A positioning method and a stuck-release method for a pigging tool after it gets stuck

Abstract

The present invention discloses a positioning method after a pig becomes stuck, which includes calculating the density of the oil, gas and water according to the physical property parameters of the oil, gas and water transported in the subsea pipeline, the average pressure of the path of the subsea pipeline cleaned by the pig, the average temperature inside the subsea pipeline, the actual volume of the oil, gas and water inside the subsea pipeline, the nominal flow rate of the pig in the vertical pipe section, and the flow velocity of the pig in the horizontal pipe section, and then calculating the position of the pig in the subsea pipeline according to the time when the pig enters the subsea pipeline and the movement speed of the pig in the subsea pipeline. The present invention also discloses a method for releasing a stuck pig. The present invention can more accurately locate the stuck position of the pig in the subsea pipeline, can release the stuck pig when the pig is cleaning the insoluble salts deposited on the inner wall of the subsea pipeline, and has a better release effect and lower cost.

Description

Technical Field

[0001] The present invention relates to the technical field of subsea pipeline pigging, and more specifically, to a positioning method and a stuck release method after a pig is stuck. Background Art

[0002] An offshore platform transports extracted substances to an FPSO (Floating Production Storage and Offloading unit) through a subsea pipeline. The inlet end of the subsea pipeline is connected to the offshore platform, and the outlet end of the subsea pipeline is connected to the FPSO. Most subsea pipelines are for multi-phase mixed transportation of oil, gas and water. During the mixed transportation process, the three-phase fluid often contains media such as carbon dioxide, hydrogen sulfide, salts such as chlorides, sand and gravel transported by the formation, and wax. It is necessary to perform pigging operations on the subsea pipeline regularly, such as every month, to improve the pipeline transportation efficiency. The dynamic balance of scale formation in the produced water in the subsea pipeline is as follows: Due to the influence of factors such as internal friction of the fluid in the subsea pipeline, frictional resistance of the pipeline wall along the way, interaction between turbulent flow and laminar flow, and heat exchange with seawater, the pressure and temperature of the subsea pipeline continuously decrease from the inlet end to the outlet end. The oil, gas and water are gradually stratified, the partial pressure of carbon dioxide decreases, and the fluid dissolution equilibrium is broken. Precipitates such as calcium carbonate, magnesium carbonate, and barium sulfate continuously precipitate out, resulting in scale continuously precipitating out along the flow direction of the fluid in the subsea pipeline. The hard calcium carbonate scale layer shows a fan-shaped distribution on the cross-section of the subsea pipeline. The closer to the outlet end of the subsea pipeline, the more serious the scaling is, and the mixed transportation efficiency of the subsea pipeline continuously decreases, which intensifies electrochemical corrosion and bacterial corrosion, resulting in the thinning of the subsea pipeline wall thickness, local corrosion perforation or corrosion failure, directly affecting the internal corrosion condition of the subsea pipeline.

[0003] Therefore, it is necessary to use a pig to perform pigging operations on the internal pipelines that are prone to scaling, such as subsea pipelines. In the conventional pigging operations of offshore installations, the pigs selected are mainly scraper balls and high / low density foam balls. Their interference fit design causes the scale blocks in the mixed transportation subsea pipeline to be continuously peeled off and accumulate at the front end of the pig. As the accumulated scale blocks gradually increase, the resistance received by the pig increases. Moreover, for the scraper ball, its crushing pressure is much higher than the high set point of the production shutdown pressure of the mixed transportation subsea pipeline during production operation. Therefore, the phenomenon of "stuck ball" of the pig occurs, resulting in the shutdown of the production of the upstream offshore platform and the inability to transport the produced oil and gas. The production operation of the downstream floating production storage and offloading unit will also be troubled by the working condition fluctuations. Therefore, quickly judging the "stuck ball" position point after the pig is stuck and then efficiently formulating an emergency stuck release plan can effectively reduce the loss of oil and gas production.

[0004] There is a method for unblocking a pig when it gets stuck in a high-wax subsea multiphase pipeline, which includes the following steps: S1. Determine the position where the pig gets stuck; S2. Lower a continuous pipeline to the blocked section at the end of the subsea pipeline to establish a medium circulation channel; S3. Drive out the residual liquid in this section of the subsea pipeline; S4. Inject a cleaning reagent at the end of the subsea pipeline through a pressure boosting device; S5. Let it stand and soak for 5 hours after adding the cleaning reagent; S6. Inject gas for air-lift liquid return, and detect the saturation of the cleaning reagent to judge the dissolved wax amount; S7. Install a burstable blind plate and continue to discharge the residual liquid in the subsea pipeline; S8. Apply pressure at the inlet end of the subsea pipeline to push out the stuck pig.

[0005] However, the above scheme only considers the empirical formulas of the pig running time, pipeline flow rate, and pipeline volume, and the calculated stuck position has a large error, and the positioning of the stuck position of the pig is not accurate enough, resulting in inaccurate calculation of the dosage of reagents such as the injected cleaning agent. At the same time, the above scheme only considers the blockage of the subsea multiphase pipeline caused by the wax accumulation in the pipeline, and does not consider the blockage of the subsea pipeline caused by the precipitation of slightly soluble or insoluble salts such as calcium carbonate, magnesium carbonate, and barium sulfate. Summary of the Invention

[0006] The purpose of the present invention is to overcome the deficiencies of the prior art that the positioning of the pig blockage position is not accurate enough and the blockage of the subsea pipeline caused by insoluble salt precipitation is not considered, and to provide a positioning method and an unblocking method for the pig after blockage. A positioning method for the pig after blockage provided by the present invention can more accurately position the blockage position of the pig in the subsea pipeline. A method for unblocking the pig after blockage provided by the present invention can unblock the pig when it gets stuck while cleaning the insoluble salts deposited on the inner wall of the subsea pipeline, and has a better unblocking effect and lower cost.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] A positioning method for the pig after blockage includes the following steps:

[0009] S1.1: According to the physical property parameters of the oil, gas, and water transported in the subsea pipeline during the production process, calculate the density ρ of the oil, gas, and water. The calculation formula is as follows:

[0010]

[0011] G t =ρ o +ρ ng Q p +ρ w V w

[0012]

[0013] Vt ——At pressure p and temperature T, with each production of 1m 3 The total volume of the oil, gas and water mixture of the ground-degassed crude oil, in m 3 / m 3 ;

[0014] B o ——Volume coefficient of crude oil, unit: m 3 / m 3 ;

[0015] Z——gas compressibility factor, dimensionless;

[0016] p st ——Absolute standard pressure, 1.01325×10 5 Pa;

[0017] T st ——Standard temperature, 293.15K;

[0018] R p ——Production gas-oil ratio, m 3 / m 3 ;

[0019] R s ——dissolved gas-oil ratio, m 3 / m 3 ;

[0020] V w ——Production water-oil ratio, %;

[0021] ρ o ——Density of produced surface degassed crude oil, kg / m 3 ;

[0022] ρ ng ——Density of produced natural gas, kg / m 3 ;

[0023] ρ w ——Density of produced water, kg / m 3 ;

