Joint process of high-pressure driving and chemical dissolution for restoring reservoir drainage gas channel

Abstract

This invention discloses a combined process for restoring reservoir drainage and gas production channels using high-pressure drive and chemical dissolution, relating to the field of efficient oilfield exploitation technology. The process includes: S1, conducting production profile testing and sampling analysis of blockages in the target gas well to determine the type, distribution location, and reservoir physical parameters of the blockages, and preparing a corresponding chemical dissolving agent based on the analysis results. This invention couples the mechanical fracture-creating effect of high-pressure pulsed fluid with the cavitation effect and vibrational mass transfer effect of ultrasound. Based on the initial dissolution of blockages by the chemical dissolving agent, the stress waves generated by the high-pressure pulse expand the reservoir microfractures. Simultaneously, the collapse of microbubbles generated by ultrasound enhances the dissolution reaction rate, and the vibration promotes the dissolving agent's penetration into the micropores, achieving a synergistic effect of chemical dissolution and physical displacement, thoroughly removing blockages from the pore throats, and avoiding secondary precipitation of dissolution products.

Description

Technical Field

[0001] This invention relates to the field of efficient oilfield exploitation technology, specifically a combined process of high-pressure drive and chemical dissolution to restore reservoir drainage and gas production channels. Background Technology

[0002] A reservoir refers to an underground rock formation with a certain porosity and permeability, capable of storing and allowing the seepage of oil and gas fluids. It is the material basis for the formation and exploitation of oil and gas reservoirs. The reservoir drainage and gas production channel refers to the fluid flow network inside the gas reservoir, which is composed of pores, fractures, and throats. It is the only path for the drainage of formation water and the production of natural gas. Its connectivity and unobstructedness directly determine the production capacity and service life of gas wells. In the middle and late stages of gas reservoir development, as the formation pressure decreases, formation water will gradually invade the gas production channel. Scale-forming ions in the water will precipitate under temperature and pressure changes to form inorganic scale. At the same time, heavy components in crude oil and drilling fluid residues will form organic scale. The two mix and block the pores and throats, leading to a sharp decline in gas well production capacity or even shutdown. Therefore, efficiently restoring the blocked drainage and gas production channel is a key technical means to maintain stable gas well production and improve the recovery rate of gas reservoirs.

[0003] In existing technologies, the restoration of reservoir drainage and gas production channels mainly employs either a single chemical dissolution method or a high-pressure hydraulic displacement method. The chemical dissolution method suffers from problems such as excessive reaction of the solvent in the near-wellbore zone, difficulty in mass transfer in the far-wellbore zone, and inability to completely remove blockages in micropores. Furthermore, the dissolution products are prone to secondary precipitation. The high-pressure hydraulic displacement method can only remove loose blockages in large channels and has limited effectiveness in removing blockages in the micropores of tight reservoirs. Simply increasing the pressure can also easily cause damage to the reservoir rock framework and wellbore. When the two processes are simply used in series, they cannot achieve synergistic effects and cannot meet the development needs of low-permeability tight gas reservoirs. Therefore, it is of great significance to develop a combined process of high-pressure drive and chemical dissolution to restore reservoir drainage and gas production channels. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a combined process for restoring reservoir drainage and gas production channels using high-pressure drive and chemical dissolution. This process can solve the problems of poor solvent mass transfer, incomplete removal of micropore blockage, and insufficient process synergy in the prior art. It can achieve synergistic effect of chemical dissolution and physical displacement, thoroughly remove blockages in pore throats, and avoid secondary precipitation of dissolution products.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a combined process for restoring reservoir drainage and gas production channels using high-pressure drive and chemical dissolution, the process comprising the following steps:

[0006] S1. Conduct production profile testing and blockage sampling analysis on the target gas well to determine the type, distribution location, and reservoir physical parameters of the blockage, and prepare the corresponding chemical solvent based on the analysis results;

[0007] S2. Use clean water circulation to clean the wellbore, remove scale and deposits from the inner wall of the wellbore until the returned fluid is clear and free of impurities. Run in a high-pressure working string with a downhole ultrasonic transducer, align the downhole ultrasonic transducer with the target blockage section, and connect the upper end of the string to the surface high-pressure pulse generator and chemical injection pump.

[0008] S3, with a depth of 0.5-1.0m 3 The prepared chemical solvent is injected into the reservoir at a rate of / h, with the injection volume determined based on the thickness of the blocked section, at 2-3m / m. 3 After injection, the well is shut in for a reaction time of 2-4 hours;

[0009] S4. Start the surface high-pressure pulse generator to generate high-pressure pulse fluid with a frequency of 5-10Hz and a peak pressure of 30-50MPa. At the same time, start the downhole ultrasonic transducer to emit ultrasonic waves with a frequency of 20-40kHz. The two act synchronously on the reservoir, and the processing time is 60-90min.

[0010] S5, with a range of 1.5-2.0m 3 The system uses a flow rate of / h to perform reverse circulation and backflow, carrying the dissolved products and stripped plugging particles out of the reservoir until the ion concentration and turbidity of the returned fluid return to the background value of the formation water.

