RU2823638C1 - Method for measuring oil well production and determining oil gas factor - Google Patents

Abstract

FIELD: oil, gas and coke-chemical industry.

SUBSTANCE: method for measuring oil well product and determining oil gas factor involves feeding oil well product into a measuring tank with a calibrated part, separating gas from oil therein, measurement of mass flow rate of crude oil by time of filling the calibrated part of the tank with liquid and maximum specified hydrostatic pressure drop in it at closed liquid drain line. After short-term shutdown of the well and connection of the measuring installation to it, preliminary circulation of the produced product is performed through the bypass line of the installation to restore the structure of the incoming three-phase product into the well manifold line, and then the product is sent to the measuring tank. Filling of the measuring container is carried out with simultaneous measurement by the counter of the excess volume of the incoming free gas and the dissolved gas leaving the oil at pressure in the container close to atmospheric, and upon reaching the maximum specified hydrostatic pressure drop in the tank, the controller of the control unit automatically shuts off the flow of products into the measuring tank. Gas oil ratio is calculated as the ratio of the total amount of gas measured by the counter when the reservoir is filled to the mass of oil entering the reservoir during the same period.

EFFECT: enabling increase in the crude oil mass flow rate and associated petroleum gas volumetric flow measurement accuracy.

1 cl, 1 dwg

Description

The proposed invention relates to the field of measuring the flow rate of oil, gas and water from oil wells using mobile units and can be used to determine the gas-oil factor of oil at low gas contents of products arriving at the wellhead.

There is a known method for measuring the production of an oil well, based on measuring the rate of filling of two measuring tanks and their subsequent emptying of liquid (RF Patent No. 2082107 Method for determining the amount of oil, gas and water in well production. Application 05.18.95, publ. 06.20.97) . The measured filling time of the containers allows the program to calculate the flow rate of the oil-water mixture, and from the rate of emptying the containers to calculate the volumetric flow rate of the gas phase. Oil watering or water flow rate is determined by the difference in the reflection coefficient of electromagnetic waves along the height of the liquid column in the cylinder at the moment of its filling.

This method has the disadvantage of the presence of dispersed phases of water and gas in the product, which causes an increase in measurement error. In addition, GOR calculations do not take into account the residual amount of dissolved gas in oil.

There is a known method for determining the flow rates of oil, associated gas and water (Patent RU No. 2504653 C1. Application 07/30/2012, published 01/20/2014). To measure the liquid flow rate, the measuring tank is filled with the well product, and after the maximum level of the water-oil mixture is reached, the inlet valve of the measuring tank is closed and held for time to separate free gas from the liquid. After determining the flow rate of the water-oil mixture based on the filling rate and the volume of separated liquid, the gas phase is gradually withdrawn from the upper part of the measuring tank by a compressor through a reducer reducing to atmospheric pressure. The compressor pumps the extracted gas into the well reservoir. The gas is pumped out until the pressure in the measuring tank drops to atmospheric value. The gas factor is calculated based on the compressor performance and its operating time.

However, the use of a compressor is complicated due to changes in gas injection pressure into the reservoir, which varies over wide ranges even within one oil field.

There is a known method for measuring the flow rates of oil and associated gas from oil wells (Patent RU No. 2439316 C2. Application 04/05/2010, published 01/10/2012). The method includes the flow of produced products from a tubing string into a separator and the separation of gas and oil in it. Next, sequential selection of oil and gas is carried out from the separator with measurement of their quantity using a float and a flow switch according to the time of filling and emptying of the measuring part of the separator, respectively. Switching the flow of oil and gas is carried out by increasing the pressure on each side of the double-sided piston of the flow switch while blocking the oil and gas outlets from the separator with a float at the upper and lower ends of the vertical perforated pipe.

The disadvantage of this method is that when the pressure in the separator increases, the gas phase is compressed and the response of the flow switch is delayed. This, in turn, leads to a significant error in measuring the time of oil filling and draining, as well as the reliability of the measurements taken.

In addition, the use of this method for a mobile version of a measurement installation can take a long period of time in the case of high viscosity of the produced product or a small amount of free gas in the liquid, for example, high water cut of the product or low gas-oil ratio.

A method and device for measuring oil flow rate is known (RF Patent No. 2236584 Method and device for measuring oil flow rate. Application 12/17/2002, published 09/20/2004). They include supplying a gas-water-oil mixture into a measuring tank, dividing it into gas and water-oil mixture (WMS), which is an emulsion, measuring the flow rate of the WMS by the rate of filling of the calibrated part of this tank and draining the WMS with a frequency determined by the intensity of the product supply specific well, calculation of the proportion of water and the proportion of oil in the liquid phase of this product based on the measured value of the density of the VNS and the known values of the density of formation water and degassed oil, and subsequent calculation of the oil flow rate. In addition to the calibrated part of the measuring tank, the settling chamber is filled with the VNS at a given frequency, kept in it for a certain amount of time, after which the density of the settled VNS is measured, followed by emptying of this chamber.

