A front cabin type secondary explosion composite perforation method for coal bed gas well

Abstract

The application relates to a front-cabin type secondary explosion composite perforating method for a coal bed gas well, belonging to the technical field of coal bed gas fracturing, and aims to improve the reconstruction effect of perforating deepening and permeability improvement of a low-permeability and low-porosity coal bed gas well. A main perforating bomb is first detonated to open a stratum and establish an initial channel, a front-cabin propellant enters the perforating channel in a coaxial follow-up effect formed by a metal jet generated by the explosion of the perforating bomb, the metal jet ignites the front-cabin propellant in the perforating channel, high-energy secondary products are generated by combustion, chemical reactions occur between the high-energy products and a stratum fluid mixture, secondary explosions occur, a secondary high-pressure and high-temperature shock wave is formed, seam extension energy is supplemented, perforating channels continue to extend in the form of cracks, seam extension and hole expansion effects are generated, a multi-directional seam network crack system is finally formed, the perforating channel compaction zone is reconstructed, and a production increasing technology for improving reservoir conductivity is achieved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of coalbed methane fracturing, and particularly relates to a front cabin type secondary explosion composite perforation method for a coalbed methane well. BACKGROUND

[0002] Most of the coal reservoirs in China have the characteristics of low pressure, low permeability and low saturation. Although some breakthroughs have been made in the development of low-permeability and deep coalbed methane by using conventional yield improvement and pressure reduction technologies, the gas well productivity is generally low, and the economic benefits are poor, which seriously restricts the development of low-permeability and deep coalbed methane.

[0003] So far, the development of coalbed methane well perforation completion technology has experienced three stages, namely, accurately opening the coal reservoir, protecting the coal reservoir and further liberating the coal reservoir. The external perforation technology in China can be roughly divided into the following aspects: (1) high-efficiency perforation completion technology aiming to improve the coalbed methane productivity, such as composite perforation technology; (2) perforation process technology aiming to protect the coal reservoir and improve and enhance the perforation completion effect, such as negative pressure perforation process technology, super positive pressure perforation process technology and dynamic negative pressure perforation process technology; (3) integrated operation process aiming to improve operation efficiency, including perforation and testing combined operation process for improving the authenticity of test data; (4) stimulation measures aiming to restore the productivity of coalbed methane wells and prolong the service life, such as perforation and explosion combined operation stimulation technology and deflagration fracturing stimulation technology.

[0004] With the gradual increase of the development depth of coalbed methane fields, especially in the face of the special geological conditions of many low-efficiency coalbed methane wells and deep coalbed methane wells, perforation technology is facing more and more complex problems. The front cabin type secondary explosion composite perforation technology is a new perforation process, which needs to be improved according to the special production mechanism and occurrence conditions of coalbed methane, and provides technical support for the development of low-yield coalbed methane wells and deep coalbed methane. SUMMARY

[0005] The present application provides a front cabin type secondary explosion composite perforation technology for coalbed methane wells, which is pollution-free to the environment and can improve the collection rate of coalbed methane fields, protect the coal reservoir and improve the productivity of coalbed methane wells.

[0006] The present application adopts the following technical solutions:

[0007] A front cabin type secondary explosion composite perforation method for a coalbed methane well adopts a front cabin efficiency-improving cartridge and a perforating charge assembly, and directly loads the front end of the hole by means of the shock wave generated by secondary explosion, thereby improving the fracture efficiency, and comprising the following steps:

[0008] The first step is to calibrate the depth: before perforating, use small gamma logging, and compare with the well logging curve after the coalbed methane well is completed. The position of the target coal seam is determined accurately before perforating;

[0009] The second step is to use cable or tubing conveyed perforating gun: through tubing or cable to convey the front cabin type secondary explosion composite perforating gun to the designated position;

[0010] The third step is the front cabin type secondary explosion composite perforating operation: after reaching the accurate position after calibration, the ground cable is ignited or the ground rod is thrown to impact the detonator, the perforating bullet starts the first explosion, the perforating bullet explosion metal jet ignites the front cabin explosive combustion to produce high-energy secondary products mixed with the formation fluid mixture to produce a chemical reaction, a secondary explosion occurs, forming a secondary high-pressure and high-temperature shock wave, which reforms the perforation channel compaction zone for the second time;

[0011] The fourth step is to raise the cable or tubing and close the well: after the perforation is completed, the cable or tubing is raised, and the perforating gun is completely raised to the wellhead after the hoist is stopped, or the tubing and perforating gun are completely raised to the wellhead, and the perforating gun is disassembled. The perforating operation worker is strictly prohibited from standing at both ends of the perforating gun, and the well site supervisor inspects the perforation emission rate, which should not be less than 95%.