[0011] S6. Remove the high-pressure working string, restore normal production of the gas well, and regularly monitor changes in gas well production capacity and produced water quality.

[0012] Further, in step S1, the blockage material is sampled at the upper 5m, middle, and lower 5m of the blockage layer. X-ray diffraction analysis is used to determine the inorganic components of the blockage material, and infrared spectroscopy analysis is used to determine the organic components of the blockage material. The reservoir physical properties include porosity, permeability, formation temperature, and formation pressure. The chemical solvent is composed of chelating agent EDTA-2Na, surfactant sodium dodecylbenzenesulfonate, corrosion inhibitor imidazoline, and deionized water, with a mass ratio of 12-18:2-4:1-3:75-85. The chemical solvent is prepared at 25-35℃ and mixed uniformly by mechanical stirring at a speed of 300-500 r / min for 30-60 min.

[0013] Furthermore, in step S2, the temperature of the clean water is 20-30℃, and the circulating cleaning is carried out by alternating forward and reverse circulation. The forward circulation time is 30-45 minutes, and the reverse circulation time is 30-45 minutes. The high-pressure working string adopts a combination structure of N80 steel grade tubing and P110 steel grade casing. The tubing is connected by threads and coated with high-temperature and high-pressure resistant sealing grease. The sealing pressure rating is not less than 70MPa. The downhole ultrasonic transducer is fixed to the lower end of the tubing through a special connector. The positioning error of the downhole ultrasonic transducer is controlled within ±0.5m. The surface high-pressure pulse generator and chemical agent injection pump are connected to the four-way connector at the upper end of the string through a high-pressure pipeline.

[0014] Furthermore, in step S3, the chemical solvent is injected in stages, with each stage containing 2-3 mg / L of solvent. 3 After each injection stage, the pump should be stopped for 10-15 minutes. During the injection process, the wellhead injection pressure should be monitored in real time. When the wellhead injection pressure exceeds 80% of the reservoir fracture pressure, the injection rate should be reduced to 0.3-0.5 m³ / min. 3 / h, continue injection until the total injection volume is reached. The reservoir fracture pressure is obtained by field small-scale fracturing test or logging data. During the shut-in reaction, the wellhead pressure change is recorded every 30 minutes.

[0015] Furthermore, in step S4, the high-pressure pulse generated by the ground high-pressure pulse generator is a square wave pulse with a pulse width of 10-20ms. The peak pressure is adjusted in a step-by-step manner, with the initial peak pressure being 30MPa and increasing by 5MPa every 15 minutes until the set peak pressure is reached. The pulse interval is adjusted according to the wellhead pressure feedback. When the wellhead pressure fluctuation exceeds 2MPa, the pulse interval is increased to 15-20s.

[0016] Furthermore, in step S4, the output power of the downhole ultrasonic transducer is 500-1000W, and the ultrasonic waves are emitted in an alternating mode of continuous and intermittent transmission. The continuous transmission time is 10 minutes and the intermittent time is 2 minutes. There are 2-3 downhole ultrasonic transducers, which are evenly arranged along the axis of the high-pressure working string. The distance between two adjacent downhole ultrasonic transducers is 15-20m, covering the entire target blockage section.

[0017] Furthermore, in step S4, the ground high-voltage pulse generator and the downhole ultrasonic transducer are synchronously controlled by the ground control system. The ground control system transmits control signals and power to the downhole ultrasonic transducer through an armored cable, and simultaneously receives the working voltage, working current and temperature parameters fed back by the downhole ultrasonic transducer. The emission time of the high-voltage pulse is consistent with the emission phase of the ultrasonic wave.

[0018] Furthermore, in step S5, the reverse circulation backflow is carried out using a low-volume followed by a high-volume method, with an initial backflow volume of 0.8-1.2 m³. 3 / h, continue for 30 minutes, then increase to 1.5-2.0m 3 During the flowback process, the wellhead back pressure is controlled at 0.5-1.0 MPa. Samples of the flowback fluid are collected every 15 minutes to detect the calcium ion concentration, sulfate ion concentration, and turbidity of the flowback fluid. When the fluctuation range of three consecutive test results does not exceed 5%, the flowback operation is stopped, and the flowback fluid is collected into a special storage tank for harmless treatment.

[0019] Furthermore, in step S6, for the first three months after the gas well resumes production, the daily gas production, daily water production, and wellhead pressure of the gas well are monitored once a day, and a sample of the produced fluid is collected every three days for water quality analysis. After three months, the monitoring of production parameters is adjusted to be conducted every three days, and a sample of the produced fluid is collected every 15 days. The monitoring data is recorded and stored digitally to establish a dynamic database of gas well production.

