Liquid propellant downhole detonation string and method of use

Abstract

This invention provides a liquid explosive downhole detonation string and its usage method. The liquid explosive downhole detonation string consists of a drop tool, a delayed detonator, a deflagration fracturing ignition device, and a sealed outer shell. The sealed outer shell encapsulates liquid explosive. The drop tool and delayed detonator are made of soluble metal, and the outer shell is made of PC, POM, or PEI material. In use, the string is lowered into the wellbore in one trip. A ball is dropped and pressurized to activate the delayed detonator first, then pressurization is applied to release the tubing. After the tubing is pulled up to a safe distance, a delayed detonation occurs, completing the deflagration fracturing. The advantages of this invention are: it simplifies the traditional two-trip tubing operation to one trip, eliminating the need for precise preparation of the isolation fluid; the sealed enclosure prevents leakage or dilution of the liquid explosive by the well fluid, making it suitable for various reservoirs; the drop separation and delayed design improve safety; the tool is soluble and the shell is flammable, eliminating the risk of falling objects, and significantly improving the operational efficiency, reliability, and safety of liquid explosive deflagration fracturing.

Description

Technical Field

[0001] This invention relates to the field of oilfield reservoir stimulation technology, and more specifically to a liquid explosive downhole detonation string and its usage method. Background Technology

[0002] The efficient development of low-permeability reservoirs is a key research direction for the production succession of offshore oilfields. Explosive fracturing technology (also known as "high-energy gas fracturing technology") is suitable for near-water thin-layer stimulation due to its low cost, simple construction, rapid effectiveness, low platform resource requirements, and lack of geostress limitations. In the past decade, it has been applied in over 30 wells in offshore oilfields, efficiently restoring production to numerous low-yield, inefficient, and long-term shut-in key and difficult wells, resulting in a cumulative increase of 517,800 cubic meters of oil, a production increase ratio of 10.49. It has become one of the main reservoir stimulation technologies in offshore oilfields. However, with the needs of exploration and development, the development of medium-deep reservoirs exceeding 3000m is increasing. These reservoirs have complex conditions and low production capacity, facing a more urgent need for rapid production increases. Currently, explosive fracturing technology faces many disadvantages in these well conditions, including weak stimulation (fracture length 1-15 meters) and high peak pressure (60-120 MPa), affecting both effectiveness and safety.

[0003] From a technological development perspective, after developing deflagration fracturing technology in 1985, China has focused on adapting to deeper well conditions, longer fracturing ranges, and lower peak initiation pressures. Starting in 1994, the country began developing upgraded deflagration fracturing technology, namely liquid propellant deflagration fracturing (also known as "liquid propellant high-energy gas fracturing technology"). Liquid propellant deflagration fracturing technology generates a large amount of heat and gases such as CO, CO2, and H2O, resulting in a peak pressure of 50-80 MPa, which can last for 40-50 seconds. Using this operation to fracture reservoirs, the length of a single fracture can reach 25-50 meters, comparable to the scale of hydraulic fracturing, while the cost is only half or less of hydraulic fracturing. This technology has already been successfully applied in the field.

[0004] Currently, the liquid explosive combustion fracturing technology mainly requires the preparation of a mixture of ammonium nitrate, glycerol, and water as liquid explosive during construction. During the construction process, after pulling out the tubing string from the wellbore and cleaning the well, the first tubing string needs to be run into the injection tubing string. After flushing the well, the isolation fluid-liquid explosive-isolation fluid is injected in sequence. After pulling out the first tubing string, the second igniter tubing string is run into the liquid explosive position (the igniter is brought in by tubing string or cable depending on the well inclination) to ignite the liquid explosive. Finally, the igniter is pulled out and the production tubing string is run into production. (For details, see the literature reports: ① Wu Jinjun et al., Experimental application research of liquid explosive high-energy gas fracturing technology in horizontal wells [J]. Drilling and Production Technology, 2007, 30(1): 50-53. ② Ye Xianjun et al., Research on liquid explosive high-energy gas fracturing technology and its application in deep oil and gas reservoirs [J]. Petroleum Exploration and Development, 2000, 27(3): 67-69. ③ Liu Faxi et al., Liquid explosive high-energy gas fracturing and its development direction [J]. Henan Petroleum, 2000, 14(2): 29-31) The aforementioned working tubulars and construction methods have the following three major problems affecting safety and effectiveness, thus limiting the development and application of the technology: Question 1: The operation procedure is very complicated and requires precise control. During the operation, it is necessary to prepare both liquid explosives and isolation fluid with a density that matches the liquid explosives used on site. Otherwise, the isolation effect may be poor or the fluid may be too viscous and difficult to pump. In addition, the injection process requires pumping in stages. The operation requires at least two trips to run the tubing string. For medium and deep wells, the tubing string running time is long and there is a risk of fluid leakage.

