Gas-liquid two-phase flow metering device and method for low-yield well

Abstract

A gas-liquid two-phase flow metering device for a low-yield well mainly comprises an inlet pipe, a declination pipe, an ascending pipe, a horizontal communicating pipe, a descending pipe and an outlet pipe, and the included angle between the declination pipe and the horizontal direction is 20-30 degrees; the ascending pipe is vertically arranged, an inlet is provided with a one-way valve, the top is provided with an ultrasonic probe, and the horizontal communicating pipe is provided with a temperature sensor and a pressure sensor. Gas-liquid mixed flow is converted into single-phase liquid and single-phase gas alternate flow, so that the problem of two-phase flow measurement in spatial distribution is converted into the problem of single-phase flow in time sequence, and accurate measurement of flow can be realized by measuring the time of passing through a fixed-volume pipeline. Compared with a traditional metering mode, the device is simple in structure, low in metering cost and suitable for intermittent liquid and gas production pumping wells or low-yield wells.

Description

Technical Field

[0001] This invention belongs to the field of fluid metering, specifically relating to an apparatus and method for metering the gas and liquid phase flow rates produced by low-yield wells. Background Technology

[0002] In the petroleum industry, it is typically necessary to measure the flow rate of gas and liquid produced at the wellhead. Since oil well products are usually mixtures of gas and liquid, traditional single-phase metering methods are unsuitable, necessitating the use of multiphase metering techniques. Currently, research on multiphase metering mainly focuses on three methods: gas-liquid separation metering, gas-liquid mixed-phase metering, and split-sampling metering.

[0003] The complete separation method involves using separation equipment to separate a gas-liquid mixture into single-phase gas and single-phase liquid, which are then measured using a standard single-phase flow meter. This method transforms the measurement of two-phase flow into the measurement of single-phase flow, offering advantages such as reliable operation, high measurement accuracy, wide measurement range, and immunity to changes in the flow pattern of the gas and liquid phases. However, gas-liquid separation metering presents several challenges: ① The separation equipment is bulky and expensive; ② Due to the large buffer volume, there is a metering delay and poor real-time performance; ③ Dedicated metering stations and testing pipelines are required, significantly increasing metering costs.

[0004] Gas-liquid mixed-phase metering is currently the mainstream method for multiphase metering in industrial settings. This method eliminates the need for separation devices, resulting in a small size and compact structure. The total gas-liquid flow rate is typically measured using throttling devices such as Venturi jets, while phase fraction is measured using phase fraction sensors such as capacitance, conductivity, and radiation sensors. Gas-liquid mixed-phase flow metering presents the following challenges: ① Directly facing a two-phase gas-liquid flow, the complexity of the gas-liquid flow can lead to errors exceeding 10%; ② Using throttling devices like Venturi jets results in significant resistance losses; ③ Phase fraction sensors are affected by factors such as pipeline flow patterns and fluid salinity, requiring periodic calibration, and radiation methods also pose a risk of radioactive contamination.

[0005] The principle of gas-liquid two-phase split sampling and metering is to proportionally separate a small, representative multiphase mixture (splitter) from a multiphase flow, then separate it into single-phase gas and liquid, and measure the flow rate of each phase using a conventional flow meter. Finally, the total flow rate is determined based on the proportional relationship. Current technical challenges include: ① Phase separation usually occurs when the gas-liquid two-phase mixture passes through the sampling device, causing the sampled fluid to lose its representativeness; ② The sampling ratio is affected by upstream flow patterns and downstream pressure fluctuations, making it difficult to maintain stability; ③ Samplers with moving parts, such as impellers, are difficult to operate stably for extended periods under harsh field conditions.

[0006] To overcome the shortcomings of existing technologies, this invention proposes a gas-liquid two-phase flow metering device for low-production wells, which simultaneously measures the gas and liquid flow rates by measuring the changes in the liquid level in a vertical pipe. Summary of the Invention

[0007] This invention relates to a gas-liquid two-phase flow metering device for low-yield wells, mainly comprising an inlet pipe, a downward-sloping pipe, an upward-moving pipe, a horizontal connecting pipe, a downward-moving pipe, and an outlet pipe, which are connected sequentially; the angle between the downward-sloping pipe and the horizontal direction is... The angle is 20°-30°; the upward pipe is arranged vertically, and the gas inlet is equipped with a one-way valve; an ultrasonic probe is installed at the top of the upward pipe; a temperature sensor and a pressure sensor are installed on the horizontal connecting pipe.

