A new method for determining the moisture pipeline pigging cycle

Abstract

This invention relates to a novel method for determining the cleaning cycle of wet gas pipelines. When the wet gas pipeline is not prone to liquid accumulation, the cleaning is performed using the conventional cleaning cycle. When the wet gas pipeline is prone to liquid accumulation, if the peak wellhead pressure during cleaning exceeds the design pressure of the wet gas pipeline... P 0 The cleaning cycle is calculated using the following criteria: 0.9 times the design pressure of the wet gas pipeline or 0.9 times the maximum cleaning blockage volume of the wet gas pipeline end-segment plug trap. If the peak wellhead pressure during cleaning is less than 0.9 times the design pressure of the wet gas pipeline and the maximum cleaning blockage volume is less than 0.9 times the design volume of the wet gas pipeline end-segment plug trap, the cleaning cycle is calculated using the corrosion rate method. This invention accurately determines the degree of liquid accumulation in different wet gas pipelines, whether cleaning is necessary, and when to initiate cleaning operations.

Description

Technical Field

[0001] This invention relates to the field of natural gas gathering and transmission pipeline technology, specifically to a novel method for determining the cleaning cycle of wet gas pipelines. Background Technology

[0002] There are currently three common methods for determining the pipeline cleaning cycle: the minimum gas transmission efficiency method, the maximum allowable pressure drop method, and the maximum liquid accumulation method.

[0003] The minimum gas delivery efficiency method and the maximum pressure drop method are essentially the same, both using pressure changes as the criterion. In actual production, the gas delivery efficiency of wet gas pipelines is often low, making it impossible to use a 95% delivery efficiency as the primary basis for determining whether to perform pipeline cleaning. Generally, wellhead pressure is used to determine whether to take cleaning measures. However, in actual operation, once the pipeline cleaning device is engaged, the wellhead pressure will increase to a certain extent. Therefore, when using wellhead pressure to determine the timing of pipeline cleaning, the potential increase in wellhead pressure should be taken into account.

[0004] The maximum liquid accumulation method compares the amount of liquid accumulated inside the pipeline with the effective volume of the slug trap (or production separator) as the basis for determining the pigging cycle. However, in actual production, when the slug flow enters the slug trap, part of the liquid in the slug trap is processed and enters the downstream treatment facility. The amount of liquid slug accumulated in the slug trap is only the cumulative amount over time of the portion exceeding the maximum processing capacity of the slug trap. Therefore, the maximum liquid accumulation method has a large error. The surge in the volume of the slug flow at the end of the pipeline should be used as the basis for determining the pigging cycle. Summary of the Invention

[0005] The present invention aims to address the above-mentioned problems by proposing a novel method for determining the cleaning cycle of wet pipelines.

[0006] The technical solution of this invention is as follows:

[0007] A novel method for determining the cleaning cycle of moisture pipelines, the method is as follows:

[0008] Gas flow rate within the moisture pipe v With critical liquid carrying rate v g Compare and determine whether moisture pipes are prone to liquid accumulation;

[0009] In cases where liquid does not easily accumulate in the humid pipeline, normal pipeline cleaning is performed using the standard cleaning cycle T0.

[0010] In situations where moisture easily accumulates in ventilated pipes

[0011] If the peak wellhead pressure during the cleaning process P max > Moisture pipe design pressureP 0 0.9 times or the maximum amount of blockage in the cleaning section S flag >Design volume of the clogging trap at the end of the moisture pipeline S 0 0.9 times, respectively P max =0.9 P 0 and S flag =0.9 S 0 As a boundary, calculate the cleaning cycle. T lim ;

[0012] If the peak wellhead pressure during the cleaning process P max <Design pressure of moisture pipeline P 0 0.9 times and the maximum cleaning section blockage volume S flag <Design volume of the clogging trap at the end of the moisture pipeline> S 0 The corrosion rate method was used to calculate the cleaning cycle, which is 0.9 times that of the original cycle. T lim .

[0013] The peak wellhead pressure during the pipe cleaning process P max > Moisture pipe design pressure P 0 At 0.9, the pig is deployed into the wet gas pipeline, based on the wellhead pressure at the time of pig deployment. P 1 As a boundary, the first cleaning cycle is calculated. T lim1 ;in, P 1 = P max / 1.1=0.82 P 0 .

[0014] The S flag =0.9 S 0 As a boundary, the second cleaning cycle is calculated. T lim2 Take the first cleaning cycle. T lim1 Second cleaning cycle T lim2 The minimum value is the cleaning cycle. Tlim .