[0024] G t ——With every 1m of production 3 Total mass of oil, gas and water in the ground degassed crude oil, kg / m 3 ;

[0025] ρ——The average density of oil, gas and water mixture within a certain pressure range and temperature range, kg / m 3 ;

[0026] S1.2: Calculate the average pressure drop in the submarine pipeline Calculate the end pressure P2 of the path of the submarine pipeline cleaned by the pig, so as to calculate the average pressure of the path of the submarine pipeline cleaned by the pig. The specific process is as follows:

[0027]

[0028] g——Acceleration due to gravity, 9.80665 m / s 2 ;

[0029] λ——Friction coefficient of the oil-gas-water mixture in the vertical pipe section, dimensionless;

[0030] D——Inner diameter of the submarine pipeline, mm;

[0031] P1——Starting point pressure of the submarine pipeline cleaned by the pig, MPa;

[0032] P2——End point pressure of the submarine pipeline cleaned by the pig, MPa;

[0033] ——Average pressure of the submarine pipeline cleaned by the pig, MPa;

[0034] Q O ——Daily oil production, m 3 / d;

[0035] S1.3: Calculate the average temperature inside the submarine pipeline according to the temperature T1 at the inlet end and the temperature T2 at the outlet end of the submarine pipeline

[0036]

[0037] T1——Temperature at the inlet end of the submarine pipeline, unit K;

[0038] T2——Temperature at the outlet end of the submarine pipeline, unit K;

[0039] ——Average temperature inside the submarine pipeline, unit K;

[0040] S1.4: According to the average pressure inside the submarine pipeline and the average temperature Calculate the actual volume of oil, gas and water inside the submarine pipeline Thus calculate the nominal flow rate Q in the vertical pipe section of the submarine pipeline 垂直 :

[0041]

[0042] S1.5: Use the nominal flow rate Q of the pig in the vertical pipe section 垂直Calculate the velocity ν of the pig in the vertical pipe section 垂直 :

[0043]

[0044] D 垂直 —— Outer diameter of the vertical subsea pipeline section, mm;

[0045] Δθ 垂直 —— Wall thickness of the vertical subsea pipeline section, mm;

[0046] S1.6: Calculate the average pressure o based on the end pressure P2 and the pressure P at the outlet end of the subsea pipeline as the average pressure in the horizontal pipe section of the subsea pipeline:

[0047]

[0048] —— Average pressure in the horizontal pipe section of the subsea pipeline, MPa;

[0049] P o —— Pressure at the outlet end of the subsea pipeline, MPa;

[0050] Here, take P o which can be read from the detection instrument in the floating production storage and offloading unit. Use P o and P2 to calculate the average pressure value, which is regarded as the average pressure in the horizontal pipe section.

[0051] S1.7: Calculate the actual volume of oil, gas, and water in the horizontal pipe section of the subsea pipeline based on the average pressure in the horizontal pipe section of the subsea pipeline and the average temperature inside the subsea pipeline, and then calculate the nominal flow rate Q 水平 in the horizontal pipe section of the subsea pipeline:

[0052]

[0053] S1.8: Use the nominal flow rate Q 垂直 in the horizontal pipe section of the subsea pipeline to calculate the velocity ν 水平 of the pig in the horizontal pipe section:

[0054]

[0055] D 水平 —— Outer diameter of the horizontal subsea pipeline section, mm;

[0056] Δθ 水平 —— Wall thickness of the horizontal subsea pipeline section, mm;

[0057] S1.9: Calculate the position of the pig in the subsea pipeline based on the time when the pig enters the subsea pipeline and the movement speed of the pig in the subsea pipeline:

[0058]

[0059] t 卡 —— The time from when the pig enters the subsea pipeline to when it gets stuck;

[0060] t1 —— The time from when the pig enters the subsea pipeline to when it leaves the vertical pipeline section;

[0061] In the offshore platform production operation, the subsea pipeline transports the produced substances from the offshore platform to the floating production, storage and offloading unit. At this time, the substances transported in the subsea pipeline are generally oil-gas-water mixtures. When using a pig to conduct a pigging operation on the subsea pipeline, the pig is introduced into the subsea pipeline from the inlet end of the subsea pipeline, that is, the end connected to the offshore platform. After the pig enters the subsea pipeline, it needs to be pressurized from the inlet end of the subsea pipeline to push the pig forward in the subsea pipeline. Usually, the oil-gas-water mixture transported in the subsea pipeline is pumped in to achieve pressurization. This can avoid the situation that after the pigging operation is completed, the substances remaining in the subsea pipeline are difficult to discharge after injecting new substances. At the same time, the used oil-gas-water mixture can be obtained locally, and the original pumps and related devices for transporting the oil-gas-water mixture can be used, making the operation more convenient.

[0062] Since the pumped-in oil-gas-water mixture is from the inlet end of the subsea pipeline, relevant data such as the oil production, water production, gas production of each oil well, the pressure and temperature data at the inlet end of the subsea pipeline at the offshore platform, and the pressure and temperature at the outlet end of the subsea pipeline at the floating production, storage and offloading unit can be collected during the production operation. Parameters such as temperature and pressure will affect the volume of the oil-gas-water mixture. At the same time, different proportions of the oil-gas-water mixture will also cause volume changes. The positioning method in the present invention comprehensively considers multiple factors and calculates more accurately the specific position where the pig gets stuck in the subsea pipeline, providing guidance for subsequent pig release operations.

[0063] The subsea pipeline from the offshore platform to the floating production storage and offloading unit includes two vertical pipe sections and a horizontal pipe section located between the two vertical pipe sections at both ends. The two vertical pipe sections are the first vertical pipe section and the second vertical pipe section respectively. The subsea pipeline extends from the offshore platform to the seabed as the first vertical pipe section, then extends horizontally on the seabed to below the floating production storage and offloading unit as the horizontal pipe section, and finally extends from the seabed to the floating production storage and offloading unit as the second vertical pipe section. Both the first vertical pipe section and the second vertical pipe section hang downward. The vertical pipe section and the horizontal pipe section are connected by an expansion bend. Due to various factors such as sea waves in seawater, the vertical pipe section is not necessarily completely perpendicular to the horizontal plane. For the convenience of description and understanding, the vertical pipe section is approximated as a vertical state. After the pig enters the inlet end of the subsea pipeline, taking the pig as the boundary, the subsea pipeline passed by the pig is the subsea pipeline at the rear end of the pig, and the subsea pipeline not yet passed by the pig is the subsea pipeline at the front end of the pig. Since scale gradually precipitates in the fluid in the subsea pipeline along the flow direction, there are different degrees of interference fits at different positions of the pig in the subsea pipeline. The oil, gas, water medium, etc. at the rear end of the pig are regarded as uniformly distributed and pushed, and there is no residual scale on the inner wall of the subsea pipeline after the pig migrates and scrapes. Thus, the moving speed of the pig is calculated in sections.