[0020] Furthermore, after step S5 is completed, 0.5-1.0 mg / L is injected first. 3 The pre-isolation fluid is then injected into the reservoir, followed by the injection of a hydrophobic-hydrophilic modifier. This modifier consists of nano-silica, fluorocarbon surfactants, and deionized water, with a mass ratio of 1-3:0.5-1.5:95.5-98.5. The injection rate is 0.3-0.5 m³ / s. 3 / h, injection volume is 0.5-1.0m per meter of blockage layer. 3 After injection, inject 1.0-1.5m. 3 The post-displacement fluid completely replaces the modifier in the tubing into the reservoir. The well is shut in and left to stand for 12-24 hours before proceeding to step S6.

[0021] Compared with existing technologies, this combined process of high-pressure drive and chemical dissolution to restore reservoir drainage and gas production channels has the following advantages:

[0022] This invention couples the mechanical fracturing effect of high-pressure pulsed fluid with the cavitation effect and vibrational mass transfer effect of ultrasound. Based on the initial dissolution of blockages by chemical solvents, the stress waves generated by high-pressure pulses expand the reservoir microfractures. At the same time, the collapse of microbubbles generated by ultrasound enhances the dissolution reaction rate, and the vibration promotes the dissolution agent to penetrate into the micropores. This achieves a synergistic effect of chemical dissolution and physical displacement, thoroughly removes blockages in the pore throat, avoids secondary precipitation of dissolution products, and effectively improves the recovery efficiency of drainage and gas production channels in low-permeability tight gas reservoirs and the degree of gas reservoir activation. Compared with traditional processes, the channel recovery rate is improved and the construction cycle is shortened.

[0023] Other advantages, objectives and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination or study, or may be learned from the practice of the invention. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0025] Figure 1 A flowchart illustrating the combined process of high-pressure drive and chemical dissolution to restore reservoir drainage and gas production channels;

[0026] Figure 2 A flowchart illustrating the steps of a combined process for restoring reservoir drainage and gas production channels using high-pressure drive and chemical dissolution. Detailed Implementation

[0027] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0028] This invention provides a combined process for restoring reservoir drainage and gas production channels using high-pressure drive and chemical dissolution. Specifically designed for the treatment of blockages in drainage and gas production channels of low-permeability tight gas reservoirs, this process forms a complete closed-loop technical solution. Based on chemical dissolution, the process couples high-pressure pulse mechanical fracturing with ultrasonic cavitation vibration, sequentially completing six core stages: pre-construction preparation, wellbore pretreatment, pre-chemical dissolution, high-pressure pulse-ultrasonic coupling treatment, reverse circulation backflow, long-term modification and protection, and production monitoring. Before construction, production profile testing and blockage sampling analysis determine the blockage composition and reservoir porosity, permeability, formation temperature, and formation pressure parameters, and a dedicated chemical dissolving agent is prepared according to a fixed ratio. Wellbore pretreatment uses temperature-controlled clean water for forward and reverse circulation cleaning, followed by the installation of a high-pressure work string equipped with a downhole ultrasonic transducer, and connection between the surface high-pressure pulse generator and the chemical agent injection pump. Pre-chemical dissolution employs a segmented injection mode, precisely controlling the discharge and injection rates, and completing the initial dissolution of the blockage after well shut-in. During the coupling process, high-pressure pulse and ultrasonic equipment are activated simultaneously, with strict control over pulse frequency, peak pressure, ultrasonic frequency, and output power. Phase synchronization enables synergistic effects of multiple physical fields. Reverse circulation flowback employs gradient flow control to thoroughly remove dissolved products and blockage particles. Subsequently, a hydrophobic-hydrophilic modifier is injected, along with isolation and displacement fluids. After well shut-in and settling, gas well production resumes, with production data dynamically monitored throughout the process.

[0029] This solution breaks through the limitations of traditional single processes, solves the technical problems of difficult mass transfer of solvents, incomplete removal of micropore blockage, and secondary precipitation of dissolved products, and significantly improves the restoration efficiency of drainage and gas production channels and the degree of gas reservoir utilization, thus meeting the high-efficiency exploitation needs of low-permeability tight gas reservoirs.

[0030] Example 1

[0031] This embodiment targets a low-permeability tight gas well with a permeability of 0.3 mD, where calcium carbonate and ferrous sulfide are mixed and causing blockage. Based on the requirements of field tests, the coupling treatment parameters are calculated using formulas to achieve precise restoration of the drainage and gas production channels. Field tests have shown that the channel restoration effect and production capacity improvement effect are both excellent.

[0032] See Figure 1 and Figure 2 The specific implementation process of this embodiment is as follows:

[0033] S1. Production profile testing was conducted on the target gas well. The blockage zone was 2800-2850m. Samples were taken from the upper 5m, middle, and lower 5m of the zone. X-ray diffraction and infrared spectroscopy analysis determined that the blockage material consisted of 65% calcium carbonate, 25% ferrous sulfide, and 10% organic impurities. The reservoir permeability was measured at 0.3mD, porosity at 4.2%, formation temperature at 85℃, and formation pressure at 32MPa. Through multi-point sampling and component analysis, the chemical solvent composition could be precisely matched to enhance the targeted dissolution ability against the mixed blockage material. The chemical solvent was prepared by mixing EDTA-2Na, sodium dodecylbenzenesulfonate, imidazoline, and deionized water in a mass ratio of 15:3:2:80. The mixture was stirred at 400r / min for 45 minutes at 30℃ until homogeneous.