[0015] The corrosion rate method is used to calculate the pigging cycle. T lim It can be obtained through the following formula:

[0016] T lim =( x lim × T 0 ) / x max

[0017] In the formula: x lim The maximum corrosion rate limit for humid pipelines is mm / a;

[0018] x max The maximum corrosion rate is expressed in mm / a.

[0019] T 0 For the standard cleaning cycle, d.

[0020] The specific process for determining whether a moisture pipe is prone to liquid accumulation is as follows:

[0021] Calculate the gas flow rate in the moisture pipeline. v and critical liquid carrying velocity v g ;

[0022] When the gas flow rate v ≥Critical liquid carrying rate v g This indicates that the natural gas in the wet pipeline has a good liquid-carrying capacity and is not prone to liquid accumulation, thus shortening the cleaning cycle. T lim =Routine cleaning cycle T 0 ;

[0023] When the gas flow rate v <Critical liquid carrying rate v g This indicates that moisture is prone to accumulating in the duct.

[0024] The technical effects of this invention are as follows:

[0025] This invention can accurately identify pipelines prone to liquid accumulation in different wet gas pipelines. Furthermore, by calculating the peak wellhead pressure and the maximum blockage in the cleaning section, it accurately determines the degree of liquid accumulation in different wet gas pipelines, identifies whether cleaning is necessary, and when to conduct cleaning operations. This method has been applied and verified in wet gas pipeline cleaning operations at the Yan'an Gas Field and can meet the needs of determining the cleaning cycle for wet gas pipelines under complex operating conditions. Attached Figure Description

[0026] Figure 1 This is a flowchart of the method for determining the cleaning cycle of the novel wet gas pipeline according to the present invention.

[0027] Figure 2 The graph shows the variation of the wellhead pressure and relative gas transmission efficiency of the wet gas pipeline over time in Experiment Example 2 of this invention.

[0028] Figure 3 The graph shows the variation of the wellhead pressure and relative gas transmission efficiency of the wet gas pipeline over time in Experiment Example 3 of this invention. Detailed Implementation

[0029] A novel method for determining the cleaning cycle of moisture pipelines, the method is as follows:

[0030] Gas flow rate within the moisture pipe v With critical liquid carrying rate v g Compare and determine whether moisture pipes are prone to liquid accumulation;

[0031] The judgment process is as follows:

[0032] Calculate the gas flow rate in the moisture pipeline. v and critical liquid carrying velocity v g ;

[0033] When the gas flow rate v ≥Critical liquid carrying rate v g When the natural gas in the pipeline has good liquid-carrying capacity and is not prone to liquid accumulation, special cleaning is not required, and the cleaning cycle is short. T lim =Routine cleaning cycle T 0 According to the daily routine cleaning cycle T 0 Perform routine maintenance;

[0034] When the gas flow rate v <Critical liquid carrying rate v g This indicates that moisture is prone to accumulating in the duct.

[0035] If moisture accumulates in the pipes, additional cleaning is required.

[0036] (1) If the peak pressure at the wellhead during the cleaning process P max > Moisture pipe design pressure P 0 0.9 times or the maximum amount of blockage in the cleaning section S flag >Design volume of the clogging trap at the end of the moisture pipeline S 0 0.9 times, respectively P max =0.9 P 0 and S flag =0.9 S 0 As a boundary, calculate the cleaning cycle. T lim ;

[0037] The specific process is as follows:

[0038] Peak wellhead pressure during pipe cleaning P max > Moisture pipe design pressure P 0 At 0.9, the pig is deployed into the wet gas pipeline, based on the wellhead pressure at the time of pig deployment. P 1 As a boundary, the first cleaning cycle is calculated. T lim1 ;in, P 1 = P max / 1.1=0.82 P 0 .

[0039] by S flag =0.9 S 0 As a boundary, the second cleaning cycle is calculated. T lim2 Take the first cleaning cycle. T lim1 Second cleaning cycle T lim2 The minimum value is the cleaning cycle. T lim .

[0040] That is, the cleaning cycle T lim = min( T lim1 ,T lim2 ).

[0041] (2) If the peak pressure at the wellhead during the cleaning process P max <Design pressure of moisture pipeline P 0 0.9 times and the maximum cleaning section blockage volume S flag <Design volume of the clogging trap at the end of the moisture pipeline> S 0 The corrosion rate method was used to calculate the cleaning cycle, which is 0.9 times that of the original cycle. T lim .

[0042] The specific process is as follows:

[0043] The corrosion rate method is used to calculate the pigging cycle. T lim It can be obtained through the following formula:

[0044] T lim =( x lim × T 0 ) / x max

[0045] In the formula: x lim The maximum corrosion rate limit for humid pipelines is mm / a;

[0046] x max The maximum corrosion rate is expressed in mm / a.