[0012] Further, the first step of calibration is performed by using a GR-CCL depth calibration instrument. The position of the coal reservoir should be consistent with the logging curve. The GR-CCL depth calibration instrument is also used to measure the last short sleeve, and then the magnetic positioning signal is used to preliminarily calibrate the depth.

[0013] Further, in the second step of cable conveyed perforating gun, before the perforating gun is lowered into the well, it is ensured that the wellbore is filled with perforating fluid. The cable is lowered into the well at a speed of 600 m / h within 100 meters of the well depth. When the well depth exceeds 100 meters, the cable speed is increased to 3600 m / h. The GR-CCL depth calibration instrument is used to measure the last short sleeve, and then the magnetic positioning signal is used to preliminarily calibrate the depth.

[0014] Further, in the third step of the front cabin type secondary explosion composite perforating operation, when the cable is used to convey the perforating gun, the success of the detonator explosion is judged by observing the voltage and current of the power supply, and the success of the perforation is judged by observing the vibration of the wellhead pipeline. When the tubing is used to convey the perforating gun, a perforating monitor is installed at the ground wellhead to judge whether the perforation is successful.

[0015] Further, the perforating gun is composed of tubing, screen pipe, detonator, connecting body, secondary explosion front cabin explosive box perforating gun and tail plug from top to bottom. The connecting body is provided with a booster tube, a bullet fixing rack is arranged between the booster tube and the tail plug, a perforating bullet is arranged on the bullet fixing rack, and an outer blind hole is arranged on the connecting body.

[0016] Further, during the cable pulling and well shut-in, the tension should be recorded every 200m during the lifting, so as to calculate the maximum safe tension at different depths, the initial lifting speed of the cable is 4000m / h, when the distance from the wellhead is 100m, the lifting speed is reduced to 1600m / h, and finally to the wellhead 20m, the lifting speed is reduced to 700m / h.

[0017] The present application is to improve the reconstruction effect of low permeability and low porosity coalbed methane well perforation depth and permeability, especially to overcome the technical bottleneck restricting the efficient exploration and development of deep coalbed methane, and to deal with the major scientific problems of complex occurrence state and strong vertical and horizontal stress of deep coalbed methane

[0018] The beneficial effects of the present application are as follows:

[0019] 1. The perforating bomb explodes to open the formation channel, the front cabin propellant produces high-energy materials, and the secondary explosion produces a shock wave to directly load the front end of the hole, prolongs the crack, and the crack length is large, and the crack efficiency is high.

[0020] 2. Abrasive materials can be added in advance in the front cabin propellant, which enters the crack to produce a supporting effect, and the crack does not close.

[0021] 3. The solid propellant front cabin cartridge for coalbed methane well has good temperature resistance, pressure resistance, friction resistance and anti-static performance, and has stable quality, reliable performance and high safety in field use, and will not cause any safety accidents such as blasting gun and fracture.

[0022] 4. The high-pressure gas generated by the secondary explosion can flush and compact the compacted zone and return the coal debris and coal powder in the hole, break and eliminate the compacted zone, eliminate the compacted zone effect caused by perforation, and improve the seepage characteristics.

[0023] 5. The matched pyrotechnics and accessories select high-temperature and high-pressure resistant materials, and adjust the technical parameters of the whole system, and the technical performance is reliable within 48h under the environment of temperature 163℃ and pressure 105MPa.

[0024] 6. The whole system has reliable working performance within 48h under the environment of temperature 163℃ and pressure 105MPa.