[0005] Question 2: Liquid explosives are prone to concentration reduction in lost reservoirs or after mixing with well fluids.

[0006] Liquid explosives typically have a density of 1.25 kg / L or higher, making them highly susceptible to leakage into the formation. This can lead to ignition failure or insufficient detonation, significantly reducing the success rate of the process. Domestic leakage prevention measures, after measuring the leakage rate, generally involve adding plugging agents such as barium sulfate in addition to rapid ignition, which can easily cause reservoir contamination risks.

[0007] At the same time, there is a large amount of well fluid in the wellbore. If the isolation fluid is not prepared up to standard, it is very easy to mix with the well fluid, which will also cause ignition failure or insufficient explosion effect.

[0008] Question 3: The high pressure lasts for a long time after ignition of liquid propellant, posing a safety risk of damage to the igniter tube and falling objects. Ignition devices generally use solid gunpowder-related accessories for ignition. After ignition, the peak pressure of 50-80 MPa can last for 40-50 seconds. At the same time, depending on the real-time well conditions, high-pressure gas continues to overflow from the wellhead for 24-48 hours after the operation, and the wellhead pressure can reach more than 10 MPa. The downhole operation string, including the transmission tubing or cable and the solid gunpowder igniter, all pose safety risks such as long-term high-pressure damage and falling objects.

[0009] To address the aforementioned problems, Chinese invention patent CN105064972B, "A Liquid Explosive Capsule Fracturing Projectile for Oil and Gas Field Reservoirs and its Application Process," proposes a novel method. This method involves sealing liquid explosives within a capsule shell, then sequentially connecting multiple liquid explosive capsules via a central tube and connecting pipes to form a liquid explosive capsule fracturing projectile. The projectile is then transported to the target formation via a cable. An igniter ignites the propellant, and the high temperature generated by the combustion is transferred through the central aluminum tube, igniting the liquid explosive and applying its high-temperature, high-pressure combustion energy to the target rock layer to achieve fracturing operations.

[0010] This technical approach has the following three problems: Firstly, this patented technique uses cable operation and is only suitable for wells with an inclination of less than 45 degrees.

[0011] Secondly, if the capsule is not resistant to temperature and pressure, it is prone to leakage, which will affect the detonation of the liquid gunpowder. The high temperature and high pressure energy that bursts at the moment of detonation will also cause the liquid gunpowder to leak and become ineffective.

[0012] Third, the capsule may cause debris to fall into the well after the operation.

[0013] In summary, there is currently a lack both domestically and internationally of a liquid explosive fracturing string and its construction method that is convenient to construct, can complete liquid explosive fracturing operations in a single run of tubing, does not require precise preparation of isolation fluid, is suitable for various reservoirs, eliminates concerns about liquid explosive leakage or well fluid mixing, and provides higher safety for downhole operations. Specifically, there is a liquid explosive downhole detonation string and its implementation method. Summary of the Invention

[0014] This invention overcomes the shortcomings of the prior art and provides a liquid explosive downhole detonation string and its usage method.

[0015] A liquid explosive downhole detonation string includes: a drop tool, a delayed detonator, a deflagration fracturing igniter, and a sealed shell. The drop tool is configured to work in conjunction with the delayed detonator, which is fixedly mounted on the sealed shell. The delayed detonator is configured to work in conjunction with the deflagration fracturing igniter, which is located inside the sealed shell. Liquid explosive is disposed between the deflagration fracturing igniter and the sealed shell.

[0016] The tool and oil pipe are detachably connected.

[0017] The drop tool is a hydraulic drop tool. When sufficient pressure is applied to the drop tool through the oil pipe, the drop tool separates from the oil pipe and the delayed detonator by throwing a ball.

[0018] Both the throwing tool and the ball set in the throwing tool are made of soluble metal.

[0019] The time-delay detonator is a hydraulic time-delay detonator with a delay time of more than 30 minutes. The time-delay detonator is made of soluble metal material.

