CN106194165B - Gas hydrates block monitoring device and method in the test of deep water gas well - Google Patents
Gas hydrates block monitoring device and method in the test of deep water gas well Download PDFInfo
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Abstract
Gas hydrates block monitoring device in being tested the present invention relates to a kind of deep water gas well, and it includes downhole data acquiring and transmission system, platform control system and hydrate inhibitor automatic injection system.The temperature, pressure data of fluid in the real-time monitoring and test tubing string of downhole data acquiring and transmission system, and transfer data to platform control system；Platform control system carries out calculating assessment to gas hydrates stopping state in test string, send corresponding pre-warning signal, and the instruction of injection hydrate inhibitor is sent according to tubing string blockage, start corresponding hydrate inhibitor injection pump, pipeline and hydrate inhibitor fill nipple are injected by hydrate inhibitor, hydrate inhibitor is injected into test string.The present invention can be calculated position, the Hydrate Plugging order of severity and the generation completely plugged required time that in deep water gas well test jobs, Hydrate Plugging occurs in test string, and can instruct the formulation of hydrate prophylactico-therapeutic measures.
Description
Technical Field
The invention belongs to the field of ocean deepwater oil and gas exploration and development, and particularly relates to a device and a method for monitoring natural gas hydrate blockage in deepwater gas well testing.
Background
With the gradual exhaustion of onshore oil and gas resources, exploration and development activities gradually turn to the deepwater field, and the contribution of newly added oil and gas exploration reserves in the deepwater field to the overall newly added oil and gas exploration reserves in the global range continuously rises. Eighteen reports of the Party clearly propose the strategy of building the ocean Enhance of China, strengthen the development of ocean oil and gas resources, and have important significance for building the ocean Enhance of China. Many technical challenges are encountered in deepwater oil and gas drilling operation, wherein natural gas hydrate generation under low-temperature and high-pressure conditions brings many challenges to deepwater well completion operation, testing operation, oil and gas gathering and transportation and the like.
Deep water gas well testing is an important operation link for recognizing oil and gas reservoirs and evaluating reservoir potential. The conventional deep water gas well testing system at home and abroad is shown in fig. 1, the main components of the system are a deep water gas well testing string 101 and related auxiliary equipment installed on the testing string, the related auxiliary equipment mainly comprises an underwater testing tree 102, an blowout prevention valve 103 and a flow control head 104, the underwater testing tree 102 is installed on a seabed wellhead, the blowout prevention valve 103 is positioned in the testing string at the upper part of the underwater testing tree, the flow control head 104 is installed at an upper wellhead (the top end of the deep water gas well testing string 101) and is connected with an outflow pipeline on a testing platform, a wellhead thermometer 105 and a wellhead pressure gauge 106 monitor the temperature and pressure parameters of formation fluid, the formation fluid is further processed (such as gas-liquid separation, combustion and the like) after passing through an outflow oil nozzle 107 and a wellhead flowmeter 108, and the auxiliary equipment are used for controlling the outflow of the formation fluid, controlling the pressure in the testing string, preventing a blowout accident from occurring and metering the temperature, pressure and flow of the fluid.
In the normal test operation process, the fluid produced by the stratum enters the test pipe column, flows upwards to the test platform through the test pipe column, carries out gas-liquid separation treatment on the flowing fluid on the platform, and the separated gas burns through the torch, and the separated liquid is stored in the corresponding storage tank on the platform.
