Submarine pipeline high-risk hydrate generation area identification method

Abstract

The invention discloses a submarine pipeline high-risk hydrate generation area identification method, which comprises the following steps of: performing three-dimensional multiphase flow simulation on a submarine pipeline to obtain along-line flow parameters, judging hydrate generation conditions by combining hydrate generation temperature, hydrate generation pressure and pipeline liquid holdup during pipeline flow, and constructing hydrate generation risk evaluation matrixes I and II; the high-risk hydrate generation area of the submarine pipeline is identified, and an effective means is provided for guaranteeing safe operation of the submarine pipeline.

Description

Technical Field

[0001] The present invention relates to a method for identifying high-risk hydrate formation areas in subsea pipelines, and is related to the identification of hydrate formation risk areas in subsea pipelines. Background Art

[0002] In the field of offshore oil and gas resource development, subsea pipelines, as key infrastructure for oil and gas transportation, their safe and stable operation is of crucial importance. However, the formation of hydrates has always been one of the major challenges affecting the normal operation of subsea pipelines.

[0003] With the continuous growth of global energy demand, offshore oil and gas resources have gradually been exploited. Hydrates are ice-like crystalline compounds formed by natural gas and water under certain temperature and pressure conditions. Once a large amount of hydrates are formed in subsea pipelines, it is extremely easy to cause pipeline blockage, resulting in blocked fluid flow, abnormal pressure increase, and even serious accidents such as pipeline rupture, thus posing serious safety hazards to offshore oil and gas exploitation and transportation.

[0004] At present, there are many difficulties in identifying the hydrate formation risk areas in subsea pipelines. On the one hand, the subsea environment is complex and changeable, and factors such as temperature, pressure, fluid composition, and flow rate interact with each other, making the mechanism of hydrate formation not fully understood, and it is difficult to accurately judge its formation location and conditions. The geological conditions and seawater properties in different sea areas vary significantly, further increasing the complexity of identification.

[0005] On the other hand, the existing identification technologies and methods still have limitations. Some traditional detection means, such as methods based on temperature and pressure monitoring, can only provide macroscopic environmental parameters and cannot accurately determine the specific areas where hydrates are formed; while some detection technologies based on principles such as acoustics and optics can, to a certain extent, detect hydrates, but due to the interference of the complex subsea environment, the detection accuracy and reliability need to be improved.

[0006] In addition, with the continuous expansion of the scale of subsea oil and gas pipelines, how to efficiently and comprehensively identify the risk areas of subsea pipelines is also an urgent problem to be solved currently. Existing methods are often inefficient when dealing with large-scale data and complex pipeline systems and are difficult to meet the needs of actual engineering.

[0007] The present invention relies on numerical simulation to establish a method for identifying high-risk hydrate formation areas in subsea pipelines, which has important practical significance for ensuring the safe and stable development of offshore oil and gas resources. Summary of the Invention

[0008] The present invention proposes a method for identifying high-risk hydrate formation areas in subsea pipelines to identify the hydrate formation risk areas in subsea pipelines and reduce pipeline blockage and rupture accidents caused by hydrate formation.

[0009] To achieve the above object, the present invention is implemented by the following technical solutions:

[0010] S1: Establish a full-scale model of the subsea pipeline, conduct multiphase flow simulation, calculate the flow parameters along the pipeline, and collect data;

[0011] S2: Combine the multiphase flow simulation parameters and data to clarify the hydrate formation model in the pipeline;

[0012] S3: Determine the hydrate formation temperature and pressure under pipeline flow conditions by studying the hydrate formation model;

[0013] S4: Calculate the liquid holdup of the pipeline and judge the hydrate formation situation in the pipeline;

[0014] S5: Based on the calculation results of the difference ΔT between the hydrate formation temperature and the pipeline flow temperature and the difference ΔP between the pipeline flow pressure and the hydrate formation pressure, establish a hydrate formation risk evaluation matrix I and a hydrate formation risk evaluation matrix II.

[0015] S6: When the liquid holdup of the pipeline > 0, according to the change trend of the hydrate phase equilibrium curve without adding any hydrate inhibitor, taking the slope of 1 as the critical point, determine the critical temperature T l ;

[0016] S7: Compare the pipeline flow temperature T m and the critical temperature T l to determine the hydrate formation risk evaluation matrix;

[0017] S8: Determine the high-risk hydrate formation area of the subsea pipeline through the hydrate formation risk evaluation matrix.

[0018] Furthermore, the calculation formula of the hydrate formation model in the pipeline is: In the formula, p is the pressure, Pa; R is the gas constant, J / (mol·K); T is the temperature, K; V is the molar volume, m 3 / mol; a is the energy parameter of the equation of state, Pa·m 6 / mol 2 ; b is the volume parameter of the equation of state, m 3 / mol; c is the volume correction parameter of the equation of state, m 3 / mol.

