CN100340843C - Oil-gas-water three phase flow continuously metering system - Google Patents

Abstract

The present invention is a continuous metering system for three-phase flow of oil, gas and water. composition. The invention can be used for the metering of the three-phase flow of oil, gas and water in the oil field. It is characterized by the use of a small and efficient horizontal three-phase separator with a built-in oil chamber, and a dual liquid level plus voltage stabilization measurement and control scheme to keep the internal pressure of the separator, the oil-water interface of the water chamber and the liquid level of the oil chamber always stable, effectively eliminating The influence of the fluctuation of incoming air volume or incoming liquid volume on the separation effect and measurement accuracy significantly improves the accuracy of flow measurement and realizes continuous automatic metering of oil, gas and water. The invention has the characteristics of high measurement precision, small volume, safety and reliability.

Description

Oil-gas-water three-phase flow continuous metering system

Technical field

The invention is a continuous metering system of oil, gas and water three-phase flow. It is used for automatic and continuous measurement of oil, gas and water production in oil fields.

Background technique

With the deepening of oilfield development, especially after the oilfield enters the high water cut period, the gas production and liquid production of oil wells generally fluctuate greatly, and there are no rules to follow; low-yield oil wells also have intermittent liquid production, and the intermittent time varies. Short-term measurement is difficult to obtain the real output; oil well production varies greatly and fluctuates greatly, resulting in large difference and fluctuation in the output of associated gas in different oil wells; there are many sand and impurities in the oil well production fluid, which has a great impact on the instrument and its measurement . At present, the traditional metering systems used in various oilfields at home and abroad mainly include the following types:

1. Two-phase separation metering system. To separate the gas from the liquid, the oil and water are not separated. Usually, the sampling test method, average density method, density meter and flow meter are used to measure the ratio of oil to water in the mixed liquid to obtain the flow rate of each phase. Due to the incomplete drainage of the separator and the mixing of oil-water mixtures with different ratios, the representativeness of the water-containing instrument measurement is poor, which leads to inaccurate measurement of the density of the oil-water mixture, increases the error of measurement, and also brings inconvenience to the assessment. Density meters are expensive.

2. Three-phase flow metering system. Instead of using a separator, the three-phase flow of oil, gas and water is directly measured. Flow is generally measured by radiographic, capacitance or differential pressure methods. The defects of this prior art are: first, the gas-liquid ratio and the oil-water ratio are measured by a radiation attenuation meter, which has radioactivity, large volume, low precision and high price. Second, the capacitance method is only applicable to the situation where the oil in the oil-gas-water mixture is the continuous phase. However, most oil fields in China have entered a high water cut period and the capacitance method is no longer applicable when the water in the mixture is the continuous phase. Third, using a differential pressure sensor to measure the differential pressure of the pipeline can only obtain the total density of the oil-gas-water mixture in the sampling pipeline. It is necessary to deduce complex mathematical formulas to obtain the ratios of each phase. When the water content in the mixture is high, each phase The ratio calculation error is large, and the measurement accuracy is low.

3. Three-phase separation metering system. The traditional three-phase separation metering system adopts the method of metering after three-phase separation of oil, gas and water, and its volume is generally large. The gas outlet of the separator adopts a self-operated pressure regulating valve to control the gas discharge, and the self-operated pressure regulating valve is mechanically operated and cannot be continuous. Smoothly adjust the internal pressure of the separator. When there is a large fluctuation in the amount of incoming gas or liquid, it is easy to exceed the processing capacity of the system, resulting in poor separation effect and a serious drop in measurement accuracy. This system also fails to be fully unattended, and cannot automatically handle various failures that occur, which increases the inconvenience of control and management.

Contents of Invention

The object of the present invention is to provide a continuous metering system for three-phase flow of oil, gas and water.