[0025] 7. The system can be used for on-site construction by using tubing delivery or cable delivery.

[0026] 8. The system can be started by using the ground throwing stick or the ground pressurization method.

[0027] 9. After the perforation of the system, the perforating gun does not break, has no cracks, and has no diameter expansion.

[0028] 10. The perforation diameter of the system is 13mm, and the hole depth is 1247mm.

[0029] 11. The technology is safe and reliable, does not damage the tubing and casing, and does not contaminate the coal reservoir. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 Figure 1 is a schematic diagram of the connection sequence of the front cabin explosive box perforating gun;

[0031] Wherein: 1-tubing; 2-screen pipe; 3-initiator; 4-connector; 5-boosting tube; 6-outer blind hole; 7-front cabin explosive box before secondary explosion; 8-perforating bullet; 9-solid bullet holder; 10-perforating gun; 11-tail plug.

[0032] Figure 2 Figure 2 is a schematic diagram of the string structure of the front cabin explosive box perforating gun before secondary explosion;

[0033] Wherein: 12-rod; 13-detonating cord.

[0034] Figure 3 Figure 3 is a schematic diagram of the connection swing of the field ground equipment;

[0035] Wherein: 14-derrick; 15-workover truck; 16-winch; 17-target coal seam. DETAILED DESCRIPTION

[0036] A front cabin type secondary explosion composite perforating method for coalbed methane wells, comprising the following steps:

[0037] 1) Depth calibration: Before perforating the target well, the GR-CCL depth calibration instrument is used for depth calibration, the coal reservoir position and the logging curve are consistent, and the GR-CCL depth calibration instrument is lowered to the last short casing, then the magnetic positioning signal is used for preliminary depth calibration, and the final depth is determined.

[0038] 2) Cable or tubing conveyed perforating gun: Before operation, the construction steps and matters needing attention are understood in detail, to ensure that the perforation position is accurate, and to confirm that the alarm and shutdown setting of the logging system is correct, then the cable or tubing is lowered to the predetermined depth, the GR-CCL depth calibration instrument logging is kept to the uppermost short casing at all times, and the depth is compared with the depth at the time of lowering, and the depth is corrected if necessary.

[0039] 3) Front cabin type secondary explosion composite perforating operation: After reaching the accurate position of the designed depth calibration, the initiator is detonated through the ground cable or the ground rod, the perforating bullet begins to detonate for the first time, the perforating bullet explosion metal jet ignites the front cabin explosive combustion to produce high-energy secondary products, which reacts with the formation fluid mixture to produce a secondary explosion, forming a secondary high-pressure and high-temperature shock wave, which reforms the perforation channel compaction zone for the second time.

[0040] 4) Cable or tubing is pulled out, well is closed: when cable transmission perforation is used, after perforation is completed, the cable is pulled up, tension is recorded every 200m, and the pulling speed is strictly controlled, the winch unit is stopped after the perforation tool string is completely pulled out of the wellhead; or when tubing transmission perforation is used, after perforation is completed, the tubing is pulled up, it is strictly forbidden to pull up and drop down suddenly, and the tubing pulling speed is not more than 400m / h, the perforating gun is disassembled, the perforation firing rate is supervised and inspected on site, and the firing rate should be not less than 95%.

[0041] In the depth correction, the well logging curve of the well needs to be collected in advance before the on-site construction, and the position of the target coal reservoir and the lithology of the top and bottom plate are analyzed to compare the depth correction data.

[0042] In the cable transmission perforating gun, the zero point needs to be adjusted at the instrument wellhead before being lowered, the calculated zero depth in the depth system is updated, and the wellbore is also filled with perforating fluid to ensure that the liquid level is above 800 meters in the perforation section.

[0043] In the tubing transmission perforating gun, the tubing length size must be accurately measured on the ground when the tubing is lowered, the tubing thread oil must be applied to the tubing coupling, the tubing must be fully buckled to ensure that the tubing connection is firm, and the depth must be corrected after the tubing is lowered to the designed position, with an error of not more than 0.2m. Then, the well is backwashed with hot active water for 5 cycles to clean the tubing.