[0008] The check valve consists of a valve seat, a valve stem, a check disc, and an anti-detachment disc. The valve seat has a disc-shaped structure with a guide hole in the center. A bypass annular gap is provided between the guide hole and the outer edge of the valve seat. The valve stem is installed in the guide hole and can slide up and down along the guide hole. A check disc is provided at the top of the valve stem, and the diameter of the check disc is 1.1-1.2 times the diameter of the bypass annular gap. An anti-detachment disc is provided at the bottom of the valve stem, and the diameter of the anti-detachment disc is 1.1-1.2 times the diameter of the guide hole.

[0009] This invention relates to a method for measuring the gas-liquid two-phase flow rate in low-yield wells, and the specific implementation steps are as follows:

[0010] (1) An ultrasonic probe installed at the top of the ascending pipe is used to monitor the distance between the ultrasonic probe and the gas-liquid interface of the ascending pipe. When the measured distance is less than the liquid level change in the ascending pipe and the total length L of the ascending pipe is equal, it indicates that liquid has started to enter the ascending pipe. Record the time t at this time. L0 As liquid continuously enters the upstream pipe, the liquid level rises continuously, and the measured L... m The length keeps decreasing, when L m When the liquid level decreases to near zero, it indicates that the liquid has been completely drained from the upstream pipe. Record the time t at this point. L1 The time required for the liquid to fill the entire upward pipe is calculated as follows: ;

[0011] (2) Based on the real-time measurement curves of pressure P and temperature T over time by the pressure sensor, the time when the discharge begins corresponds to the maximum pressure P. max Time, denoted as t g0 Pressure reduced to minimum P min The corresponding time t g1 The difference between the two moments is the exhaust time. ;

[0012] (3) Based on the gas property equation, use the formula Calculate exhaust time Internal average gas density.

[0013] (4) The diameter of the upstream pipe is D, and the height is L. The formula is used. Calculate the average mass flow rate of the liquid phase during the drainage stage.

[0014] (5) Use the formula Calculate the average mass flow rate of the gas phase during the exhaust stage.

[0015] Compared with the prior art, the present invention has the following advantages:

[0016] (1) This invention converts gas-liquid mixed flow into alternating flow of single-phase liquid and single-phase gas, thereby transforming the spatial distribution of two-phase flow measurement problem into a time series of single-phase fluid problem, and thus achieving accurate flow measurement by measuring the time it takes to pass through a fixed volume pipe;

[0017] (2) Compared with traditional metering methods, the present invention has a simple structure and low metering cost, and is suitable for intermittent liquid and gas producing oil wells or low-production wells. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the components of the present invention;

[0019] Figure 2 Schematic diagram of a check valve;

[0020] Figure 3 A schematic diagram of the valve seat structure of a check valve;

[0021] Figure 4 Schematic diagram of liquid blockage at the outlet of the downward-sloping pipe;

[0022] Figure 5 This is a schematic diagram of fluid accumulation in the ascending tube;

[0023] Figure 6 This is a schematic diagram of the upward pipe draining;

[0024] Figure 7 This is a schematic diagram of the exhaust pipe.

[0025] Figure 8 This is a diagram illustrating the end of the exhaust process;

[0026] Figure 9 This is a schematic diagram of liquid phase flow measurement;

[0027] Figure 10 This is a graph showing the characteristic changes of pressure over time within a cycle.

