RU2779284C1 - Method for measuring oil gas ratio - Google Patents

Abstract

FIELD: oil industry.

SUBSTANCE: invention relates to the oil industry and can be used to determine the gas factor of oil, as well as oil and water flow rates by mobile measuring units. A method for measuring the gas factor of oil is proposed, including the flow of oil well production into a measuring tank with a calibrated part, separating it into gas and liquid phases, successively withdrawing gas and liquid from the tank, measuring the liquid flow rate by the filling rate of the calibrated part of the tank, and the gas flow rate - by the rate of its emptying, measuring the hydrostatic pressure drop in the tank when its calibrated part is completely filled to determine the amount of water in the produced product, filling the settling chamber with a water-oil mixture at a given frequency, the upper part of which is connected to the gas outlet line from the tank, measuring the dissolved gas in the oil by its selection from the container. At the same time, at the end of the cycle of filling the calibrated part of the container with well products, the oil-water mixture is taken under pressure into the settling chamber from the upper level of the calibrated part of the container, after which a demulsifier is introduced into the chamber to separate the oil-water mixture, followed by draining the separated water under pressure from the lower part of the settling chamber to the moment oil appears in the drained liquid, which is then also taken under pressure into a device for determining dissolved gas in oil. Moreover, during the period of draining liquids from the settling chamber, the valve for extracting oil from the calibrated part of the container is left closed.

EFFECT: providing the possibility of measuring free and dissolved gas in oil in the presence of a significant amount of formation water in the well production.

1 cl, 1 dwg

Description

The invention relates to the oil industry and can be used to determine the gas factor of oil, as well as oil and water flow rates by mobile measuring units.

Measurement of oil, gas and water flow rates at oil production facilities is carried out by automated group measuring units of a stationary or mobile type. To measure the flow rates of oil, gas and water, a method is known based on determining the filling rate in turn of two measuring tanks and their subsequent emptying (RF Patent for invention No. The flow rate of the water-oil mixture is determined by the time of filling the tanks, and the flow rate of the gas phase is determined by the rate of emptying the tanks. Oil flooding or water flow rate is determined by the difference in the reflection coefficient of electromagnetic waves over the height of the liquid column in the cylinder at the time of its filling.

The disadvantage of this method is that during measurements in the liquid filling the cylindrical container, there are dispersed water and gas phases in the form of drops and bubbles, which leads to a significant measurement error. In addition, a sufficient amount of dissolved associated gas remains in the oil phase, which does not leave the oil at operating pressure (usually the pressure of the pressure header) and therefore cannot be taken into account in the calculations of the GOR of oil or gas flow rate.

Known installation for determining the flow rate of well production (RF Patent for the invention No. 2133826, declared 01/05/1998, published 07/27/1999). The flow rate of water is determined from the known densities of oil and water and the hydrostatic pressure of the liquid column in the measuring cylinder. When the upper level in the measuring tank is reached, the sensors give a signal to switch the flow to another tank and measure the hydrostatic pressure, which is used to determine the average density of the liquid. From the previously known densities of oil and water, the water content in the liquid volume is calculated.

However, the measurement method used by the installation has a significant error due to the presence of both free dispersed and dissolved gas in the oil volume.

A known method for determining the flow rates of oil, associated gas and water (RF Patent for the invention No. 2504653, declared 30.07.2012, publ. 20.01.2014). The method includes filling the measuring tank with the well product, and after reaching the maximum level of the water-oil mixture, the inlet valve of the measuring tank is closed and timed to separate the free gas from the liquid. After determining the flow rate of the water-oil mixture according to the filling rate and the volume of the separated liquid, the gas phase is gradually taken from the upper part of the measuring tank by the compressor through a reducer to atmospheric pressure. The compressor at the same time pumps the sampled gas into the reservoir of the well. The gas is pumped out until the pressure in the measuring vessel drops to atmospheric value. The GOR is calculated from the compressor capacity and running time.

However, the implementation of the method is complicated by the use of a compressor, the performance of which, ceteris paribus, depends on the gas injection pressure into the reservoir, which varies over a wide range even within the same oil field.

A common disadvantage of the considered analogues and the prototype is the impossibility of measuring the residual amount of dissolved gas in oil. The described methods and devices measure only the amount of free gas from the oil at the pressure in the flow header of the oil well. At the same time, a sufficient amount of dissolved gas may still remain in the oil, which is not taken into account in GOR calculations.

A method and device for determining the dissolved gas in oil are known (RF Patent for the invention No. 2541378, applied on 12/14/2012, published on 06/20/2014). The method includes taking an oil sample under pressure, introducing a calibrated volume of oil into the device and creating a predetermined "oil-gas" phase ratio, bringing the system into thermodynamic equilibrium at various pressures and temperatures, and obtaining experimental data to build the dependence of the residual gas factor on temperature and pressure for each oil field.