[0019] Furthermore, the judgment of the hydrate formation situation in the pipeline is carried out according to the following steps;

[0020] 201: When the liquid holdup < 0, it is judged that no hydrate will be formed in the pipeline;

[0021] 202: When the liquid holdup > 0, it is judged that hydrates may be formed in the pipeline.

[0022] Furthermore, the hydrate formation risk evaluation matrix I is established according to the following steps;

[0023] 301: When △P < 0 bara, if △T < 0 °C, the hydrate formation risk level is "None";

[0024] 302: When △P < 0 bara, if 0 °C < △T ≤ 3 °C, 3 °C < △T ≤ 5 °C or △T > 5 °C, the hydrate formation risk level is "Low";

[0025] 303: When 0 bara < △P ≤ 0.5 bara, if △T < 0 °C, 0 °C < △T ≤ 3 °C, 3 °C < △T ≤ 5 °C or △T > 5 °C, the hydrate formation risk levels are all "Low";

[0026] 304: When 0.5 bara < △P ≤ 1.5 bara, if △T < 0 °C, 0 °C < △T ≤ 3 °C, 3 °C < △T ≤ 5 °C, the hydrate formation risk level is "Low";

[0027] 305: When 0.5 bara < △P ≤ 1.5 bara, if △T > 5 °C, the hydrate formation risk level is "Medium";

[0028] 306: When △P > 1.5 bara, if △T < 0 °C, 0 °C < △T ≤ 3 °C, 3 °C < △T ≤ 5 °C, the hydrate formation risk level is "Medium";

[0029] 307: When △P > 1.5 bara, if △T > 5 °C, the hydrate formation risk level is "High".

[0030] Furthermore, the hydrate formation risk evaluation matrix II is established according to the following steps;

[0031] 401: When △P < 0 bara, if △T < 0 °C, the hydrate formation risk level is "None";

[0032] 402: When △P < 0 bara, if 0 °C < △T ≤ 3 °C, 3 °C < △T ≤ 5 °C or △T > 5 °C, the hydrate formation risk is "Low";

[0033] 403: When 0 bara < △P ≤ 38 bara, if △T < 0 °C, 0 °C < △T ≤ 3 °C, 3 °C < △T ≤ 5 °C or △T > 5 °C, the hydrate formation risk levels are all "Low";

[0034] 404: When 38 bara < △P ≤ 63 bara, if △T < 0 °C, 0 °C < △T ≤ 3 °C, 3 °C < △T ≤ 5 °C, the hydrate formation risk level is "Low";

[0035] 405: When 38 bara < △P ≤ 63 bara, if △T > 5 °C, the hydrate formation risk level is "Medium";

[0036] 406: When △P > 63 bara, if △T < 0 °C, 0 °C < △T ≤ 3 °C, 3 °C < △T ≤ 5 °C, the hydrate formation risk level is "Medium";

[0037] 407: When △P > 63 bara, if △T > 5 °C, the hydrate formation risk level is "High".

[0038] Further, the critical temperature T in step S6 l Take 2.

[0039] Further, the determination of the hydrate formation risk evaluation matrix in step S7 is calculated according to the following steps:

[0040] 601: When T m <T l , select the hydrate formation risk evaluation matrix I;

[0041] 602: When T m >T l , select the hydrate formation risk evaluation matrix II.

[0042] Further, in step S8, through the calculation of the hydrate formation risk evaluation matrix, it is determined that the high-risk hydrate formation area of the subsea pipeline is "High". Brief Description of the Drawings

[0043] Figure 1 is the flow chart for identifying the high-risk hydrate area of the subsea pipeline of the present invention

[0044] Figure 2 is the division diagram of the hydrate formation risk area of the subsea pipeline of the present invention Detailed Description of the Invention

[0045] A method for identifying the high-risk hydrate formation area of a subsea pipeline, characterized by comprising the following steps:

[0046] S1: Establish a full-scale model of the subsea pipeline, conduct multiphase flow simulation, calculate the flow parameters along the pipeline, and collect data;

[0047] S2: Combine the multiphase flow simulation parameters and data to clarify the hydrate formation model in the pipeline;

[0048] S3: Determine the hydrate formation temperature and pressure under pipeline flow conditions by studying the hydrate formation model;

[0049] S4: Calculate the liquid holdup of the pipeline and judge the hydrate formation situation in the pipeline;

[0050] S5: Based on the calculation results of the difference △T between the hydrate formation temperature and the pipeline flow temperature and the difference △P between the pipeline flow pressure and the hydrate formation pressure, establish the hydrate formation risk evaluation matrix I and the hydrate formation risk evaluation matrix II.

