Natural gas well nitrogen foam sand washing and blockage removing method

Abstract

The invention provides a natural gas well nitrogen foam sand washing plug removal method which comprises the following steps: 1) one day before construction, respectively pumping plug removal chemicals into a construction well oil pipe and an annulus; 2) nitrogen foam sand washing: preparing a foaming agent solution and a defoaming agent solution; a ground valve is adjusted, and the foam liquid enters the well from the oil pipe and returns out of the sleeve; after the nitrogen purity is 98%, nitrogen injection is started, the pressure change condition and the outlet liquid return condition are observed, the nitrogen discharge capacity and the pump truck discharge capacity are adjusted according to the field liquid return condition, well washing circulation is established, and sand washing is started after foam liquid is seen clean at an outlet; if pressure building is formed, the pump is stopped for observation, and foam sand washing is conducted again after the pressure is diffused; the sand washing operation is stopped after the well is washed until liquid returning at an outlet is clean and no sand is settled; and (3) reverse lifting induced spraying for reproduction. The method has the advantages of reducing operation procedures and time, reducing operation cost, reducing operation risks, effectively protecting a shaft and a stratum, efficiently washing sand and removing blockage, improving the seepage performance of the stratum, being environment-friendly and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and gas production methods, and in particular relates to a nitrogen foam sand flushing and blockage removal method for a natural gas well, which is applied to a low-yield natural gas well with blockage in the well entry zone. Background Art

[0002] Nitrogen foam well washing technology is a cleaning technology that uses nitrogen and water-soluble surfactants to generate foam well washing fluid, uses high-pressure nitrogen to deliver the foam fluid to the bottom of the well and inject it into the wellbore, and removes sediments and impurities in the wellbore through the buoyancy and mechanical flushing of the foam.

[0003] At present, the main technical problems are: (1) Wellbore sand blockage. During the production of a gas well, formation sand will enter the wellbore with the airflow. When the sand accumulates to a certain extent, it will cause wellbore blockage, and the sand will settle again during the sand flushing process. (2) Formation blockage. During the production of a gas well, the formation may be blocked due to various reasons, such as formation particle migration, scaling, asphaltene precipitation, etc. (3) Frequent tubing operation. The traditional sand flushing method requires frequent tubing operation, which not only increases the operation time and cost, but also poses risks of tubing damage and drill stuck during the tubing operation. Summary of the invention

[0004] The purpose of the invention is to provide a method for removing blockage by using nitrogen foam sand flushing in a natural gas well.

[0005] In order to achieve the above object, the technical solution of the present invention is as follows: A method for removing blockage by nitrogen foam sand flushing in a natural gas well comprises the following steps performed in sequence: 1) Pre-blocking agent One day before construction, inject plugging agents into the oil pipe and annulus of the construction well to promote effective circulation during the nitrogen foam sand flushing construction process; 2) Nitrogen foam sandblasting 2.1) Prepare foaming agent solution and defoaming agent solution; 2.2) Adjust the ground valve so that the foam liquid enters the well through the oil pipe and returns from the casing; 2.3) Start the nitrogen truck group to adjust the purity control valve. Start injecting nitrogen after the nitrogen purity reaches 98%. Control the nitrogen displacement. Start the injection pump to control the injection liquid displacement. Observe the pressure change and the return liquid at the outlet. Adjust the nitrogen displacement and pump truck displacement according to the return liquid at the site. Establish a well washing cycle. Start sand flushing after clean foam liquid is seen at the outlet. If there is a lot of gas during sand flushing, transfer the process to the production process. 2.4) If the pressure continues to rise during construction and forms pressure build-up, stop the pump and observe for 2-3 hours, and then perform foam sand washing again after the pressure has dissipated; 2.5) After the sand flushing operation is completed, make sure that the wellbore is thoroughly cleaned. When the well outlet is clean and there is no sediment, stop the sand flushing operation and report to the construction supervisor for the next process; 3) Reverse lift and induced blowdown resumption: 3.1) After the sand flushing is qualified, nitrogen generation reverse lift and induced blowdown resumption operation is carried out; 3.2) Adjust the ground valve and conduct reverse lift and blowout induction operations. By calculating the nitrogen injection volume when liquid accumulation is seen at the wellhead, take countermeasures in advance and change the operation process in time to prevent safety hazards caused by sudden large amounts of liquid accumulation in the wellbore; 3.3) Continue to inject nitrogen from the annulus until no liquid is discharged from the wellbore; When the spraying force becomes stronger during the construction process, the spraying should be controlled to prevent secondary sand from coming out of the formation; When it is observed that the gas lift is empty, that is, when no liquid is coming out of the nozzle, report to the supervisor for confirmation and stop the gas lift; After the injection is completed, the pipeline is purged; If the wellbore is blocked during the gas lift operation, the wellbore will be cleared by foam sand flushing again. 3.4) After the pipeline purge is completed, shut down the nitrogen booster and nitrogen generator; 3.5) Depressurize the surface operation pipeline, then dismantle it and resume the production process at the well site; The calculation formula of nitrogen injection volume when liquid accumulation is seen at the wellhead is: ; in: Q 氮气 is the nitrogen injection volume when liquid accumulation is seen at the wellhead, m 3 ; h 油 is the tubing depth, m; h 液 is the depth at the liquid surface, m; r 内 is the inner diameter of the oil pipe, m; r 外 is the outer diameter of the oil pipe, m; R 内 is the inner diameter of the casing, m; T 1 is the ground temperature, K; T 2 is the reservoir temperature, K; P1 is the ground pressure, MPa.