It has a horizontal three-phase separator, an oil chamber is arranged in the horizontal three-phase separator, and the outlet pipe of the oil chamber is connected with the oil flow meter, the oil regulating valve, and the phase mixer). The top is equipped with an oil-water interface instrument, a liquid level gauge, a pressure sensor II, and an air outlet pipe. The air outlet pipe is connected with a gas flow meter, an air path regulating valve, and a phase mixer. , pressure sensor I, and temperature sensor I are connected, and the bottom of the horizontal three-phase separator is equipped with an outlet pipe, which is connected with the water flow meter, water regulating valve, and phase mixer. The side of the phase separator is connected to the sand washing pipe in the middle, the phase mixer is connected to the pressure sensor III, the temperature sensor II, the outlet valve, the outlet valve is connected to the bypass valve, and the inlet valve, the pressure sensor I, the temperature sensor I, the oil-water Interface instrument, liquid level gauge, pressure sensor II, sand flushing pump, gas flow meter, gas path regulating valve, oil path flow meter, oil path regulating valve, water path flow meter, water path regulating valve, pressure sensor III, temperature sensor II and Industrial control computer connected.

Advantages of the present invention:

1) A small and efficient horizontal three-phase separator with a built-in oil chamber is used. The system is small in size, and the oil, gas and water are separated and measured in phases. The water content in the oil and the oil content in the water are relatively stable, and the measurement accuracy is significantly improved. The mixing in the water chamber The oil surrounds the built-in oil chamber to keep the temperature of the oil in the oil chamber from lowering and ensure the fluidity of the oil.

2) The oil circuit, gas circuit and water circuit of the system adopt PID control, the oil circuit regulating valve controls the oil-gas interface of the oil chamber, the gas circuit adopts the gas circuit regulating valve to control the internal pressure of the separator, and the water circuit regulating valve controls the oil-water interface of the water chamber, without external intervention , The adjustment range of oil volume, air volume and water volume is large.

3) The gas flow meter 9 selected by the system measures the gas flow. The gas path regulating valve 10 controls the pressure in the separator to be always controlled at the set pressure value, which is greater than the pressure of the gas-liquid output. When the fluctuation of the incoming gas volume causes the pressure in the separator to change, the pressure in the separator will be automatically adjust.

4) According to the water content in the incoming liquid, change the set value of the oil-water interface in the water chamber to change the oil content of the water in the water chamber accordingly. The oil-water interface instrument detects the oil-water interface signal in the water chamber of the separator and inputs it into the industrial Control the computer, automatically control the waterway regulating valve, adjust the water flow, keep the oil-water interface in the water chamber stable, so as to maintain the stability of the oil content in the water and the water content in the oil, and eliminate the effect of the fluctuation of the incoming gas or liquid on the separation effect and measurement. Influence.

5) Due to the high viscosity of the crude oil after oil-water separation, the flow resistance of the oil passage is too large, resulting in a decrease in the flow capacity of the oil passage. Therefore, a flow resistance regulating valve is installed in the water passage of the system to balance the oil passage and The flow capacity of the waterway enables smooth flow of oil and water.

6) The built-in oil chamber of the separator collects the crude oil in the upper layer of the mixed liquid in the water chamber, and the water content of the oil in the oil chamber is significantly reduced. The liquid level gauge detects the oil-gas interface signal in the oil chamber of the separator, and inputs it into the industrial control computer for automatic control. The oil circuit regulating valve adjusts the oil flow, keeps the oil-gas interface in the oil chamber stable, and eliminates the adverse effects of the fluctuation of incoming air or liquid on the measurement accuracy.

7) The system has an automatic sand flushing function, and the sand flushing pump can be automatically started at regular intervals to flush the bottom of the separator to prevent the deposition of sediment entrained in the incoming fluid from the oil well, ensuring the long-term, continuous and safe operation of the system.

8) The instruments used in the system are all explosion-proof, and all detection and control signals are isolated through safety barriers to control the energy flowing into dangerous places below the ignition energy of flammable and explosive media, so as to ensure that the metering system can operate in flammable, Safe operation in explosive places.

9) The system is unattended during operation. It can conveniently switch between automatic and manual control according to needs. It operates completely automatically and can automatically deal with various failure phenomena. It can realize three-phase oil, gas and water without interrupting the normal production of oil wells. Continuous metering of flow.

10) The system is equipped with powerful software, which can monitor the operating status of the system at any time, display and print out data such as oil, water, gas volume, moisture content, etc., and automatically generate various production reports.

