An iterative optimization design method for high-voltage pulse discharge rock breaking system

Abstract

The present invention discloses an iterative optimization design method for a high-voltage pulse discharge rock-breaking system, and belongs to the field of pulse power technology. The method includes: determining the rock-breaking requirements, determining the types of rock and liquid medium and the borehole diameter; determining the volt-second characteristics, and drawing the volt-second curves of the rock and liquid medium under actual working conditions; optimizing the electric field of the crushing electrode, iteratively optimizing the electric field of the crushing electrode, so that the electric field distribution of the crushing electrode meets the rock-breaking requirements; optimizing the output voltage pulse, iteratively optimizing the design of the driving source, so that the output voltage pulse meets the rock-breaking requirements. Starting from the actual rock-breaking requirements, the present invention optimizes the design of the crushing electrode and the driving source respectively through finite element simulation and circuit simulation software, provides guidance for the design of the high-voltage pulse discharge rock-breaking system, improves the design efficiency of the high-voltage pulse rock-breaking system, reduces the design cost of the system, and improves the rock-breaking efficiency, reliability, service life of the system, and applicability to different working conditions.

Description

Technical Field

[0001] The present invention belongs to the field of pulse power technology, and more specifically, relates to an iterative optimization design method for a high-voltage pulse discharge rock breaking system. Background Art

[0002] In the field of oil and gas development, drilling projects have always been the most cost-intensive projects. At the same time, they are full of risks of different types and magnitudes, and require a high level of technical level for engineering operations. According to the statistical results of oil and gas field development at home and abroad, the funds consumed by drilling will account for more than 50% of the total development cost, and the risks generated will account for 80% of all possible risks. Rock breaking technology is one of the main core technologies of this project. The technical level of rock breaking directly affects the efficiency and cost of drilling, and thus has a decisive impact on the entire oil and gas production project. For some complex terrain environments, rock breaking is often difficult, which makes the drilling speed slow and the time long in the drilling project, increasing the cost of development. Moreover, as the drilling depth of the mechanical drill bit increases during the drilling process, the drill bit will be affected by the high temperature and high pressure environment downhole, the difficulty of drilling projects gradually increases, and the drilling speed gradually decreases.

[0003] High-voltage pulse discharge rock-breaking technology is a newly developed technology in recent decades. It applies pulse power technology to drilling projects, and uses the voltage waveform, electrode form, liquid medium and rock to form a discharge channel inside the rock. With the injection of external energy, the high-temperature and high-pressure plasma channel expands rapidly outward, generating huge mechanical stress in a short period of time, and generating shock waves to the outside, forming cracks in the surrounding rock formations. Under the action of multiple pulses, the rock is broken through the cumulative effect. The premise for high-voltage pulse discharge rock-breaking technology to achieve efficient rock breaking is that the plasma channel is formed inside the rock, which places high requirements on the wavefront steepness of the output voltage waveform, and needs to reach a high voltage of several hundred kilovolts within 100ns. In addition, due to the different borehole diameters, crushing electrodes with different outer diameters are required, and the crushing electrodes are generally designed to be coaxial claw-shaped.

[0004] The existing high-voltage pulse rock breaking system first designs the driving source, and then designs the crushing electrode according to the different apertures. There are problems such as the mismatch between the driving source and the crushing electrode. As the outer diameter of the crushing electrode increases, the distributed capacitance of the crushing electrode increases and the leakage resistance decreases, resulting in a slower rise steepness of the output voltage pulse, which cannot meet the requirements of rock crushing. Different combinations of rocks and liquid media have different requirements for rise time and breakdown field strength. The existing high-voltage pulse rock breaking system ignores the optimization of the crushing electrode and the driving source for different working conditions when designing. Ignoring the optimization of the crushing electrode leads to problems such as local electric field distortion of the crushing electrode and the inability of the electric field distribution to adapt to the actual working conditions. After the rock is crushed in some areas, the discharge occurs through the liquid medium, resulting in the termination of the rock breaking process; ignoring the optimization of the driving source leads to poor coordination between the output voltage pulse amplitude and the rise time, making the rock unable to be crushed or the rock crushing efficiency is low, the rock breaking speed is slow, and the rock breaking cost is high. The existing design method lacks simulation verification and iterative optimization before system design. After the system design is completed, the applicability of the device is directly verified through rock breaking experiments. If it cannot meet the actual rock breaking needs, the system needs to be designed again, resulting in a long design cycle and high manufacturing cost of the high-voltage pulse rock breaking system. Summary of the invention