[0006] Preferably, it also includes: a calculation formula for nitrogen displacement: ; in, V 氮气 is the nitrogen displacement, m 3 / h; ρ is the foam density, Kg / L; GLR is the gas-liquid ratio; P 1 is the ground pressure, MPa; P 2 is the pressure in the middle of the tubing, MPa; T 1 is the ground temperature, K; T 2 is the temperature in the middle of the deep part of the tubing, K.

[0007] Compared with the prior art, the present invention has the following advantages and technical effects: In the past, the gas well moving string nitrogen foam sand flushing and plugging removal process required well repair operations before measures were taken. Well repair operations would indirectly lead to blockage in the near-well area, affecting the gas production of the gas well after resumption of production. At the same time, compared with the fixed string, the moving string nitrogen foam sand flushing and plugging removal process is complex and costly. The gas well adopts the fixed string nitrogen foam sand flushing and plugging removal process. First, the plugging remover is squeezed into the wellbore and its vicinity to improve the blockage problem. After that, the foam sand flushing operation can effectively restore the gas well production capacity. The entire process is economical and efficient: (1) Reduce operation steps and time The fixed tubing technology avoids the complicated operation of frequently raising and lowering the tubing. The traditional sand flushing and blockage removal method may require multiple raising and lowering of the tubing to replace tools or adjust the tubing position, while this technology can perform sand flushing and blockage removal in the existing tubing state, greatly simplifying the operation process. This can effectively shorten the construction period, reduce the time that equipment occupies the wellhead, and improve the production timeliness of the gas well.

[0008] (2) Reduce operating costs Since the number of times the pipe is lifted and lowered is reduced, the cost of equipment rental (such as workover rigs and other equipment used to lift and lower the pipe) and manual operation is reduced accordingly. At the same time, the shortened operation time also means reducing energy consumption during the construction process, such as reducing the operating time of power equipment, thereby reducing energy costs.

[0009] (3) Reduce operational risks There are many risks in the process of raising and lowering the tubing, such as tubing stuck, blowout, etc. The nitrogen foam sand flushing and plugging removal process without moving the tubing avoids these risks. In gas well operations, blowout is a very dangerous situation. This process operates under the existing tubing state and does not need to destroy the original wellbore pressure balance, reducing the possibility of blowout caused by pressure fluctuations. In addition, when the tubing is stationary, it also reduces the risk of damage, deformation or sticking of the tubing during movement.

[0010] (4) Effectively protect the wellbore and formation Nitrogen foam has the characteristics of low density. Compared with conventional sand flushing fluid, the liquid column pressure it generates in the wellbore is lower, which can effectively reduce the pressure damage to the wellbore and formation. During the sand flushing process, the flushing force of the foam on the wellbore is relatively mild, which reduces the corrosion and wear of the wellbore pipe. For the formation, the lower pressure can prevent the formation from compaction and the decrease of permeability. At the same time, when the foam carries the plugging-removing agent into the formation, it can contact the formation in a relatively gentle manner, reducing the damage to the original pore structure of the formation.