11) It can be used to measure oil well production in the anhydrous period, low water-cut period, medium water-cut period, high water-cut period, high water-cut period and ultra-high water-cut period of oil well production. By changing the size of the separator and supporting different types of instruments, the metering system can be used in various harsh situations in the oil field. Taking a three-phase separator with a volume of 0.8m3 as an example, this metering system can achieve the following technical indicators:

Daily liquid volume measurement range: 5-450t

Daily gas volume measurement range: 80-3500Nm ³

Moisture content measurement range: 0-99%

Daily water production measurement error ≤ 2.5%

Daily oil production measurement error ≤ 2.5%

Daily gas production measurement error ≤ 5%

Description of drawings

The accompanying drawing is a schematic structural diagram of the oil-gas-water three-phase flow continuous metering system.

Detailed ways

The oil-gas-water three-phase flow continuous metering system has a horizontal three-phase separator 4, and an oil chamber 12 is arranged in the horizontal three-phase separation device. 17 connected, on the top of the horizontal three-phase separator, there are oil-water interface instrument 5, liquid level gauge 6, pressure sensor II7, gas outlet pipe, and the gas outlet pipe is connected with gas flow meter 9, gas path regulating valve 10, and phase mixer 17 , the upper part of the horizontal three-phase separator is provided with an oil inlet pipe and is connected with the inlet valve 1, the pressure sensor I2, and the temperature sensor I3. Valve 15, flow resistance regulating valve 16 are connected to phase mixer 17, and the outlet pipe is connected to the sand washing pipe inserted into the lateral middle of the horizontal three-phase separator through sand washing pump 8, and phase mixer 17 is connected to pressure sensor III18 and temperature sensor II19 , the outlet valve 20 is connected, the outlet valve 20 is connected with the bypass valve 22, the inlet valve 1, the pressure sensor I2, the temperature sensor I3, the oil-water interface instrument 5, the liquid level gauge 6, the pressure sensor II7, the sand washing pump 8, the gas Flow meter 9, gas path regulating valve 10, oil path flow meter 11, oil path regulating valve 13, water path flow meter 14, water path regulating valve 15, pressure sensor III18, temperature sensor II19 are connected with industrial control computer 21.

The inlet of the invention is connected to the gas-liquid mixing pipe from the oil well, and the gas-liquid outlet is connected with the oil well output pipe. The gas-liquid mixture produced by the oil well enters the horizontal three-phase separator 4 through the opened inlet valve 1 for three-phase separation of oil, gas and water. After preliminary separation, the gas is discharged from the gas outlet on the top of the separator, and the crude oil on the upper part of the mixed liquid in the water chamber overflows into the built-in oil chamber of the separator, and is discharged from the outlet of the oil chamber. The mixed liquid in the water chamber surrounds the oil chamber to keep the oil The temperature of the oil in the chamber does not drop, and the water in the water chamber is discharged from the water outlet at the bottom of the separator. The working pressure of the separator, the oil-water interface of the water chamber and the liquid level of the oil chamber are preset. The internal pressure of the separator is detected by the signal of the pressure sensor II7, and the industrial control computer 21 controls the gas path regulating valve 10 to increase or decrease the gas flow to adjust the pressure in the separator, so that the internal pressure of the separator is kept stably at the set value. In terms of fixed value, the stabilized pressure control of the separator is realized in this way, and the influence of the fluctuation of incoming air volume on the separation effect and measurement accuracy is eliminated. The oil-water interface of the separator water chamber is detected by the signal of the oil-water interface instrument 5, and the industrial control computer 21 controls the waterway regulating valve 15 to increase or decrease the water flow to adjust the oil-water interface of the separator water chamber, so that the oil-water interface of the separator water chamber The interface is kept stably at the pre-set value, so that the oil-water interface of the water chamber can be automatically adjusted. According to the water content of the oil well to be measured, the set value of the oil-water interface can be adjusted, and the oil content in the water can be changed accordingly and maintained. Stable, the oil flow can be corrected by the oil content in the water, which improves the oil metering accuracy. When measuring high water-cut oil wells, the crude oil after preliminary separation of oil and water can flow stably into the oil chamber built into the separator, and the water content in the oil in the oil chamber is significantly reduced, and then the oil flow rate is corrected by the density parameter detected by the oil flow meter , and the oil content in the water in the water chamber remains stable after separation, and the oil flow can be corrected, so that the oil measurement accuracy is greatly improved. Due to the high viscosity of the crude oil after oil-water separation, the flow resistance of the oil passage is too large, and the fluidity of the oil passage becomes poor. Therefore, a flow resistance regulating valve is installed in the water passage to balance the circulation of the oil passage and the water passage by increasing the resistance of the water passage. ability. The liquid level of the separator oil chamber is detected by the signal of the liquid level gauge 6, and the industrial control computer 21 controls the oil circuit regulating valve 13 to increase or decrease the oil flow, so that the liquid level of the separator oil chamber is stably maintained at the preset value. In terms of value, the automatic adjustment of the liquid level of the oil chamber is realized in this way. When the liquid level in the oil chamber is lower than the overflow plate of the water chamber, the liquid level gauge 6 detects the oil-air interface in the oil chamber; when the liquid level in the oil chamber is higher than the overflow plate of the water chamber, the liquid level gauge 6 detects the The total liquid level in the horizontal three-phase separator, so that two liquid levels can be measured with one liquid level gauge. At this time, the thickness of the oil layer in the separator can be calculated according to the measurement signals of the oil-water interface instrument and the liquid level gauge. When the amount of incoming gas or liquid fluctuates, the metering system automatically adjusts the flow of the three phases to keep the internal pressure of the separator, the oil-water interface of the water chamber and the liquid level of the oil chamber always stable, eliminating the adverse effects of fluctuations on the separation effect and metering , which improves the measurement accuracy of the system.

