RU2781205C1 - Method for measuring oil well production - Google Patents

Abstract

FIELD: oil industry.

SUBSTANCE: invention relates to the oil industry and can be used to determine the mass flow rate of oil, as well as the gas factor of oil with the measurement of the residual amount of dissolved gas in oil under operating measurement conditions. A method for measuring oil well production by a mobile unit includes the flow of oil well production into a measuring tank with a calibrated part, separating it into gas and liquid phases and measuring the mass flow rate of the liquid by the time of filling the calibrated part of the tank and by the maximum specified hydrostatic pressure drop in it with a closed drain line liquids. Prior to filling, the produced product is preliminarily circulated through the measuring vessel to achieve the pressure in the well pressure line and the minimum specified hydrostatic pressure drop. Next, the drain of the liquid from the tank is blocked and the measuring tank is filled with products while maintaining a constant pressure in it by removing from the tank an additional volume of gas entering it and measuring this volume with a meter installed after the bypass valve set to the pressure in the pressure line of the well. When the maximum predetermined value of the hydrostatic pressure difference in the tank is reached, the product inlet line to the tank is closed, the valve on the bypass line of the bypass valve is opened and the gas is continued to be removed from the tank and its volume is measured until the atmospheric pressure value is reached in the tank. The GOR of oil is calculated as the ratio of the amount of gas measured by the meter, minus the volume of liquid that entered the tank during its filling, to the mass of oil that entered the tank during the filling cycle.

EFFECT: measurement of the total amount of associated gas produced together with oil is provided.

1 cl, 1 dwg

Description

The invention relates to the oil industry and can be used to determine the mass flow rate of oil, as well as the gas factor of oil with the measurement of the residual amount of dissolved gas in oil under operating measurement conditions.

Measurement of oil flow rate in wells is carried out under conditions of partial release of free gas with a decrease in pressure in the wellbore or manifold line. At the same time, a certain amount of dissolved gas still remains in the oil, which must be taken into account in the calculations of the gas factor of oil.

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 No. 2082107. A method for determining the amount of oil, gas and water in well production. Appl. 05/18/95 Published. 06/20/97 /. 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 a pressure header) and therefore cannot be taken into account in the calculations of the GOR of oil.

A known method of measuring the flow rates of oil and associated gas oil wells /patent RU No. 2439316 C2. Appl. 04/05/2010. Published 01/10/2012/. The method includes the flow of produced products from the tubing string into the separator and the separation of gas and oil in it. Further, oil and gas are sequentially withdrawn from the separator with their quantity measured using a float and a flow switch according to the time of filling and emptying the measuring part of the separator, respectively. The switching of oil and gas flows is carried out by increasing the pressure on each side of the two-way piston of the flow switch while blocking the oil and gas outlets from the separator at the upper and lower ends of the vertical perforated pipe with a float.

The disadvantage of this method is that when the pressure in the separator is increased, 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 loading and unloading oil, as well as the reliability of the measurements.

In addition, the application of this method for a mobile version of the 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, a high water cut of the product or a low oil GOR.

A known method for determining the flow rates of oil, associated gas and water /Patent RU No. 2504653 C1. A method for determining the flow rates of oil, associated gas and water. Appl. 07/30/2012. Published 01/20/2014/. To measure the flow rate of the liquid, the measuring tank is filled with the production of the well, 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 use of a compressor is complicated due to a change in the gas injection pressure into the reservoir, which varies over a wide range even within the same oil field.

Known method and device for measuring oil production /RF Patent No. 2236584. Method and device for measuring oil production. Appl. 12/17/2002 Published. 20.09.2004 /. It includes supplying a gas-water-oil mixture to a measuring tank, separating it into gas and a water-oil mixture (WOM), which is an emulsion, measuring the WOM flow rate by filling the calibrated part of this tank and draining the WMS at a frequency determined by the intensity of product supply a specific well, calculation of the proportion of water and the proportion of oil in the liquid phase of this production from the measured value of the density of the WSS 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.

A significant disadvantage of this method is its low efficiency in the production of high-viscosity or high-watered oil with low gas content. When producing high-viscosity oil, the time of oil displacement from the tank increases significantly, as well as the displacement pressure. In addition, the duration of measurements increases significantly at low GORs of oil due to the low rate of emptying of the measuring vessel in the cycle of accumulation of free gas in it. With a minimum gas content of the well production, which is observed when the water cut is 95 ... 99%, the cycle time for emptying the separator from the liquid can be many hours, which is unacceptable for measurements.