[0051] S6: When the liquid holdup of the pipeline > 0, according to the change trend of the hydrate phase equilibrium curve without adding any hydrate inhibitor, taking the slope of 1 as the critical point, determine the critical temperature T l ;

[0052] S7: Compare the pipeline flow temperature T m and the critical temperature T l to determine the hydrate formation risk evaluation matrix;

[0053] S8: Determine the high-risk hydrate formation area of the subsea pipeline through the hydrate formation risk evaluation matrix.

[0054] The calculation formula of the pipeline hydrate formation model:

[0055] In the formula, p is the pressure, Pa; R is the gas constant, J / (mol·K); T is the temperature, K; V is the molar volume, m 3 / mol; a is the energy parameter of the equation of state, Pa·m 6 / mol 2 ; b is the volume parameter of the equation of state, m 3 / mol; c is the volume correction parameter of the equation of state, m 3 / mol.

[0056] The judgment of the hydrate formation situation in the pipeline is carried out according to the following steps:

[0057] 201: When the liquid holdup < 0, judge that no hydrate will be formed in the pipeline;

[0058] 202: When the liquid holdup > 0, judge that hydrate may be formed in the pipeline.

[0059] The hydrate formation risk evaluation matrix I is established according to the following steps:

[0060] 301: When △P < 0 bara, if △T < 0 °C, the hydrate formation risk level is "None";

[0061] 302: When △P < 0 bara, if 0℃ < △T ≤ 3℃, 3℃ < △T ≤ 5℃ or △T > 5℃, the hydrate formation risk level is "Low";

[0062] 303: When 0 bara < △P ≤ 0.5 bara, if △T < 0℃, 0℃ < △T ≤ 3℃, 3℃ < △T ≤ 5℃, △T > 5℃, the hydrate formation risk levels are all "Low";

[0063] 304: When 0.5 bara < △P ≤ 1.5 bara, if △T < 0℃, 0℃ < △T ≤ 3℃, 3℃ < △T ≤ 5℃, the hydrate formation risk level is "Low";

[0064] 305: When 0.5 bara < △P ≤ 1.5 bara, if △T > 5℃, the hydrate formation risk level is "Medium";

[0065] 306: When △P > 1.5 bara, if △T < 0℃, 0℃ < △T ≤ 3℃, 3℃ < △T ≤ 5℃, the hydrate formation risk level is "Medium";

[0066] 307: When △P > 1.5 bara, if △T > 5℃, the hydrate formation risk level is "High".

[0067] The hydrate formation risk evaluation matrix II is established according to the following steps:

[0068] 401: When △P < 0 bara, if △T < 0℃, the hydrate formation risk level is "None";

[0069] 402: When △P < 0 bara, if 0℃ < △T ≤ 3℃, 3℃ < △T ≤ 5℃ or △T > 5℃, the hydrate formation risk is "Low";

[0070] 403: When 0 bara < △P ≤ 38 bara, if △T < 0℃, 0℃ < △T ≤ 3℃, 3℃ < △T ≤ 5℃, △T > 5℃, the hydrate formation risk levels are all "Low";

[0071] 404: When 38 bara < △P ≤ 63 bara, if △T < 0℃, 0℃ < △T ≤ 3℃, 3℃ < △T ≤ 5℃, the hydrate formation risk level is "Low";

[0072] 405: When 38 bara < △P ≤ 63 bara, if △T > 5℃, the hydrate formation risk level is "Medium";

[0073] 406: When △P > 63 bara, if △T < 0 °C, 0 °C < △T ≤ 3 °C, or 3 °C < △T ≤ 5 °C, the hydrate formation risk level is "Medium".

[0074] 407: When △P > 63 bara, if △T > 5 °C, the hydrate formation risk level is "High".

[0075] The critical temperature T in step S6 l Take 2.

[0076] The determination of the hydrate formation risk evaluation matrix in step S7 is calculated according to the following steps:

[0077] 601: When T m <T l , select the hydrate formation risk evaluation matrix I;

[0078] 602: When T m >T l , select the hydrate formation risk evaluation matrix II.

[0079] In step S8, through the calculation of the hydrate formation risk evaluation matrix, it is determined that the high-risk hydrate formation area of the subsea pipeline is "High".