[0011] (5) Efficient sand flushing and blockage removal The nitrogen foam sand flushing and plugging removal process can effectively remove sand in the wellbore. The good sand carrying capacity of the foam can smoothly carry the sand from the bottom of the wellbore to the ground, and can prevent the sand from settling again in the wellbore. For formation blockage, the plugging removal agent carried by the foam can penetrate into the formation pores and effectively dissolve or disperse the blockages, such as asphaltene and scale, to restore the permeability of the formation and make the gas production channel of the gas well unblocked, thereby significantly increasing the production of the gas well.

[0012] (6) Improve formation seepage performance During the unblocking process, nitrogen foam carries the unblocking agent into the formation pores, which can not only remove the blockage but also improve the microscopic pore structure of the formation. The expansion and contraction characteristics of the foam can have a certain "massage" effect on the formation pores, making the connectivity of the formation pores better.

[0013] (7) Environmentally friendly Nitrogen is an inert gas. During the entire sand flushing and plugging removal process, it will not react chemically with the formation fluid and rock to produce harmful by-products. Compared with some traditional plugging removal methods that use more chemical agents, the nitrogen foam sand flushing and plugging removal process reduces pollution to the environment. Moreover, after construction, nitrogen will naturally escape from the wellbore and formation, and no substances harmful to the environment will remain. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 A working principle diagram of a natural gas well nitrogen foam sand flushing and plugging removal method provided in this application; In the figure: 1 the first valve, 2 the second valve, 3 the third valve, 4 the fourth valve, 5 the fifth valve, 6 the sixth valve, 7 the seventh valve, 8 the eighth valve, 9 the ninth valve, 10 the tenth valve, 11 the eleventh valve, 12 the twelfth valve, 13 the thirteenth valve, 14 the fourteenth valve, 15 the fifteenth valve, 16 the sixteenth valve, 17 the seventeenth valve, 18 the eighteenth valve, 19 the nineteenth valve, 20 the twentieth valve. DETAILED DESCRIPTION