[0064] For the first vertical pipe section closer to the offshore platform, since this section is a vertical pipe section and is close to the pump, the flow velocity of the fluid is fast and the sediment is small, and the pig is basically not blocked in this section. For the second vertical pipe section, since it is located downstream and the sediment is basically completely precipitated in the horizontal pipe section, the sediment will not be deposited in the second vertical pipe section. At the same time, since the second vertical pipe section is vertically placed, it is also difficult for the sediment to be deposited on the inner side wall of the second vertical pipe section. Therefore, the pig is generally only blocked in the horizontal pipe section. Only in extreme cases, there is a certain possibility of being blocked in the vertical pipe section, but the possibility is extremely small, and being blocked in the vertical pipe section is generally not caused by sediment. In summary, the calculation process given in this solution is mainly for the blockage of the pig in the horizontal pipe section, and the vertical pipe section in steps S1.1 to S1.9 is the first vertical pipe section.

[0065] A method for unblocking a pig after blockage includes the following steps:

[0066] S1: Locate the pig using the positioning method for the pig after blockage as described above;

[0067] S2: After determining the location of the pig, insert the coiled tubing into the subsea pipeline until the outlet of the coiled tubing reaches the scale removal area at the front end of the pig. At the same time, calculate the dosage of the foaming agent required according to the volume of the liquid in the subsea pipeline at the front end of the pig, and calculate the dosage of the scale dissolving agent required according to the volume of the pipeline at the front end of the pig.

[0068] S3: Inject a certain amount of foaming agent into the subsea pipeline through coiled tubing to generate foam, and pump nitrogen into the subsea pipeline through coiled tubing to empty the foam.

[0069] S4: Prepare the scale inhibitor solution according to the calculated dosage of the scale inhibitor, inject the prepared scale inhibitor solution into the subsea pipeline through coiled tubing, and react for a certain period of time.

[0070] S5: Start the pressure pump to pressurize the subsea pipeline at the back end of the pig. If the pressure is normal, the pig is successfully unblocked and continues to run. If the pressure at the front end of the subsea pipeline during the pressure application process still continues to rise to the highest point, the unblocking fails, and repeat steps S3 and S4.

[0071] S6: When the pig continues to run after successful unblocking in step S5, if the pig gets blocked again, repeat steps S1 - S5 until the pig reaches the end of the subsea pipeline to complete the pigging operation for all positions of the subsea pipeline.

[0072] According to the above positioning method after the pig is blocked, the position of the pig can be more accurately located, and the actual dosage during unblocking will be more accurate. It can not only avoid the need to repeatedly use reagents due to insufficient dosage, increasing the operation time and cost, but also prevent excessive dosage resulting in waste and damage to the inner wall of the subsea pipeline.

[0073] In the unblocking method of the present invention, first, a foaming agent is used in combination with nitrogen to empty the liquid in the subsea pipeline in front of the pig; then, an appropriate amount of scale inhibitor solution is injected into the subsea pipeline from which the liquid has been emptied and wait for the scale inhibitor solution to react for a period of time, so that the sediment blocking the movement of the pig in front of the pig reacts and dissolves with the scale inhibitor solution; start the pressure pump located on the offshore platform to pressurize the inlet end of the subsea pipeline, that is, pressurize the back end of the pig. If the pressure does not increase, it means that the pig can move forward and the unblocking is successful. If the pressure keeps rising and rises to the highest point that the subsea pipeline can withstand, stop pressurizing to avoid damaging the subsea pipeline, and determine that the pig is still blocked and the unblocking fails. Repeat the above steps of draining liquid and dissolving scale to unblock again.

[0074] Since the positioning method provided by the present invention after the pig is blocked can more accurately calculate the position where the pig is blocked in the subsea pipeline, therefore, the dosage of reagents such as foaming agent and scale inhibitor can be more accurately controlled. It can not only avoid waste caused by excessive foaming agent and scale inhibitor and excessive corrosion of the inner wall of the subsea pipeline by the scale inhibitor, but also avoid incomplete liquid discharge due to insufficient foaming agent dosage resulting in dilution of the scale inhibitor, and avoid unblocking failure due to insufficient scale inhibitor dosage.

[0075] The scale inhibitor needs to be configured into a scale inhibitor solution with a certain concentration before it can be injected into the subsea pipeline through the coiled tubing. The dosage of the foaming agent is determined by the volume of the liquid in the subsea pipeline at the front end of the pig. When it is blocked for the first time, the volume of the liquid in the subsea pipeline at the front end of the pig is the volume from the front end of the pig in the subsea pipeline to the outlet end of the subsea pipeline. If the first scale removal fails as described in step S5, then the liquid in the subsea pipeline at the front end of the pig at this time is the volume of the injected scale inhibitor solution, and the dosage of the foaming agent used at this time is calculated according to the volume of the scale inhibitor solution.

[0076] Further, between steps S3 and S4, the following steps are also included:

[0077] S31: Calculate the dosage of the cleaning agent according to the volume from the front end of the pig in the subsea pipeline to the outlet end of the subsea pipeline, configure the cleaning agent solution, and inject the configured cleaning agent solution into the subsea pipeline through the coiled tubing for pre-cleaning;

[0078] S32: Calculate the required foaming agent according to the dosage of the cleaning agent solution in step S31, inject the foaming agent into the subsea pipeline through the coiled tubing for foaming, pump nitrogen into the subsea pipeline through the coiled tubing to empty the foam, and then perform step S4.

[0079] The above steps S31 and S32 are cleaning operations. In order to allow the scale inhibitor to react fully with the sediment, before using the scale inhibitor after emptying the liquid in the subsea pipeline at the front end of the pig, use the cleaning agent to clean the sediment and the oil stains attached to the surface of the subsea pipeline. After using the cleaning agent solution, use the foaming agent and nitrogen to empty the cleaning agent solution for subsequent scale removal operations. When the pig is blocked for the first time, use the scale inhibitor to thoroughly clean the oil stains on the subsea pipeline at the front end of the pig. After unblocking, if the pig is blocked again, cleaning may not be required. If the first cleaning operation does not clean the entire subsea pipeline at the front end of the pig, but only cleans the sediment that has fallen off at the front end of the pig, then cleaning operations need to be performed again when the pig is blocked again.

[0080] Further, in step S2, the subsea pipeline includes a first vertical pipe section with its top inlet connected to an offshore platform, a second vertical pipe section with its top outlet connected to a floating production storage and offloading unit, and a horizontal pipe section provided between the first vertical pipe section and the second vertical pipe section;

[0081] If the pig is blocked in the horizontal pipe section, the volume of the configured scale inhibitor solution is the volume from the front end of the pig in the horizontal pipe section to the connection between the horizontal pipe section and the second vertical pipe section; if the pig is blocked in the second vertical pipe section, the volume of the configured scale inhibitor solution is not greater than the volume from the front end of the pig in the second vertical pipe section to the top outlet of the second vertical pipe section.