However, due to the existence of deep water, low temperature and high pressure conditions, natural gas hydrate is often generated in the test pipe column in the test process, so that the pipe column is blocked, and the normal operation of the test operation is influenced. The existing technology can only simply and preliminarily judge which positions in a test tubular column system can meet the temperature and pressure conditions for generating the hydrate according to the hydrate generation phase equilibrium theory, but cannot judge when and where the hydrate can be blocked and the severity of the blockage caused by the hydrate. WANG Zhi-yuan et al propose to determine the hydrate generation area in the deep water gas well test process according to the hydrate generation phase equilibrium theory and combining with the calculation of the temperature and pressure field of the shaft (Journal of hydrodynamics.2014,26 (4): 840-847). The patent CN104088623A determines a hydrate formation area in a test string according to a hydrate formation phase equilibrium theory, and provides a hydrate control method according to the hydrate formation area, but the patent can not be used for monitoring and analyzing when and where the hydrate blockage occurs in the test string, and the severity of the hydrate blockage. The patent CN104343416A discloses a deep water gas well testing system and a testing method, which proposes determining a hydrate generation area in a testing pipe column according to a hydrate generation phase equilibrium theory, and further adopting an underground throttling method to prevent and control hydrates. Patent CN104895560A discloses a method for testing wellbore pressure, temperature field simulation and hydrate prediction in deep water, which can only determine where in a testing wellbore meets the temperature and pressure conditions of hydrate generation, does not relate to the problems of hydrate generation rate, hydrate deposition blockage and the like, and cannot be used for monitoring and analyzing when and where in a testing string hydrate blockage is caused and the severity of the blockage.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention provides a device and a method for monitoring natural gas hydrate blockage in a deepwater gas well test. By monitoring underground temperature and pressure data in real time and combining the hydrate blockage prediction method provided by the invention, the position of the hydrate blockage in the test pipe column is determined, the hydrate blockage severity is judged, the time required for complete blockage is calculated, an early warning signal is sent out, a hydrate inhibitor is automatically injected into the test pipe column, and the safe and efficient operation of the deepwater gas well test operation is ensured.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows:
natural gas hydrate blocks up monitoring devices in deep water gas well test includes: the system comprises a downhole data acquisition and transmission system, a platform control system and an automatic hydrate inhibitor injection system. The underground data acquisition and transmission system monitors temperature and pressure data of fluid in the test pipe column in real time and transmits the monitored temperature and pressure data to the platform control system; the platform control system calculates and evaluates the plugging severity of the natural gas hydrate in the test string, the time required for the string to be completely plugged and the position where the complete plugging occurs at first, sends out corresponding early warning signals and sends out an instruction for injecting a hydrate inhibitor according to the plugging condition of the string; and the hydrate inhibitor automatic injection system starts a corresponding hydrate inhibitor injection pump according to an instruction sent by the platform control system, and injects the hydrate inhibitor into the test pipe column through the hydrate inhibitor injection pipeline and the hydrate inhibitor injection joint.
Compared with the prior art, the invention has the following beneficial effects: in the aspect of hydrate prediction and prevention and control in deepwater gas well test, the prior art can predict where in a pipe column a temperature and pressure condition favorable for hydrate generation exists only according to a hydrate generation phase equilibrium theory, but cannot judge the position and time where hydrate blockage can not form and the position and time where the hydrate blockage occurs.
Drawings
FIG. 1 is a schematic diagram of a prior art deepwater gas well testing system.
FIG. 2 is a schematic diagram of a natural gas hydrate blockage monitoring device in a deepwater gas well test.
FIG. 3 is a schematic diagram of a method for monitoring natural gas hydrate blockage in deepwater gas well testing.
In the figure: 101. testing a tubular column of the deepwater gas well; 102. testing the tree underwater; 103. an anti-blowout valve; 104. a flow control head; 105. a well head thermometer; 106. a wellhead pressure gauge; 107. discharging an oil nozzle; 108. a wellhead flowmeter; 201a, a first temperature and pressure sensor group; 201b, a second temperature and pressure sensor group; 201c, a third temperature and pressure sensor group; 202. an optical cable; 301. an optical fiber interface; 302. a photo-electric demodulator; 303. a computer; 304. an alarm; 305. a hydrate inhibitor storage tank; 306. a signal actuator; 307a, a first hydrate inhibitor injection pump; 307b, a second hydrate inhibitor injection pump; 307c, a third hydrate inhibitor injection pump; 308a, a first hydrate inhibitor injection line; 308b, a second hydrate inhibitor injection line; 308c, a third hydrate inhibitor injection line; 309a, a first hydrate inhibitor injection joint; 309b, a second hydrate inhibitor injection joint.