The disadvantages of this method include its low efficiency in the production of high-viscosity or high-water-cut oil with low gas content. When producing highly viscous oil, the time it takes to displace oil from the tank, as well as the displacement pressure, increases significantly. In addition, the duration of measurements increases significantly at low GORs of oil due to the low rate of emptying of the measuring container in the cycle of accumulation of free gas in it. With a minimum gas content of well production, which is observed when the water cut of wells is 95...98%, the cycle time for emptying the separator of liquid can be many hours, which is unacceptable for measurements.

The closest to the proposed invention in technical essence is a method for measuring oil well production (Patent RU No. 2733954 C1. Application 08.13.2019, publ. 10.08.2020. BI No. 28). The method involves entering an oil well's production into a measuring tank with a calibrated part, separating it into gas and liquid phases, measuring the liquid flow rate based on the filling rate of the calibrated part of the tank and the hydrostatic pressure drop in the tank when its calibrated part is completely filled. The filling of liquid into the separator tank is stopped when the specified hydrostatic pressure difference is reached in the separator tank. Subsequent drainage of the liquid from the separator is carried out with an increase in pressure in the separator tank by installing an adjustable throttle on the gas outlet line, and the increase in pressure in the separator tank is carried out in proportion to the decrease in the amount of gas in the extracted product, and if there is a complete absence of gas in the product, the gas outlet line is completely blocked.

The disadvantage of the method chosen as a prototype is the impossibility of measuring the residual amount of dissolved gas in the oil filling the separator during measurements.

In addition, it takes quite a lot of time to increase the gas pressure in the separator to ensure liquid drainage when the gas content of the incoming product is low. The lowest content of free gas in the production of a well occurs in old depleted reservoirs with a high water cut in the formation fluid.

The technical objective of the proposed method is to increase the accuracy of measuring the mass flow rate of crude oil and the volumetric flow rate of associated petroleum gas at low values of gas content of oil. The problem is solved by the fact that in the known method, which includes introducing oil well production into a measuring tank with a calibrated part, separating gas from oil in it, measuring the mass flow rate of crude oil based on the time of filling the calibrated part of the tank with liquid and the maximum specified hydrostatic pressure drop in it at closed liquid drain line, according to the invention, after a short-term shutdown of the well and connecting a measuring installation to it, preliminary circulation of the produced product is carried out through the bypass line of the installation to restore the structure of the incoming three-phase product into the well manifold line and then the product is directed into the measuring tank through a choke that maintains pressure on at its inlet, equal to the pressure in the manifold line, and the filling of the measuring tank is carried out with simultaneous measurement by the meter of the excess volume of incoming free gas formed in it and the dissolved gas leaving the oil at a pressure in the tank close to atmospheric, and upon reaching the maximum specified hydrostatic drop in the tank pressure, the controller of the control unit automatically shuts off the flow of product into the measuring tank, and the gas factor of oil is calculated as the ratio of the total amount of gas measured by the meter when filling the tank to the mass of oil entering the tank during the same period.

The drawing shows a diagram of a mobile installation for implementing the method.

A manifold line 2 with a burst valve 3 and taps 4 and 5 is connected to well 1. The mobile unit is connected to taps 4 and 5 using flexible high-pressure hoses 6 and 7. On the input line 8, an electromagnetic valve 10, a manually operated ball valve 11 and a throttle, which is a rotating pair, are installed in the measuring tank 9: a cylinder 12 with a blind piston 13, supported from below by a spring 14. The lower end part of the cylinder 12 by line 15 is connected to the bypass line 16, on which a ball valve 17 is installed. The bypass 16 is connected to the manifold 2 of the well through a flexible hose 7. The lower part of the measuring tank 9 by the drain line 18 through the valve 19 is also connected to the manifold 2 of the well.

The upper part of the measuring tank 9 is connected by a gas line 20 to the upper part of the differential pressure sensor 21. The lower part of the sensor 21 is connected to the drain line 18. Valves 22 and 23 are also installed on the gas line 20, the last of which is located on the pipe with the gas meter 24 installed. The switching of the solenoid valve 10 is controlled by a controller (not shown in the drawing). The drawing also shows the conventional pressure line 25 of the well.