[0082] This method mainly aims at the blockage of the pig caused by sediment. Usually, the sediment scraped off by the pig accumulates in front of the pig, blocking the movement of the pig. It may also be that there is too much sediment on the inner wall of the subsea pipeline, making it difficult to scrape off. When the pig is blocked in the horizontal pipe section, only the horizontal pipe section in front of the pig needs to be filled with scale dissolving agent, and the liquid level of the scale dissolving agent in the second vertical pipe section is higher than the pig, so that the sediment blocking the pig in front of the pig can be fully immersed in the scale dissolving agent. It is not necessary to fill the second vertical pipe section with scale dissolving agent, which saves the dosage of the scale dissolving agent and reduces the corrosion of the subsea pipeline by the scale dissolving agent. When the pig is blocked in the second vertical pipe section, the dosage of the scale dissolving agent only needs to immerse the fallen sediment.

[0083] Further, in step S3, the top outlet of the second vertical pipe section is connected to the dirty oil tank in the floating production storage and offloading unit, and the foam in the subsea pipeline in front of the pig is discharged into the dirty oil tank after being filled with nitrogen.

[0084] After injecting the foaming agent, the liquid in front of the pig in the subsea pipeline foams. After injecting nitrogen, the foam is discharged from the subsea pipeline, and the discharged foam is collected by using the dirty oil tank originally provided in the floating production storage and offloading unit.

[0085] Further, in step S3, a sampling position is provided on the connecting pipeline between the top outlet of the second vertical pipe section and the dirty oil tank. If there is no foam in the continuous sampling at the sampling position, it can be determined that the foam has been exhausted.

[0086] Further, in step S3, a sampling position is provided on the connecting pipeline between the top outlet of the second vertical pipe section and the dirty oil tank. If there is no foam in the continuous sampling at the sampling position, it can be determined that the foam has been exhausted.

[0087] A ball valve can be provided at the sampling position. Open the ball valve regularly. If there is no continuous foam observed, it is determined that the foam has been emptied.

[0088] Further, the foaming agent includes 15%-25% (mass fraction) of coconut oil acyl propyl hydroxysulfobetaine, 5%-10% (mass fraction) of dodecyl imidazoline, 3%-15% (mass fraction) of alkyl polyether ammonium oxide, 1%-3% (mass fraction) of organic solution, 0.5%-1% (mass fraction) of inorganic salt solution, and the rest is water; according to the volume of the liquid in the subsea pipeline in front of the pig, the dosage of the foaming agent is 100-500 mg / L.

[0089] The organic solution is one or more of ethanol, isopropanol, ethylene, ethylene glycol or triethanolamine. The inorganic salt solution is one or more of sodium formate, sodium silicate, sodium sulfate, sodium metasilicate pentahydrate or sodium phosphate dibasic.

[0090] Further, the scale-dissolving agent solution comprises 10% (mass fraction) of HCl, 5% (mass fraction) of HF and 2% of corrosion inhibitor, with the balance being water.

[0091] Further, the water used in preparing the scale-dissolving agent solution can be replaced by seawater in equal mass.

[0092] Further, the cleaning agent is a multifunctional cleaning agent BH-QXJ-01.

[0093] Among them, the foaming agent, scale-dissolving agent and cleaning agent can also use other commercially available finished products, and only need to be diluted and used according to the usage instructions of the finished pharmaceutical agent.

[0094] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0095] (1) It can calculate the blocking position of the pig in the subsea pipeline more accurately, so as to better guide the unblocking operation.

[0096] (2) During unblocking, a foaming agent is used to foam the liquid in front of the pig in the subsea pipeline to more thoroughly drain the liquid, avoiding dilution of the scale-dissolving agent. Then, a scale-dissolving agent is used to dissolve the sediment to relieve the blockage of the sediment on the movement of the pig. At the same time, due to the accurate calculation of the blocking position of the pig in the subsea pipeline, the dosage calculations of the scale-dissolving agent and the diluent can also be more accurate.

[0097] (3) Before using the scale-dissolving agent, a cleaning agent is used to remove the oil stains attached to the surface of the sediment, so that the scale-dissolving agent can react fully with the sediment. Description of the Drawings

[0098] Figure 1 It is a schematic diagram of the connection structure of the offshore platform and the floating production storage and offloading unit of the present invention through a subsea pipeline;

[0099] Figure 2 It is a schematic diagram of injecting the scale-dissolving agent solution in Embodiment 3.

[0100] The illustration marks are explained as follows:

[0101] 1 - Offshore platform, 2 - Floating production storage and offloading unit, 3 - Subsea pipeline, 31 - First vertical pipe section, 32 - Horizontal pipe section, 33 - Second vertical pipe section, 4 - Pig, 5 - Sediment, 6 - Coiled tubing, 7 - Scale-dissolving agent solution liquid level. Detailed Embodiments

[0102] The present invention will be further described below in conjunction with specific embodiments. Among them, the attached drawings are only for illustrative purposes, showing only schematic diagrams rather than physical diagrams, and should not be construed as a limitation to this patent; in order to better illustrate the embodiments of the present invention, some components in the attached drawings will be omitted, enlarged or reduced, which does not represent the size of the actual product; for those skilled in the art, it is understandable that some well-known structures and their descriptions in the attached drawings may be omitted.

[0103] In the attached drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", etc. indicating the orientation or positional relationship, they are based on the orientation or positional relationship shown in the attached drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the terms describing the positional relationship in the attached drawings are only for illustrative purposes and should not be construed as a limitation to this patent. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific circumstances.

[0104] Embodiment 1

[0105] A positioning method after the pig 4 is blocked, comprising the following steps:

[0106] S1.1: According to the physical property parameters of the oil, gas and water transported in the subsea pipeline during the production process, calculate the density ρ of the oil, gas and water, and the calculation formula is as follows:

[0107]

[0108] G t = ρ o + ρ ng R p + ρ w V w

[0109]

[0110] V t —— At pressure p and temperature T, the total volume of the oil, gas and water mixture accompanying the production of 1 m 3 of surface degassed crude oil per unit m 3 / m 3 ;

[0111] B o —— Crude oil volume factor, unit m 3 / m 3 ;

[0112] Z —— Gas compressibility factor, dimensionless;

[0113] pst —— Absolute standard pressure, 1.01325×10 5 Pa;

[0114] T st —— Standard temperature, 293.15K;

[0115] R p —— Producing gas - oil ratio, m 3 / m 3 ;

[0116] R s —— Solution gas - oil ratio, m 3 / m 3 ;

[0117] V w —— Producing water - oil ratio, %;

[0118] ρ o —— Density of the produced surface - degassed crude oil, kg / m 3 ;

[0119] ρ ng —— Density of the produced natural gas, kg / m 3 ;

[0120] ρ w —— Density of the produced water, kg / m 3 ;

[0121] G t —— Total mass of oil, gas and water accompanying the production of 1 m 3 of surface - degassed crude oil, kg / m 3 ;

[0122] ρ —— Average value of the density of the oil - gas - water mixture within a certain pressure range and temperature range, kg / m 3 ;

[0123] S1.2: Calculate the end pressure P2 of the path of the subsea pipeline cleaned by the pig by calculating the average pressure drop within the subsea pipeline and then calculate the average pressure of the path of the subsea pipeline cleaned by the pig The specific process is as follows:

[0124]