[0044] In the front cabin type secondary explosion composite perforation operation, the perforating gun string from top to bottom should follow a certain connection order, which is tubing + screen pipe + initiator + connecting body (booster pipe) + secondary explosion front cabin cartridge perforating gun + tail plug from top to bottom. The perforation effect needs to be judged by observing the ground monitoring instrument and the vibration of the wellhead pipeline on the ground. During the perforation operation, the wellhead pressure is closely observed, and once well fluid overflow occurs, the perforation operation is immediately stopped, and the wellhead gate and blowout preventer are immediately closed.

[0045] In the cable pulling out and well closing, attention should be paid to the maximum safe tension of the cable when pulling it out to ensure that the tension is less than the maximum safe tension. If it is stuck, the cable clamp is broken to hold the cable for 10 minutes after the tension is pulled to the safe tension. If the tension does not decrease significantly, the cable is loosened, and the core is prepared for fishing.

[0046] Embodiment

[0047] As shown in Figure 1 , Figure 2 , Figure 3 The connection order, string structure and on-site ground equipment connection layout of the secondary explosion front cabin cartridge perforating gun are shown, and the specific process steps are as follows:

[0048] 1. Well site preparation

[0049] 1) Prepare perforating equipment and provide sufficient lighting, mainly in the wellhead area, the size of the hook (the size of the hook is expected to be 13 meters high from the ground during operation), and the ground area between the wellhead and the logging truck.

[0050] 2) On-site provide a crane or workover truck with a minimum safe load of more than 8 tons, an arm height of more than 20 meters, and a minimum safe load of 5 tons for the small hook to assist in perforating operations.

[0051] 3) Ensure that the perforation section of the coalbed methane well is more than 800 meters above the liquid level.

[0052] 2. Front cabin type secondary explosion composite perforating operation process

[0053] The construction process is as follows: first depth calibration to determine the depth reference value → wellbore filled with perforating fluid → tubing delivery of perforating gun to 10m above the design position → second depth calibration to determine the pipe string depth adjustment value → up and down adjustment of pipe string depth to make the perforating gun directly face the target layer → installation of wellhead and blowout preventer on the ground → ground launching and ignition (or ground pressurized ignition) → front cabin type secondary explosion composite perforating operation → lifting of the perforating pipe string → ground inspection of the firing rate, and re-perforation if the firing rate is less than 95% → well shut-in and production.

[0054] 3. Application example

[0055] This technology was jointly developed and applied by the State Key Laboratory of Coal and Coalbed Methane Co-production and the patent completion unit, and has carried out engineering demonstration in the reservoir reconstruction of deep coalbed methane wells and low-yield wells. Through this technology, a secondary high-pressure and high-temperature shock wave can be formed in the coal reservoir productivity channel, so that the perforation channel continues to extend and expand in the form of cracks. Selecting a deep coalbed methane low-yield well in Wuxiang block, front cabin type secondary explosion composite perforating stimulation reconstruction measures were implemented. The coal seam in this block has a large burial depth, low porosity and permeability, and low fracture development degree, and the coal reservoir has high fracture pressure gradient and firmness coefficient, so the coal reservoir is relatively hard and dense. The gas production is relatively high when the ordinary perforation is put into production, but the production declines sharply after a period of production, and the analysis shows that the coalbed methane seepage channel is blocked, and the deep micro-fracture and micro-fissure development in the coal reservoir is imperfect, resulting in few gas production channels.

[0056] In February 2020, 10 deep low-yield coalbed methane wells were selected for front cabin type secondary explosion composite perforating stimulation reconstruction, to remove the blockage of the coal reservoir pore channel, create and extend secondary cracks, connect the original fissures, and increase the coalbed methane permeability and conductivity. The production of these 10 wells was continuously observed and tracked, and the production data was statistically analyzed for 600 days. The effect comparison before and after the reconstruction is shown in Table 1. As shown in Table 1, the gas production of these 10 wells was very low before the reconstruction, and the daily average gas production of each well was more than 700m 3 / d after the reconstruction, and the daily average gas production of some wells reached 798m 3The average daily gas production increased by 594 m 3 The average daily gas production increased by 594 m The average daily gas production increased by 594 m

