Method for pigging a gas field tie-in pipeline

Abstract

The application discloses a kind of gas field stringing pipeline's pigging method, specifically according to the following steps implementation: by gas gathering branch pipe maximum allowable operating pressure design and make pigging ball, and interception device is designed and installed in the end pipeline of gas gathering branch pipe;Pigging ball is sent by the way of using gas gathering branch pipe starting point connection movable ball launcher or opening well site straight pipe section, obtain the pigging ball after sending;Interception device collides with the pigging ball after sending, if collision breaks, then the pigging ball after sending directly dissolves, complete pigging;If collision is not broken, then the pigging ball after sending is blocked and deformed after pressure, complete pigging.The application realizes that pigging ball breaking pressure difference is within the allowable range by reasonably designing pigging ball wall thickness, to avoid the risk of branch pipe overpressure caused by pigging ball blockage.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of gas field gathering pipeline cleaning method, and particularly relates to a gas field series connection pipeline cleaning method. BACKGROUND

[0002] The gas field gathering pipeline adopts an inter-well series connection mode. The gathering pipelines from different well sites are connected to a gas gathering main pipe and then are centrally and uniformly transported to a gas gathering station for treatment. The pipelines between the well sites and the gas gathering main pipe are gas gathering branch pipes. The gas field pigging operation is an important means for removing liquid accumulation in the pipelines, reducing pipeline corrosion and improving pipeline transportation efficiency.

[0003] The pigging technology mainly adopts a leather cup pig or a rubber pig to complete the pigging operation of the gas gathering main pipe through a pig launching device and a pig collecting device arranged at the starting end and the ending end of the pipeline. However, the gas gathering branch pipe cannot be pigged by using the above technology, which causes liquid accumulation in the low-lying part of the pipeline for a long time, increases the operating pressure of the pipeline and increases the risk of freezing and blocking in winter, thereby affecting the winter gas supply.

[0004] Based on the fact that the gas gathering branch pipe cannot be cleaned, the prior art proposes a water-soluble pig. The pig has a water-soluble characteristic and can achieve a certain pigging effect. However, some fragments enter the station separator, the pig is not completely dissolved to block the liquid discharge pipeline, and the pig breaking pressure difference design is not reasonable to cause the pipe overpressure after being blocked. SUMMARY

[0005] The application aims to provide a gas field series connection pipeline cleaning method which has the characteristics of simultaneously cleaning the gas gathering main pipe and the gas gathering branch pipe and fully dissolving the pig fragments.

[0006] The technical scheme of the application is a gas field series connection pipeline cleaning method which is implemented according to the following steps.

[0007] Step 1. A pig is designed and manufactured by using the maximum allowable operating pressure of the gas gathering branch pipe, and an intercepting device is designed and installed in the pipeline at the ending end of the gas gathering branch pipe.

[0008] Step 2. The pig is launched by using a movable pig launching device connected to the starting end of the gas gathering branch pipe or by opening the straight pipe section of the well site to obtain the launched pig.

[0009] Step 3. The launched pig collides with the intercepting device. If the pig is broken, the launched pig is directly dissolved to complete the pigging. If the pig is not broken, the launched pig is deformed and dissolved after being blocked and pressurized to complete the pigging.

[0010] The application also has the characteristic that Step 1 is implemented according to the following steps.

[0011] Step 1.1, the pipe pig breaking pressure difference ΔPs should be no more than the maximum allowable operating pressure and design pressure P of the branch pipe 2max The difference between the pigging time dry pipe operating pressure P1, avoid pipeline overpressure, pipe pig breaking pressure difference ΔPs is

[0012] ΔP s ≤P 2max -P1 (1)

[0013] Where, ΔPs is the pipe pig breaking pressure difference, P 2max The maximum operating pressure of the branch pipe, P1 is the dry pipe operating pressure during pigging;

[0014] Step 1.2, indoor test is carried out by using microcomputer controlled static stiffness fatigue testing machine, and the pipe pig breaking pressure difference-wall thickness relationship curve model after the pipe pig is blocked by the interception device in the pipeline is obtained;

[0015] Step 1.3, according to the pipe pig breaking pressure difference-wall thickness relationship curve model after the pipe pig is blocked by the interception device in the pipeline, the pipe pig wall thickness is designed;

[0016] Step 1.4, according to the pipe pig wall thickness, the pipe pig is made of water-soluble resin material which can be broken by water or collision or blocking;

[0017] Step 1.5, the interception device is designed and installed in the pipeline at the end of the gas branch pipe.