Closest to the proposed invention in terms of technical essence is a method for measuring the production of an oil well /Patent RU No. 2733954 C1. Appl. 08/13/2019. Published 08.10.2020. BI No. 28/. The method includes the flow of oil well production into a measuring tank with a calibrated part, separating it into gas and liquid phases, measuring the liquid flow rate by 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. Liquid filling into the separator tank is stopped when the specified hydrostatic pressure difference in the separator tank is reached. The subsequent draining of liquid from the separator is carried out with an increase in pressure in the separator vessel by installing an adjustable throttle on the gas outlet line, and the increase in pressure in the separator vessel is carried out in proportion to the decrease in the amount of gas in the produced product, and in the 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 a lot of time to increase the gas pressure in the separator to ensure that the liquid is drained at a low gas content of the incoming product. The lowest content of free gas in the produced well production takes place in old depleted deposits with high water cut in the reservoir fluid.

The technical objective of the proposed method is to ensure the measurement of the total amount of associated gas produced together with oil.

The problem is solved by the fact that in a known method, including the flow of oil well production into a measuring tank with a calibrated part, separating it into gas and liquid phases, measuring the mass flow rate of the liquid by the time of filling the calibrated part of the tank and the maximum given hydrostatic pressure drop in it when closed liquid drain lines, according to the invention, before filling, the produced product is pre-circulated through the measuring tank with the achievement of pressure in it in the pressure line of the well and the minimum specified hydrostatic pressure drop, after which the liquid drain from the tank is blocked and the measuring tank is filled with products while maintaining constant pressure by removing from the tank an additional volume of gas entering it and measuring this volume with a meter installed after the bypass valve, set to the pressure in the pressure line of the well, and when the tank reaches the maximum about the given value of the hydrostatic pressure drop, the product inlet line to the tank is closed, the valve on the bypass line of the bypass valve is opened and gas is continued to be removed from the tank and its volume is measured until the atmospheric pressure value is reached in the tank, and the GOR of oil is calculated as the ratio of the amount of gas measured by the meter to subtracting the volume of liquid that entered the tank during its filling, to the mass of oil that entered the tank during the filling cycle.

The figure shows a diagram of the installation for implementing the method.

On the input line 1 of the water-gas-oil mixture (VGNS) inlet to the measuring tank 2, a valve 3, an electromagnetic valve 4 and a check valve 5 are installed. On the output line 6 for the water-oil mixture (VNS), a valve 7 and an electromagnetic valve 8, as well as a check valve 9 are installed. The gas line 10 through the valve 11 is connected to the upper part of the differential pressure sensor 12. The lower part of the sensor 12 is connected to the output line 6 of the measuring tank 2. On both sides of the check valve 9, the intake 13 and pressure 14 lines of the pump 15 are connected to the line 6. A drainage line with a tap 16 is introduced into the lower part of the measuring tank 2. A gas meter 18 is connected to the gas line 10 through the bypass valve 17. A valve 19 is installed on the bypass line of the bypass valve 17.

A pressure sensor 20 and a temperature sensor 21 are mounted on the measuring vessel 2. To control the operation, the installation includes a controller (not shown in the drawing) with a program for switching valves 4 and 8, as well as a program for calculating the mass flow rate of oil and the gas factor of oil.

The method is carried out as follows. Installation through closed valves 3 and 7 is connected to the manifold line of the well (not shown). Solenoid valves 4 and 8, valve 19 remain closed, and valve 11 is open. Next, the valves 3 and 7 are opened, the downhole equipment is put into operation and the electromagnetic valves 4 and 8 are opened, which allows the produced well product to circulate through line 1, the measuring tank 2 and line 6 into the pressure line (not shown in the drawing).

During the circulation period, the pressure in the tank 2 will rise to the value of the pressure in the pressure line of the well. The free gas entering container 2, accumulating in the upper part of the container, will push the liquid level to a level corresponding to the minimum hydrostatic pressure drop. The difference corresponding to the zero value is taken as the minimum value.