[0005] In view of the defects of the prior art or the need for improvement, the purpose of the present invention is to provide an iterative optimization design method for a high-voltage pulse discharge rock breaking system, so as to improve the design efficiency of the high-voltage pulse discharge rock breaking system, reduce the design cost of the high-voltage pulse discharge rock breaking system, and improve the system's rock breaking efficiency, reliability, service life and applicability to different working conditions.

[0006] To achieve the above object, the present invention provides an iterative optimization design method for a high-voltage pulse discharge rock breaking system, comprising:

[0007] Step 1: Determine rock breaking requirements: determine the types of rock and liquid media and the drilling diameter under actual working conditions;

[0008] Step 2: Determine the volt-second characteristics: Draw the volt-second curves of rock and liquid medium under actual working conditions and determine the rise time t of the required voltage pulse r , rock breakdown field strength E a And the liquid breakdown field strength E b ;

[0009] Step 3, Optimize the electric field of the crushing electrode: Determine the outer diameter of the crushing electrode according to the borehole diameter; determine the electric field distribution requirements of the crushing electrode according to the volt-second characteristics of rock and liquid. By adjusting the number and shape of the crushing electrode poles, the electric field distribution of the crushing electrode is iteratively optimized to meet the electric field distribution requirements and obtain the distributed capacitance C of the crushing electrode. w With the leakage resistor R w .

[0010] Step 4: Optimize the output voltage pulse: According to the distributed capacitance and leakage resistance of the broken electrode, the output voltage pulse is iteratively optimized by adjusting the drive source design so that the output voltage pulse rise time t r ' and the output voltage amplitude U' meet the requirements.

[0011] The specific process is to first determine the actual rock breaking conditions, determine the crushing aperture, rock type and liquid medium type used between the crushing electrodes under the conditions, and measure the main electrical parameters of the liquid medium such as dielectric constant and conductivity.

[0012] Furthermore, the volt-second characteristic curve of rock breakdown field strength and action voltage rise time is drawn according to the rock type and liquid medium type, and the voltage rise time and the breakdown field strength of rock and liquid medium are determined according to the volt-second characteristic curve and its intersection. Since the breakdown of rock and liquid medium is dispersed, the breakdown field strength curve has a certain width, resulting in multiple intersections of the characteristic curves of the two media. The intersection with the shortest rise time is taken as the reversal critical point of the electrical strength of rock and liquid medium, and the time less than a few nanoseconds of the horizontal coordinate of this point is taken as the rise time t of the required voltage pulse. r For the required voltage pulse rise time t r , take the upper limit of the breakdown field strength of the rock volt-second characteristic curve as the required rock breakdown field strength E a , take the lower limit of the breakdown field strength of the liquid medium volt-second characteristic curve as the required liquid medium breakdown field strength E b .

[0013] Furthermore, the electric field distribution of the crushing electrode is designed and optimized. The crushing electrode adopts a coaxial claw design, which mainly includes two parts, a high-voltage electrode and a low-voltage electrode. Both are axisymmetric structures. The number of claw ends (the part of the claw-shaped crushing electrode that contacts the rock) is equal. The claw ends are staggered and placed at equal distances during design. The high-voltage electrode claw end and the adjacent low-voltage electrode claw end constitute the basic action unit for rock crushing. The number of crushing electrode pole pairs is the number of high-voltage electrode claw ends.

[0014] Furthermore, the finite element analysis software was used to build a simulation model of the crushing electrode. The main steps are:

[0015] 1. Set the outer diameter of the crushing electrode model according to the drilling diameter requirements;

[0016] 2. Design the initial pole pairs and shape of the broken electrode model according to the actual working conditions;

[0017] 3. Set the working environment of the crushing electrode model according to the electrical parameters of the liquid medium in the rock breaking requirements;

[0018] 4. Set the voltage pulse amplitude U acting on the crushing electrode.