[0047] T 0 For the standard cleaning cycle, d.

[0048] Specific Experiment Example 1

[0049] Table 1 shows the natural gas composition data for a certain well area. The water content of the natural gas is 0.6 m³. 3 / 10 4 m 3 A certain No. 1 wet gas pipeline has a design pressure of 8 MPa, an outer diameter of 88.9 mm, a wall thickness of 6 mm, a total length of 2.13 km, and is made of L245NS sulfur-resistant steel pipe. Its gas transmission capacity is 5.82 × 10⁻⁶ m³ / h. 4 m 3 / d, gas gathering station inlet pressure 5.2MPa, operating temperature 20℃, maximum elevation difference of humid gas pipeline 90m;

[0050] Table 1 Natural Gas Components

[0051] <![CDATA[CH4]]> <![CDATA[C2H6]]> <![CDATA[C3H8]]> <![CDATA[i-C4H 10 ]]> <![CDATA[n-C4H 10 ]]> <![CDATA[i-C5H 12 ]]> <![CDATA[n-C5H 12 ]]> Heavy hydrocarbons <![CDATA[CO2]]> <![CDATA[H2S]]> He <![CDATA[N2]]> 92.878 0.618 0.066 0.004 0.004 0.001 0.001 0.001 3.803 0.148 0.048 2.428

[0052] The critical liquid-carrying velocity of the wet gas pipeline was calculated using the minimum pressure gradient method. v g It is 1.89 m / s, while the actual gas flow rate is... v The gas flow rate is 2.79 m / s. v >Critical liquid carrying rate v g This indicates that the natural gas in the wet gas pipeline has a good liquid-carrying capacity, is not prone to liquid accumulation, does not require special pipeline cleaning, and the cleaning cycle is short. T lim =Routine cleaning cycle T 0 According to the daily routine cleaning cycle T 0 Perform routine maintenance, specifically every 90 days.

[0053] Specific Experiment Example 2

[0054] The natural gas composition data are the same as in Table 1, and the water content of the natural gas is 0.6 m. 3 / 10 4 m 3 A certain No. 2 wet gas pipeline has a design pressure of 8 MPa, an outer diameter of 114 mm, a wall thickness of 6.5 mm, a total length of 11.11 km, and is made of L245NS sulfur-resistant steel pipe. Its gas transmission capacity is 2.62 × 10⁻⁶ m³ / h. 4 m 3 / d, gas gathering station inlet pressure 5.68MPa, operating temperature 20 ℃, maximum elevation difference of wet gas pipeline 220 m;

[0055] 1. Calculate the critical liquid-carrying velocity of the wet gas pipeline using the minimum pressure gradient method. v g It is 4.69 m / s, while the actual gas flow rate is... v The gas flow rate is 0.66 m / s. v <Critical liquid carrying rate v g This indicates that the wet gas pipeline has poor liquid carrying capacity and significant liquid accumulation problem under the current operating conditions, which is consistent with the on-site operating conditions.

[0056] 2. Conduct transient simulation calculations for pipeline #2 (wet gas pipeline). The changes in wellhead pressure and relative gas transmission efficiency of this wet gas pipeline over time are shown in [reference needed]. Figure 2 ;

[0057] 3. Design pressure of moisture pipeline P 0 Given a pressure of 8 MPa, calculate the peak wellhead pressure during the cleaning process. Pmax =7.2MPa, then the wellhead pressure when the pipeline cleaning tool is added during normal operation is 7.2MPa. P 1 =6.55MPa. Reference Figure 2 The cleaning cycle can be determined. T lim1 =5d;

[0058] 4. The design volume of the clogging trap at the end of the moisture pipeline is 5m³. 3 The maximum blockage limit for the end-stage cleaning section during the wet gas pipeline cleaning process is [value missing]. S flag =4.5m 3 Calculate the cleaning cycle based on this value. T lim2 Infinitely large;

[0059] 5. Take T lim1 and T lim2 The minimum value determines the pipeline cleaning cycle. T lim It is 5d.

[0060] Specific Experiment Example 3

[0061] The natural gas composition data are the same as in Table 1, and the water content of the natural gas is 0.6 m. 3 / 10 4 m 3 A certain No. 3 wet gas pipeline has a design pressure of 8 MPa, an outer diameter of 88.9 mm, a wall thickness of 6 mm, a total length of 5.07 km, and is made of L245NS sulfur-resistant steel pipe. Its gas transmission capacity is 3.12 × 10⁻⁶ m³ / h. 4 m 3 / d, gas gathering station inlet pressure 5.2MPa, operating temperature 20 ℃, maximum elevation difference of wet gas pipeline 180m;

[0062] 1. Calculate the critical liquid-carrying velocity of the wet gas pipeline using the minimum pressure gradient method. v g The velocity is 5.97 m / s, while the actual gas flow rate is... v The gas flow rate is 1.49 m / s. v <Critical liquid carrying rate v g This indicates that the wet gas pipeline has poor liquid carrying capacity and significant liquid accumulation problem under the current operating conditions, which is consistent with the on-site operating conditions.