[0020] The sealed enclosure is made of PC, POM or PEI and can withstand temperatures below 210℃.

[0021] The hydraulic starting pressure of the drop tool is greater than that of the delayed detonator.

[0022] The deflagration fracturing ignition device includes a detonating cord, a detonating tube, and a solid igniter. The detonating cord is connected to the solid igniter through the detonating tube.

[0023] Liquid gunpowder consists of ammonium nitrate, glycerin, and water.

[0024] A method for using a liquid explosive downhole detonation string, the specific steps of which include: S1. Pre-treatment of the well shaft; S2. After filling the sealed shell with liquid explosive, assemble the deflagration fracturing igniter, delayed detonator and drop tool accordingly. After assembly, lower the entire device into the wellbore through the tubing, so that the lowering position of the sealed shell covers the position of the perforation section. S3. After dropping the ball into the tubing, add hydraulic pressure to the tubing to first reach the starting pressure of the delayed detonator. The delayed detonator will then start to detonate after a delay. Continue to pressurize until the starting pressure of the release tool is reached, at which point the tubing will detach from the liquid explosive downhole detonation string.

[0025] After the ball is thrown into the oil pipe, hydraulic pressure is applied. When the pressure reaches the activation pressure of the time-delay detonator, the time-delay detonator begins to detonate after a delay. Continue to pressurize until the activation pressure of the drop tool is reached, at which point the oil pipe separates from the drop tool. S4. Raise the oil pipe so that the distance between the oil pipe and the detonation position is greater than 150 meters. S5. When the delayed detonator reaches the detonation time, it is ignited by the deflagration fracturing igniter, causing the liquid gunpowder to start burning from top to bottom. S6. After the downhole detonation of liquid explosives is completed, observe the wellhead until the pressure drops to 0, then pull out the tubing and run in the production string to start production.

[0026] The beneficial effects of this invention are as follows: 1. Convenient and efficient operation procedure: The traditional two-pass tubing trip is simplified to one-pass tubing trip to complete all operations. There is no need for precise preparation of isolation fluid, which significantly improves operation efficiency and process success rate.

[0027] 2. High adaptability and reliability: The liquid explosive is encapsulated in a sealed shell, which can effectively prevent reservoir leakage and mixing with well fluid, avoid the reduction of liquid explosive concentration, ensure the detonation effect, and is suitable for various reservoir conditions.

[0028] 3. Significantly improved operational safety: The drop tool enables rapid separation of the oil pipe from the detonation mechanism, keeping the oil pipe away from the high-pressure area; the delayed detonator provides ample time for pipe string separation and evacuation; the detonation string is made of soluble metal and flammable plastic, the tool can dissolve on its own and the shell can participate in combustion, completely eliminating the risk of falling objects.

[0029] In summary, this invention effectively solves the three core problems restricting the application of liquid explosive fracturing technology, comprehensively improving the convenience, safety, and success rate of operations. Furthermore, compared with the technology in existing Chinese patent document CN105064972B, this application has made significant improvements and innovations, employing tubing transmission, suitable for various well deviation conditions, ensuring tubing string safety, further clarifying the characteristics and functions of the liquid explosive shell, and ensuring safe implementation of on-site operations. Attached Figure Description

[0030] Figure 1 This is a schematic diagram illustrating the working principle of the present invention; In the diagram: 1. Oil pipe; 2. Wellbore; 3. Drop tool; 4. Delayed detonator; 5. Deflagration fracturing ignition device; 501. Detonating cord; 502. Detonation tube; 503. Solid ignition charge; 6. Sealed outer shell; 7. Perforation section; 8. Liquid explosive. Detailed Implementation

[0031] Example A liquid explosive downhole detonation string includes: a drop tool 3, a delayed detonator 4, a deflagration fracturing igniter 5, and a sealed housing 6. The drop tool 3 is configured to work in conjunction with the delayed detonator 4, which is fixedly mounted on the sealed housing 6. The delayed detonator 4 is configured to work in conjunction with the deflagration fracturing igniter 5, which is located inside the sealed housing 6. Liquid explosive 8 is disposed between the deflagration fracturing igniter 5 and the sealed housing 6.

[0032] The drop tool 3 is detachably connected to the oil pipe 1.