[0018] Step 1.2 is implemented according to the following steps:

[0019] Step 1.2.1, the testing machine gradually applies force to the pipe pig above the interception device in the simulated pipeline, and the microcomputer obtains the testing machine pressure curve;

[0020] Step 1.2.2, according to the testing machine pressure curve, the inflection point pressure is obtained, which is the pipe pig breaking pressure; the inflection point pressure divided by the cross-sectional area in the pipeline is the pipe pig breaking pressure difference;

[0021] Step 1.2.3, the pipe pig wall thickness-pipe pig breaking pressure difference relationship curve is simulated by pipe pig breaking test of different wall thickness;

[0022] Step 1.2.4, according to the pipe pig breaking pressure difference calculated in step 1.1, the simulated wall thickness-breaking pressure difference relationship curve model is obtained.

[0023] Step 2 is implemented according to the following steps:

[0024] Step 2.1, close the wellhead and control valve, and release pressure through the pressure gauge of the flowmeter;

[0025] Step 2.2, remove the straight pipe section between the control valves, connect the temporary moving ball launching device between the valves for ball launching operation; or directly launch the ball into the straight pipe section, and restore the wellhead flow process to launch the ball.

[0026] The intercepting device in step 1 is a plurality of metal bars or metal nets perpendicular to the pipeline.

[0027] The passing size of the metal bars or metal nets is not greater than the passing size of the blowdown pipeline of the station separator.

[0028] The beneficial effects of the present application are:

[0029] 1. The present application uses water-soluble resin material which can be dissolved by water and broken by collision or blockage to make the cleaning ball, which can clean the gas production main pipe and branch pipe at the same time.

[0030] 2. The present application uses the characteristics of water-soluble cleaning ball which can be dissolved by water and broken by blockage, combined with the temporary ball launching process of the starting well site and the application of metal bars or metal nets at the end of the branch pipe, to realize the branch pipe cleaning operation without ball recovery, and avoid the incomplete dissolution of cleaning ball fragments into the gas gathering station to affect the station system.

[0031] 3. The present application realizes the cleaning ball breaking pressure difference within the allowable range by reasonable design of the cleaning ball wall thickness, avoiding the risk of branch pipe overpressure caused by cleaning ball blockage. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 is the flow chart of the cleaning method of the gas field series pipeline of the present application;

[0033] Figure 2 is a schematic diagram of the pipe network in the cleaning method of the gas field series pipeline of the present application;

[0034] Figure 3 is a structural schematic diagram of the metal bar in the cleaning method of the present application;

[0035] Figure 4 is a structural schematic diagram of the metal net in the cleaning method of the present application;

[0036] Figure 5 is a pressure change curve diagram of the microcomputer controlled static stiffness fatigue testing machine in the cleaning method of the present application. DETAILED DESCRIPTION

[0037] The present application will be described in detail below in combination with the drawings and specific embodiments.

[0038] Example 1

[0039] The cleaning method of the gas field series pipeline is implemented according to the following steps:

[0040] For example, Figure 1As shown, step 1 involves designing and fabricating a pigging ball based on the maximum allowable operating pressure of the gas extraction branch pipe, and designing and installing an interception device inside the end pipe of the gas extraction branch pipe.

[0041] Step 1.1: The pressure difference ΔPs during pigging should not exceed the maximum allowable operating pressure and design pressure P of the branch pipe. 2max The pressure difference between the main pipeline operating pressure P1 and the pressure difference Ps during pigging is used to avoid pipeline overpressure. The pressure difference ΔPs during pigging ball breakage is...

[0042] ΔP s ≤P 2max -P1 (1)

[0043] Where ΔPs is the pressure difference caused by the breaking of the pigging ball, P 2max P1 is the maximum operating pressure of the branch pipe, and P2 is the operating pressure of the main pipe during pigging.

[0044] Step 1.2: Use a microcomputer-controlled static stiffness fatigue testing machine to conduct indoor tests and obtain a curve model of the relationship between the crushing pressure difference and the wall thickness after the pigging ball is blocked by the interception device in the pipeline;

[0045] Step 1.2.1: The testing machine gradually applies force to the pigging ball above the interception device in the simulated pipeline, and the microcomputer acquires the pressure curve of the testing machine;

[0046] Step 1.2.2: According to the pressure curve of the testing machine, the inflection point pressure is the crushing pressure of the pigging ball; the inflection point pressure divided by the cross-sectional area of ​​the pipeline is the crushing pressure difference of the pigging ball.