[0015] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. The described embodiments are only part of the embodiments of the present invention, not all of them. Therefore, based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0016] The present application provides a method for removing plugging by nitrogen foam sand flushing in a natural gas well, comprising the following steps performed in sequence: 1) Pre-blocking agent One day before construction, pump 1-2m into the oil pipe and annulus of the construction well. 3 Blockage-removing agent to promote effective circulation during nitrogen foam sand washing construction; 2) Nitrogen foam sandblasting 2.1) Prepare foaming agent solution and defoaming agent solution; 2.2) Adjust the ground valve, so that the foam enters the well through the tubing and returns through the casing; 2.3) Open the nitrogen truck group to adjust the purity control valve. Start injecting nitrogen after the nitrogen purity reaches 98% (volume fraction) and control the nitrogen displacement (in the nitrogen foam sand flushing operation, the nitrogen displacement refers to the volume of nitrogen injected into the formation per unit time. For details, see the above nitrogen displacement calculation formula. The nitrogen displacement calculated by this formula mainly considers the following factors: one is to balance the static pressure of the formation, and the other is to ensure the sand flushing effect. During the on-site construction process, the nitrogen displacement will be dynamically adjusted according to the pressure change and the return liquid at the outlet). At the same time, start the injection pump to control the injection liquid displacement, observe the pressure change and the return liquid at the outlet, adjust the nitrogen displacement and pump truck displacement according to the on-site return liquid situation, establish a well washing cycle, and start sand flushing after seeing the clean foam liquid at the outlet. If there is a lot of gas discharge during the sand flushing process, the process will be transferred to the production process; 2.4) If the pressure continues to rise during construction and forms pressure build-up, stop the pump and observe for 2-3 hours, and then perform foam sand washing again after the pressure has dissipated; 2.5) After the sand flushing operation is completed, make sure that the wellbore is thoroughly cleaned. When the well outlet is clean and there is no sediment, stop the sand flushing operation and report to the construction supervisor for the next process; 3) Reverse lift and induced blowdown resumption: 3.1) After the sand flushing is qualified, nitrogen generation reverse lift and induced blowdown resumption operation is carried out; 3.2) Adjust the ground valve and conduct reverse lift and blowout induction operations. By calculating the nitrogen injection volume when liquid accumulation is seen at the wellhead, take countermeasures in advance and change the operation process in time to prevent safety hazards caused by sudden large amounts of liquid accumulation in the wellbore; 3.3) Continue to inject nitrogen from the annulus until no liquid is discharged from the wellbore; When the spraying force becomes stronger during the construction process, the spraying should be controlled to prevent secondary sand from coming out of the formation; When it is observed that the gas lift is empty, that is, when no liquid is coming out of the nozzle, report to the supervisor for confirmation and stop the gas lift; After the injection is completed, the pipeline is purged; If the wellbore is blocked during the gas lift operation, the wellbore will be cleared by foam sand flushing again. 3.4) After the pipeline purge is completed, shut down the nitrogen booster and nitrogen generator; 3.5) Depressurize the surface operation pipeline, then dismantle it and resume the production process at the well site; The calculation formula of nitrogen injection volume when liquid accumulation is seen at the wellhead is: ; in: Q 氮气 The nitrogen injection volume when liquid accumulation is seen at the wellhead (the liquid at the wellhead refers to the liquid accumulation in the wellbore. The process is: nitrogen is injected from the annulus to lift the liquid accumulation in the wellbore to the wellhead), m 3 ; h 油 is the tubing depth, m; h 液 is the depth at the liquid surface, m; r 内 is the inner diameter of the oil pipe, m; r 外 is the outer diameter of the oil pipe, m; R 内 is the inner diameter of the casing, m; T 1 is the ground temperature, K; T 2 is the reservoir temperature, K; P 1 is the ground pressure, MPa.

[0017] The calculation formula for the nitrogen injection volume when liquid accumulation is seen at the wellhead is: (1) Application 1) Determine the construction progress In the process of nitrogen foam sand flushing and plugging removal in natural gas wells, calculating the nitrogen injection volume when liquid accumulation is seen at the wellhead can help the staff judge the progress of sand flushing and plugging removal construction. When the injected nitrogen volume reaches the calculated liquid volume at the wellhead, it can be roughly inferred that the degree of sand body being pushed and the situation that liquid begins to be taken out of the wellhead can be reasonably arranged. 2) Optimize construction parameters This data plays a key role in optimizing subsequent construction parameters such as nitrogen injection volume and injection speed. By comparing the actual nitrogen injection volume when liquid is seen with the theoretical calculated value, the actual seepage characteristics and sand plugging of the formation can be evaluated. If the actual nitrogen injection volume when liquid is seen is higher than expected, it may mean that the formation permeability is low or the sand plugging is more serious than expected. It is necessary to adjust parameters such as nitrogen injection speed or pressure to ensure the construction effect. 3) Evaluate the blocking effect It is helpful to evaluate the initial effect of nitrogen foam sand flushing and plugging removal. Liquid at the wellhead is an important sign of the construction stage. The nitrogen injection volume when liquid is seen combined with the properties of the liquid (such as sand content, water quality, etc.) can preliminarily determine whether the sand body has begun to be effectively removed, and then infer whether the plugging removal measures are working as expected; (2) Advantages 1) Improve construction safety Accurately calculating the amount of nitrogen injected when liquid is seen at the wellhead can help you prepare countermeasures in advance to prevent safety hazards caused by a sudden large amount of liquid returning from the wellhead. For example, when the expected amount of liquid is reached, construction personnel can adjust the pressure control parameters of the wellhead blowout prevention equipment in advance to ensure that the wellhead device can safely control the returned liquid and gas to avoid accidents such as blowouts. 2) Save construction costs Through accurate calculation, excessive nitrogen injection can be avoided. Nitrogen is an important consumable in the entire construction process. Reasonable control of its usage can reduce construction costs. If it is not reasonably calculated, a large amount of nitrogen may be blindly injected, which not only wastes resources, but also increases equipment loss and labor costs due to excessive injection time. 3) Improve construction efficiency Knowing the amount of nitrogen injection when liquid is seen at the wellhead can help construction personnel arrange subsequent work processes more accurately and improve construction efficiency. For example, when liquid is seen, the operation process can be changed in time, such as adjusting the injection method of the flushing fluid or starting the treatment of the return fluid, reducing unnecessary waiting time and making the entire unblocking process more compact and efficient.