Detailed Description
As shown in fig. 2, the device for monitoring natural gas hydrate blockage in deepwater gas well test comprises: the system comprises a downhole data acquisition and transmission system, a platform control system and an automatic hydrate inhibitor injection system. The underground data acquisition and transmission system monitors temperature and pressure data of fluid in the test pipe column in real time and transmits the monitored temperature and pressure data to the platform control system; the platform control system calculates and evaluates the plugging severity of the natural gas hydrate in the test string, the time required for the string to be completely plugged and the position where the complete plugging occurs at first, sends out corresponding early warning signals and sends out an instruction for injecting a hydrate inhibitor according to the plugging condition of the string; and the hydrate inhibitor automatic injection system starts a corresponding hydrate inhibitor injection pump according to an instruction sent by the platform control system, and injects the hydrate inhibitor into the test pipe column through the hydrate inhibitor injection pipeline and the hydrate inhibitor injection joint.
A downhole data acquisition and transmission system comprising: a first warm-pressure sensor group 201a, a second warm-pressure sensor group 201b, a third warm-pressure sensor group 201c and an optical cable 202. The first temperature and pressure sensor group 201a is installed above a test horizon, the second temperature and pressure sensor group 201b is installed below the underwater test tree 102 at a distance of 10 meters, and the third temperature and pressure sensor group 201c is installed 400 meters below the sea surface; the first temperature and pressure sensor group 201a, the second temperature and pressure sensor group 201b and the third temperature and pressure sensor group 201c are used for monitoring temperature and pressure data of the deepwater gas well test string 101 at the position, and the monitored temperature and pressure data are transmitted to the platform control system through the optical cable 202.
A platform control system comprising: an optical fiber interface 301, a photoelectric demodulator 302, a computer 303 and an alarm 304. The optical fiber interface 301 is connected with the optical cable 202, the photoelectric demodulator 302 is connected with the optical fiber interface 301 through an optical fiber, the photoelectric demodulator 302 is connected with the computer 303, and the computer is connected with the alarm 304; the underground temperature and pressure data acquired by the underground data acquisition and transmission system are transmitted to a photoelectric demodulator 302 through an optical cable 202 and an optical fiber interface 301, the photoelectric demodulator 302 converts optical signals into electric signals, the electric signals are transmitted to a computer 303, the computer 303 calculates and analyzes the blockage condition of the natural gas hydrate in the deepwater gas well testing string 101 according to the underground data monitored by the underground data acquisition and transmission system, judges the position of the blockage of the hydrate and the blockage danger level, calculates the time required for the complete blockage of the distance, and sends an alarm instruction and a hydrate inhibitor injection instruction, and the alarm 304 sends an early warning signal of a corresponding level after receiving the alarm instruction to prompt the severity degree of the blockage of the hydrate in the deepwater gas well testing string 101 and the remaining time for the distance from the complete blockage of the string by the hydrate.
The early warning signal is classified into the following grades: the hydrates are deposited and attached on the inner wall of the deepwater gas well testing pipe column 101 to cause the effective inner diameter of the pipe column to be reduced, as shown in fig. 3, the severity of blockage of the hydrates in the deepwater gas well testing pipe column 101 is represented by the reduction degree of the effective inner diameter of the testing pipe column, and early warning signals are divided into four grades. If the deposition and adhesion of hydrate causes the effective pipe diameter (d) of the test pipe column e ) The reduction is: 0.7d ti ≤d e <0.9d ti Then a first-level alarm is performed, and the alarm 304 sends out a first-level early warning signal, wherein d ti Testing the initial inner diameter of the string 101 for the deepwater gas well; if 0.6d ti ≤d e <0.7d ti If so, a secondary alarm is carried out, and the alarm 304 sends out a secondary early warning signal; if 0.4d ti ≤d e <0.6d ti If yes, a third-level alarm is carried out, and the alarm 304 sends out a third-level early warning signal; if d is e <0.4d ti Then, four-level alarm is performed, and the alarm 304 sends out four-level early warning signals.