[0019] After the simulation model is built, finite element simulation is performed on the crushing electrode to obtain the electric field distribution of the crushing electrode and determine whether the crushing electrode and its electric field distribution meet the following conditions:

[0020] 1. d<0.7S, where d is the maximum width of the electrode claw end and S is the minimum spacing between the electrode claw ends.

[0021] 2. The average electric field strength in each area between the high-voltage electrode and the low-voltage electrode of the crushing electrode is greater than the required rock breakdown field strength E a .

[0022] 3. The average electric field strength in each area between the high-voltage electrode and the low-voltage electrode of the crushing electrode is less than the required liquid breakdown field strength E b .

[0023] 4. The maximum value of the average electric field strength E in each area between the high-voltage electrode and the low-voltage electrode of the crushing electrode max With the minimum value E min satisfy

[0024] If the crushing electrode and its electric field distribution do not meet the above conditions, the crushing electrode electric field distribution is iteratively optimized by adjusting the number of pole pairs and shape of the crushing electrode to meet the above conditions. If the crushing electrode and its electric field distribution meet the above conditions, the distributed capacitance C of the crushing electrode under this working condition is calculated by finite element analysis. w With the leakage resistor R w In actual design, the crushing electrode and its electric field distribution can be preferentially made to meet requirements 1 and 4, and then the voltage pulse amplitude U acting on the crushing electrode can be adjusted to meet other design requirements.

[0025] Furthermore, the output voltage pulse waveform is optimized, where the driving source topology is a Marx generator, which adopts a coaxial design, and its main parameters are the single-stage capacitor capacity C, the capacitor charging voltage U c , Marx generator level n, discharge circuit inherent resistance R, discharge circuit inherent inductance L, etc. Its main distributed parameters are the overall distributed inductance L s , capacitor distributed inductance L p , Gas switch spark inductance L g , Gas switch spark resistance R g , gas switch distributed capacitance L g , coupling capacitor to ground C s Etc. In addition, the conduction time of the gas switch needs to be considered.

[0026] Furthermore, a driving source circuit simulation model is built using circuit simulation software, and the main steps are as follows:

[0027] 1. Build a driving source simulation circuit model considering distributed parameters;

[0028] 2. Carry out initial design of the driving source according to actual design requirements;

[0029] 3. Determine the main parameters and distribution parameters of the driving source according to the driving source design;

[0030] 4. According to the simulation results of the broken electrode, the model load is set to an RC load consisting of a distributed capacitor and a leakage resistor in parallel.

[0031] After the circuit simulation model is built, perform circuit transient simulation on the driving source to obtain the output high-voltage pulse waveform and determine whether the output high-voltage pulse meets the following conditions:

[0032] 1. Output high voltage pulse rise time t r ' is less than the required output voltage rise time t r ;

[0033] 2. The output high voltage pulse peak value U' is greater than the required voltage pulse amplitude U.

[0034] If the output high-voltage pulse does not meet the above conditions, the output high-voltage pulse can be iteratively optimized by adjusting the drive source design to meet the above conditions; if the output high-voltage pulse meets the above conditions, the iterative optimization design process of the high-voltage pulse discharge rock breaking system is completed, and the high-voltage pulse discharge rock breaking system can be manufactured according to the optimization design results. In actual design, the output voltage pulse can be effectively adjusted by adjusting the inherent inductance of the discharge circuit, and a design without inherent resistance of the discharge circuit can be used to meet the needs.

[0035] Compared with the prior art, the above technical solution conceived by the present invention can achieve the following beneficial effects:

[0036] 1. The design of the present invention is based on actual needs, ensuring that the system can meet different rock breaking requirements and ensuring the reliability of the designed high-voltage pulse discharge rock breaking system.

[0037] 2. The design of the present invention can be adjusted according to different working conditions to meet the universal applicability of the designed high-voltage pulse discharge rock breaking system to different working conditions.