[0018] In one embodiment of the present application, it also includes: a calculation formula for nitrogen displacement: ; in, V氮气 is the nitrogen displacement, m 3 / h; ρ is the foam density, Kg / L; GLR is the gas-liquid ratio; P 1 is the ground pressure, MPa; P 2 is the pressure in the middle of the tubing, MPa; T 1 is the ground temperature, K; T 2 is the temperature in the middle of the deep part of the tubing, K.

[0019] The calculation formula for the above nitrogen displacement is: (1) Application 1) Determine construction parameters Nitrogen displacement is one of the key parameters in the nitrogen foam sand flushing and plugging removal process. By calculating the nitrogen displacement, the nitrogen injection rate during the construction process can be reasonably determined, thereby ensuring the effective distribution of the foam system in the wellbore and formation. During the sand flushing process, the appropriate nitrogen displacement can effectively return the sand particles carried by the foam from the wellbore to prevent the sand particles from settling again, thus ensuring the cleanliness of the wellbore. For plugging removal, accurate nitrogen displacement helps to deliver the plugging remover (such as chemical plugging remover carried by foam) to the plugged part at an appropriate speed and pressure; 2) Evaluate equipment needs After knowing the nitrogen displacement, you can select the appropriate nitrogen making equipment and injection equipment according to its size. For example, if the calculated nitrogen displacement is large, you need to select a nitrogen making machine and injection pump with a large enough displacement and pressure that can meet the requirements. This can avoid the construction being unable to proceed smoothly due to improper equipment selection, such as insufficient equipment displacement to provide enough nitrogen, or insufficient equipment pressure to effectively inject nitrogen foam into the formation; 3) Predict construction results The nitrogen displacement is closely related to the performance of the foam and the treatment effect on the formation. Combining the quality of the foam (such as foam stability, expansion ratio, etc.) and the nitrogen displacement, the migration of the foam in the wellbore and formation can be predicted; (2) Advantages 1) Improve sand cleaning efficiency Reasonable nitrogen displacement can make the foam have good sand carrying capacity. Compared with traditional sand flushing fluid, nitrogen foam has low density and can work under lower liquid column pressure, reducing damage to the formation. Moreover, appropriate nitrogen displacement can make the foam form a more stable flow state in the wellbore, more effectively carry sand to the ground, and improve sand cleaning efficiency, especially for some natural gas wells with serious sand production, it can quickly clean up the sand accumulation in the wellbore; 2) Enhance the blocking effect Calculating the appropriate nitrogen displacement helps optimize the foam plugging removal process. Nitrogen foam can enter the tiny pores of the formation at a lower injection pressure, and use the Jamin effect and surface tension characteristics of the foam to make the plugging removal agent better contact with the blockage. The appropriate nitrogen displacement can ensure that the foam carries enough plugging removal agent to penetrate into the formation and fully expand in the pores to squeeze and dissolve the blockage, effectively improving the permeability of the formation and enhancing the plugging removal effect. 3) Reduce construction risks Accurately calculating the nitrogen displacement can avoid the risks caused by injecting too much or too little nitrogen. If the nitrogen displacement is too large, it may cause excessive pressure in the wellbore, causing safety accidents such as formation rupture; if the nitrogen displacement is too small, the expected sand cleaning and blockage removal effects cannot be achieved. By reasonably calculating and controlling the nitrogen displacement, the construction can be carried out within a safe pressure range, while ensuring the construction quality and reducing construction risks.

[0020] The methods and devices not described in detail in the present invention are all prior art and will not be described in detail.

[0021] In order to better understand the present invention, the present invention is further specifically described below through the following examples, but it should not be understood as a limitation of the present invention. Some non-essential improvements and adjustments made by technicians in this field based on the above invention content are also considered to fall within the protection scope of the present invention.