An automatic hydrate inhibitor injection system comprising: hydrate inhibitor storage tank 305, first hydrate inhibitor injection pump 307a, second hydrate inhibitor injection pump 307b, third hydrate inhibitor injection pump 307c, first hydrate inhibitor injection line 308a, second hydrate inhibitor injection line 308b, and third hydrate inhibitor injection line 308c. Hydrate inhibitor storage tank 305 is mounted on the test platform for storing hydrate inhibitors, such as methanol, ethylene glycol, and the like; the hydrate inhibitor storage tank 305 is connected with a first hydrate inhibitor injection pump 307a, a second hydrate inhibitor injection pump 307b and a third hydrate inhibitor injection pump 307c through pipelines respectively, and hydrate inhibitors are supplied to the first hydrate inhibitor injection pump 307a, the second hydrate inhibitor injection pump 307b and the third hydrate inhibitor injection pump 307 c; the signal execution mechanism 306 is connected with the computer 303 of the platform control system, and operates the first hydrate inhibitor injection pump 307a, the second hydrate inhibitor injection pump 307b and the third hydrate inhibitor injection pump 307c according to an instruction sent by the platform control system, wherein the operation includes starting and stopping the pumps; the first hydrate inhibitor injection joint 309a is installed on the deepwater gas well test string 101 600 meters below the mudline; the second hydrate inhibitor injection joint 309b is installed on the deepwater gas well test string 101 300 meters below the sea surface; a first hydrate inhibitor injection line 308a connects the first hydrate inhibitor injection pump 307a and the first hydrate inhibitor injection junction 309a, a second hydrate inhibitor injection line 308b connects the second hydrate inhibitor injection pump 307b and the subsea test tree 102, and a third hydrate inhibitor injection line 308c connects the third hydrate inhibitor injection pump 307c and the second hydrate inhibitor injection junction 309b.
The first hydrate inhibitor injection pump 307a, the second hydrate inhibitor injection pump 307b, and the third hydrate inhibitor injection pump 307c operate independently, can be started or stopped simultaneously, and are specified as follows.
If the severity of the hydrate blockage in the deepwater gas well test string 101 reaches three or more levels (a three-level early warning signal and a four-level early warning signal appear), starting a corresponding hydrate inhibitor injection pump, and injecting a hydrate inhibitor into the deepwater gas well test string 101, wherein the specific flow is as follows.
(1) If the position where the effective inner diameter of the deepwater gas well test string 101 is most rapidly reduced is located below the subsea test tree 102, the first hydrate inhibitor injection pump 307a is started to inject hydrate inhibitor into the deepwater gas well test string 101 through the first hydrate inhibitor injection fitting 309 a.
(2) If the location where the test string effective inner diameter is most rapidly decreasing is between the subsea test tree 102 and the second hydrate inhibitor injection fitting 309b, the second hydrate inhibitor injection pump 307b is activated to inject hydrate inhibitor into the deepwater gas well test string 101 through the subsea test tree 102.
(3) If the test string effective inner diameter most rapidly decreases above the second hydrate inhibitor injection connection 309b, the third hydrate inhibitor injection pump 307c is activated to inject hydrate inhibitor into the deepwater gas well test string 101 through the second hydrate inhibitor injection connection 309b.
The method for monitoring natural gas hydrate blockage in the deep water gas well test adopts the device for monitoring natural gas hydrate blockage in the deep water gas well test, and comprises the following steps:
(1) metering gas production Q by wellhead flowmeter 108 g And water yield Q w The temperature T of the fluid at the well head is measured by a well head thermometer 105 wh The wellhead fluid pressure p is measured by a wellhead pressure gauge 106 wh 。
(2) The first temperature and pressure sensor group 201a, the second temperature and pressure sensor group 201b and the third temperature and pressure sensor group 201c are used for measuring the temperature T1, T2 and T3 and the pressure p1, p2 and p3 of the fluid in the deepwater gas well testing string 101 at the corresponding depth respectively.
(3) And calculating the temperature and pressure distribution of the fluid in the deepwater gas well testing pipe column. And (3) calculating the pressure distribution in the deep water gas well test pipe column 101 by the formula (1) according to the data obtained by measurement in the steps (1) and (2) and the parameters of the test pipe column, the geothermal gradient, the water depth, the well depth and the well body structure.
In the formula, p is the pressure distribution in the test string; s is the distance to the test horizon; t is time; a is the effective flow area of the test pipe column; rho m The average density of the fluid mixture in the test string is measured; v. of m Is the average flow rate of the fluid mixture; f. of F Is the coefficient of friction resistance; d e To test the effective internal diameter of the pipe string.