[0028] 1-Inlet pipe; 2-Downward tilting pipe; 3-Upward pipe; 4-Horizontal connecting pipe; 5-Downward pipe; 6-Outlet pipe; 7-One-way valve; 8-Ultrasonic probe; 9-Temperature sensor; 10-Pressure sensor; 11-Valve seat; 12-Valve stem; 13-Check disc; 14-Anti-detachment disc; 15-Guide hole; 16-Bypass annular gap. Detailed Implementation

[0029] like Figure 1 As shown, this invention mainly relates to a gas-liquid two-phase flow metering device for low-yield wells, comprising an inlet pipe 1, a downward-sloping pipe 2, an upward-moving pipe 3, a horizontal connecting pipe 4, a downward-moving pipe 5, and an outlet pipe 6. The inlet pipe 1, downward-sloping pipe 2, upward-moving pipe 3, horizontal connecting pipe 4, downward-moving pipe 5, and outlet pipe 6 are connected sequentially; the angle between the downward-sloping pipe 2 and the horizontal direction is... The angle is 20°-30°; the upward pipe 3 is arranged vertically, and the gas inlet is equipped with a one-way valve 7; an ultrasonic probe 8 is installed at the top of the upward pipe 3; a temperature sensor 9 and a pressure sensor 10 are installed on the horizontal connecting pipe 4.

[0030] like Figure 2 , 3 As shown, the one-way valve 7 consists of a valve seat 11, a valve stem 12, a check disc 13, and an anti-detachment disc 14. The valve seat 11 has a disc-shaped structure with a guide hole 15 in the center. A bypass annular gap 16 is provided between the guide hole 15 and the outer edge of the valve seat 11. Several support ribs are also provided in the annular gap. The valve stem 12 is installed in the guide hole 15 and can slide up and down along the guide hole 15. A check disc 13 is provided at the top of the valve stem 12. The diameter of the check disc 13 is 1.1-1.2 times the diameter of the bypass annular gap 16. An anti-detachment disc 14 is provided at the bottom of the valve stem 12. The diameter of the anti-detachment disc 14 is 1.1-1.2 times the diameter of the guide hole 15.

[0031] Figure 4 This diagram illustrates liquid blockage at the outlet of the downward-sloping pipe 2. Gas-liquid two-phase flow passes through inlet pipe 1 and downward-sloping pipe 2, which is at a certain angle to the horizontal. The gas and liquid move downwards, with the liquid phase accelerating, resulting in stratified gas-liquid flow. The bottom outlet of downward-sloping pipe 2 is connected to upward-flowing pipe 3, which is vertically arranged. Due to the small gas-liquid flow rate and low velocity, the liquid cannot flow directly to the top of upward-flowing pipe 3, thus accumulating at the outlet of downward-sloping pipe 2. At this point, the liquid occupies the entire pipe cross-section, forming a liquid plunger.

[0032] Under low gas-liquid flow conditions, when gas and liquid pass through the present invention, four typical stages will occur: liquid accumulation in the upper pipe 3, liquid discharge in the upper pipe 3, gas intake in the upper pipe 3, and gas exhaust in the upper pipe 3, which will continuously cycle.

[0033] Figure 5This diagram illustrates the liquid accumulation in the upward pipe 3. As the gas-liquid flow from above increases, the pressure above also increases. Under the influence of differential pressure, the anti-detachment disc 14 pushes the valve stem 12 upward along the guide hole 15, allowing liquid to enter the upward pipe 3 through the bypass annular gap 16, thus causing the liquid level in the upward pipe 3 to rise continuously. Because the valve stem 12 has an anti-detachment disc 14 at its bottom, with a diameter 1.1-1.2 times the diameter of the guide hole 15, the movement range of the valve stem 12 is limited, preventing it from detaching. If the upstream pressure suddenly decreases or the flow is interrupted, the check disc 13 falls back under gravity. The check disc 13, with a diameter 1.1-1.2 times the diameter of the bypass annular gap 16, covers the bypass annular gap 16, preventing backflow of liquid.

[0034] Figure 6 This is a schematic diagram of the liquid discharge from the upward pipe 3. When the liquid phase in the upward pipe 3 reaches the top outlet of the upward pipe 3, the liquid begins to enter the downward pipe 5 through the horizontal connecting pipe 4, and then enters the downstream pipeline system through the outlet pipe 6.

[0035] Figure 7 This is a schematic diagram of gas entering the upward pipe 3. As liquid continuously enters the upward pipe 3, gas begins to enter the upward pipe 3 and begins the exhaust process.