[0034] S2. The wellbore is cleaned using 25℃ clean water in both forward and reverse rotation, for 40 minutes in the forward rotation and 40 minutes in the reverse rotation. This forward and reverse rotation cleaning can thoroughly remove various deposits from the inner wall of the wellbore, providing unobstructed wellbore conditions for subsequent downhole tool running and chemical injection. A high-pressure work string consisting of N80 tubing and P110 casing is run in. The tubing threads are coated with high-temperature and high-pressure resistant sealing grease, with a sealing pressure rating of 70MPa. The sealing structure of the high-pressure work string ensures no leakage during high-pressure operations. The downhole ultrasonic transducer has a positioning error of ±0.5m and connects to the surface high-pressure pulse generator, chemical injection pump, and four-way connector on the work string.

[0035] S3, with 0.8m 3 / h displacement, segmented injection of chemical solvent, 2.5m per segment. 3 After each stage is completed, the pump is stopped for 12 minutes. This segmented injection and intermittent pump stoppage allows the chemical solvent to gradually penetrate deeper into the reservoir, ensuring full contact with the plugging material. The total injection volume is 12.5 m³. 3 The well is shut in for 3 hours, and the wellhead pressure is recorded every 30 minutes. Real-time pressure monitoring can prevent overpressure from damaging the reservoir skeleton.

[0036] S4. Activate the surface control system to synchronously regulate the high-pressure pulse and ultrasonic waves. The high-pressure pulse is a square wave pulse with a pulse width of 15ms, an initial peak pressure of 30MPa, and an increase of 5MPa to 40MPa every 15 minutes, with a pulse frequency of 8Hz. The square wave pulse can generate a stable stress wave effect, expanding the existing microfractures in the reservoir. The downhole ultrasonic transducer has a total output power of 700W, an ultrasonic frequency of 30kHz, and emits continuously for 10 minutes followed by a 2-minute interval. Two transducers are arranged 18m apart along the tubing string axis. The cavitation effect of the ultrasonic waves can enhance the reaction efficiency between the chemical solvent and the blockage material, and the dual-field synchronous action can improve the channel clearing efficiency. This step uses a formula to calculate the processing parameters, as follows:

[0037] Formula for matching peak pressure of high-pressure pulse with ultrasonic power: In the formula This refers to the peak pressure of the high-pressure pulse, in MPa. The total output power of the ultrasonic transducer is expressed in W; the coefficients 0.05 and constant 25 were determined by fitting the data from an indoor multiphysics coupling experiment.

[0038] Coupling treatment time versus permeability matching formula: In the formula: This represents the coupling processing time, in minutes. The value represents reservoir permeability, expressed in mD, ranging from 0.1 to 1.0 mD. Coefficients 30 and constants 90, 0.1, and 1.0 were determined based on experiments demonstrating the effectiveness of treatment on reservoirs with different permeabilities. Calculations show that the coupling treatment time in this embodiment is 80 minutes.

[0039] S5, at 1.0m 3 / h initial displacement backflow for 30 minutes, increasing to 1.8m 3 / h flowback, wellhead back pressure 0.8MPa; gradient flowback can first carry out large particles of blockage at a low speed and then carry out fine residue at a high speed. The flowback fluid is tested every 15 minutes, and flowback is stopped when the data fluctuation is ≤5% for three consecutive times. Continuous water quality testing can accurately determine the end point of flowback; the flowback fluid is collected in a dedicated storage tank for treatment, which meets the environmental protection construction requirements of the oilfield.

[0040] S6, Inject 0.8m 3 A pre-filter is used, followed by the injection of a hydrophobic and volatile-modifying agent; the pre-filter prevents the modifier from reacting with residual chemicals. The mass ratio of nano-silica, fluorocarbon surfactant, and deionized water is 2:1:97, with a discharge volume of 0.4 m³. 3 / h, injection volume 2.5m 3 Inject 1.2m 3 The post-displacement fluid can completely push the modifier into the reservoir channel; after shutting in the well and letting it stand for 18 hours, the modifier can fully adhere to the channel wall to form a protective layer, and the high-pressure working string can be pulled out to resume production.

[0041] After S7 resumes production, daily gas production, daily water production, and wellhead pressure are monitored for the first three months, and water quality is tested every three days. After three months, the monitoring of production parameters is adjusted to be conducted every three days, and a dynamic database of gas well production is established. Full-cycle dynamic monitoring can keep track of the gas well production status in real time, provide timely feedback on the effects of process implementation, and provide data support for subsequent production adjustments.