[0063] 2. Transient simulation calculations were conducted for pipeline #3 (wet gas pipeline). The changes in wellhead pressure and relative gas transmission efficiency of this wet gas pipeline over time are shown in [reference needed]. Figure 3 ;

[0064] 3. Design pressure of moisture pipeline P 0 Given a pressure of 8 MPa, calculate the peak wellhead pressure during the cleaning process. P max ==7.2MPa, then the wellhead pressure when the pipeline cleaning machine is added during normal operation of the wet gas pipeline. P 1 =6.55MPa. Reference Figure 3 Calculate the cleaning cycle based on this value. T lim1 Infinitely large;

[0065] 4. The design volume of the clogging trap at the end of the moisture pipeline is 5m³. 3 The maximum blockage limit for the end-stage cleaning section during the wet gas pipeline cleaning process is [value missing]. S flag =4.5m 3 Calculate the cleaning cycle based on this value. T lim2 Infinitely large;

[0066] 5. Calculate the maximum corrosion rate of this humid pipeline. x max =0.13mm / a, the maximum limit of corrosion rate for wet gas pipelines x lim =0.076mm / a, typical cleaning cycle T 0 =90 d;

[0067] pass T lim =( x lim × T 0 ) / x max Calculated T lim =52.6 days; therefore, the cleaning cycle for this moisture pipeline is... T lim It lasts for 52 days.

Claims

1. A novel method for determining the cleaning cycle of wet pipelines, characterized in that: The method is as follows: Gas flow rate within the moisture pipe v With critical liquid carrying rate v g Compare and determine whether moisture pipes are prone to liquid accumulation; In cases where liquid does not easily accumulate in the humid pipeline, normal pipeline cleaning is performed using the standard cleaning cycle T0. In situations where moisture easily accumulates in ventilated pipes If the peak wellhead pressure during the cleaning process P max > Moisture pipe design pressure P 0 0.9 times or the maximum amount of blockage in the cleaning section S flag >Design volume of the clogging trap at the end of the moisture pipeline S 0 0.9 times, respectively P max =0.9 P 0 and S flag =0.9 S 0 As a boundary, calculate the cleaning cycle. T lim ; If the peak wellhead pressure during the cleaning process P max <Design pressure of moisture pipeline P 0 0.9 times and the maximum cleaning section blockage volume S flag <Design volume of the clogging trap at the end of the moisture pipeline> S 0 The corrosion rate method was used to calculate the cleaning cycle, which is 0.9 times that of the original cycle. T lim ; The peak wellhead pressure during the pipe cleaning process P max > Moisture pipe design pressure P 0 At 0.9, the pig is deployed into the wet gas pipeline, based on the wellhead pressure at the time of pig deployment. P 1 As a boundary, the first cleaning cycle is calculated. T lim1 ; in, P 1 = P max / 1.1=0.82 P 0 ; The S flag =0.9 S 0 As a boundary, the second cleaning cycle is calculated. T lim2 Take the first cleaning cycle. T lim1 Second cleaning cycle T lim2 The minimum value is the cleaning cycle. T lim ; That is, the cleaning cycle T lim = min( T lim1 , T lim2 ).

2. The method for determining the cleaning cycle of the novel wet pipeline according to claim 1, characterized in that: The corrosion rate method is used to calculate the pigging cycle. T lim It can be obtained through the following formula: T lim =( x lim × T 0 ) / x max In the formula: x lim The maximum corrosion rate limit for humid pipelines is mm / a; x max The maximum corrosion rate is expressed in mm / a. T 0 For the standard cleaning cycle, d.

3. The method for determining the cleaning cycle of the novel wet pipeline according to claim 2, characterized in that: The specific process for determining whether a moisture pipe is prone to liquid accumulation is as follows: Calculate the gas flow rate in the moisture pipeline. v and critical liquid carrying velocity v g ; When the gas flow rate v ≥Critical liquid carrying rate v g This indicates that the natural gas in the wet pipeline has a good liquid-carrying capacity and is not prone to liquid accumulation, thus shortening the cleaning cycle. T lim =Routine cleaning cycle T 0 ; When the gas flow rate v <Critical liquid carrying rate v g This indicates that moisture is prone to accumulating in the duct.

Images