The fluid temperature distribution in the deepwater gas well test string 101 is calculated from equation (2).
In the formula, T f Testing the temperature of fluid in the pipe column; c m Is the average heat capacity of the fluid mixture; r is to To test the outer diameter of the pipe column; u shape to Is the total heat transfer coefficient of the wellbore; k is a radical of e Is the formation thermal conductivity; w is a m Is the fluid mixture mass flow rate; t is D Dimensionless temperature; t is ei Is the formation virgin temperature; Δ h is the heat of formation of natural gas hydrate; r is hf Is the natural gas hydrate formation rate; m h Is the molar mass of natural gas hydrate.
(4) And determining the natural gas hydrate generation area in the deepwater gas well testing pipe column. According to the natural gas hydrate generation phase equilibrium theory, hydrate generation temperatures at different depths are calculated, when the fluid temperature is lower than the hydrate generation temperature, hydrates can be generated in the testing pipe column, and therefore the natural gas hydrate generation area in the deep water gas well testing pipe column is determined.
(5) And calculating the generation rate of the natural gas hydrates at different depths in the deepwater gas well test pipe column. Hydrate is generated in the natural gas hydrate generation area in the step (4), but a certain time is needed for the generated natural gas hydrate to cause the blockage of the test string, and the generation rate of the natural gas hydrate at different depths in the deep water gas well test string 101 is calculated by using the following formula.
Wherein u is a coefficient; a. The s Is the gas-liquid contact area; k is a radical of 1 And k 2 Is the reaction constant; delta T sub Is the supercooling degree.
(6) And calculating the effective inner diameter of the deepwater gas well testing pipe column. And a part of the generated natural gas hydrate deposits and adheres to the inner wall of the test string to form a hydrate layer which grows continuously, so that the effective inner diameter of the deepwater gas well test string 101 is reduced continuously, the thickness of the hydrate layer is calculated by the formula (4), and the effective inner diameter of the deepwater gas well test string 101 is calculated by the formula (5).
In the formula, delta h Is the hydrate layer thickness; rho h Is the hydrate density; d ti To test the original internal diameter of the pipe string.
(7) And judging the severity of the blockage of the hydrate in the test pipe column, determining the position where the blockage of the hydrate occurs first, and calculating the time required for the test pipe column to be completely blocked by the hydrate. The change condition of the effective inner diameter of the deepwater gas well testing string 101 at different depths along with the time is obtained through the steps (1) to (6), and as shown in fig. 3, the effective inner diameter of the string is continuously reduced along with the continuous growth of a hydrate layer on the inner wall of the string. The severity of the blockage of the deepwater gas well test string 101 by the hydrate is represented by the change of the effective inner diameter of the test string, and the severity of the blockage of the hydrate in the test string, the position where the blockage of the hydrate occurs first and the time required for the complete blockage of the test string by the hydrate can be judged according to fig. 3. As shown in fig. 3, the effective inner diameter of the test string at the position 150 meters from the sea surface is reduced most rapidly, as shown in curve a, the hydrate blockage situation at the position is the most serious, three-level blockage can be achieved at 28h, the alarm sends out a three-level early warning signal, and as the position (150 meters deep) where the effective inner diameter of the string is reduced most rapidly is positioned above the second hydrate inhibitor injection joint 309b, the third hydrate inhibitor injection pump 307c is started, and the hydrate inhibitor is injected from the second hydrate inhibitor injection joint 309b. As can also be seen in fig. 3, if the hydrate inhibitor is not injected into the deepwater gas well test string 101, it takes about 45 hours so that the test string is completely plugged with hydrate and the location that is first completely plugged with hydrate occurs at a depth of 150 meters (the location where plugging first occurs and the time required are related to various factors such as gas production, water depth, etc.).
(8) And (4) according to the calculation and analysis results in the steps (6) and (7), the platform control system sends out a corresponding alarm instruction, so that the alarm 304 sends out a corresponding early warning signal. The early warning signals were classified into four classes according to the severity of the plugging of the test string by hydrates, as shown in fig. 3. If the deposition and adhesion of hydrate causes the effective pipe diameter (d) of the test pipe column e ) The reduction is: 0.7d ti ≤d e <0.9d ti If so, the alarm sends out a primary early warning signal; if 0.6d ti ≤d e <0.7d ti If yes, the alarm sends out a secondary early warning signal; if 0.4d ti ≤d e <0.6d ti If yes, the alarm sends out a third-level early warning signal; if d is e <0.4d ti And the alarm sends out a four-stage early warning signal.