[0042] In summary, this embodiment fully implements the entire process of the present invention, employing high-pressure pulse and ultrasonic dual-field synchronous coupling, combined with segmented chemical agent injection and gradient discharge backflow, and equipped with a hydrophobic and oxy-modifier for long-term protection. Field testing has verified that it can fully open the main channel for reservoir drainage and gas production and the micropore channel, achieving deep synergy between chemical dissolution and physical displacement. The dissolution products can be completely carried out of the reservoir with the backflow fluid, eliminating the risk of secondary precipitation in long-term production. The construction process has a high degree of standardization and good equipment synergy, perfectly adapting to the severe blockage treatment needs of deep, low-permeability tight gas reservoirs. The overall process stability and reliability meet the standards for field application.

[0043] Example 2

[0044] This embodiment addresses a tight gas well with a permeability of 0.5 mD, where calcium sulfate and organic scale form a mixture that causes blockage. It optimizes the coupling treatment parameters, simplifies the modifier injection process, and achieves efficient and low-cost construction. Testing shows that the channel recovery effect is good, and the production capacity is significantly improved.

[0045] See Figure 1 and Figure 2 The specific implementation process of this embodiment is as follows:

[0046] S1. The tested blockage zone was 2650-2690m. Sampling and analysis revealed the blockage to be 58% calcium sulfate, 32% organic scale, and 10% clay impurities. The reservoir permeability was 0.5mD, porosity was 5.1%, formation temperature was 78℃, and formation pressure was 28MPa. Accurate analysis of reservoir properties and blockage composition allows for optimization of the chemical solvent ratio, improving the dissolution effect on mixed blockages of calcium sulfate and organic scale. The chemical solvent was prepared with a mass ratio of 16:3:2:79 and stirred at 450r / min for 40min at 32℃.

[0047] S2. Cleaning is performed using 28℃ clean water in both forward and reverse rotations for 35 minutes each. Temperature-controlled cleaning reduces low-temperature stimulation to the wellbore, ensuring structural stability. The high-pressure working tubing has a sealing pressure rating of 70MPa, and the ultrasonic transducer has a positioning error of ±0.5m. Precise positioning ensures dual-field action covers all blocked sections, facilitating connection to surface equipment.

[0048] S3, with 0.9m 3 / h displacement, segmented injection of chemical solvent, 3m per segment 3 Stop the pump for 10 minutes; segmented injection can increase the saturation range of the chemical agent, with a total injection volume of 12m³. 3 The shut-in reaction time is 2.5 hours. Shortening the shut-in reaction time can improve the overall construction efficiency and meet the rapid treatment needs of moderately clogged gas wells.

[0049] S4, high-pressure pulse frequency 9Hz, peak pressure 45MPa, pulse width 18ms, ultrasonic frequency 35kHz, output power 800W, 3 transducers arranged 16m apart, coupling processing time 72min; optimized pulse and ultrasonic parameters can match the transformation needs of medium permeability reservoirs, and dual-field phase synchronization can avoid energy cancellation and improve the synergistic effect.

[0050] S5, Initial backflow rate 1.1m 3 / h, increased to 1.9m after 30 minutes. 3 / h, wellhead back pressure 0.9MPa; gradient flowback can efficiently carry dissolved products, stabilize wellhead back pressure to prevent sand production from the reservoir, ensure the safety of flowback operation, and stop operation after flowback until data is stable.

[0051] S6, Inject 0.6m 3 Isolation fluid, 2.0m 3 Modifier, 1.0m 3 Displacement fluid simplifies the dosage of isolation fluid and displacement fluid, reducing construction costs while ensuring protective effects and adapting to the needs of batch construction on site; shut in the well and let it stand for 16 hours, then pull out the tubing to resume production, and monitor production data according to standard procedures.

[0052] In summary, this embodiment optimizes construction parameters and simplifies some auxiliary operation procedures while retaining the core coupling process. Field testing has verified that it can effectively restore the unobstructed flow of reservoir drainage and gas production channels, has a stable effect on removing mixed scale blockages, and the hydrophobic and anaerobic modifier can form a long-lasting protective layer to inhibit the re-scaling and blockage of channels. The construction efficiency and treatment effect are balanced, making it suitable for rapid treatment of tight gas wells with moderate blockage and offering high flexibility in field construction.

[0053] Example 3

[0054] This embodiment targets a low-permeability gas well with a permeability of 0.8 mD and a single calcium carbonate blockage scenario. It simplifies equipment parameters, adopts a basic coupling mode, and balances construction efficiency and cost. The channel restoration effect has been tested and found to meet the standards, resulting in a steady increase in production capacity.

[0055] See Figure 1 and Figure 2 The specific implementation process of this embodiment is as follows:

[0056] S1. The test blockage section is 2500-2540m, with the blockage material consisting of 90% calcium carbonate and 10% impurities. The reservoir permeability is 0.8mD, porosity is 6.3%, formation temperature is 72℃, and formation pressure is 25MPa. For single calcium carbonate blockage, simplifying the chemical agent ratio can reduce material costs and meet the economic requirements of large-scale remediation. The chemical solvent is prepared with a mass ratio of 14:3:2:81, and stirred at 350r / min for 50min at 28℃.