[0047] Step 1.2.3: Simulate the relationship curve between the wall thickness of the pigging ball and the pressure difference during pigging ball breakage through pigging ball breakage tests with different wall thicknesses;

[0048] Step 1.2.4: Based on the calculated and set differential pressure of the pigging ball in Step 1.1, obtain the simulated curve model of the relationship between wall thickness and differential pressure.

[0049] like Figure 5 As shown, in step 1.3, the design wall thickness of the pigging ball is determined by the curve model of the relationship between the crushing pressure difference and the wall thickness after the pigging ball is blocked by the interception device in the pipeline. The operating pressure of the main pipe during pigging is 2.0 MPa, and the maximum allowable operating pressure of the branch pipe (usually the design pressure) is 4.0 MPa. According to formula (1), the crushing pressure difference of the pigging ball during branch pipe pigging should not be greater than 2.0 MPa, and the design crushing pressure difference is 1.5 MPa. The corresponding design wall thickness of the pigging ball is determined by the curve of the relationship between the wall thickness of the pigging ball and the crushing pressure difference simulated by indoor test. The crushing pressure difference of the pigging ball is controlled by reasonably designing the wall thickness of the pigging ball.

[0050] Step 1.4: Based on the wall thickness of the pigging ball, use a water-soluble resin material that can dissolve in water and break upon impact or blockage to make the pigging ball;

[0051] As Figure 3 Or Figure 4 As shown in the figure, step 1.5, the interception device is designed and installed in the pipeline at the end of the gas gathering branch pipe. The interception device is a number of metal bars or metal mesh perpendicular to the pipeline; the passing size of the metal bars or metal mesh is not greater than the passing size of the separator blowdown pipeline in the station.

[0052] Step 2, the pigging ball is launched by using the movable ball launching device at the starting point of the gas gathering branch pipe or by opening the straight pipe section of the well site, and the launched pigging ball is obtained;

[0053] Step 2.1, close the wellhead and control valve, and release pressure through the pressure gauge between the wellhead and the flowmeter;

[0054] Step 2.2, remove the straight pipe section between the control valves, connect the temporary movable ball launching device between the valves for ball launching operation; or directly put the ball into the straight pipe section to restore the wellhead flow process and launch the ball.

[0055] Step 3, the interception device collides with the launched pigging ball, if the collision breaks, the launched pigging ball directly dissolves, completing the pigging; if the collision does not break, the launched pigging ball is blocked and deformed after pressure build-up, and then dissolves, completing the pigging.

[0056] After the pigging ball is launched at the well site at the starting point of the branch pipe, it travels with the gas flow to the end of the branch pipe and collides with the metal bars or metal mesh, breaks, or is blocked if the collision does not break, causing pressure build-up in the upstream pipe of the pigging ball. When the pressure difference between the upstream and downstream of the pigging ball reaches the designed breaking pressure difference, the pigging ball deforms and breaks. Small fragments pass through the metal bars or wire mesh into the dry pipe and gradually dissolve in water, and large fragments dissolve in water in the branch pipe and then enter the dry pipe to dissolve; this avoids incomplete dissolution of large fragments in the dry pipe and their entry into the gas gathering station along with the gas flow, which blocks the small-diameter pipelines such as the separator blowdown pipeline and instrument pipeline in the station, affecting the normal operation of the gas gathering station. Finally, the string pipeline is safely and effectively pigged without collecting the ball.

[0057] Example 2

[0058] The pigging method for the string pipeline of a gas field is implemented according to the following steps:

[0059] As Figure 1 shown in the figure, step 1, design and make a pigging ball according to the maximum allowable operating pressure of the gas gathering branch pipe, and design and install an interception device in the pipeline at the end of the gas gathering branch pipe;

[0060] Step 1.1, the pigging ball breaking pressure difference ΔPs should be not greater than the difference between the maximum allowable operating pressure and the design pressure P 2max of the branch pipe and the dry pipe operating pressure P1 during pigging, to avoid overpressure of the pipeline. The pigging ball breaking pressure difference ΔPs is

[0061] ΔP s≤P 2max -P1 (1)

[0062] Where ΔPs is the pressure difference caused by the breaking of the pigging ball, P 2max P1 is the maximum operating pressure of the branch pipe, and P2 is the operating pressure of the main pipe during pigging.