(9) And according to the level of the early warning signal of hydrate blockage in the test string, the automatic hydrate inhibitor injection system responds. If a three-level or four-level early warning signal occurs, the platform control system sends a hydrate inhibitor injection instruction, starts a hydrate inhibitor injection pump, and injects the hydrate inhibitor into the deepwater gas well test string 101.
If the position where the effective inner diameter of the deepwater gas well test string 101 is most rapidly reduced is located below the subsea test tree 102, the first hydrate inhibitor injection pump 307a is started to inject hydrate inhibitor into the deepwater gas well test string 101 through the first hydrate inhibitor injection fitting 309 a.
If the location where the test string effective inner diameter is most rapidly decreasing is between the subsea test tree 102 and the second hydrate inhibitor injection fitting 309b, the second hydrate inhibitor injection pump 307b is activated to inject hydrate inhibitor into the deepwater gas well test string 101 through the subsea test tree 102.
If the test string effective inner diameter most rapidly decreases above the second hydrate inhibitor injection connection 309b, the third hydrate inhibitor injection pump 307c is activated to inject hydrate inhibitor into the deepwater gas well test string 101 through the second hydrate inhibitor injection connection 309b.
Claims (2)
1. A natural gas hydrate blockage monitoring device in deepwater gas well testing is characterized in that:
the device comprises: the system comprises an underground data acquisition and transmission system, a platform control system and an automatic hydrate inhibitor injection system; the underground data acquisition and transmission system monitors temperature and pressure data of fluid in the test pipe column in real time and transmits the monitored temperature and pressure data to the platform control system; the platform control system calculates and evaluates the plugging severity of the natural gas hydrate in the test string, the time required for the string to be completely plugged and the position where complete plugging occurs at first, sends out corresponding early warning signals and sends out an instruction for injecting a hydrate inhibitor according to the plugging condition of the string; the hydrate inhibitor automatic injection system starts a corresponding hydrate inhibitor injection pump according to an instruction sent by the platform control system, and injects the hydrate inhibitor into the test pipe column through a hydrate inhibitor injection pipeline and a hydrate inhibitor injection joint;
a downhole data acquisition and transmission system comprising: the system comprises a first temperature and pressure sensor group, a second temperature and pressure sensor group, a third temperature and pressure sensor group and an optical cable; the first temperature and pressure sensor group is arranged above the test layer, the second temperature and pressure sensor group is arranged below the underwater test tree at the distance of 10m, and the third temperature and pressure sensor group is arranged 400m below the sea surface; the first temperature and pressure sensor group, the second temperature and pressure sensor group and the third temperature and pressure sensor group are used for monitoring temperature and pressure data of a deepwater gas well testing pipe column at the position, and the monitored temperature and pressure data are transmitted to the platform control system through optical cables;
a platform control system comprising: the system comprises an optical fiber interface, a photoelectric demodulator, a computer and an alarm; the optical fiber interface is connected with the optical cable, the photoelectric demodulator is connected with the optical fiber interface through an optical fiber, the photoelectric demodulator is connected with the computer, and the computer is connected with the alarm; the method comprises the following steps that underground temperature and pressure data acquired by an underground data acquisition and transmission system are transmitted to a photoelectric demodulator through an optical cable and an optical fiber interface, the photoelectric demodulator converts optical signals into electric signals, the electric signals are transmitted to a computer, the computer calculates and analyzes the blocking condition of the natural gas hydrate in a deep water gas well test string according to the underground data monitored by the underground data acquisition and transmission system, judges the position where the hydrate blocking occurs, the blocking danger level, calculates the time required for the complete blocking of the distance, and sends out an alarm instruction and a hydrate inhibitor injection instruction, and after receiving the alarm instruction, the alarm sends out early warning signals of corresponding levels to prompt the severity of the hydrate blocking in the deep water gas well test string and the remaining time for the distance from the string to the complete blocking of the hydrate;