[0036] Figure 8 This is a schematic diagram of the end of the exhaust process. When all the gas accumulated above enters the downstream through the upward pipe 3, the exhaust process ends. The gas-liquid flow rate is low in the upstream, and the liquid phase begins to accumulate at the bottom of the downward pipe 2, thus starting a new cycle.

[0037] Figure 9 This is a schematic diagram of liquid flow measurement. The ultrasonic probe 8, installed on the upstream pipe 3, has both receiving and transmitting ultrasonic pulse functions. When the ultrasonic probe 8 emits ultrasonic pulses at an extremely high frequency, an echo is generated when the ultrasonic pulse comes into contact with the liquid level. The echo propagates in the reverse direction and is received again by the ultrasonic probe 8. The time difference between the occurrence and reception is measured. According to the formula Determine the distance from the ultrasonic probe 8 to the gas-liquid cross section.

[0038] The total length of the ascending pipe 3 is L. When liquid enters the ascending pipe 3 through the one-way valve 7, the length of L measured ultrasonically is... m The total length L of the uplink tube 3 is equal to the current length, and the time t is recorded. L0 As liquid continuously enters the upward pipe 3, the liquid level continues to rise, and the measured L... m The length keeps decreasing, when L m When the liquid level decreases to near 0, it indicates that the liquid has been completely discharged from the upstream pipe 3. Record the time t1 at this point. Therefore, the time it takes for the liquid to completely fill the upstream pipe 3 is: .

[0039] The diameter of the entire upward pipe 3 is D, and the height is L. The formula is used... Calculate the liquid phase flow rate.

[0040] Figure 10 The pressure variation over time within a cycle is shown. As the liquid phase gradually enters the upward pipe 3, but before the liquid height reaches the horizontal connecting pipe 4, the medium flows in the horizontal pipe, and its pressure depends on the downstream system pressure, which is typically a separator with a fixed pressure P0. When the gas pushes the liquid to reach the horizontal connecting pipe 4, the measured pressure is the pressure upstream of the liquid column minus the pressure of the liquid column itself. The length of the liquid column in the upward pipe 3 gradually shortens. As the liquid column gradually passes through the horizontal connecting pipe 4 and enters the downstream, the measured pressure gradually increases. When the liquid column completely passes through the horizontal connecting pipe 4, the pressure reaches its maximum value P. max Without the obstruction of the liquid plug, the upstream gas accelerates rapidly through the upstream pipe 3 into the downstream, causing a rapid pressure drop. When the pressure drops to the same level as the downstream separator pressure, venting stops, thus initiating a new cycle. The start of venting corresponds to the maximum pressure P. max Time, denoted as t g0 Pressure reduced to minimum P min The corresponding time t g1 The difference between the two moments is the exhaust time. .

[0041] The entire exhaust process is equivalent to discharging the high-pressure gas distributed in the upward pipe 3 into... The flow rate is calculated as follows: .

[0042] in, This represents the average gas density during the exhaust phase. Since gas density is a function of temperature and pressure, the formula is used. calculate.

[0043] In summary, this invention relates to a gas-liquid two-phase flow metering device for low-yield wells, and the specific implementation method is as follows:

[0044] (1) The ultrasonic probe 8 installed at the top of the ascending pipe 3 is used to monitor the distance between the ultrasonic probe 8 and the gas-liquid interface of the ascending pipe 3. When the measured distance is less than the liquid level change in the ascending pipe 3 and the total length L of the ascending pipe 3 is equal, it indicates that liquid has started to enter the ascending pipe 3. Record the time t at this time. L0 As liquid continuously enters the upward pipe 3, the liquid level continues to rise, and the measured L... m The length keeps decreasing, when L m When the liquid level decreases to near zero, it indicates that the liquid has been completely drained from the upstream pipe 3. Record the time t at this point. L1 The time required for the liquid to fill the entire upward pipe 3 is calculated as follows: ;

[0045] (2) Based on the real-time measurement curves of pressure P and temperature T over time by pressure sensor 10, the time when the discharge begins corresponds to the maximum pressure P. max Time, denoted as t g0 Pressure reduced to minimum P min The corresponding time t g1 The difference between the two moments is the exhaust time. ;

[0046] (3) Based on the gas property equation, use the formula Calculate exhaust time Internal average gas density;

[0047] (4) The diameter of the entire upward pipe 3 is D, and the height is L. The formula is used. Calculate the average mass flow rate of the liquid phase during the drainage stage;

[0048] (5) Use the formula Calculate the average mass flow rate of the gas phase during the exhaust stage.