The system generally operates in the following five states:

In the first state, the system has just been powered on.

The oil, gas and water circuits of the system are all switched to the manual state, the valves of the gas circuit are closed, the valves of the water circuit and the oil circuit are fully opened, the oil-water interface of the water chamber and the liquid level of the oil chamber are not controlled, and the mixed liquid flows freely into the pipeline through the separator. The separator and piping are preheated depending on the temperature of the mixture. When the pressure sensor II7 detects that the internal pressure of the separator reaches the normal working pressure, the gas path is switched to the automatic state, and the industrial control computer 21 controls the gas path regulating valve 10 to adjust the pressure in the separator through the PID algorithm, so that the inside of the separator The pressure is kept stable at the set value. After the system runs for a period of time, the temperature sensor II19 detects that the temperature of the outlet reaches the operating requirements, and manually adjusts the oil circuit and water circuit regulating valves to make the oil-water interface of the water chamber and the liquid level of the oil chamber reach the preset value. Set the value, switch the oil circuit and water circuit to the automatic state, and the system enters the normal operation state.

In the second state, the system is running normally.

After the start-up process of the system is over, the oil, gas and water circuits of the system are all switched to the automatic state, and the industrial control computer 21 controls the gas circuit regulating valve 10, the oil circuit regulating valve 13 and the water circuit regulating valve 15 through the PID algorithm, so that the pressure in the separator, the water circuit The oil-water interface of the chamber and the liquid level of the oil chamber are both stably controlled at the preset value. When the amount of incoming air or liquid fluctuates, the system can adjust the three-phase flow of oil, gas and water in time to eliminate the adverse effects of fluctuations.

The third state is that the system flushes sand.

There are many sands and impurities in the incoming liquid, and it is easy to stick to the bottom of the separator after long-term operation, which has a great impact on the system. The present invention adopts an automatic sand flushing measure, the system automatically starts the sand flushing water pump 8 at regular intervals, stops the PID control of the waterway at the same time, sets the waterway regulating valve 15 to fully open, and passes the water from the water outlet of the separator through the sand flushing water pump 8 to pass through the separator The sand flushing port of the separator is re-introduced into the separator, and the vortex is artificially created inside the separator, and the sediment adhered to the bottom of the separator is washed away, and discharged from the water outlet of the separator. After flushing for a period of time, the system automatically stops the sand flushing water pump 8 and starts the waterway PID control simultaneously. During the sand flushing period, the oil content in the water will change, which can be corrected through the measurement curve, and the measurement accuracy will not be affected. The system automatically flushes the sand at regular intervals, which eliminates the phenomenon of sediment accumulation in the separator and ensures that the system can run continuously for a long time.

The fourth state is that the system is down.

Close the inlet valve 1 of the system, switch the three oil, gas and water circuits of the system to the manual state, close the gas circuit valve, fully open the water circuit regulating valve 15 and the oil circuit regulating valve 13, and drain all the liquid in the separator water chamber and oil chamber. discharge.

