RU2244825C1 - Method and device for measuring gas loss in gas-liquid mixtures - Google Patents

Abstract

FIELD: oil extractive industry.

SUBSTANCE: mixture is separated on liquid and gas in separator. Liquid is periodically collected and forced away by gas while measuring absolute pressure and gas temperature in separator tank near upper and lower fixed liquid levels, and times of forcing away of fixed liquid volume. Additionally measured are absolute pressure and temperature in moment when liquid reaches intermediate fixed level. Then liquid is forced from intermediate fixed level to lower fixed level separator is switched off from well, and mass loss of gas is calculated from provided relation. Device for realization of method consists of separator with feeding pipe, in which a three-drive valve is mounted, and draining pipe, which through said valve is connected to liquid outlet channel and to gas outlet channel. Separator is provided with sensors of temperature and pressure and sensors of upper, intermediate and lower levels, mounted in such a manner, that they separate fixed volumes between each other in separator tank, in case of equality of which calculations are simplified.

EFFECT: higher precision.

2 cl, 1 dwg

Description

The invention relates to the field of measuring gas flow in gas-liquid mixtures coming from oil wells.

A known method of measuring gas flow in gas-liquid mixtures coming from oil wells [1. G.S.Abramov et al., Automated measuring devices for measuring the flow rate of oil wells. Scientific and technical journal “Automation and telemechanization and communication in the oil industry, No. 1-2, 2001, s.16-18]. The method includes separating the mixture in the separator into liquid and gas, periodically accumulating liquid in the separator tank and displacing it with gas, measuring the absolute pressure and gas temperature in the separator tank at the upper and lower fixed liquid levels, and the time of displacing a fixed volume of liquid. The gas volumetric flow rate is calculated from the known dependence in accordance with the “PVT method”.

The known method associated with the use for measuring gas flow q ₀ , the PVT method [2. “Automation of the production of oil wells”, M., Nedra, 1975, p.90-96], leads to the following errors:

Δq ₁ - methodological error due to the inability to determine with sufficient accuracy the value of the volume occupied by the gas in the entire system, including the supply pipe, separator and outlet pipe, and its mass at the initial time;

Δq ₂ - systematic error due to variability of the absolute pressure in the separator (in the devices described in [1], the calculating formula for q ₀ is similar to the formula described in [. 2, page 96] for the special case where P _a = const). The condition for the constancy of absolute pressure is practically impossible [2, p. 94];

Δq ₃ - methodological error due to the variability of the absolute temperature of the gas T in the measurement interval.

The technical challenge facing the invention is to increase the accuracy of measurements by eliminating the error due to the inability to determine with sufficient accuracy the value of the volume occupied by the gas in the entire system, and the inconstancy in the separator of the absolute pressure and absolute temperature of the gas.

To solve the technical problem when measuring gas flow in gas-liquid mixtures coming from oil wells, including the separation of the mixture into liquid and gas in the separator, periodic accumulation of liquid and its displacement by gas with measurement of the absolute pressure and temperature of the gas in the separator tank at upper and lower fixed levels liquid, and the time of displacement of a fixed volume of liquid, and the calculation of the volumetric flow rate of gas, additionally measure the absolute pressure and temperature at the time the liquid reaches the weft fixed level, wherein when the displacement fluid from the intermediate fixed level to the lower level produces a fixed separator disconnection from the well, and gas mass flow, corrected to standard conditions, is calculated from the dependence -

V = V ₂ = V ₃ - calibrated values of the volume of the separator between fixed levels (upper and intermediate, intermediate and lower);

ρ ₁ is the density of the gas at the time the liquid is displaced from the upper fixed level;

ρ ₂ - gas density at the time of displacement of the fluid to an intermediate fixed level;

ρ ₃ - gas density at the time of displacement of the liquid to a lower fixed level;

t ₂ -t ₁ - the time of fluid displacement from the upper fixed level to an intermediate fixed level.

Moreover, the design of the device for implementing the method remains close to that in the known devices [1], containing a separator with a calibrated volume between the marks of the upper and lower fixed levels, a three-way valve at the separator outputs for gas and liquid, level sensors for generating signals when the liquid reaches fixed levels, an absolute pressure sensor and an absolute temperature sensor.

To solve the technical problem, a three-way electric valve was added to the device to disconnect the separator from the well, and an additional sensor of an intermediate fixed level was installed in the separator, dividing the calibrated volume between the marks of the upper and lower fixed levels into two fixed volumes.

A device for preliminary gas selection, the design of which does not affect the feasibility of the proposed measurement method, is excluded from the known scheme.

The invention is illustrated in the drawing, which shows a diagram of a device for measuring the average mass flow rate of gas.

The device consists of a separator 1 with a supply pipe 2, in which a three-way valve 3 is installed for connecting the separator to the wells, and a discharge pipe 4 with a three-way valve 5. The discharge pipe 4 through the valve 5 is connected to the channel 6 of the fluid outlet (VZh) and to channel 7 gas outlet (SH) from the separator 1. The separator is equipped with sensors 8, 9 and 10 of the upper, intermediate and lower levels and sensors 11 and 12 of temperature and pressure in the separator. Level sensors are installed so that equal fixed volumes are separated in the separator tank, and three-way valves are equipped with electric drives.