an automatic hydrate inhibitor injection system comprising: a hydrate inhibitor storage tank, a first hydrate inhibitor injection pump, a second hydrate inhibitor injection pump, a third hydrate inhibitor injection pump, a first hydrate inhibitor injection line, a second hydrate inhibitor injection line, and a third hydrate inhibitor injection line; the hydrate inhibitor storage tank is installed on the test platform and used for storing a hydrate inhibitor, and is respectively connected with the first hydrate inhibitor injection pump, the second hydrate inhibitor injection pump and the third hydrate inhibitor injection pump through pipelines and used for providing the hydrate inhibitor for the first hydrate inhibitor injection pump, the second hydrate inhibitor injection pump and the third hydrate inhibitor injection pump; according to an instruction sent by a platform control system, a first hydrate inhibitor injection pump, a second hydrate inhibitor injection pump and a third hydrate inhibitor injection pump execute corresponding operations, wherein the operations comprise starting and stopping the pumps; the first hydrate inhibitor injection joint is arranged on a deepwater gas well test pipe column 600m below a mud line; the second hydrate inhibitor injection joint is arranged on a deepwater gas well test string 300m below the sea surface; the first hydrate inhibitor injection pipeline is connected with a first hydrate inhibitor injection pump and a first hydrate inhibitor injection joint, the second hydrate inhibitor injection pipeline is connected with a second hydrate inhibitor injection pump and an underwater test tree, and the third hydrate inhibitor injection pipeline is connected with a third hydrate inhibitor injection pump and a second hydrate inhibitor injection joint;
the first hydrate inhibitor injection pump, the second hydrate inhibitor injection pump and the third hydrate inhibitor injection pump work independently and can be started or stopped simultaneously;
when the hydrate blockage severity in the deep water gas well testing pipe column reaches a third-level early warning signal and a fourth-level early warning signal, starting a corresponding hydrate inhibitor injection pump, and injecting a hydrate inhibitor into the deep water gas well testing pipe column;
if the position where the effective inner diameter of the deepwater gas well testing pipe column is reduced fastest is positioned below the underwater testing tree, starting a first hydrate inhibitor injection pump, and injecting a hydrate inhibitor into the deepwater gas well testing pipe column through a first hydrate inhibitor injection joint; if the position of the test pipe column with the fastest effective inner diameter reduction is positioned between the underwater test tree and the second hydrate inhibitor injection joint, starting a second hydrate inhibitor injection pump, and injecting the hydrate inhibitor into the deepwater gas well test pipe column through the underwater test tree; and if the position where the effective inner diameter of the test string is reduced most quickly is positioned above the second hydrate inhibitor injection joint, starting a third hydrate inhibitor injection pump, and injecting the hydrate inhibitor into the deepwater gas well test string through the second hydrate inhibitor injection joint.
2. A method for monitoring natural gas hydrate blockage in a deepwater gas well test is characterized in that the device for monitoring natural gas hydrate blockage in the deepwater gas well test is adopted, and the method for monitoring natural gas hydrate blockage in the deepwater gas well test comprises the following steps:
(1) gas production Q measured by wellhead flowmeter g And water yield Q w Measuring the temperature T of the fluid at the well head by means of a well head thermometer wh Measuring the pressure p of the fluid at the well head by means of a pressure gauge at the well head wh ；
(2) Respectively measuring the temperature T1, T2 and T3 and the pressure p1, p2 and p3 of the fluid in the deepwater gas well testing string at the corresponding depth by utilizing the first temperature and pressure sensor group, the second temperature and pressure sensor group and the third temperature and pressure sensor group;
(3) calculating the temperature and pressure distribution of fluid in the deep water gas well testing pipe column, and calculating the pressure distribution in the deep water gas well testing pipe column according to the data obtained by the measurement in the steps (1) and (2) and the parameters of the testing pipe column, the geothermal gradient, the water depth, the well depth and the well body structure by the formula (1);
in the formula, p is the pressure distribution in the test string; s is the distance to the test horizon; t is time; a is the effective flow area of the test pipe column; rho m The average density of the fluid mixture in the test string is measured; v. of m Is the average flow rate of the fluid mixture; f. of F Is the coefficient of friction resistance; d e To test the effective inner diameter of the pipe column;