[0033] The drop tool 3 is a hydraulic drop tool. When the oil pipe 1 injects sufficient pressure into the drop tool 3, the drop tool 3 separates from the oil pipe 1 and the delayed detonator 4 by throwing a ball.

[0034] Both the dropper 3 and the ball set in the dropper 3 are made of soluble metal.

[0035] The delayed detonator 4 is a hydraulic delayed detonator with a delay time of more than 30 minutes. The delayed detonator 4 is made of soluble metal material.

[0036] The sealed housing 6 is made of PC, POM or PEI and has a temperature resistance of less than 210℃.

[0037] The hydraulic starting pressure of the drop tool 3 is greater than the hydraulic starting pressure of the delayed detonator 4.

[0038] The deflagration fracturing igniter 5 includes a detonating cord 501, a detonation tube 502, and a solid ignition charge 503. The detonating cord 501 is connected to the solid ignition charge 503 through the detonation tube 502. The ignition conditions for the deflagration fracturing igniter 5 are a temperature greater than 300℃ and a pressure greater than 10MPa.

[0039] The components of Liquid Gunpowder 8 include ammonium nitrate, glycerin, and water.

[0040] like Figure 1 As shown, the working principle of this invention is as follows: The liquid explosive downhole detonation string is connected to the tubing 1 via a drop tool 3, enabling controlled separation. The drop tool 3 and the delayed detonator 4 are triggered by hydraulic pressure supplied by the tubing 1, thus achieving separation and delayed detonation. The sealed outer shell 6 serves as a container for the liquid explosive 8, preventing dilution and ensuring the quality of the detonation.

[0041] Furthermore, the drop-off tool 3 and the delayed detonator 4 do not separate after detonation; they remain connected via a snap-locking mechanism. To ensure safety, the delayed detonator requires a delay time greater than 30 minutes to allow sufficient time for the oil pipe 1 to move away from the high-temperature, high-pressure environment of the detonation. The hydraulic trigger threshold of the drop-off tool 1 must be at least 30% greater than the hydraulic trigger threshold of the delayed detonator 4 as a safety pressure limit.

[0042] Preferably, the sealed outer shell 6 is made of PC high-strength plastic material. The continuous use temperature resistance of PC high-strength plastic material is 120℃-130℃, and the compressive strength is 70-85MPa.

[0043] When the sealed outer shell 6 is made of high-strength PC plastic, the hydraulic starting pressure of the drop tool 3 is 15MPa, and the hydraulic starting pressure of the delayed detonator 4 is 10MPa.

[0044] Preferably, the sealed outer shell 6 is made of POM high-strength plastic material, which has a continuous temperature resistance of 90~110℃ and a compressive strength of 70-100MPa.

[0045] When the sealed outer shell 6 is made of POM high-strength plastic material, the hydraulic starting pressure of the drop tool 3 is 13MPa, and the hydraulic starting pressure of the delayed detonator 4 is 9MPa.

[0046] Preferably, the sealed outer shell 6 is made of PEI high-strength plastic material, which has a continuous temperature resistance of 170~180℃ and a compressive strength of 110-130MPa.

[0047] When the sealed outer shell 6 is made of PEI high-strength plastic material, the hydraulic starting pressure of the drop tool 3 is 18MPa, and the hydraulic starting pressure of the delayed detonator 4 is 13MPa.

[0048] A method for using a liquid explosive downhole detonation string, the specific steps of which include: S1. Pre-treat wellbore 2; S2. After filling the sealed shell 6 with liquid explosive 8, assemble the deflagration fracturing igniter 5, the delayed detonator 4 and the drop tool 3 accordingly. After assembly, lower the entire device into the wellbore 2 through the oil pipe 1, so that the lowering position of the sealed shell 6 covers the position of the perforation section 7. S3. After throwing the ball into tubing 1, add hydraulic pressure to tubing 1 to first reach the starting pressure of the delayed detonator 4. The delayed detonator 4 starts to detonate after a delay. Then continue to pressurize to the starting pressure of the release tool 3, and tubing 1 is separated from the liquid explosive downhole detonation string.