[0057] S2 uses 22℃ clean water for forward and reverse circulation cleaning, 30 minutes each time; short-time forward and reverse cleaning can quickly complete wellbore pretreatment, simplify the equipment connection process and shorten the construction preparation time, and the high-pressure operation string has a sealing pressure rating of 70MPa to complete the equipment connection.

[0058] S3, with 1.0m 3 / h displacement for injecting chemical solvent, total injection volume 10m 3 One-time injection simplifies the operation process; the shut-in reaction time is 2 hours, which shortens the shut-in reaction time and improves construction efficiency. It is suitable for the rapid treatment of slightly blocked gas wells.

[0059] S4, high-pressure pulse frequency 10Hz, peak pressure 40MPa, ultrasonic frequency 40kHz, output power 600W, two transducers arranged 20m apart, coupling processing time 65min; the basic coupling parameters can meet the channel clearing requirements of shallow gas wells, and reducing the number of transducers can reduce equipment investment.

[0060] S5, initial return discharge volume 1.2m 3 / h, increased to 2.0m 3 / h, wellhead back pressure 1.0MPa; rapid backflow can shorten the construction cycle, fixed flow rate is easy to operate, suitable for large-scale on-site construction, and complete backflow treatment.

[0061] S6. After injecting the modifier, shut in the well and let it stand for 12 hours. Directly injecting the modifier can simplify the protection process and maximize construction efficiency while ensuring basic protection. Pull out the tubing to resume production and implement the standard monitoring process.

[0062] In summary, this embodiment adopts a simplified coupling process and basic construction parameters, which reduces construction costs while ensuring the core treatment effect. Field testing has verified that it can effectively remove surface and shallow blockages in the reservoir, restore the basic production capacity of the gas well, and has complete channel protection measures. There is no secondary sedimentation problem. The process is simple to operate and has low equipment requirements. It is suitable for large-scale batch treatment of slightly blocked and low-permeability gas wells and has good economic efficiency and scalability.

[0063] Comparative Example

[0064] This comparative example uses a simple series process of traditional chemical dissolution and high-pressure hydraulic displacement, without employing ultrasonic coupling, long-term modification protection, and refined backflow control. It treats the same gas well conditions as Example 1 and serves as a control scheme to verify the superiority of the technical solution of this invention. It is a complete and feasible traditional process technology solution.

[0065] This comparative example employs a conventional oilfield process combining chemical dissolution and high-pressure hydraulic displacement. This process lacks multi-physics coupling, long-term channel protection, and refined operational control. It addresses a mixed-blockage scenario in a low-permeability tight gas well with a permeability of 0.3 mD, fully implementing the traditional process. It serves as a comparison with the technical solution of this invention. The specific implementation process of this comparative example is as follows:

[0066] S1. Conduct production profile testing and blockage sampling analysis on the target gas well to detect reservoir permeability of 0.3mD, porosity of 4.2%, formation temperature of 85℃, and formation pressure of 32MPa. Prepare chemical solvent according to the same formula as in Example 1.

[0067] S2. Use 25℃ clean water in positive circulation to clean the wellbore for 40 minutes. Run in a conventional high-pressure working string without a downhole ultrasonic transducer. Connect the surface high-pressure pump and the chemical injection pump.

[0068] S3, with 0.8m 3 / h displacement, single injection of chemical solvent, total injection volume 12.5m 3 After shutting in the well for 3 hours, segmented injection and pressure monitoring are not performed.

[0069] S4. Start the ground high-pressure pump and perform high-pressure hydraulic displacement at a constant pressure of 40MPa for 60 minutes. There is no ultrasonic synergy and no multi-field synchronous control.

[0070] S5, with a length of 1.8m 3 A fixed discharge rate of / h is used for reverse circulation backflow. Operation is stopped after the effluent is clear. Gradient discharge rate control and continuous water quality monitoring are not implemented.

[0071] S6. Directly retrieve the working tubing to restore gas well production without injecting any isolation fluid, modifier, or displacement fluid, and monitor production data in a conventional manner.

[0072] In summary, this comparative example fully implemented the traditional chemical dissolution and high-pressure displacement series process without employing any of the core innovative technologies of this invention. Field testing and verification showed that it could only remove some loose blockages in the near-wellbore zone of the reservoir, but could not remove blockages in the fine pores far from the well. The mass transfer depth of the chemical solvent was insufficient, and the dissolution products were prone to forming secondary precipitation at the pore throat. After long-term production, the gas well productivity dropped rapidly, which could not meet the long-term treatment needs of low-permeability tight gas reservoirs.