The method has a disadvantage, consisting in the inadmissibility of the presence of the aqueous phase of the production of the formation in the selected oil sample. The virtual absence of dissolved gas in water leads to a significant error in the measurement of dissolved gas in oil. It should be noted that in the overwhelming majority of cases, water will be present in the selected oil samples in volumes reaching up to 98% of the volume of the sampled liquid.

A method and device for measuring the oil production rate are known (RF Patent for the invention No. 2236584, applied on 12/17/2002, published on 09/20/2004). The method includes supplying a gas-water-oil mixture to a measuring tank, dividing it into gas and a water-oil mixture (WOM), which is an emulsion, measuring the WOM flow rate by the filling rate of the calibrated part of this tank, and the free gas flow rate by the rate of emptying the tank from WPS with a frequency determined by the intensity of the product supply by a particular well, calculation of the proportion of water and the proportion of oil in the liquid phase of this product from the measured value of the density of the WPS and the known values of the density of formation water and degassed oil, and the subsequent calculation of the oil production rate. In addition to the calibrated part of the measuring tank, the settling chamber is filled with the WLS at a given frequency, kept in it for a certain amount of time, after which the density of the settled WLS is measured, followed by emptying of this chamber.

The method has the same disadvantages associated with the need to pre-measure the density of the mixture to calculate the water content in the volume of the measured container, as well as the presence of formation water in the oil sample, which does not allow correct measurements of the dissolved gas in the oil.

The closest in technical essence to the proposed solution is a method for measuring the production of an oil well, implemented in the RF patent for utility model No. 168317 (appl. gas in oil, liquid is taken from the main tank into a small tank, it is blocked from the main tank and the amount of gas released is measured by a counter when the pressure in the small tank drops to atmospheric value.

The method has the disadvantage of low measurement accuracy of the dissolved gas at high water cut of the formation production. A small oil content and a large volume of formation water withdrawn into a small reservoir will cause extremely small volumes of dissolved water to enter the meter.

The technical result of the claimed invention is to enable the measurement of free and dissolved gas in oil in the presence of a significant amount of formation water in the well production.

The stated technical result is solved by the described method, including the flow of oil well production into a measuring tank with a calibrated part, separating it into gas and liquid phases, sequential selection of gas and liquid from the tank, measuring the liquid flow rate by the filling rate of the calibrated part of the tank, and the gas flow rate - by the rate of its emptying, measurement of the hydrostatic pressure drop in the tank when its calibrated part is completely filled to determine the amount of water in the produced product, filling the settling chamber with a water-oil mixture at a given frequency, the upper part of which is connected to the gas discharge line from the tank, measuring the dissolved gas in the oil by its selection from the container.

What is new is that at the end of the cycle of filling the calibrated part of the tank with well products, the water-oil mixture is taken under pressure into the settling chamber from the upper level of the calibrated part of the tank, after which a demulsifier is introduced into the chamber to separate the water-oil mixture, followed by draining the separated water from the bottom under pressure. settling chamber until oil appears in the drained liquid, which is then also taken under pressure into a device for determining dissolved gas in oil, and during the period of draining liquids from the settling chamber, the valve for extracting oil from the calibrated part of the tank is left closed.

In FIG. 1 shows the hydraulic part of the scheme for implementing the method.

To the discharge manifold 1 of the well (not shown in Fig. 1) with a crane 2, a measuring tank 5 of the mobile unit is connected using the inlet 3 and outlet 4 taps. The lower part of the container 5 is connected by a line 6 to a three-way valve 7 with an electric drive, which, on the one hand, is also connected to the collector 1 by a line 8 and an outlet valve 4, and on the other hand, by a gas line 9 to the upper part of the measuring container 5.

Upper 10 and lower 11 sensors of hydrostatic liquid levels are installed in the tank. In the lower part of the tank 5 there is an inlet pipe 12 for draining the liquid, and in the upper part of the tank 5 there is an inlet pipe 13 for removing the separated gas.

A line 14 is connected to the upper part of the tank 5 after the inlet valve 3. The switching on of the three-way valve 7 is controlled by the controller of the control unit 15 according to the signals of the hydrostatic pressure sensors 10 and 11. Settling chamber 16 is installed in close proximity to tank 5, the upper part of which is connected through valve 17 to the upper level of the calibrated part of tank 5, located directly below the level of sensor 10. In addition, the upper part of settling chamber 16 is also connected through valve 17 and line 18 with a gas line 9. A demulsifier supply line is connected to the upper part of the chamber 16 through a valve 19. Drain valves 20 and 21 are installed in the lower part of the settling chamber 16. The settling chamber 16 is connected to the calibrated part of the container 5 at different levels by means of a valve 22. The valve 21 is connected to a device 23 for measuring dissolved gas in oil.

The method is carried out as follows.