The flow measurement G is as follows.

The gas-liquid mixture from the wells through a three-way valve 3 and a supply pipe 2 is fed into the separator 1, where the gas is separated from the liquid that accumulates in the lower part of the separator, gradually filling its volume. At this time, the second three-way valve 5 closes the liquid outlet (VL) from the separator, but opens the gas outlet (VG) from the separator through channel 7 and the discharge pipe 4 to the collector.

After the liquid reaches a level above H ₃ , which is detected by the sensor 8, a command is issued to switch the valve 5 to the position when the gas outlet to the collector is closed and the liquid outlet to the collector is open. The liquid due to the energy of the gas accumulated by the separator begins to be displaced into the collector.

At the time t ₁ of liquid reduction to level H ₃ (fixed by the sensor 8 of the level switch), the measurement of gas flow rate G begins, which ends at the time (time t ₃ ) of liquid reduction to level H ₁ (fixed by the sensor 10).

In the process of measuring the gas flow at time t ₂ while lowering the fluid to an intermediate level of H ₂ (fixed by the sensor 9), the valve 3 receives a command to shut off the pipe 2, while the well is connected to the reservoir.

After emptying the separator from the liquid, a command is sent to the taps 3 and 5 to switch them to their original position and the accumulation of liquid in the separator begins again.

The process is cyclically repeated.

At time t ₁ in the volume V _{4 of the} aforementioned system: pipe 7+ separator + pipe 8, unfilled with liquid, gas is stored in mass

where ρ ₁ is the gas density at time t ₁ , determined by the measured values of the absolute pressure P _a in the separator by the sensor 12 and the absolute temperature T by the sensor 11 according to the known formula

where ρ _{about the} density of the gas under standard conditions;

P _a is the absolute pressure value;

T is the absolute temperature value;

P _about , T _about - the absolute pressure and absolute temperature in standard conditions, respectively.

During the displacement of liquid from the volume V ₃ equal to t ₂ -t ₁ , a certain mass of gas will flow into the separator due to the measured gas mass flow rate G, and at the same time, the volume V ₃ (calibrated in advance) will be added to the volume of the system V ₄ . Therefore, you can write:

where ρ ₂ is the gas density at time t ₂ determined by sensors 11 and 12 (calculated by formula 2).

At time t ₂ , the three-way valve with electric actuator K1 switches to the position: the separator input is locked, and the gas-liquid mixture enters the collector. Due to this, the gas inflow into the volume V ₄ + V ₃ is interrupted, and the gas accumulated in this volume displaces the volume of liquid V ₂ (also calibrated in advance), filling it with gas until time t ₃ , i.e. can be written:

or, with the equality V ₃ = V ₂ = V,

where ρ ₃ is the gas density at time t ₃ determined by sensors 11 and 12.

Solving together (1), (3) and (5), we obtain an algorithm for determining the mass flow rate of gas G (7):

ρ ₁ V ₄ + G (t ₂ -t ₁ ) = ρ ₃ V ₄ + 2ρ ₃ V

G (t ₂ -t ₁ ) = ρ ₃ V ₄ -ρ ₁ V ₄ + 2ρ ₃ V

G (t ₂ -t ₁ ) = ρ ₂ V ₄ + ρ ₂ V-ρ ₁ V4

(ρ ₃ -ρ ₁ ) V ₄ + 2ρ ₃ V = (ρ ₂ -ρ ₁ ) V ₄ + ρ ₂ V

Claims (2)

1. The method of measuring gas flow in gas-liquid mixtures coming from oil wells, including the separation of the mixture into liquid and gas in the separator, periodic accumulation of liquid and its displacement by gas with measurement of absolute pressure and gas temperature in the separator tank at upper and lower fixed liquid levels and the time of displacing a fixed volume of liquid and calculating the volumetric flow rate of gas, characterized in that they additionally measure the absolute pressure and temperature at the time the liquid reaches the intermediate a fixed level, and when the fluid is displaced from an intermediate fixed level to a lower fixed level, the separator is disconnected from the well, and the gas mass flow rate reduced to standard conditions is calculated from the dependence

where V = V ₂ = V ₃ - calibrated values of the volumes of the separator between fixed levels (upper and intermediate, intermediate and lower); ρ ₁ is the density of the gas at the time the liquid is displaced from the upper fixed level; ρ ₂ - gas density at the time of displacement of the fluid to an intermediate fixed level; ρ ₃ - gas density at the time of displacement of the liquid to a lower fixed level; t ₂ -t ₁ - the time of fluid displacement from the upper fixed level to an intermediate fixed level. 2. A device for measuring the mass flow rate of gas, containing a separator with a calibrated volume between the marks of the upper and lower fixed levels, a three-way valve at the outputs of the separator for gas and liquid, level sensors for generating signals when the liquid reaches fixed levels, an absolute pressure sensor and an absolute temperature sensor , characterized in that, in order to increase the accuracy of measurement, a three-way electric valve is additionally introduced into the device to disconnect the separator from the well, and in sep Ator the optional intermediate sensor fixed level dividing calibrated volume is between the upper and lower levels fixed on two fixed volume.