[0073] Comparison Projects Example 1 Example 2 Example 3 Comparative Example Core process architecture High-voltage pulse + ultrasonic dual-field synchronous coupling High-voltage pulse + ultrasonic dual-field synchronous coupling High-voltage pulse + ultrasonic dual-field synchronous coupling Chemical dissolution + high-pressure displacement in simple series Chemical injection method Segmented injection, real-time pressure monitoring Segmented injection, intermittent pump stoppage One-time injection, simplified control One-time injection, no monitoring Downhole core equipment High-pressure work string with ultrasonic transducer High-pressure work string with ultrasonic transducer High-pressure work string with ultrasonic transducer Conventional high-pressure work string Passage protection measures Pre-filter + Modifier + Post-filter Displacement Fluid Pre-filter + Modifier + Post-filter Displacement Fluid Modifier direct protection No access protection measures Return operation mode Gradient displacement staged return Gradient displacement staged return Fixed displacement rapid return Single displacement crude backflow Multi-field coordinated control Pulse and ultrasound phase synchronization Pulse and ultrasound phase synchronization Pulse and ultrasound synchronous start No collaboration, independent operation Reservoir channel recovery status The main channel and micropores are completely opened. The main channel has been opened and the micropores have been basically opened. The main channel and the micropores were opened. Only the section near the main well passage has been cleared. Dissolution product treatment Completely portable, with no residual sediment. Basically carries, with no residual sediment. Mostly carried, with no residual sediment. Residual accumulation, prone to secondary precipitation

[0074] As can be seen from the comparison table above, this comparison focuses on the four core innovations of this invention: multi-physics field synchronous coupling, segmented precise injection, long-term channel protection, and gradient-based refined backflow. The differences between the solutions are intuitively demonstrated through technical features such as process architecture, equipment configuration, operation methods, and control logic. All three embodiments fully utilize the innovative technologies of this invention, making only adaptation adjustments to parameter complexity and construction processes. They can cover the remediation needs of low-permeability gas reservoirs with different burial depths and degrees of blockage, ensuring thorough reservoir channel unblocking, no secondary sedimentation, and strong construction adaptability. The comparative embodiment uses a traditional, extensive series process without any innovative technology, only achieving temporary unblocking of shallow, mildly blocked reservoirs, exhibiting inherent defects such as incomplete unblocking, secondary sedimentation, and narrow applicability. This comparison fully demonstrates that the innovative technical design of this invention solves the pain points of traditional processes from the entire process of mechanism, control, and protection, and the technical solution possesses outstanding creativity, practicality, and field promotion value.

[0075] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A combined process for restoring reservoir drainage and gas production channels using high-pressure drive and chemical dissolution, characterized in that, The process includes the following steps: S1. Conduct production profile testing and blockage sampling analysis on the target gas well to determine the type, distribution location, and reservoir physical parameters of the blockage, and prepare the corresponding chemical solvent based on the analysis results; S2. Use clean water circulation to clean the wellbore, remove scale and deposits from the inner wall of the wellbore until the returned fluid is clear and free of impurities. Run in a high-pressure working string with a downhole ultrasonic transducer, align the downhole ultrasonic transducer with the target blockage section, and connect the upper end of the string to the surface high-pressure pulse generator and chemical injection pump. S3, with a depth of 0.5-1.0m 3 The prepared chemical solvent is injected into the reservoir at a rate of / h, with the injection volume determined based on the thickness of the blocked section, at 2-3m / m. 3 After injection, the well is shut in for a reaction time of 2-4 hours; S4. Start the surface high-pressure pulse generator to generate high-pressure pulse fluid with a frequency of 5-10Hz and a peak pressure of 30-50MPa. At the same time, start the downhole ultrasonic transducer to emit ultrasonic waves with a frequency of 20-40kHz. The two act synchronously on the reservoir, and the processing time is 60-90min. S5, with a range of 1.5-2.0m 3 The system uses a flow rate of / h to perform reverse circulation and backflow, carrying the dissolved products and stripped plugging particles out of the reservoir until the ion concentration and turbidity of the returned fluid return to the background value of the formation water. S6. Remove the high-pressure working string, restore normal production of the gas well, and regularly monitor changes in gas well production capacity and produced water quality.

2. The combined process of high-pressure drive and chemical dissolution to restore reservoir drainage and gas production channels according to claim 1, characterized in that, In step S1, the blockage material was sampled at 5m above, 5m in the middle, and 5m below the blockage layer. X-ray diffraction analysis was used to determine the inorganic components of the blockage material, and infrared spectroscopy analysis was used to determine the organic components. Reservoir properties included porosity, permeability, formation temperature, and formation pressure. The chemical solvent consisted of chelating agent EDTA-2Na, surfactant sodium dodecylbenzenesulfonate, corrosion inhibitor imidazoline, and deionized water, with a mass ratio of 12-18:2-4:1-3:75-85. The chemical solvent was prepared at 25-35℃ and mixed uniformly by mechanical stirring at a speed of 300-500 r / min for 30-60 min.