[0125] —— Average velocities of the oil - gas - water mixture at the cross - sectional areas of the two inlets and outlets of the subsea pipeline, m / s;

[0126] g —— Acceleration due to gravity, 9.80665m / s 2 ;

[0127] λ —— Resistance coefficient of the oil-gas-water mixture in the vertical pipe section, dimensionless;

[0128] D —— Inner diameter of the subsea pipeline, mm;

[0129] P1 —— Pressure at the starting point of the subsea pipeline cleaned by the pig, MPa;

[0130] P2 —— Pressure at the ending point of the subsea pipeline cleaned by the pig, MPa;

[0131] —— Average pressure of the subsea pipeline cleaned by the pig, MPa;

[0132] Q0 —— Daily oil production, m 3 / d;

[0133] S1.3: Calculate the average temperature inside the subsea pipeline based on the temperature T1 at the inlet end and the temperature T2 at the outlet end of the subsea pipeline

[0134]

[0135] T1 —— Temperature at the inlet end of the subsea pipeline, unit K;

[0136] T2 —— Temperature at the outlet end of the subsea pipeline, unit K;

[0137] —— Average temperature inside the subsea pipeline, unit K;

[0138] S1.4: Based on the average pressure and the average temperature inside the subsea pipeline, calculate the actual volume of the oil-gas-water inside the subsea pipeline and then calculate the nominal flow rate Q of the vertical pipe section in the subsea pipeline 垂直 :

[0139]

[0140] S1.5: Use the nominal flow rate Q of the pig in the vertical pipe section 垂直 to calculate the flow velocity ν of the pig in the vertical pipe section 垂直 :

[0141]

[0142] D 垂直 —— Outer diameter of the vertical subsea pipe section, mm;

[0143] Δθ 垂直 —— Wall thickness of the vertical subsea pipe section, mm;

[0144] S1.6: Calculate the average pressure O based on the end pressure P2 and the pressure P at the outlet end of the subsea pipeline as the average pressure of the horizontal pipe section in the subsea pipeline:

[0145]

[0146] —— Average pressure of the horizontal pipe section in the subsea pipeline, MPa;

[0147] P O —— Pressure at the outlet end of the subsea pipeline, MPa;

[0148] Here, take P O which can be read from the detection instrument in the floating production storage and offloading unit. The average pressure value calculated using P O and P2 is regarded as the average pressure in the horizontal pipe section.

[0149] S1.7: Calculate the actual volume of oil, gas, and water in the horizontal pipe section of the subsea pipeline based on the average pressure of the horizontal pipe section in the subsea pipeline and the average temperature inside the subsea pipeline and then calculate the nominal flow rate Q 水平 in the horizontal pipe section of the subsea pipeline:

[0150]

[0151] S1.8: Calculate the flow velocity v 垂直 of the pig in the horizontal pipe section using the nominal flow rate Q 水平 in the horizontal pipe section of the subsea pipeline:

[0152]

[0153] D 水平 —— Outer diameter of the horizontal subsea pipe section, mm;

[0154] Δθ 水平 —— Wall thickness of the horizontal subsea pipe section, mm;

[0155] S1.9: Calculate the position of the pig in the subsea pipeline based on the time when the pig enters the subsea pipeline and the movement speed of the pig in the subsea pipeline:

[0156]

[0157] t 卡 —— Time from when the pig enters the subsea pipe to when it gets stuck;

[0158] t1 —— Time from when the pig enters the subsea pipe to when it leaves the vertical pipe section;

[0159] During the exploitation operation of the offshore platform 1, the subsea pipeline 3 transports the extracted materials from the offshore platform 1 to the floating production, storage and offloading unit 2. At this time, the substances transported in the subsea pipeline 3 are generally oil-gas-water mixtures. When using a pig 4 to conduct pigging operation on the subsea pipeline 3, the pig 4 is introduced into the subsea pipeline 3 from the inlet end of the subsea pipeline 3, that is, the end where the subsea pipeline 3 is connected to the offshore platform 1. After the pig 4 enters the subsea pipeline 3, it needs to be pressurized from the inlet end of the subsea pipeline 3 to push the pig 4 forward in the subsea pipeline 3. Usually, the oil-gas-water mixture transported in the subsea pipeline 3 is pumped in to achieve pressurization. This can avoid the situation that after the pigging operation is completed, the substances remaining in the subsea pipeline 3 are difficult to discharge after injecting new substances. At the same time, the oil-gas-water mixture used can be obtained locally, and the original pumps and related devices for transporting the oil-gas-water mixture can be used, making the operation more convenient.

[0160] Since the extracted oil-gas-water mixture is pumped into the subsea pipeline 3 from the inlet end, relevant data such as the oil production, water production, gas production of each oil well, the pressure and temperature data at the inlet end of the subsea pipeline 3 at the offshore platform 1, and the pressure and temperature at the outlet end of the subsea pipeline 3 at the floating production, storage and offloading unit 2 can be collected during the exploitation operation. Parameters such as temperature and pressure will affect the volume of the oil-gas-water mixture. At the same time, different proportions of the oil-gas-water mixture will also cause volume changes. The positioning method in the present invention comprehensively considers multiple factors and more accurately calculates the specific position where the pig 4 is blocked in the subsea pipeline 3, providing guidance for subsequent unblocking operations.

[0161] The subsea pipeline 3 from the offshore platform 1 to the floating production storage and offloading unit 2 includes two vertical pipe sections and a horizontal pipe section 32 located between the two end vertical pipe sections. The two vertical pipe sections are respectively the first vertical pipe section 31 and the second vertical pipe section 33. The subsea pipeline 3 extends from the offshore platform 1 to the seabed as the first vertical pipe section 31, then extends horizontally on the seabed to below the floating production storage and offloading unit 2 as the horizontal pipe section 32, and finally extends from the seabed to the floating production storage and offloading unit 2 as the second vertical pipe section 33. Both the first vertical pipe section 31 and the second vertical pipe section 33 droop downward. The vertical pipe sections are connected to the horizontal pipe section 32 through expansion bends. Due to various factors such as sea waves in seawater, the vertical pipe sections are not necessarily completely perpendicular to the horizontal plane. For the convenience of description and understanding, the vertical pipe sections are approximated to be in a vertical state. After the pig 4 enters the inlet end of the subsea pipeline 3, taking the pig 4 as the boundary, the subsea pipeline 3 passed by the pig 4 is the subsea pipeline 3 at the rear end of the pig 4, and the subsea pipeline not yet passed by the pig 4 is the subsea pipeline 3 at the front end of the pig 4. Since scale precipitates gradually along the flow direction of the fluid in the subsea pipeline, there are different degrees of interference fits at different positions of the pig 4 in the subsea pipeline 3. The oil, gas, water medium, etc. at the rear end of the pig 4 are regarded as evenly distributed and pushed, and there is no residual scale on the inner wall of the subsea pipeline after the pig 4 migrates and scrapes. Therefore, the moving speed of the pig 4 is calculated in sections.