[0063] Step 1.2: Use a microcomputer-controlled static stiffness fatigue testing machine to conduct indoor tests and obtain a curve model of the relationship between the crushing pressure difference and the wall thickness after the pigging ball is blocked by the interception device in the pipeline;

[0064] Step 1.2.1: The testing machine gradually applies force to the pigging ball above the interception device in the simulated pipeline, and the microcomputer acquires the pressure curve of the testing machine;

[0065] Step 1.2.2: According to the pressure curve of the testing machine, the inflection point pressure is the crushing pressure of the pigging ball; the inflection point pressure divided by the cross-sectional area of ​​the pipeline is the crushing pressure difference of the pigging ball.

[0066] Step 1.2.3: Simulate the relationship curve between the wall thickness of the pigging ball and the pressure difference during pigging ball breakage through breakage tests with pigging balls of different wall thicknesses;

[0067] Step 1.2.4: Based on the calculated and set differential pressure of the pigging ball in Step 1.1, obtain the simulated curve model of the relationship between wall thickness and differential pressure.

[0068] like Figure 5 As shown, in step 1.3, the design wall thickness of the pigging ball is determined by the curve model of the relationship between the crushing pressure difference and the wall thickness after the pigging ball gets stuck in the interception device in the pipeline. The operating pressure of the main pipe during pigging is 3.0 MPa, and the maximum allowable operating pressure of the branch pipe (usually the design pressure) is 4.0 MPa. According to formula (1), the crushing pressure difference of the pigging ball during branch pipe pigging should not be greater than 1.0 MPa, and the design crushing pressure difference is 0.8 MPa. The corresponding design wall thickness of the pigging ball is determined by the curve of the relationship between the wall thickness of the pigging ball and the crushing pressure difference simulated by indoor test. The crushing pressure difference of the pigging ball is controlled by reasonably designing the wall thickness of the pigging ball.

[0069] Step 1.4: Based on the wall thickness of the pigging ball, use a water-soluble resin material that can dissolve in water and break upon impact or blockage to make the pigging ball;

[0070] like Figure 3 or Figure 4 As shown, step 1.5 involves designing and installing an interception device inside the end pipe of the gas extraction branch pipe. The interception device consists of several metal bars or metal mesh perpendicular to the pipe; the passage size of the metal bars or metal mesh shall not exceed the passage size of the sewage discharge pipe of the separator within the station.

[0071] Step 2: Launch the pigging ball by connecting it to a mobile launching device at the starting point of the gas production branch pipe or by opening the straight pipe section at the well site.

[0072] Step 2.1, close the wellhead and control valve, and release pressure through the pressure gauge between the wellhead and the flowmeter;

[0073] Step 2.2, remove the straight pipe section between the control valves, connect the temporary mobile ball launching device between the valves for ball launching operation, or directly put the ball into the straight pipe section to restore the wellhead flow process.

[0074] Step 3, the interception device collides with the launched pigging ball, if the collision breaks, the launched pigging ball directly dissolves, completing pigging; if the collision does not break, the launched pigging ball is blocked and deformed after pressure build-up, completing pigging.

[0075] After the pigging ball is launched through the branch pipe starting point well site, it travels with the gas flow to the end of the branch pipe and collides with the metal barrier or metal mesh, breaks, or is blocked under the condition that the collision does not break, causing pressure build-up in the upstream pipeline of the pigging ball. When the pressure difference between the upstream and downstream of the pigging ball reaches the designed breaking pressure difference, the pigging ball deforms and breaks. Small fragments enter the dry pipe through the metal barrier or wire mesh and gradually dissolve in water, and large fragments enter the dry pipe after dissolving into small pieces in the branch pipe; to avoid incomplete dissolution of large fragments in the dry pipe and their entry into the gas gathering station along with the gas flow, which blocks the small-diameter pipelines such as the separator blowdown pipeline and instrument pipeline in the station, affecting the normal operation of the gas gathering station. Finally, the string pipeline is safely and effectively pigged without collecting the ball.