[0022] Example 1 A method for removing blockage by nitrogen foam sand flushing in a natural gas well, specifically comprising the following steps performed in sequence: 1) Pre-blocking agent One day before construction, pump 1-2m into the oil pipe and annulus of the construction well. 3 Blockage-removing agent to promote effective circulation during nitrogen foam sand washing construction; 2) Nitrogen foam sandblasting 2.1) Prepare foaming agent solution and defoaming agent solution; 2.2) Adjust the ground valve (see Figure 1, open the first valve 1, the eighth valve 8, the ninth valve 9, the tenth valve 10, the eleventh valve 11, the twelfth valve 12, the thirteenth valve 13, the fourteenth valve 14, the fifteenth valve 15, the sixteenth valve 16, the seventeenth valve 17, the eighteenth valve 18, and the nineteenth valve 19), and the foam enters the well through the oil pipe and returns out through the casing; Figure 1 Also included is a twentieth valve 20; 2.3) Start the nitrogen truck group to adjust the purity control valve. Start injecting nitrogen after the nitrogen purity reaches 98%. Control the nitrogen displacement. Start the injection pump to control the injection liquid displacement. Observe the pressure change and the return liquid at the outlet. Adjust the nitrogen displacement and pump truck displacement according to the return liquid at the site. Establish a well washing cycle. Start sand flushing after clean foam liquid is seen at the outlet. If there is a lot of gas during the sand flushing process, transfer the process to the production process. 2.4) If the pressure continues to rise during construction and forms pressure build-up, stop the pump and observe for 2-3 hours, and then perform foam sand washing again after the pressure has dissipated; 2.5) After the sand flushing operation is completed, make sure that the wellbore is thoroughly cleaned. When the well outlet is clean and there is no sediment, stop the sand flushing operation and report to the construction supervisor for the next process; 3) Counter-inducement spraying and resumption of production 3.1) After the sand flushing is qualified, nitrogen production reverse lift and injection recovery operation shall be carried out; 3.2) Adjust the ground valve (see Figure 1 , close the ninth valve 9, the tenth valve 10, the eleventh valve 11, the twelfth valve 12, the thirteenth valve 13, the fourteenth valve 14, the fifteenth valve 15, the sixteenth valve 16, the seventeenth valve 17, the eighteenth valve 18, and the nineteenth valve 19; open the second valve 2, the third valve 3, the fourth valve 4, the fifth valve 5, the sixth valve 6, and the seventh valve 7) to carry out reverse lift induced spraying operations; 3.3) Continue to inject nitrogen from the annulus until no liquid is discharged from the wellbore; When the spraying force becomes stronger during the construction process, the spraying should be controlled to prevent secondary sand from coming out of the formation; When it is observed that the gas lift is empty, that is, when no liquid is coming out of the nozzle, report to the supervisor for confirmation and stop the gas lift; After the induced spraying is finished, close valves 3, 4, 5, and 6, open valve 20, and purge the pipeline; If the wellbore is blocked during the gas lift operation, the wellbore will be cleared by foam sand flushing again. 3.4) After the pipeline purge is completed, shut down the nitrogen booster and nitrogen generator; 3.5) Depressurize the surface operation pipeline, then dismantle it and resume the production process at the well site; 3.6) Recording of various operation data: Fill in the nitrogen production device construction record form; fill in the construction confirmation form and have Party A sign for acceptance: 3.7) Clean up the work site and leave after completion; The calculation formula of nitrogen injection volume when liquid accumulation is seen at the wellhead is: ; in: Q 氮气 is the nitrogen injection volume when liquid accumulation is seen at the wellhead, m 3 ; h 油 is the tubing depth, m; h 液 is the depth at the liquid surface, m; r 内 is the inner diameter of the oil pipe, m; r 外 is the outer diameter of the oil pipe, m; R 内 is the inner diameter of the casing, m; T 1 is the ground temperature, K; T 2 is the reservoir temperature, K; P 1 is the ground pressure, MPa; The calculation formula of nitrogen displacement is: ; in, V 氮气 is the nitrogen displacement, m 3 / h; ρ is the foam density, Kg / L; GLR is the gas-liquid ratio; P 1 is the ground pressure, MPa; P 2 is the pressure in the middle of the tubing, MPa; T 1 is the ground temperature, K; T 2 is the temperature in the middle of the deep part of the tubing, K.