[0162] For the first vertical pipe section 31 closer to the offshore platform 1, since this section is a vertical pipe section and is close to the pump, the flow velocity of the fluid is fast and the sediment 5 is small, and the pig 4 is basically not blocked in this section. For the second vertical pipe section 33, since it is located downstream and the sediment is basically completely deposited in the horizontal pipe section, the sediment 5 will not be deposited in the second vertical pipe section 33. At the same time, since the second vertical pipe section 33 is vertically placed, it is also difficult for the sediment 5 to be deposited on the inner side wall of the second vertical pipe section 33. Therefore, the pig 4 is generally only blocked in the horizontal pipe section 32, and there is only a certain possibility of being blocked in the vertical pipe section in extreme cases, but the possibility is extremely small, and being blocked in the vertical pipe section is generally not caused by the sediment 5. In summary, the calculation process given in this solution is mainly for the blockage of the pig in the horizontal pipe section 32, and the vertical pipe section in steps S1.1 to S1.9 is the first vertical pipe section 31.

[0163] Embodiment 2

[0164] As Figure 1 and Figure 2 shown, a method for unblocking a blocked pig 4 includes the following steps:

[0165] S1: Use the positioning method for the blocked pig 4 as described above to position the pig 4;

[0166] S2: After determining the location of the pigging tool 4, insert the coiled tubing 6 into the subsea pipeline 3 until the outlet of the coiled tubing 6 reaches the front end of the pigging tool 4 where the scale is peeled off. At the same time, calculate the dosage of the foaming agent required according to the volume of the liquid in the subsea pipeline 3 at the front end of the pigging tool 4, and calculate the dosage of the scale-dissolving agent required according to the volume of the pipeline at the front end of the pigging tool 4;

[0167] S3: Inject a certain amount of foaming agent into the subsea pipeline 3 through the coiled tubing 6 to generate foam, and pump nitrogen into the subsea pipeline 3 through the coiled tubing 6 to empty the foam;

[0168] S4: Prepare the scale-dissolving agent solution according to the calculated dosage of the scale-dissolving agent, inject the prepared scale-dissolving agent solution into the subsea pipeline 3 through the coiled tubing 6, and react for a certain period of time;

[0169] S5: Start the pressure pump to pressurize the subsea pipeline 3 behind the pigging tool 4. If the pressure is normal, the unblocking is successful and the pigging tool 4 continues to run. If the pressure at the front end of the pigging tool 4 in the process of pressurization still continues to rise to the highest point, the unblocking fails, and repeat steps S3 and S4;

[0170] S6: When the pigging tool 4 continues to run after the unblocking is successful in step S5, if the pigging tool 4 is blocked again, repeat steps S1 - S5 until the pigging tool 4 reaches the end of the subsea pipeline 3 to complete the pigging operation for all positions of the subsea pipeline 3.

[0171] According to the above positioning method after the pigging tool 4 is blocked, the location of the pigging tool 4 can be positioned more accurately, and the actual dosage during unblocking will be more accurate. It can not only avoid the need to repeatedly use reagents due to insufficient dosage, increasing the operation time and cost, but also prevent excessive dosage resulting in waste and damage to the inner wall of the subsea pipeline 3.

[0172] In the unblocking method of the present invention, first, use the foaming agent in combination with nitrogen to empty the liquid in the subsea pipeline 3 at the front end of the pigging tool 4; then, inject an appropriate amount of scale-dissolving agent solution into the subsea pipeline 3 where the liquid has been emptied and wait for the scale-dissolving agent solution to react for a period of time, so that the sediment 5 blocking the movement of the pigging tool 4 at the front end of the pigging tool 4 reacts and dissolves with the scale-dissolving agent solution; start the pressure pump located on the offshore platform 1 to pressurize the inlet end of the subsea pipeline 3, that is, pressurize the back end of the pigging tool 4. If the pressure does not increase, it means that the pigging tool 4 can move forward and the unblocking is successful. If the pressure keeps rising and rises to the highest point that the subsea pipeline 3 can bear, stop pressurizing to avoid damaging the subsea pipeline 3, and determine that the pigging tool 4 is still blocked and the unblocking fails, and repeat the above steps of draining liquid and dissolving scale to unblock again.

[0173] Since the pigging tool 4 positioning method provided by the present invention can more accurately calculate the position where the pigging tool 4 is stuck in the subsea pipeline 3, the dosage of reagents such as foaming agent and scale dissolving agent required can be controlled more accurately. This can not only avoid waste caused by excessive foaming agent and scale dissolving agent and excessive corrosion of the inner wall of the subsea pipeline 3 by the scale dissolving agent, but also avoid incomplete liquid discharge due to insufficient foaming agent resulting in dilution of the scale dissolving agent, and avoid failure to release the blockage due to insufficient dosage of the scale dissolving agent.

[0174] The scale dissolving agent needs to be configured into a scale dissolving agent solution with a certain concentration before it can be injected into the subsea pipeline 3 through the coiled tubing 6. The dosage of the foaming agent is determined by the volume of the liquid in the subsea pipeline 3 at the front end of the pigging tool 4. When blocked for the first time, the volume of the liquid in the subsea pipeline 3 at the front end of the pigging tool 4 is the volume of the subsea pipeline 3 from the front end of the pigging tool 4 to the outlet end of the subsea pipeline 3. If the first scale dissolving fails as described in step S5, then the liquid in the subsea pipeline 3 at the front end of the pigging tool 4 at this time is the volume of the injected scale dissolving agent solution, and the dosage of the foaming agent used at this time is calculated according to the volume of the scale dissolving agent solution.

[0175] The following steps are also included between steps S3 and S4:

[0176] S31: According to the volume of the subsea pipeline 3 from the front end of the pigging tool 4 to the outlet end of the subsea pipeline 3, calculate the dosage of the cleaning agent and configure the cleaning agent solution, and inject the configured cleaning agent solution into the subsea pipeline 3 through the coiled tubing 6 for pre-cleaning;

[0177] S32: Calculate the required foaming agent according to the dosage of the cleaning agent solution in step S31, inject the foaming agent into the subsea pipeline 3 through the coiled tubing 6 for foaming, and pump nitrogen into the subsea pipeline 6 through the coiled tubing 6 to empty the foam, and then perform step S4.

[0178] The above steps S31 and S32 are cleaning operations. In order to allow the scale dissolving agent to react fully with the sediment 5, before using the scale dissolving agent after emptying the liquid in the subsea pipeline 3 at the front end of the pigging tool 4, use the cleaning agent to clean the sediment 5 and the oil stain attached to the surface of the subsea pipeline 3. After use, the cleaning agent solution is emptied using the foaming agent and nitrogen for subsequent scale dissolving operations. When the pigging tool 4 is blocked for the first time, use the scale dissolving agent to thoroughly clean the oil stain on the subsea pipeline 3 at the front end of the pigging tool 4, so that if the pigging tool 4 is blocked again after releasing the blockage, cleaning is no longer required. If the first cleaning operation does not clean all of the subsea pipeline 3 at the front end of the pigging tool 4, only the sediment 5 that has fallen off at the front end of the pigging tool 4 is cleaned, then when the pigging tool 4 is blocked again, a cleaning operation needs to be performed again.