[0076] Example 3

[0077] The pigging method for the gas field string pipeline is implemented according to the following steps:

[0078] As shown in Figure 1 Step 1, design and make a pigging ball according to the maximum allowable operating pressure of the gas gathering branch pipe, and design and install an interception device in the pipeline at the end of the gas gathering branch pipe;

[0079] Step 1.1, the pigging ball breaking pressure difference ΔPs should be no greater than the difference between the maximum allowable operating pressure and the design pressure P 2max of the branch pipe and the dry pipe operating pressure P1 during pigging, to avoid overpressure of the pipeline. The pigging ball breaking pressure difference ΔPs is

[0080] ΔP s ≤P 2max -P1 (1)

[0081] Where ΔPs is the pigging ball breaking pressure difference, P 2max is the maximum operating pressure of the branch pipe, and P1 is the dry pipe operating pressure during pigging;

[0082] Step 1.2, use a microcomputer-controlled static stiffness fatigue testing machine to conduct indoor tests to obtain a curve model of the relationship between the pigging ball breaking pressure difference and the wall thickness after being blocked by the interception device in the pipeline;

[0083] Step 1.2.1, the test machine gradually applies force to the pigging ball above the interception device in the simulated pipeline, and the microcomputer obtains the pressure curve of the test machine;

[0084] Step 1.2.2, according to the pressure curve of the test machine, the inflection point pressure is obtained, that is, the pig breaking pressure; the pig breaking pressure divided by the cross-sectional area of the pipeline is the pig breaking pressure difference;

[0085] Step 1.2.3, simulate the relationship curve between pig wall thickness and pig breaking pressure difference through pig breaking tests of pig with different wall thicknesses;

[0086] Step 1.2.4, according to the pig breaking pressure difference calculated in step 1.1, the simulated wall thickness and breaking pressure difference relationship curve model is obtained.

[0087] As shown in Figure 5 Step 1.3, according to the pig breaking pressure difference and wall thickness relationship curve model after the pig is blocked by the interception device in the pipeline, the design pig wall thickness is queried; according to formula (1), the pig breaking pressure difference of the pig in the branch pipe during pigging should be not more than 3.0 MPa when the dry pipe operating pressure is 1.0 MPa and the maximum allowable operating pressure of the branch pipe (usually the design pressure) is 4.0 MPa, and the design breaking pressure difference is 2.5 MPa; the corresponding pig design wall thickness is found by querying the pig wall thickness and breaking pressure difference relationship curve simulated by the indoor test. The pig breaking pressure difference is controlled by reasonably designing the pig wall thickness.

[0088] Step 1.4, according to the pig wall thickness, the pig is made of water-soluble resin material which can be broken by water or collision or blocking;

[0089] As shown in Figure 3 or Figure 4 Step 1.5, an interception device is designed and installed in the pipeline at the end of the gas gathering branch pipe. The interception device is a number of metal bars or metal nets perpendicular to the pipeline; the passing size of the metal bars or metal nets is not greater than the passing size of the station separator blowdown pipeline.

[0090] Step 2, the pig is sent out by using a movable ball launching device connected at the starting point of the gas gathering branch pipe or by opening the straight pipe section of the well site, and the pig after being sent out is obtained.

[0091] Step 2.1, close the wellhead and control valve, and release pressure through the pressure gauge of the wellhead and flowmeter;

[0092] Step 2.2, remove the straight pipe section between the control valves, connect the temporary movable ball launching device between the valves for ball launching operation; or directly put the ball into the straight pipe section and restore the wellhead flow process to launch the ball.

[0093] Step 3, the interception device collides with the launched pig, if the collision breaks, the launched pig directly dissolves, and the pigging is completed; if the collision does not break, the launched pig is blocked and deformed after pressure accumulation, and the pigging is completed.

[0094] After the pig is launched through the branch pipe starting well site, it travels with the gas flow to the end of the branch pipe and collides with the metal barrier or metal mesh and breaks, if the collision does not break, it is blocked, causing the upstream pipeline of the pig to accumulate pressure, when the pressure difference between the upstream and downstream of the pig reaches the designed breaking pressure difference, the pig deforms and breaks. Small fragments enter the dry pipe through the metal barrier or wire mesh and gradually dissolve in water, and large fragments enter the dry pipe and dissolve after being dissolved into small pieces in the branch pipe; to avoid incomplete dissolution of large fragments entering the dry pipe and entering the gas gathering station with the gas flow, blocking the small-diameter pipelines such as the separator blowdown pipeline and instrument pipeline in the station, affecting the normal operation of the gas gathering station. Finally, the string pipeline realizes safe and effective pigging operation without collecting the pig.