[0023] Table 1 Basic parameters of Example 1

[0024] Table 2 Calculation results of Example 1

[0025] Example 2 A method for deblocking a natural gas well by using nitrogen foam sand flushing is disclosed. Except for the following Tables 3 and 4, the remaining process steps and process parameters are the same as those of Example 1.

[0026] Table 3 Basic parameters of Example 2

[0027] Table 4 Calculation results of Example 2

[0028] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for removing blockage by nitrogen foam sand flushing in a natural gas well, characterized in that: The method includes the following steps in sequence: 1) Pre-blocking agent One day before construction, inject plugging agents into the oil pipe and annulus of the construction well to promote effective circulation during the nitrogen foam sand flushing construction process; 2) Nitrogen foam sandblasting 2.1) Prepare foaming agent solution and defoaming agent solution; 2.2) Adjust the ground valve so that the foam liquid enters the well through the oil pipe and returns from the casing; 2.3) Start the nitrogen truck group to adjust the purity control valve. Start injecting nitrogen after the nitrogen purity reaches 98%. Control the nitrogen displacement. Start the injection pump to control the injection liquid displacement. Observe the pressure change and the return liquid at the outlet. Adjust the nitrogen displacement and pump truck displacement according to the return liquid at the site. Establish a well washing cycle. Start sand flushing after clean foam liquid is seen at the outlet. If there is a lot of gas during sand flushing, transfer the process to the production process. 2.4) If the pressure continues to rise during construction and forms pressure build-up, stop the pump and observe for 2-3 hours, and then perform foam sand washing again after the pressure has dissipated; 2.5) After the sand flushing operation is completed, make sure that the wellbore is thoroughly cleaned. When the well outlet is clean and there is no sediment, stop the sand flushing operation and report to the construction supervisor for the next process; 3) Reverse lift and induced blowdown resumption: 3.1) After the sand flushing is qualified, nitrogen generation reverse lift and induced blowdown resumption operation is carried out; 3.2) Adjust the ground valve and conduct reverse lift and blowout induction operations. By calculating the nitrogen injection volume when liquid accumulation is seen at the wellhead, take countermeasures in advance and change the operation process in time to prevent safety hazards caused by sudden large amounts of liquid accumulation in the wellbore; 3.3) Continue to inject nitrogen from the annulus until no liquid is discharged from the wellbore; When the spraying force becomes stronger during the construction process, the spraying should be controlled to prevent secondary sand from coming out of the formation; When it is observed that the gas lift is empty, that is, when no liquid is coming out of the nozzle, report to the supervisor for confirmation and stop the gas lift; After the injection is completed, the pipeline is purged; If the wellbore is blocked during the gas lift operation, the wellbore will be cleared by foam sand flushing again. 3.4) After the pipeline purge is completed, shut down the nitrogen booster and nitrogen generator; 3.5) Depressurize the surface operation pipeline, then dismantle it and resume the production process at the well site; The calculation formula of nitrogen injection volume when liquid accumulation is seen at the wellhead is: ； in: Q 氮气 is the nitrogen injection volume when liquid accumulation is seen at the wellhead, m 3 ; h 油 is the tubing depth, m; h 液 is the depth at the liquid surface, m; r 内 is the inner diameter of the oil pipe, m; r 外 is the outer diameter of the oil pipe, m; R 内 is the inner diameter of the casing, m; T 1 is the ground temperature, K; T 2 is the reservoir temperature, K; P 1 is the ground pressure, MPa.

2. A method for removing plugging by nitrogen foam sand flushing in a natural gas well according to claim 1, characterized in that: Also includes: The calculation formula of nitrogen displacement is: ； in, V 氮气 is the nitrogen displacement, m 3 / h; ρ is the foam density, Kg / L; GLR is the gas-liquid ratio; P 1 is the ground pressure, MPa; P 2 is the pressure in the middle of the tubing, MPa; T 1 is the ground temperature, K; T 2 is the temperature in the middle of the deep part of the tubing, K.

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