[0057] Table 1 Comparison of gas production before and after the transformation of deep coalbed methane low-yield wells

[0058]

Claims

1. A front-chamber secondary explosion composite perforation method for coalbed methane wells, characterized in that: The front cabin synergistic cartridge and the perforating bullet assembly are used to directly load the front end of the hole by the shock wave generated by the secondary explosion, so that the forming efficiency is improved, including the following steps. The first step is to calibrate the depth: before perforating, a small gamma ray logging is used, and the position of the coal seam is determined accurately by comparing with the logging curve after the completion of the coalbed methane well; only when the position of the coal seam is determined accurately can the perforation be performed; The second step is to use the cable or tubing to transport the perforating gun: the front cabin secondary explosion composite perforating gun is transported to the designated position through the tubing or cable; the perforating gun is sequentially provided with the tubing, the screen pipe, the initiator, the connecting body, the secondary explosion front cabin cartridge perforating gun and the tail plug from top to bottom; the connecting body is provided with the booster tube; the booster tube and the tail plug are provided with the bullet holder; the bullet holder is provided with the perforating bullet; and the connecting body is provided with the outer blind hole; The third step is to perform the front cabin secondary explosion composite perforating operation: after reaching the accurate position after the depth calibration, the initiator is ignited by the cable on the ground or the ground is thrown to hit and explode; the perforating bullet starts the first explosion; the metal jet of the perforating bullet explosion ignites the front cabin cartridge to burn and generate high-energy secondary products, which are mixed with the formation fluid mixture to generate a chemical reaction, so that the secondary explosion occurs, and a secondary high-pressure and high-temperature shock wave is formed to perform the secondary transformation on the perforating channel compaction zone; The fourth step is to lift the cable or tubing and close the well: after the perforation is completed, the cable or tubing is lifted; after the perforating gun is completely lifted to the wellhead, the hoist is stopped; or after the tubing and the perforating gun are completely lifted to the wellhead, the perforating gun is disassembled; the blasting operation worker is strictly prohibited from standing at both ends of the perforating gun; the well site supervisor inspects the perforation emission rate; and the emission rate should be greater than 95%.

2. The method according to claim 1, wherein the method is characterized in that: The depth calibration in the first step is performed by using the GR-CCL depth calibration instrument; the position of the coal reservoir should be consistent with the logging curve; and the GR-CCL depth calibration instrument is used to measure the last short sleeve, and then the magnetic positioning signal is used to preliminarily calibrate the depth to finally determine the predetermined depth.

3. The method of claim 1, wherein the method is a front-chamber secondary explosion composite perforation method for coalbed methane wells. In the cable transportation perforating gun in the second step, before the perforating gun is lowered into the well, it is ensured that the wellbore is filled with perforating fluid; the cable is lowered into the well at a speed of 600 m / h within 100 m of the well depth; after the well depth exceeds 100 m, the cable speed is increased to 3600 m / h; the GR-CCL depth calibration instrument is used to measure the last short sleeve, and then the magnetic positioning signal is used to preliminarily calibrate the depth.

4. The method of claim 1, wherein the method is a front-chamber secondary explosion composite perforation method for coalbed methane wells. In the front cabin secondary explosion composite perforating operation in the third step, when the cable transportation perforating gun is used, whether the initiator is successfully exploded is judged by observing the voltage and current of the power transmission; whether the perforation is successful is judged by observing the vibration of the wellhead pipeline; when the tubing transportation perforating gun is used, the perforation monitoring instrument is installed on the ground wellhead to judge whether the perforation is successful.

5. The method of claim 1, wherein the method is a front-chamber secondary explosion composite perforation method for coalbed methane wells. In the lifting of the cable and the closing of the well, the tension should be recorded every 200 m during the lifting, so as to calculate the maximum safe tension at different depths; the initial lifting speed of the cable is 4000 m / h; when the distance from the wellhead is 100 m, the lifting speed is reduced to 1600 m / h; and finally, when the distance from the wellhead is 20 m, the lifting speed is reduced to 700 m / h.

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