[0095] Example 4

[0096] The pigging method of the gas field string pipeline is implemented according to the following steps:

[0097] As shown in Figure 1 Step 1, design and make the pig according to the maximum allowable operating pressure of the gas gathering branch pipe, and design and install an interception device in the pipeline at the end of the gas gathering branch pipe;

[0098] Step 1.1, the pig breaking pressure difference ΔPs should be not greater than the difference between the maximum allowable operating pressure and the design pressure P 2max of the branch pipe and the dry pipe operating pressure P1 during pigging, to avoid overpressure of the pipeline, the pig breaking pressure difference ΔPs is

[0099] ΔP s ≤P 2max -P1 (1)

[0100] Where ΔPs is the pig breaking pressure difference, P 2max is the maximum operating pressure of the branch pipe, and P1 is the dry pipe operating pressure during pigging;

[0101] Step 1.2, use a microcomputer-controlled static stiffness fatigue testing machine to conduct indoor tests to obtain a pig breaking pressure difference and wall thickness relationship curve model after the pig is blocked by the interception device in the pipeline;

[0102] Step 1.2.1, the testing machine gradually applies force to the pig above the interception device in the simulated pipeline, and the microcomputer obtains the testing machine pressure curve;

[0103] Step 1.2.2, according to the testing machine pressure curve, the inflection point pressure is obtained, which is the pig breaking pressure; the inflection point pressure divided by the cross-sectional area in the pipeline is the pig breaking pressure difference;

[0104] Step 1.2.3, simulate the relationship curve between pig ball wall thickness and pig ball breaking pressure difference by different wall thickness pig ball breaking test;

[0105] Step 1.2.4, according to the calculation of step 1.1, the set pig ball breaking pressure difference is obtained, and the simulated wall thickness and breaking pressure difference relationship curve model is obtained.

[0106] As shown in Figure 5 Step 1.3, according to the pig ball in the pipeline after the interception device is blocked, the breaking pressure difference and the wall thickness relationship curve model is used to query the design pig ball wall thickness; The dry pipe operating pressure is 2.5 MPa during pigging, and the maximum allowable operating pressure of the branch pipe (usually the design pressure) is 5.0 MPa. According to formula (1), the breaking pressure difference of the pig ball during pigging of the branch pipe should be not more than 2.5 MPa. The design breaking pressure is 2.0 MPa; The corresponding pig ball design wall thickness is found out by the simulated pig ball wall thickness and breaking pressure difference relationship curve.

[0107] Step 1.4, according to the pig ball wall thickness, using water-soluble resin material which can be broken by collision or blockage to make pig ball;

[0108] As shown in Figure 3 Or Figure 4 Step 1.5, design and install an interception device in the pipeline at the end of the gas gathering branch pipe. The interception device is a number of metal bars or metal nets perpendicular to the pipeline; The passing size of the metal bar or the metal net is not greater than the passing size of the station separator blowdown pipeline.

[0109] Step 2, the pig ball is sent out by using the movable ball launching device at the starting point of the gas gathering branch pipe or by opening the straight pipe section of the well site, and the pig ball after sending out is obtained.

[0110] Step 2.1, close the wellhead and control valve, and release pressure through the pressure gauge of the wellhead and flowmeter;

[0111] Step 2.2, remove the straight pipe section between the control valves, connect the temporary movable ball launching device between the valves for ball launching operation; Or directly put the ball into the straight pipe section, and restore the wellhead flow process to launch the ball.

[0112] Step 3, the interception device collides with the pig ball after sending out, if the collision breaks, the pig ball after sending out directly dissolves, and the pigging is completed; If the collision does not break, the pig ball after sending out is blocked and deformed to dissolve, and the pigging is completed.