[0038] 3. When designing the crushing electrode, the present invention iteratively optimizes the electric field of the crushing electrode, which can effectively avoid the problems of local distortion of the electric field of the crushing electrode, failure to meet the rock breaking requirements, and effectively avoid the termination of the rock breaking process due to defects in the electric field distribution, thereby improving the rock breaking capacity of the system. Furthermore, the crushing electrode designed by the present invention can also effectively reduce the probability of discharge from the liquid medium after partial rock breaking, increase the crushing speed, and reduce the energy consumption per unit volume of rock breaking.

[0039] 4. When designing the driving source, the present invention iteratively optimizes the driving source, which can effectively avoid the crushing failure caused by the output voltage pulse rising time being too long and the output voltage amplitude being too low, and ensure the matching of the driving source and the crushing electrode. Furthermore, the driving source designed by the present invention can make the output voltage rise time and the output voltage amplitude better match, reduce the charging voltage and capacitor energy storage, and reduce the rock breaking cost. Furthermore, the capacitor and other key components can be selected according to the design results to ensure the design margin of the capacitor and increase the service life of the system.

[0040] 5. The design process of the present invention can be completed by computer simulation software. The iterative process is short in time, which can effectively reduce the design cycle of the high-voltage pulse discharge rock breaking system and reduce the design cost of the high-voltage pulse discharge rock breaking system. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 A flowchart of an iterative optimization design method for a high-voltage pulse discharge system;

[0042] Figure 2 It is the volt-second characteristic curve of rock and different liquid media;

[0043] Figure 3 It is a broken electrode model;

[0044] Figure 4 Iterative optimization of electric field distribution after breaking electrodes;

[0045] Figure 5 Optimize simulation models for driving sources;

[0046] Figure 6 The output voltage pulse waveform is obtained after iterative optimization of the driving source. DETAILED DESCRIPTION

[0047] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0048] The present invention provides an iterative optimization design method for a high-voltage pulse discharge rock breaking system. Figure 1 As shown, the main steps are as follows:

[0049] Step 1: Determine rock breaking requirements: determine the types of rock and liquid media and the drilling diameter under actual working conditions;

[0050] Step 2: Determine the volt-second characteristics: Draw the volt-second curves of rock and liquid medium under actual working conditions and determine the rise time t of the required voltage pulse r , rock breakdown field strength E a And the liquid breakdown field strength E b ;

[0051] Step 3, Optimize the electric field of the crushing electrode: Determine the outer diameter of the crushing electrode according to the borehole diameter; determine the electric field distribution requirements of the crushing electrode according to the volt-second characteristics of rock and liquid. By adjusting the number and shape of the crushing electrode poles, the electric field distribution of the crushing electrode is iteratively optimized to meet the electric field distribution requirements and obtain the distributed capacitance C of the crushing electrode. w With the leakage resistor R w .

[0052] Step 4: Optimize the output voltage pulse: According to the distributed capacitance and leakage resistance of the broken electrode, the output voltage pulse is iteratively optimized by adjusting the drive source design so that the output voltage pulse rise time t r ' and the output voltage amplitude U' meet the requirements.

[0053] In a specific embodiment, the rock to be crushed is white granite, the liquid medium used is tap water, the relative dielectric constant of which is 81, the conductivity is 34.7 mS / m, and the required drilling diameter is 240 mm.

[0054] Specifically, the volt-second characteristic curves of rock and liquid medium are plotted, such as Figure 2 As shown in the figure, due to the certain dispersion of rock and liquid breakdown, the volt-second characteristic curve has a certain width. There are 4 intersections between the volt-second characteristic curves of rock and liquid medium. The intersection with the smallest horizontal coordinate is selected as the critical point. When the rise time is less than this point, the discharge channel will be 100% likely to be formed in the rock. In this example, for white granite and water, the horizontal coordinate of this point corresponds to a time of 110ns. In order to ensure that the discharge channel is formed in the rock, the required rise time should be less than a few nanoseconds of the horizontal coordinate of this point. The rise time of the required voltage pulse is selected as 95ns. The upper limit of the electrical strength of the volt-second characteristic curve of granite corresponding to this rise time is about 340kV / cm, and the lower limit of the electrical strength of the volt-second characteristic curve of tap water is about 980kV / cm.