calculating the temperature distribution of the fluid in the deepwater gas well testing tubular column by the formula (2);
in the formula, T f Testing the temperature of fluid in the pipe column; c m Is the average heat capacity of the fluid mixture; r is to To test the outer diameter of the pipe column; u shape to Is the total heat transfer coefficient of the wellbore; k is a radical of e Is the formation thermal conductivity; w is a m Is the fluid mixture mass flow rate; t is D Dimensionless temperature; t is ei Is the formation virgin temperature; Δ h is the heat of formation of natural gas hydrate; r is hf Is the natural gas hydrate formation rate; m h Is the molar mass of the natural gas hydrate;
(4) determining a natural gas hydrate generation area in a deepwater gas well testing tubular column; according to the natural gas hydrate generation phase equilibrium theory, calculating hydrate generation temperatures at different depths, and when the fluid temperature is lower than the hydrate generation temperature, generating hydrates in the test string, thereby determining the generation area of the natural gas hydrates in the deepwater gas well test string;
(5) calculating the generation rate of natural gas hydrates at different depths in the deep water gas well test pipe column; in the natural gas hydrate generating area in the step (4), hydrates are generated, but a certain time is needed for the generated hydrates to cause the blockage of the test string, and the generation rate of the natural gas hydrates at different depths in the deepwater gas well test string is calculated by using the following formula;
wherein u is a coefficient; a. The s Is the gas-liquid contact area; k is a radical of formula 1 And k 2 Is the reaction constant; delta T sub Is the supercooling degree;
(6) calculating the effective inner diameter of the deepwater gas well testing pipe column; a part of generated hydrate is deposited and attached to the inner wall of the testing pipe column to form a hydrate layer which grows continuously, so that the effective inner diameter of the deep water gas well testing pipe column is reduced continuously, the thickness of the hydrate layer is calculated by the formula (4), and the effective inner diameter of the deep water gas well testing pipe column is calculated by the formula (5);
in the formula, delta h Is the hydrate layer thickness; ρ is a unit of a gradient h Is the hydrate density; d is a radical of ti Testing the original inner diameter of the pipe column;
(7) judging the severity of hydrate blockage in the test pipe column, determining the position where the hydrate blockage occurs first, and calculating the time required for the test pipe column to be completely blocked by the hydrate;
(8) determining the grade of the early warning signal according to the blockage severity degree of the hydrate in the test pipe column, so that the alarm sends out a corresponding early warning signal; according to the severity of the blockage of the test pipe column by the hydrate, the early warning signal is divided into four grades, and if the grade is 0.7d ti ≤d e <0.9d ti If so, the alarm sends out a primary early warning signal; if 0.6d ti ≤d e <0.7d ti If yes, the alarm sends out a secondary early warning signal; if 0.4d ti ≤d e <0.6d ti If yes, the alarm sends out a third-level early warning signal; if d is e <0.4d ti If yes, the alarm sends out a four-stage early warning signal;
(9) according to the level of the early warning signal of hydrate blockage in the test string, the automatic hydrate inhibitor injection system responds; if a three-level or four-level early warning signal appears, the platform control system sends a hydrate inhibitor injection instruction, starts a hydrate inhibitor injection pump, and injects a hydrate inhibitor into the deepwater gas well test string;
if the position where the effective inner diameter of the deepwater gas well testing pipe column is reduced fastest is positioned below the underwater testing tree, starting a first hydrate inhibitor injection pump, and injecting a hydrate inhibitor into the deepwater gas well testing pipe column through a first hydrate inhibitor injection joint;
if the position of the test pipe column with the fastest effective inner diameter reduction is positioned between the underwater test tree and the second hydrate inhibitor injection joint, starting a second hydrate inhibitor injection pump, and injecting the hydrate inhibitor into the deepwater gas well test pipe column through the underwater test tree;
and if the position where the effective inner diameter of the test string is reduced most quickly is positioned above the second hydrate inhibitor injection joint, starting a third hydrate inhibitor injection pump, and injecting the hydrate inhibitor into the deepwater gas well test string through the second hydrate inhibitor injection joint.
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