.5 | 1.5 | 1.5 |
Parallel bond normal to shear stiffness ratio | 1.0 | 2.0 | 2.0 | 1.5 |
Parallel bond modulus, GPa | 19 | 16 | 15 | 10 |
Parallel bond tensile strength, MPa | 25 | 23 | 21 | 20 |
Parallel bond cohesion, MPa | 53 | 47 | 45 | 40 |
Parameters | Experimental Value | Simulation Value | Error, % |
---|---|---|---|
Tensile strength, MPa | 8.93 | 9.39 | 5.2 |
UCS, MPa | 148 | 153.6 | 4.6 |
Elastic modulus, GPa | 20.3 | 20.89 | 2.9 |
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Tian, L.; Yang, X.; Zhang, R.; Zheng, K.; Jiang, O.; Zheng, X. Experimental and Numerical Simulation Study on the Mechanism of Fracture-Increasing and Permeability-Increasing in Granite Pore Walls by the Air DTH Hammer Percussion Drilling. Processes 2024, 12, 758. https://doi.org/10.3390/pr12040758
Tian L, Yang X, Zhang R, Zheng K, Jiang O, Zheng X. Experimental and Numerical Simulation Study on the Mechanism of Fracture-Increasing and Permeability-Increasing in Granite Pore Walls by the Air DTH Hammer Percussion Drilling. Processes. 2024; 12(4):758. https://doi.org/10.3390/pr12040758
Chicago/Turabian StyleTian, Longjun, Xinxiang Yang, Renjie Zhang, Kai Zheng, Ou Jiang, and Xiuhua Zheng. 2024. "Experimental and Numerical Simulation Study on the Mechanism of Fracture-Increasing and Permeability-Increasing in Granite Pore Walls by the Air DTH Hammer Percussion Drilling" Processes 12, no. 4: 758. https://doi.org/10.3390/pr12040758
APA StyleTian, L., Yang, X., Zhang, R., Zheng, K., Jiang, O., & Zheng, X. (2024). Experimental and Numerical Simulation Study on the Mechanism of Fracture-Increasing and Permeability-Increasing in Granite Pore Walls by the Air DTH Hammer Percussion Drilling. Processes, 12(4), 758. https://doi.org/10.3390/pr12040758