3. The combined process of high-pressure drive and chemical dissolution to restore reservoir drainage and gas production channels according to claim 1, characterized in that, In step S2, the temperature of the clean water is 20-30℃. The circulating cleaning is carried out by alternating forward and reverse circulation. The forward circulation time is 30-45 minutes, and the reverse circulation time is 30-45 minutes. The high-pressure working string adopts a combination structure of N80 steel grade tubing and P110 steel grade casing. The tubing is connected by threads and coated with high-temperature and high-pressure resistant sealing grease. The sealing pressure rating is not less than 70MPa. The downhole ultrasonic transducer is fixed to the lower end of the tubing through a special connector. The positioning error of the downhole ultrasonic transducer is controlled within ±0.5m. The surface high-pressure pulse generator and chemical agent injection pump are connected to the four-way connector at the upper end of the string through a high-pressure pipeline.

4. The combined process of high-pressure drive and chemical dissolution to restore reservoir drainage and gas production channels according to claim 1, characterized in that, In step S3, the chemical solvent is injected in stages, with each stage containing 2-3 mg of solvent. 3 After each injection stage, the pump should be stopped for 10-15 minutes. During the injection process, the wellhead injection pressure should be monitored in real time. When the wellhead injection pressure exceeds 80% of the reservoir fracture pressure, the injection rate should be reduced to 0.3-0.5 m³ / min. 3 / h, continue injecting until the total injection volume is reached, and record the wellhead pressure change every 30 minutes during the shut-in reaction period.

5. The combined process of high-pressure drive and chemical dissolution to restore reservoir drainage and gas production channels according to claim 1, characterized in that, In step S4, the high-pressure pulse generated by the ground high-pressure pulse generator is a square wave pulse with a pulse width of 10-20ms. The peak pressure is adjusted in a step-by-step manner, with the initial peak pressure being 30MPa and increasing by 5MPa every 15 minutes until the set peak pressure is reached. The pulse interval is adjusted according to the wellhead pressure feedback. When the wellhead pressure fluctuation exceeds 2MPa, the pulse interval is increased to 15-20s.

6. The combined process of high-pressure drive and chemical dissolution to restore reservoir drainage and gas production channels according to claim 1, characterized in that, In step S4, the output power of the downhole ultrasonic transducer is 500-1000W. The ultrasonic waves are emitted in a continuous and intermittent mode, with a continuous emission time of 10 minutes and an intermittent time of 2 minutes. There are 2-3 downhole ultrasonic transducers, which are evenly arranged along the axis of the high-pressure working string. The distance between two adjacent downhole ultrasonic transducers is 15-20m, covering the entire target blockage section.

7. The combined process of high-pressure drive and chemical dissolution to restore reservoir drainage and gas production channels according to claim 1, characterized in that, In step S4, the ground high-voltage pulse generator and the downhole ultrasonic transducer are synchronously controlled by the ground control system. The ground control system transmits control signals and power to the downhole ultrasonic transducer through armored cables, and at the same time receives the working voltage, working current and temperature parameters fed back by the downhole ultrasonic transducer. The emission time of the high-voltage pulse is consistent with the emission phase of the ultrasonic wave.

8. The combined process of high-pressure drive and chemical dissolution to restore reservoir drainage and gas production channels according to claim 1, characterized in that, In step S5, the reverse circulation backflow is carried out using a low-volume followed by a high-volume method, with an initial backflow volume of 0.8-1.2 m³. 3 / h, continue for 30 minutes, then increase to 1.5-2.0m 3 During the flowback process, the wellhead back pressure is controlled at 0.5-1.0 MPa. Samples of the flowback fluid are collected every 15 minutes to detect the calcium ion concentration, sulfate ion concentration, and turbidity of the flowback fluid. When the fluctuation range of three consecutive test results does not exceed 5%, the flowback operation is stopped, and the flowback fluid is collected into a special storage tank for harmless treatment.

9. The combined process of high-pressure drive and chemical dissolution to restore reservoir drainage and gas production channels according to claim 1, characterized in that, In step S6, for the first three months after the gas well resumes production, the daily gas production, daily water production, and wellhead pressure of the gas well are monitored once a day, and a sample of the produced fluid is collected every three days for water quality analysis. After three months, the monitoring of production parameters is adjusted to be conducted every three days, and a sample of the produced fluid is collected every 15 days. The monitoring data is recorded and stored digitally to establish a dynamic database of gas well production.

10. The combined process of high-pressure drive and chemical dissolution to restore reservoir drainage and gas production channels according to claim 1, characterized in that, After step S5 is completed, inject 0.5-1.0m. 3 The pre-isolation fluid is then injected into the reservoir, followed by the injection of a hydrophobic-hydrophilic modifier. This modifier consists of nano-silica, fluorocarbon surfactants, and deionized water, with a mass ratio of 1-3:0.5-1.5:95.5-98.

5. The injection rate is 0.3-0.5 m³ / s. 3 / h, injection volume is 0.5-1.0m per meter of blockage layer. 3 After injection, inject 1.0-1.5m. 3 The post-displacement fluid completely replaces the modifier in the tubing into the reservoir. The well is shut in and left to stand for 12-24 hours before proceeding to step S6.

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