Claims

1. A method for identifying high-risk hydrate formation areas in submarine pipelines, characterized in that: The following steps are involved: S1: Establish a full-scale model of the submarine pipeline, perform multiphase flow simulation, calculate flow parameters along the pipeline, and collect data; S2: Combine multiphase flow simulation parameters and data to clarify the hydrate formation model in the pipeline; S3: Determine the hydrate formation temperature and pressure under pipeline flow conditions by studying the hydrate formation model; S4: Calculate the pipeline liquid holdup and determine the hydrate formation in the pipeline; S5: Based on the calculation results of the difference △T between the hydrate formation temperature and the pipeline flow temperature and the difference △P between the pipeline flow pressure and the hydrate formation pressure, establish the hydrate formation risk assessment matrix I and the hydrate formation risk assessment matrix II. S6: When the pipeline liquid holdup is greater than 0, the critical temperature T is determined based on the change trend of the hydrate phase equilibrium curve without adding any hydrate inhibitors, with the slope 1 as the critical point. l ; S7: Compare pipe flow temperature T m and critical temperature T l The size of hydrate formation risk assessment matrix is ​​determined; S8: Determine high-risk hydrate formation areas of submarine pipelines through the hydrate formation risk assessment matrix.

2. A method for identifying high-risk hydrate formation areas in submarine pipelines according to claim 1, characterized in that: The calculation formula of the pipeline hydrate formation model is: Where p is pressure, Pa; R is gas constant, J / (mol·K); T is temperature, K; V is molar volume, m 3 / mol; a is the energy parameter of the state equation, Pa·m 6 / mol 2 ; b is the volume parameter of the state equation, m 3 / mol; c is the volume correction parameter of the state equation, m 3 / mol.

3. A method for identifying high-risk hydrate formation areas in submarine pipelines according to claim 1, characterized in that: The hydrate formation situation in the pipeline is judged according to the following steps: 201: When the liquid holdup is less than 0, it is determined that hydrate will not be generated in the pipeline; 202: When the liquid holdup is greater than 0, it is determined that hydrates may be generated in the pipeline.

4. A method for identifying high-risk hydrate formation areas in submarine pipelines according to claim 1, characterized in that: The hydrate formation risk assessment matrix I is established according to the following steps: 301: When △P<0bara, if △T<0℃, the hydrate formation risk level is "None"; 302: When △P<0bara, if 0℃<△T≤3℃, 3℃<△T≤5℃ or △T>5℃, the hydrate formation risk level is "Low"; 303: When 0bara<△P≤0.5bara, if △T<0℃, 0℃<△T≤3℃, 3℃<△T≤5℃, △T>5℃, the hydrate formation risk level is "Low"; 304: When 0.5bara<△P≤1.5bara, if △T<0℃, 0℃<△T≤3℃, 3℃<△T≤5℃, the hydrate formation risk level is "Low"; 305: When 0.5bara<△P≤1.5bara, if △T>5℃, the hydrate formation risk level is "Medium"; 306: When △P>1.5bara, if △T<0℃, 0℃<△T≤3℃, 3℃<△T≤5℃, the hydrate formation risk level is "Medium"; 307: When △P>1.5bara, if △T>5℃, the hydrate formation risk level is "High".

5. The method for identifying high-risk hydrate formation areas of submarine pipelines according to claim 1, characterized in that: The hydrate formation risk assessment matrix II is established according to the following steps: 401: When △P<0bara, if △T<0℃, the hydrate formation risk level is "None"; 402: When △P<0bara, if 0℃<△T≤3℃, 3℃<△T≤5℃ or △T>5℃, the hydrate formation risk is "Low"; 403: When 0bara<△P≤38bara, if △T<0℃, 0℃<△T≤3℃, 3℃<△T≤5℃, △T>5℃, the hydrate formation risk level is "Low"; 404: When 38bara<△P≤63bara, if △T<0℃, 0℃<△T≤3℃, 3℃<△T≤5℃, the hydrate formation risk level is "Low"; 405: When 38bara<△P≤63bara, if △T>5℃, the hydrate formation risk level is "Medium"; 406: When △P>63bara, if △T<0℃, 0℃<△T≤3℃, 3℃<△T≤5℃, the hydrate formation risk level is "Medium"; 407: When △P>63bara, if △T>5℃, the hydrate formation risk level is "High".

6. A method for identifying high-risk hydrate formation areas in submarine pipelines according to claim 1, characterized in that: In step S6, the critical temperature T l Take 2.

7. The method for identifying high-risk hydrate formation areas of submarine pipelines according to claim 1, characterized in that: The hydrate formation risk assessment matrix determined in step S7 is calculated according to the following steps: 601: When T m <T l , select hydrate formation risk assessment matrix I; 602: When T m >T l , select Hydrate Formation Risk Assessment Matrix II.

8. The method for identifying high-risk hydrate formation areas of submarine pipelines according to claim 1, characterized in that: In step S8, the high-risk hydrate formation area of ​​the submarine pipeline is determined as "High" through calculation of the hydrate formation risk assessment matrix.

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