The mobile unit is connected with valves 3 and 4 closed and valve 2 open. For measurements, valves 3 and 4 are opened and valve 2 is closed. Through the inlet valve 3 and line 14, the well production is sent to the upper part of the tank 5.

The separated liquid, flowing down, fills the calibrated part of the container 5 between the levels of the sensors 11 and 10, while the time of filling the container 5 from the sensor 11 to the sensor 10 is fixed. 9 and 8. During the period of filling the container 5 with the well product, the separated gas is discharged along lines 9 and 8 into the flow manifold of the well 1. Based on the time the container 5 is filled with liquid from the sensor 11 to the sensor 10, the program of the control unit calculates the flow rate of the well in terms of liquid (water-oil mixture).

After the liquid level approaches the upper sensor 10 of the container 5, the control unit 15 sends a command to switch the three-way valve 7 to drain the liquid from the container 5 into the collector through lines 6 and 8. At the same time, the three-way valve 7 will block the line 9 for gas removal from the container 5 .

During this measurement cycle, the gas accumulating at the top of the tank will push the liquid level down. The time of emptying the calibrated part of the tank 5 from the liquid will be proportional to the flow rate of the free oil gas entering the tank 5 together with the liquid. In this case, the gas flow rate is determined by dividing the volume of the calibrated part of the container 5 by the time the container 5 is empty from the liquid.

At the moment the liquid level in the tank 5 reaches the sensor 10 in the cycle of filling the tank with products, the valve 22 is opened to fill the settling chamber 16 with formation products from the upper layer of the liquid filling the tank 5. In the upper layer of the liquid, the content of the aqueous phase will be minimal. The settling chamber 16 is filled with formation products with the valve 17 open in order to equalize the pressures in the tank 5 and the settling chamber 16. Next, a demulsifier is introduced into the chamber 16 and kept for some time to separate oil and water in it.

Subsequently, the valve 22 is closed and the liquid is drained under pressure from the chamber 16 through the valve 20. To avoid pressure drop in the settling chamber 16, the liquid is drained at a very low flow rate, practically separate drops. In addition, to maintain pressure in the chamber 16, the liquid is drained from it with the tap 17 open.

After the appearance of oil in the drained liquid, the valve 20 is closed and a sample of oil is taken through the valve 21 also under pressure into the device 23 for determining the dissolved gas. Sampling through the valve 21 also reduces the risk of water entering the sample from the nozzle located above the valve 20. Such an oil sampling procedure makes it possible to almost completely exclude the ingress of the aqueous phase of the formation production into it.

The GOR of oil in the proposed method is already calculated taking into account the additional amount of dissolved gas in oil, measured by the device.

Measuring the hydrostatic pressure drop of the liquid in the tank 5 according to the readings of the sensors 10 and 11 of the hydrostatic levels of the liquid in the tank 5 at given densities of oil and water makes it possible to calculate the water cut and oil and water flow rates.

The technical and economic advantages of the proposed method are the ability to measure the dissolved gas in oil, as well as the simplicity and high reliability of the metering unit.

Since November 2015, the GOR of oil (free and dissolved), flow rate and water cut of the liquid were measured according to the claimed method at two wells of JSC "Sheshmaoil" and 13 wells of the Zarechnoye field of JSC "Geotech". Well fluid flow rates, measured by the claimed method, and data on the geological report as a whole are of the same order. The exception is well 3222 due to the high viscosity of the produced product (more than 2500 mPa⋅s). At well 64, it was not possible to measure the GOR of oil due to the extremely high water cut of the fluid (95%). GOR measurements at wells 75, 78 and 2150 showed differences in comparison with geological data, although well flow rates and water cut are close in values. The performed volume of measurements of the gas factor of oil, production rates and water cut of wells showed the operability of the proposed method.

Claims (1)

A method for measuring the gas factor of oil, including the flow of oil well production into a measuring tank with a calibrated part, separating it into gas and liquid phases, successive sampling of gas and liquid from the tank, measuring the liquid flow rate by the filling rate of the calibrated part of the tank, and the gas flow rate - by speed emptying it, measuring the hydrostatic pressure drop in the tank when its calibrated part is completely filled to determine the amount of water in the produced product, filling the settling chamber with a water-oil mixture at a given frequency, the upper part of which is connected to the gas outlet line from the tank, measuring the dissolved gas in the oil by means of its extraction from the tank, characterized in that at the end of the cycle of filling the calibrated part of the tank with well products, the oil-water mixture is taken under pressure into the settling chamber from the upper level of the calibrated part of the tank, after which a demulsifier is introduced into the chamber to separate the water-oil mixture with subsequent discharge under pressure of the exfoliated water from the lower part of the settling chamber until the appearance of oil in the drained liquid, which is then also taken under pressure into a device for determining dissolved gas in oil, and during the period of draining liquids from the settling chamber, a valve for extracting oil from the calibrated part containers are left covered.

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