[0113] The pig is launched from the branch pipe starting point well site and travels along with the gas flow to the end of the branch pipe and is broken by the metal barrier or the metal mesh. If the pig is stuck without being broken, the upstream pipeline of the pig is blocked, and when the pressure difference between the upstream and downstream of the pig reaches the designed breaking pressure difference, the pig is deformed and broken. The small fragments enter the dry pipe through the metal barrier or the wire mesh and are gradually dissolved in water, and the large fragments enter the dry pipe after being dissolved into small fragments in the branch pipe and are dissolved in water; the application avoids the incomplete dissolution of the large fragments in the dry pipe, and the large fragments enter the gas gathering station along with the gas flow, block the small-diameter pipelines such as the separator blowdown pipeline and the instrument pipeline in the gas gathering station, and affect the normal operation of the gas gathering station. Finally, the stringing pipeline is not collected, and the safe and effective pigging operation is realized.

Claims

1. A method of pigging a gas field tie-in pipeline, characterised in that, The method is implemented according to the following steps: Step 1, design and manufacture the pig ball according to the maximum allowable operating pressure of the gas gathering branch pipe, and design and install an intercepting device in the pipeline at the end of the gas gathering branch pipe; Step 2, send the pig ball out in a way that the pig ball is connected with a movable ball launching device at the starting point of the gas gathering branch pipe or the straight pipe section of the well site is opened, to obtain the pig ball after being sent out; Step 3, the intercepting device collides with the pig ball after being sent out, if the pig ball is broken after the collision, the pig ball is directly dissolved to complete the pigging, if the pig ball is not broken after the collision, the pig ball is deformed and dissolved after being blocked and pressure built up, to complete the pigging.

2. The method of pigging a gas field tieback pipeline of claim 1, wherein, Step 1 is implemented according to the following steps: Step 1.1, the pig ball breaking pressure difference ΔPs should not be greater than the maximum allowable operating pressure and design pressure P of the branch pipe 2max The difference between the pigging pressure P1 and the operating pressure of the main pipe avoids overpressure of the pipeline, and the pig ball breaking pressure difference ΔPs is ΔP s ≤P 2max -P1 (1) Wherein, ΔPs is the pig breaking pressure difference, P 2max is the maximum operating pressure of the branch pipe, P1 is the operating pressure of the dry pipe during pigging. Step 1.2, indoor test is conducted by using a microcomputer-controlled static stiffness fatigue testing machine, to obtain a curve model of the relationship between the broken pressure difference and the wall thickness of the pig ball after being blocked by the intercepting device in the pipeline; Step 1.3, the wall thickness of the pig ball is queried according to the curve model of the relationship between the broken pressure difference and the wall thickness of the pig ball after being blocked by the intercepting device in the pipeline; Step 1.4, the pig ball is made of a water-soluble resin material which can be broken after being collided or blocked and dissolved after being contacted with water, according to the wall thickness of the pig ball; Step 1.5, the intercepting device is designed and installed in the pipeline at the end of the gas gathering branch pipe.

3. The method of pigging a gas field tieback pipeline of claim 2, wherein, Step 1.2 is implemented according to the following steps: Step 1.2.1, the testing machine gradually applies force to the pig ball above the intercepting device in the simulated pipeline, and the microcomputer obtains the pressure curve of the testing machine; Step 1.2.2, the inflection point pressure is obtained according to the pressure curve of the testing machine, which is the broken pressure of the pig ball; the broken pressure difference of the pig ball is obtained by dividing the inflection point pressure by the cross-sectional area of the pipeline; Step 1.2.3, the relationship curve between the wall thickness of the pig ball and the broken pressure difference of the pig ball is simulated by broken test of pig balls with different wall thicknesses; Step 1.2.4, the wall thickness and broken pressure difference relationship curve model is obtained according to the calculated pig ball broken pressure difference set in step 1.

1.

4. The method of claim 2, wherein, The wall thickness of the pig ball in step 1.3 is directly proportional to the broken pressure difference ΔPs of the pig ball.

5. The method of pigging a gas field tieback pipeline of claim 1, wherein, Step 2 is implemented according to the following steps: Step 2.1, close the wellhead and control valve, and release pressure through the pressure gauge of the flowmeter connected with the wellhead; Step 2.2, remove the straight pipe section between the control valves, connect the temporary movable ball launching device between the valves for ball launching operation, or directly put the ball into the straight pipe section to restore the wellhead flow process to launch the ball.

6. The method of pigging a gas field tieback pipeline of claim 1, wherein, The intercepting device in step 1 is a plurality of metal bars or metal nets perpendicular to the pipeline.

7. The method of pigging a gas field tieback pipeline of claim 6, wherein, The passing size of the metal bars or metal nets is not greater than the passing size of the blowdown pipeline of the separator in the station.

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