Further, according to a given program, the controller closes the solenoid valve 8 and the cycle of filling the container 2 with the well products will begin. When filling in tank 2, the pressure should rise due to the flow of well products with free gas. However, the pressure in the vessel 2 will maintain its value due to the release of the incoming free gas through the bypass valve 17 with simultaneous measurement of its volume by the meter 18. Therefore, the pressure value of the gas bypass through the valve 17 is set equal to the pressure in the pressure line of the well.

Upon reaching the maximum value of the hydrostatic pressure difference in the tank 2, the controller will close the solenoid valve 4 according to the program. The solenoid valve 8 is left closed. At this moment, the timer of the controller will fix the time of filling the container 2 with liquid.

Further, by opening the valve 19, the gas is continued to be removed from the container 2 with the measurement of its outgoing volume and the pressure in it is brought to atmospheric value. In this case, the volume of gas, including both the free and the residual amount of the dissolved part, will be removed from the tank 2 and measured. The gas leaving the tank 2 for the entire period of measurements in order to avoid emissions into the atmosphere can, for example, be pumped into the pressure line of the well by a compressor (not shown in the drawing).

After that, by turning on the pump 15, liquid is pumped out of the tank 2 into the pressure line and the installation is disconnected from the well.

The check valve 5 is installed to maintain the pressure reached in the container 2 in the cycle of its filling. A check valve 9 is installed to direct the fluid flow generated by the pump 15 to the well pressure line.

The program for calculating the mass of oil included in the tank 2 during its filling includes entering into the controller program the values of oil and water densities, as well as the water cut of the product. The measured hydrostatic pressure drop in combination with the entered data makes it possible to calculate the mass flow rate of oil entering the measuring tank 2, as well as its GOR, as the ratio of the measured volume of gas to the mass of this oil. At the same time, from the total volume of gas measured by the counter 18, the volume of compressed gas is subtracted, equal to the volume of liquid that entered the container in the cycle of its filling.

This volume of compressed gas is converted into the volume of gas under normal conditions in the calculations.

In calculations of the mass flow rate of crude oil, the time of filling the calibrated part of the measuring tank 2 fixed by the controller timer from the minimum value of the hydrostatic pressure drop to its maximum set value is used.

To calculate the mass flow rate of oil and its GOR, the volume of liquid that entered the measuring tank 2 when completely filled is calculated:

where:

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

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

B - water cut of the liquid, fractions of units;

D _em is the inner diameter of the calibrated part of the container, m;

g - acceleration of gravity, m / s ² ;

Next, the program calculates the mass of oil that entered the tank when it was completely filled:

The mass production rate of oil is calculated as follows:

where:

T is the time of filling the container 2 with liquid from the value of ΔP _min to the value of ΔP _max .

Calculation of the volume of gas, reduced to normal conditions, displaced from the tank by the volume of incoming liquid:

where:

P _n - pressure in the pressure line, Pa;

P _a - the value of atmospheric pressure, Pa.

Calculation of the gas factor of oil is carried out according to the formula:

where:

V _c - the total amount of gas measured by the meter and reduced to normal conditions, m ³ .

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 oil well production by a mobile unit, including the flow of oil well production into a measuring tank with a calibrated part, separating it into gas and liquid phases, measuring the mass flow rate of the liquid by the time of filling the calibrated part of the tank and by the maximum specified hydrostatic pressure drop in it with a closed line draining the liquid, characterized in that before the start of filling, the produced product is pre-circulated through the measuring tank with the achievement of pressure in it in the pressure line of the well and the minimum specified hydrostatic pressure drop, after which the drain of the liquid from the tank is blocked and the measuring tank is filled with products while maintaining in it constant pressure by removing from the tank an additional volume of gas entering it and measuring this volume with a meter installed after the bypass valve, set to the pressure in the pressure line of the well, and when it reaches the tank These maximum predetermined values of the hydrostatic pressure drop close the product inlet line to the tank, open the valve on the bypass line of the bypass valve and continue to remove gas from the tank and measure its volume until the atmospheric pressure value in the tank is reached, and the GOR of oil is calculated as the ratio of the amount of gas measured by the meter with the deduction of the volume of liquid that entered the tank during its filling, to the mass of oil that entered the tank during the filling cycle.

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