The method is carried out as follows. During a temporary shutdown of well 1, the mobile installation is connected by a manifold line 2 using flexible hoses 6 and 7 through inlet 4 and outlet 5 taps. During this period, measuring tank 9 is under atmospheric pressure, valves 11, 17 and 19, as well as valves 22 and 23 are closed, and burst valve 3 on manifold 2 is open. After connecting the mobile installation with manifold 2, well 1 is put into operation with pumping of products through burst valve 3 into pressure line 25. Next, valve 3 is closed and valves 4, 5, as well as valve 11 are opened. At the same time, valve 17 is opened and the well production begins to be transferred 1 via bypass line 16 to pressure line 25 of the well. The need to bypass the product through bypass line 16 is associated with restoring the structure of the three-phase product flow in manifold line 2 when the well is shut down before the subsequent filling of tank 9. Otherwise, gas and then oil that have stratified in the upper part of the tubing column may enter the tank when it is filled. with a little water.

During the same period, the pressure in the manifold line 2 will be transmitted to the throttle piston 13 from below and press it against the upper end of the cylinder 12.

After the estimated operating time of the installation, the manual tap 17 is closed through bypass 16 and the controller and operating program of the mobile installation are launched. In this case, the electromagnetic valve 10 will open and the production of the well 1 will begin to flow into the tank 9, pressing the piston 13 with the spring 14 down with its pressure exceeding the pressure in the pressure line 25. At the same time, valves 22 and 23 on the gas line are opened to measure the gas entering the tank 9 with a meter 24, as well as measuring the hydrostatic pressure drop in container 9 with sensor 21. Creating hydraulic resistance at the product inlet into the container and bringing the pressure at the inlet in front of the throttle to the pressure value in the pressure line 25 for the entire period of filling container 9 is necessary due to the atmospheric pressure in the container 9 and its inevitable accelerated filling with products entering manifold 2 under the pressure of a well pump (not shown in the drawing). This would lead to significant measurement errors in product selection parameters.

During the period of filling tank 9 with products, all gas separated from oil, together with the previously dissolved gas, is measured by meter 24. The pressure in tank 9 will slightly exceed the atmospheric value sufficient to overcome the hydraulic resistance in the gas meter and in valve 23.

When the maximum specified hydrostatic pressure drop in the tank, measured by sensor 21, is reached in the tank, the controller will close the solenoid valve 10 according to the program. To continue the operation of the well, open valve 17 on the bypass line 16 and close valve 11. After reaching atmospheric pressure in tank 9, close valves 22 and 23 .

The controller program, based on pre-entered data on the density of oil and water, as well as the water cut of the product, calculates the mass of oil entering tank 9:

where: ΔP _max , ΔP _min - respectively the maximum and minimum specified values of the hydrostatic pressure drop, Pa;

ρ _n , ρ _in - the density of oil and water, respectively, kg/m ³ ;

B is the water content of the liquid, dollars. units;

_Dem - internal diameter of the calibrated part of the container, m;

- gravity acceleration, m/s.

The mass flow rate of crude (watered) oil will be:

where: T is the time of filling the container, s.

The gas factor of oil is calculated using the formula:

Where:

V _ch - the total amount of gas, including the dissolved part, measured by the meter and reduced to standard conditions, m ³ .

It is then possible to repeat filling container 9 and measuring the listed parameters of incoming products to obtain stable average values. To do this, container 9 is freed from the product of the previous measurement, for example, by pumping it into the pressure line 25 with an additional pump.

The technical and economic advantage of the proposed method is the simplicity and reliability of its implementation, as well as the low time spent on measurements.

Claims (1)

A method for measuring the production of an oil well and determining the gas factor of oil, including introducing the production of an oil well into a measuring tank with a calibrated part, separating gas from oil in it, measuring the mass flow rate of crude oil based on the time of filling the calibrated part of the tank with liquid and the maximum specified hydrostatic pressure drop in it with a closed liquid drain line, characterized in that after a short-term shutdown of the well and connecting a measuring installation to it, a preliminary circulation of the produced product is carried out through the bypass line of the installation to restore the structure of the incoming three-phase product into the well manifold line and then the product is directed into the measuring tank through a choke that supports the pressure at its inlet is equal to the pressure in the manifold line, and the filling of the measuring tank is carried out with simultaneous measurement by the meter of the excess volume of incoming free gas formed in it and the dissolved gas leaving the oil at a pressure in the tank close to atmospheric, and upon reaching the maximum specified in the tank hydrostatic pressure drop, the controller of the control unit automatically shuts off the flow of product into the measuring tank, and the gas factor of oil is calculated as the ratio of the total amount of gas measured by the meter when filling the tank to the mass of oil entering the tank during the same period.

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