[0049] This invention utilizes a special pipeline structure to convert gas-liquid mixed flow into alternating flow of single-phase liquid and single-phase gas, thereby transforming the spatially distributed two-phase flow measurement problem into a time-series single-phase fluid problem. Accurate flow rate measurement can then be achieved by measuring the time taken to pass through a fixed-volume pipeline. Compared to traditional metering methods, this invention has a simple structure and low metering cost, making it particularly suitable for intermittently producing liquid and gas wells or low-production wells.

Claims

1. A gas-liquid two-phase flow metering device for low-yield wells, characterized in that, Mainly includes: It mainly consists of an inlet pipe (1), a downward-sloping pipe (2), an upward-moving pipe (3), a horizontal connecting pipe (4), a downward-moving pipe (5), and an outlet pipe (6), wherein the inlet pipe (1), the downward-sloping pipe (2), the upward-moving pipe (3), the horizontal connecting pipe (4), the downward-moving pipe (5), and the outlet pipe (6) are connected in sequence; the angle between the downward-sloping pipe (2) and the horizontal direction is... The angle is 20°-30°; the upward pipe (3) is arranged vertically, and the gas inlet is equipped with a one-way valve (7); an ultrasonic probe (8) is installed at the top of the upward pipe (3); a temperature sensor (9) and a pressure sensor (10) are installed on the horizontal connecting pipe (4). The one-way valve (7) consists of a valve seat (11), a valve stem (12), a check plate (13), and an anti-detachment plate (14). The valve seat (11) is a disc-shaped structure with a guide hole (15) in the center. A bypass annular gap (16) is provided between the outer edge of (15) and the valve seat (11). The valve stem (12) is installed in the guide hole (15) and can slide up and down along the guide hole (15). A check plate (13) is provided at the top of the valve stem (12). The diameter of the check plate (13) is 1.1-1.2 times the diameter of the bypass annular gap (16). An anti-detachment plate (14) is provided at the bottom of the valve stem (12). The diameter of the anti-detachment plate (14) is 1.1-1.2 times the diameter of the guide hole (15).

2. A method for metering the gas-liquid two-phase flow rate of a low-yield well, the specific implementation steps of which are as follows: Step S1: The ultrasonic probe (8) installed at the top of the ascending pipe (3) is used to monitor the distance between the ultrasonic probe (8) and the gas-liquid interface of the ascending pipe (3). When the measured distance is less than the liquid level change in the ascending pipe (3) and the total length L of the ascending pipe (3) is equal, it indicates that liquid has started to enter the ascending pipe (3). Record the time t at this time. L0 As liquid continuously enters the upward pipe (3), the liquid level continues to rise, and the measured L... m The length keeps decreasing, when L m When the liquid level decreases to near 0, it indicates that the liquid has been completely discharged from the upward pipe (3). Record the time t at this point. L1 The time required for the liquid to fill the entire ascending pipe (3) is calculated as follows: ; Step S2: Based on the real-time measurement curves of pressure P and temperature T over time by the pressure sensor (10), the time when the discharge begins corresponds to the maximum pressure P. max Time, denoted as t g0 Pressure reduced to minimum P min The corresponding time t g1 The difference between the two moments is the exhaust time. ; Step S3: Calculate the exhaust time using the following formula based on the gas property equation. Internal average gas density: ； Step S4: The diameter of the entire upward pipe (3) is D, and the height is L. The average mass flow rate of the liquid phase during the drainage stage is calculated using the following formula: ； Step S5: Calculate the average mass flow rate of the gas phase during the exhaust stage using the following formula: 。

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