[0055] Specifically, a broken electrode model is constructed, such as Figure 3As shown in the figure, the crushing electrode is divided into two parts, the high-voltage electrode in the middle part and the low-voltage electrode on the outside. The crushing electrode diameter is designed to be 250mm according to the borehole diameter, and the high-voltage electrode and the low-voltage electrode claws are staggered at equal distances. After optimization, the crushing electrode parameters are as follows: diameter 250mm, a disc is set at the center of the high-voltage electrode to ensure the electric field strength in the central area, so that the rock in the central area can be crushed, the minimum distance between the central disc of the high-voltage electrode and the claw end of the low-voltage electrode is 35mm, the minimum distance between the claw end of the high-voltage electrode and the claw end of the ground electrode is 32.16mm, the maximum width of the claw end of the crushing electrode is 19.7mm, and the crushing electrode material is copper. The electric field of the crushing electrode is analyzed by finite element analysis using COMSOL, and the working environment of the crushing electrode is set according to the actual working conditions. The liquid medium uses 25℃ water, and its conductivity and relative dielectric constant are set to 34.7mS / m and 81 respectively according to actual measurements. The granite is simulated using the COMSOL built-in rock model, and its relative dielectric constant is set to 8 and its conductivity is 210μS / m. After the parameter setting is completed, the electrostatic field and current field are imported for finite element analysis. The potentials of the high-voltage electrode and the low-voltage electrode are set to 500 kV and 0 V respectively. The results are as follows: Figure 4 As shown, five representative areas in the entire area are selected, and their average electric field strength distribution is as follows:

[0056] area Average electric field strength (kV / cm) 1 784 2 956 3 468 4 894 5 640

[0057] To meet the distribution requirements of electric field strength, the distributed capacitance C can be obtained through finite element analysis. w is 0.834nF, the leakage resistance R w is 87Ω.

[0058] Specifically, build a driving source simulation model, such as Figure 5 As shown, it is a Marx circuit topology. The output voltage needs to reach 500kV, so the Marx generator level n is 10, the charging voltage is 50kV, and the single-stage capacitance is 300nF. Where R is the isolation resistor, which can be changed to an isolation inductor according to the design scheme. In this embodiment, Marx adopts an inductive isolation coaxial design, and the isolation inductor is 240uH; R t is the wave tail resistor, which is used to adjust the wave tail time. In this example, the design is used for pulse discharge rock breaking. The wave tail time is determined by the channel resistance after the rock is broken through, so the wave tail resistor is not designed. f is the wave head resistance. The equivalent value of each wave head resistance in series is the inherent resistance of the discharge circuit, which determines the wave head time together with the inherent inductance of the circuit. In this example, the rise time is mainly adjusted by the inherent inductance of the circuit, and the wave head resistance is 0; L is the inherent inductance of the discharge circuit, which can be adjusted by manual design. In this example, it is designed to be 0.8uH; L sIt is the structural distributed inductance. Since the Marx generator adopts a coaxial design, the output current needs to flow back through the shell, so the capacitor and the shell form a loop, and there is mutual inductance between the two. The calculation method can be calculated according to the inductance calculation formula of the coaxial wire:

[0059]

[0060] Where l is the overall length of the Marx generator, R2 is the equivalent radius of the capacitor, and R is the radius of the coaxial Marx generator. After calculation, L s 408nH; L p The distributed inductance of the capacitor is determined by its structure and can be measured by the oscillation method, which is 20nH; g is the spark switch, and its conduction time is 30ns; C g is the switch distributed capacitance. The switch electrode model is built by COMSOL for finite element analysis, and it is calculated to be 4pF. Lg is the switch spark inductance, which can be calculated by the empirical formula L g =14d estimated, d is the distance between the ball gap switches, and the inductance is 8nH; R g is the switch spark resistance, which is a nonlinear time variable, and its stable value is 0.1Ω. Since this example only considers the rising edge characteristics before rock breakdown, the driving source load before rock breakdown is the distributed capacitance and leakage resistance of the crushing electrode. According to the simulation results of the crushing electrode, the load distributed capacitance C w is 0.834nF, the leakage resistance R w The circuit model is simulated using Pspice simulation software. The simulation results are as follows: Figure 6 As shown, the output voltage pulse rising edge is 94.6ns, and the output voltage peak is 589.5kV, which meets the voltage rising edge and voltage amplitude requirements. The output voltage peak is higher than the Marx generator capacitor series voltage, which is due to the overshoot caused by the underdamping condition of the discharge circuit. From the perspective of rock breaking, the overshoot of the output voltage increases the output amplitude, which is conducive to rock breaking.