[0049] After the ball is thrown into the oil pipe 1, hydraulic pressure is applied. When the pressure reaches the starting pressure of the delayed detonator 4, the delayed detonator 4 begins to detonate after a delay. Continue to pressurize until the starting pressure of the drop tool 3 is reached, and the oil pipe 1 is separated from the drop tool 3. S4. Raise oil pipe 1 so that the distance between oil pipe 1 and the detonation position is greater than 150 meters. S5. When the time-delayed detonator 4 reaches the detonation time, it is ignited by the deflagration fracturing igniter 5, causing the liquid gunpowder 8 to start burning from top to bottom. S6. After the downhole detonation of liquid explosive 8 is completed, observe the wellhead until the pressure drops to 0, then pull out tubing 1 and run in the production string to start production.

[0050] The embodiments of the present invention have been described in detail above, but the content described is only a preferred embodiment of the present invention and should not be considered as limiting the scope of the present invention. All equivalent changes and improvements made in accordance with the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A liquid explosive downhole detonation string, characterized in that, include: The package includes a drop tool (3), a time-delay initiator (4), a deflagration fracturing igniter (5), and a sealed housing (6). The drop tool (3) is set together with the time-delay initiator (4). The time-delay initiator (4) is fixedly set on the sealed housing (6). The time-delay initiator (4) is set together with the deflagration fracturing igniter (5) set inside the sealed housing (6). Liquid gunpowder (8) is provided between the deflagration fracturing igniter (5) and the sealed housing (6).

2. The liquid explosive downhole detonation string according to claim 1, characterized in that: The drop tool (3) is detachably connected to the oil pipe (1).

3. The liquid explosive downhole detonation string according to claim 2, characterized in that: The drop tool (3) is a hydraulic drop tool. When the oil pipe (1) injects sufficient pressure into the drop tool (3), the drop tool (3) is separated from the oil pipe (1) and the delayed detonator (4) by throwing a ball.

4. The liquid explosive downhole detonation string according to claim 3, characterized in that: Both the throwing tool (3) and the ball set in the throwing tool (3) are made of soluble metal.

5. The liquid explosive downhole detonation string according to claim 3, characterized in that: The time-delay detonator (4) is a hydraulic time-delay detonator. The time delay of the time-delay detonator (4) is greater than 30 minutes. The time-delay detonator (4) is made of soluble metal material.

6. The liquid explosive downhole detonation string according to claim 3, characterized in that: The sealed shell (6) is made of PC, POM or PEI and the temperature resistance of the sealed shell (6) is below 210°C.

7. The liquid explosive downhole detonation string according to claim 3, characterized in that: The hydraulic starting pressure of the drop tool (3) is greater than the hydraulic starting pressure of the delay detonator (4).

8. The liquid explosive downhole detonation string according to claim 1, characterized in that: The deflagration fracturing ignition device (5) includes a detonating cord (501), a detonation tube (502), and a solid ignition charge (503). The detonating cord (501) is connected to the solid ignition charge (503) through the detonation tube (502).

9. A liquid explosive downhole detonation string according to claim 1, characterized in that: The components of liquid gunpowder (8) include ammonium nitrate, glycerin and water.

10. A method for using a liquid explosive downhole detonation string, characterized in that, The specific steps include: S1. Pre-treat the well shaft (2); S2. After filling the sealed shell (6) with liquid explosive (8), the deflagration fracturing igniter (5), the delayed detonator (4) and the drop tool (3) are assembled accordingly. After the assembly is completed, the entire device is lowered into the wellbore (2) through the oil pipe (1) so that the lowering position of the sealed shell (6) covers the position of the perforation section (7). S3. After throwing the ball into the tubing (1), add hydraulic pressure to the tubing (1) to first reach the starting pressure of the delayed detonator (4), and the delayed detonator (4) starts to detonate after a delay. Then continue to pressurize to the starting pressure of the drop tool (3), and the tubing (1) will be separated from the liquid explosive downhole detonation string. After the ball is thrown into the oil pipe (1), hydraulic pressure is applied. When the pressure reaches the starting pressure of the delayed detonator (4), the delayed detonator (4) starts to detonate after a delay. Continue to pressurize until the starting pressure of the drop tool (3) is reached, and the oil pipe (1) is separated from the drop tool (3). S4. Raise the oil pipe (1) so that the distance between the oil pipe (1) and the detonation position is greater than 150 meters; S5. When the time-delay initiator (4) reaches the detonation time, it is ignited by the deflagration fracturing igniter (5) so that the liquid gunpowder (8) begins to burn from top to bottom. S6. After the downhole detonation of liquid explosive (8) is completed, observe the wellhead until the pressure drops to 0, then pull out the tubing (1) and run in the production string for production.

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