[0179] In step S2, the submarine pipeline 3 includes a first vertical pipe section 31 whose top inlet is connected to the offshore platform 1, a first vertical pipe section 31 whose top outlet is connected to the floating production storage and offloading unit 2, and a horizontal pipe section 32 disposed between the first vertical pipe section 31 and the second vertical pipe section 33;

[0180] If the pig 4 is stuck in the horizontal pipe section 32, Figure 2 As shown, the volume of the configured scale-dissolving solution is the volume between the front end of the pig 4 in the horizontal pipe section 32 and the connection between the horizontal pipe section 32 and the second vertical pipe section 33, so that the liquid level 7 of the scale-dissolving solution is slightly higher than the horizontal pipe section 32; if the pig 4 is stuck in the second vertical pipe section 33, the volume of the configured scale-dissolving solution is not greater than the volume between the front end of the pig 4 in the second vertical pipe section 33 and the top outlet of the second vertical pipe section 33.

[0181] This method is mainly aimed at the blockage of the pig 4 due to sediment 5. Usually, the sediment 5 scraped off by the pig 4 accumulates in front of the pig 4 and blocks the movement of the pig 4. It may also be that there are too many sediments 5 on the inner wall of the submarine pipeline 3, making it difficult to scrape them off. When the pig 4 is stuck in the horizontal pipe section 32, it is only necessary to fill the horizontal pipe section 32 at the front end of the pig 4 with a scale dissolving agent and make the liquid level of the scale dissolving agent in the second vertical pipe section 33 higher than the pig 4. This can make the sediment 5 at the front end of the pig 4 that blocks the pig 4 fully immersed in the scale dissolving agent. It is not necessary to fill the second vertical pipe section 33 with scale dissolving agent as well, saving the amount of scale dissolving agent and reducing the corrosion of the submarine pipeline 3 by the scale dissolving agent. When the pig 4 is stuck in the second vertical pipe section 33, the amount of scale dissolving agent used is only needed to immerse the fallen sediment 5.

[0182] In step S3, the top outlet of the second vertical pipe section 33 is connected to the slop tank in the floating production storage and drainage unit 2, and the foam in the submarine pipeline 3 at the front end of the pig 4 is discharged into the slop tank after being filled with nitrogen.

[0183] After the foaming agent is injected, the liquid at the front end of the pig 4 in the submarine pipeline 3 foams. After nitrogen is injected, the foam is discharged from the submarine pipeline 3 and the discharged foam is collected by the dirty oil tank originally provided in the floating production storage and drainage device 2.

[0184] In step S3, a sampling position is provided on the connecting pipe between the top outlet of the second vertical pipe section 33 and the dirty oil tank. If no foam is found in continuous sampling at the sampling position, it can be determined that the foam has been exhausted.

[0185] In step S3, a sampling position is provided on the connecting pipe between the top outlet of the second vertical pipe section 33 and the dirty oil tank. If no foam is found in continuous sampling at the sampling position, it can be determined that the foam has been exhausted.

[0186] A ball valve can be provided at the sampling position. Open the ball valve regularly. If no continuous foam is observed, it is determined that the foam has been emptied.

[0187] Example 3

[0188] In addition to the features described in Example 1, this example further includes the following features:

[0189] The foaming agent includes 15% (mass fraction) of cocoamidopropyl hydroxysultaine, 5% (mass fraction) of lauryl imidazoline, 3% (mass fraction) of alkyl polyether ammonium oxide, 1% (mass fraction) of ethanol, 0.5% (mass fraction) of sodium formate solution, and the rest is water; according to the volume of the liquid in the subsea pipeline 3 at the front end of the pig 4, the dosage of the foaming agent is 500 mg / L.

[0190] The scale inhibitor solution includes 10% (mass fraction) of HCl, 5% (mass fraction) of HF, and 2% of corrosion inhibitor, and the rest is water.

[0191] The water used in preparing the scale inhibitor solution can be replaced with seawater of equal mass. This can save precious fresh water at sea.

[0192] The cleaning agent is a multifunctional cleaning agent BH-QXJ-01.

[0193] Example 4

[0194] The foaming agent includes 25% (mass fraction) of cocoamidopropyl hydroxysultaine, 10% (mass fraction) of lauryl imidazoline, 15% (mass fraction) of alkyl polyether ammonium oxide, 3% (mass fraction) of isopropanol, 1% (mass fraction) of sodium silicate solution, and the rest is water; according to the volume of the liquid in the subsea pipeline 3 at the front end of the pig 4, the dosage of the foaming agent is 100 mg / L.

[0195] The scale inhibitor solution includes 10% (mass fraction) of HCl, 5% (mass fraction) of HF, and 2% of corrosion inhibitor, and the rest is water.

[0196] Example 5

[0197] The foaming agent includes 20% (mass fraction) of cocoamidopropyl hydroxysultaine, 8% (mass fraction) of lauryl imidazoline, 8% (mass fraction) of alkyl polyether ammonium oxide, 1% (mass fraction) of ethylene and 1% (mass fraction) of ethylene glycol, 0.8% (mass fraction) of sodium sulfate solution, and the rest is water; according to the volume of the liquid in the subsea pipeline 3 at the front end of the pig 4, the dosage of the foaming agent is 300 mg / L.

[0198] The scale-dissolving agent solution comprises 10% (mass fraction) of HCl, 5% (mass fraction) of HF and 2% of corrosion inhibitor, with the balance being water.

[0199] Obviously, the above-described embodiments of the present invention are merely examples for clearly explaining the present invention, rather than limitations on the embodiments of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made on the basis of the above description. It is not necessary and impossible to enumerate all the embodiments here. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the claims of the present invention.