[0061] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. An iterative optimization design method for a high-voltage pulse discharge rock breaking system, characterized in that: The following steps are involved: Step 1: Determine the types of rock and liquid media and the borehole diameter under actual working conditions; Step 2: Draw the volt-second curve of rock and liquid medium under actual working conditions to determine the required voltage pulse rise time, rock and liquid breakdown field strength; considering the dispersion of rock and liquid medium breakdown, the volt-second characteristic curve of rock and liquid medium has multiple intersections; The intersection point with the shortest rise time is selected as the inversion critical point of the electrical strength of the rock and the liquid medium, and the time that is a number of nanoseconds less than the horizontal coordinate of the point is taken as the rise time of the required voltage pulse. The upper limit of the breakdown field strength of the rock volt-second characteristic curve corresponding to the required voltage pulse rise time is taken as the required rock breakdown field strength, and the lower limit of the breakdown field strength of the liquid medium volt-second characteristic curve is taken as the required liquid medium breakdown field strength. Step 3: By adjusting the design of the crushing electrode, the electric field of the crushing electrode is iteratively optimized so that the electric field distribution of the crushing electrode meets the rock breaking requirements; the outer diameter of the crushing electrode is consistent with the borehole diameter, and the number of pole pairs and shape of the crushing electrode are adjusted to make the crushing electrode and its electric field distribution meet the design requirements, and the distributed capacitance and leakage resistance of the crushing electrode when the electric field distribution requirements are met are obtained; The requirements that the crushing electrode and its electric field distribution need to meet include:

1. The maximum width of the crushing electrode claw end is less than 0.7 times the minimum spacing between the claw ends; 2. The average electric field strength in each area of ​​the crushing electrode gap is greater than the required rock breakdown field strength; 3. The average electric field strength in each area of ​​the crushing electrode gap is less than the required liquid medium breakdown field strength; 4. The ratio of the maximum value to the minimum value of the average electric field strength in each area of ​​the crushing electrode is less than the ratio of the required liquid breakdown field strength to the required solid breakdown field strength; Step 4: Iteratively optimize the output voltage pulse by adjusting the drive source design so that the output voltage pulse meets the rock breaking requirements.

2. The iterative optimization design method of a high-voltage pulse discharge rock breaking system according to claim 1, characterized in that: The step 1 specifically includes determining the borehole diameter, the types of rock and liquid medium, and the electrical conductivity and dielectric constant of the rock and liquid medium.

3. The iterative optimization design method of a high-voltage pulse discharge rock breaking system according to claim 1, characterized in that: The crushing electrode is preferably designed to meet conditions 1 and 4, and the required voltage pulse amplitude acting on the crushing electrode is adjusted to meet other requirements.

4. The iterative optimization design method of a high-voltage pulse discharge rock breaking system according to claim 1, characterized in that: The step 4 specifically involves building a circuit simulation model that takes distributed parameters into consideration, and by adjusting the design of the driving source, the main parameters and distributed parameters of the driving source are changed to adjust the output voltage pulse to meet the design requirements.

5. The iterative optimization design method of a high-voltage pulse discharge rock breaking system according to claim 4, characterized in that: The leakage resistance of the broken electrode and the distributed capacitance are connected in parallel as a load.

6. The iterative optimization design method of a high-voltage pulse discharge rock breaking system according to claim 4, characterized in that: The requirements that the output voltage pulse needs to meet include:

1. The output voltage pulse rise time is less than the required voltage pulse rise time; 2. The output voltage pulse peak value is greater than the required voltage pulse amplitude.

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