The fifth state is system failure.

The system can automatically deal with the faults that occur, avoid manual intervention, and realize safe operation. System faults are divided into the following nine situations: power failure, oil circuit regulating valve 13 fault, gas circuit regulating valve 10 fault, water circuit regulating valve 15 fault, flow meter fault, pressure sensor II7 fault, pipeline blockage, backflow fault, industrial Control computer 21 malfunctions.

When a fault occurs, the industrial control computer 21 automatically judges the type of the fault and executes a corresponding fault handling program. It ensures the long-term safe operation of the system.

The principle and experiments have proved that under various working conditions with large gas volume and small liquid volume, small gas volume and large liquid volume, large gas volume and liquid volume, small gas volume and liquid volume, or even extremely small gas volume and extremely large liquid volume, The system can operate normally and efficiently. The working pressure in the separator can always be controlled at the pressure required for liquid discharge and is not affected by incoming gas-liquid volume and external pressure fluctuations; according to the water content in the incoming liquid, the set value of the oil-water interface in the water chamber can be adjusted , correspondingly change the oil content of the water in the water chamber and keep it stable; the built-in oil chamber collects the crude oil in the upper layer of the mixed liquid in the water chamber, so the water content of the oil in the oil chamber is significantly reduced and keeps it stable; the measurement and control system adopted by the system The technology enables the pressure in the separator, the oil-water interface of the water chamber and the oil-gas interface of the oil chamber to be controlled stably and reliably, and the separation effect is not affected by the amount of incoming gas and liquid. Especially when measuring oil wells with high water content, the water content in oil and oil content in water can always remain stable, and the oil flow can be corrected accordingly, which greatly improves the measurement accuracy of the system. The oil flow meter 11 and the water flow meter 14 used in the present invention have no rotating parts, and are intelligent and digital. The gas flow meter 9 can detect the volume flow rate of the separated gas, and convert it into the gas flow rate under standard conditions through temperature and pressure compensation; the oil flow meter 11 can detect the mass flow rate, density and temperature of the separated oil; the water flow meter 14 The volume flow rate of the separated water is detected, and the above-mentioned detected flow signal is input into the industrial control computer 21 to accurately calculate the three-phase output of gas, oil, and water in the oil well. According to the output of oil, gas and water, different The supporting instrument of the measuring range has a wide range of applications. The industrial control computer can automatically start the sand flushing water pump at regular intervals to flush the bottom of the separator to prevent the deposition of sediment entrained in the fluid from the oil well. The system can easily switch between automatic and manual control, and can display, print and output data such as clean oil, clean water, gas volume and water content at any time, and automatically generate various production reports.

Claims (1)

1. oil-gas-water three phase flow quantity continuous metering system, it is characterized in that it has horizontal three-phase separator (4), in horizontal three-phase separator, be provided with built-in grease chamber (12), grease chamber's outlet and oil circuit flowmeter (11), oil circuit variable valve (13), mixed-phase device (17) joins, be provided with water-oil interface instrument (5) at the horizontal three-phase separator top, liquid level gauge (6), pressure transducer II (7), escape pipe, escape pipe and gas meter (9), gas circuit variable valve (10), ((17) join mixed-phase device, horizontal three-phase separator top be provided with oil inlet pipe and with admission valve (1), pressure transducer I (2), temperature sensor I (3) joins, the horizontal three-phase separator bottom is provided with rising pipe, rising pipe and water route flowmeter (14), waterway regulating valve (15), flow resistance variable valve (16), mixed-phase device (17) joins, rising pipe joins through sand surfing water pump (8) and the sand surfing pipe that inserts horizontal three-phase separator side direction middle part, mixed-phase device (17) and pressure transducer III (18), temperature sensor II (19), outlet valve (20) joins, outlet valve (20) and bypass valve (22), admission valve (1) joins, pressure transducer I (2), temperature sensor I (3), water-oil interface instrument (5), liquid level gauge (6), pressure transducer II (7), sand surfing water pump (8), gas meter (9), gas circuit variable valve (10), oil circuit flowmeter (11), oil circuit variable valve (13), water route flowmeter (14), waterway regulating valve (15), pressure transducer III (18), temperature sensor II (19) joins with industrial control computer (21).

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