Claims

1. A positioning method after a pig becomes blocked, characterized in that, It includes the following steps: S1.1: Calculate the density ρ of the oil, gas, and water according to the physical property parameters of the oil, gas, and water transported in the subsea pipeline during the production process. The calculation formula is as follows: G t = ρ o + ρ ng R p + ρ w V w V t —— At pressure p and temperature T, per production of 1 m 3 Total volume of the oil-gas-water mixture of surface degassed crude oil, unit m 3 / m 3 ; B o —— Crude oil volume coefficient, unit m 3 / m 3 ; Z - gas compressibility factor, dimensionless; p st —— Absolute standard pressure, 1.01325×10 5 Pa; T st ——Standard temperature, 293.15 K; R p —— Production gas-oil ratio, m 3 / m 3 ; R s —— Dissolved gas-oil ratio, m 3 / m 3 ; V w —— Production water-oil ratio, %; ρ o —— Density of the produced surface degassed crude oil, kg / m 3 ; ρ ng —— Density of the produced natural gas, kg / m 3 ; ρ w —— Density of the produced water, kg / m 3 ; G t —— Total mass of oil, gas and water of surface degassed crude oil per 1 m 3 production, kg / m 3 ; ρ—the average density of the oil-gas-water mixture within a certain pressure range and temperature range, kg / m 3 ; S1.2: By calculating the average pressure drop in the subsea pipeline Calculate the end pressure P2 of the path of the subsea pipeline cleaned by the pig, so as to calculate the average pressure of the path of the subsea pipeline cleaned by the pig The specific process is as follows: g——acceleration due to gravity, 9.80665 m / s 2 ; λ - friction factor of the oil, gas, and water mixture in the vertical pipe section, dimensionless; D - inner diameter of the subsea pipeline, mm; P1 - starting point pressure of the subsea pipeline cleaned by the pig, MPa; P2 - ending point pressure of the subsea pipeline cleaned by the pig, MPa; ——Average pressure of the subsea pipeline cleaned by the pig, MPa; Q O —— Oil production per day, m 3 / d; S1.3: Calculate the average temperature inside the subsea pipeline based on the temperature T1 at the inlet end and the temperature T2 at the outlet end of the subsea pipeline S1.4: According to the average pressure in the subsea pipeline and the average temperature calculate the actual volume of oil, gas and water in the subsea pipeline and thus calculate the nominal flow rate Q in the vertical pipe section of the subsea pipeline 垂直 : S1.5: Use the nominal flow rate Q of the pig in the vertical pipe section 垂直 to calculate the velocity ν of the pig in the vertical pipe section 垂直 : π is the ratio of the circumference of a circle to its diameter; D 垂直 —— Outer diameter of vertical subsea pipeline section, mm; Δθ 垂直 —— Wall thickness of the vertical subsea pipeline section, mm; S1.6: Calculate the average pressure O based on the end pressure P2 and the pressure P at the outlet end of the subsea pipeline as the average pressure of the horizontal pipe section in the subsea pipeline: S1.7: According to the average pressure of the horizontal pipe section in the subsea pipeline and the average temperature inside the subsea pipeline calculate the actual volume of oil, gas and water in the horizontal pipe section of the subsea pipeline so as to calculate the nominal flow rate Q in the horizontal pipe section of the subsea pipeline 水平 : S1.8: Using the nominal flow rate Q in the horizontal pipe section of the subsea pipeline 垂直 Calculate the velocity ν of the pig in the horizontal pipe section 水平 : D 水平 —— Outer diameter of horizontal submarine pipeline section, mm; Δθ 水平 —— Wall thickness of horizontal submarine pipeline section, mm; S1.9: Calculate the position of the pig in the subsea pipeline based on the time when the pig enters the subsea pipeline and the movement speed of the pig in the subsea pipeline: t 卡 —— The time from when the pig enters the subsea pipeline to when it gets stuck; t1 - time from when the pig enters the subsea pipeline to when it leaves the vertical pipe section.

2. A method for releasing a pigging tool after it gets stuck, characterized in that, It includes the following steps: S1: Locate the pig using the pig blockage positioning method as described in Claim 1; S2: After determining the position of the pig, insert the coiled tubing into the subsea pipeline until the outlet of the coiled tubing reaches the front end of the pig where the scale is peeled off. At the same time, calculate the dosage of the foaming agent according to the volume of the liquid in the subsea pipeline at the front end of the pig, and calculate the dosage of the scale dissolving agent according to the volume of the pipeline at the front end of the pig; S3: Inject a certain amount of foaming agent into the subsea pipeline through the coiled tubing to generate foam, and pump nitrogen into the subsea pipeline through the coiled tubing to empty the foam; S4: Prepare the scale dissolving agent solution according to the calculated dosage of the scale dissolving agent, inject the prepared scale dissolving agent solution into the subsea pipeline through the coiled tubing, and react for a certain period of time; S5: Start the pressure pump to pressurize the subsea pipeline behind the pig. If the pressure is normal, the pig is successfully unblocked and continues to run. If the pressure at the front end of the subsea pipeline where the pig is located continues to rise to the highest point during the pressure boosting process, the unblocking fails, and repeat steps S3 and S4; S6: When the pig continues to run after being successfully unblocked in step S5, if the pig is blocked again, repeat steps S1 - S5 until the pig reaches the end of the subsea pipeline to complete the pigging operation for all positions of the subsea pipeline.

3. The method for releasing a pigging tool jammed according to claim 2, wherein The following steps are also included between steps S3 and S4: S31: Calculate the dosage of the cleaning agent according to the volume from the front end of the pig in the subsea pipeline to the outlet end of the subsea pipeline, prepare the cleaning agent solution, and inject the prepared cleaning agent solution into the subsea pipeline through the coiled tubing for pre - cleaning; S32: Calculate the required foaming agent according to the dosage of the cleaning agent solution in step S31, inject the foaming agent into the subsea pipeline through the coiled tubing to generate foam, pump nitrogen into the subsea pipeline through the coiled tubing to empty the foam, and then proceed to step S4.

4. The method for releasing the blockage of the pig after blockage according to claim 2, wherein In step S2, the subsea pipeline includes a first vertical pipe section with its top inlet connected to an offshore platform, a second vertical pipe section with its top outlet connected to a floating production storage and offloading unit, and a horizontal pipe section provided between the first vertical pipe section and the second vertical pipe section; If the pig is stuck in the horizontal pipeline section, the volume of the scale-dissolving agent solution configured is the volume between the front end of the pig in the horizontal pipeline section and the connection of the horizontal pipeline section to the second vertical pipeline section; if the pig is stuck in the second vertical pipeline section, the volume of the scale-dissolving agent solution configured is not greater than the volume between the front end of the pig in the second vertical pipeline section and the top outlet of the second vertical pipeline section.

5. The method for releasing the blockage after the pig is blocked according to claim 4, characterized in that, In the step S3, the top outlet of the second vertical pipeline section is communicated with the dirty oil tank in the floating production, storage and offloading unit, and the foam in the subsea pipeline at the front end of the pig is discharged into the dirty oil tank after being filled with nitrogen.

6. The method for releasing the blockage of the pig after blockage according to claim 5, wherein, In the step S3, a sampling position is provided on the connecting pipeline between the top outlet of the second vertical pipeline section and the dirty oil tank. It can be determined that the foam has been completely discharged if there is no foam in continuous sampling at the sampling position.

7. The method for releasing a pigging tool jammed according to claim 2, wherein The foaming agent includes 15%-25% (mass fraction) of cocamidopropyl hydroxysultaine, 5%-10% (mass fraction) of dodecyl imidazoline, 3%-15% (mass fraction) of alkyl polyether ammonium oxide, 1%-3% (mass fraction) of organic solution, 0.5%-1% (mass fraction) of inorganic salt solution, and the rest is water; According to the volume of the liquid in the subsea pipeline at the front end of the pig, the dosage of the foaming agent is 100-500 mg / L.

8. The method for releasing blockage after a pig becomes stuck according to claim 2, wherein, The scale-dissolving agent solution includes 10% (mass fraction) of HCl, 5% (mass fraction) of HF + 2% of corrosion inhibitor, and the rest is water.

9. The method for releasing blockage after a pig becomes stuck according to claim 8, characterized in that, The water used in configuring the scale-dissolving agent solution is replaced by seawater of equal mass.

10. The method for releasing the blockage after the pig is blocked according to claim 3, wherein, The cleaning agent is the multifunctional cleaning agent BH-QXJ-01.

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