Method of measuring liquid flow in gas-liquid mixtures

FIELD: oil and gas production.

SUBSTANCE: invention relates to gas-liquid systems coming from oil production wells. Mixture is separated into liquid and gas in separator. Liquid is periodically accumulated in separator container and then displaced with gas. During this operation, differential pressure for liquid reaching its lower and upper recorded levels and time required for filling recorded volumes are measured as well as absolute pressure and temperature of gas in container. Liquid flow value expressed in weight is calculated using special mathematical dependence. At oil field, liquid and gas enter separator from preliminary gas intake installation or from the first separation step.

EFFECT: increased accuracy of measurement due to avoided gas density registration and excluded necessity of using strictly cylindrically-shaped measuring container.

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

There is a method of measuring fluid flow in gas-liquid mixtures coming from oil wells [1. Gsanremo and other Automated measuring system for measuring the flow rate of oil wells. Scientific-technical journal “automation and implementation of telemechanics and communication in the oil industry, No. 1-2, 2001, S. 16-18]. The method involves separation of the mixture in the separator for liquid and gas, periodic accumulation of fluid in the tank of the separator and the displacement of gas by measuring the differential pressure when the liquid reaches the lower and upper fixed levels and time filling fixed volumes. The mass flow rate calculated using the known dependence in accordance with a hydrostatic method of measuring mass [2. GOST 29976-86 Oil and petroleum products. Methods of measurement of mass, Gosstandart of the USSR, 1986)], which provides a measure of the fluid mass in the open cylindrical tanks at atmospheric pressure.

The application of hydrostatic method unchanged leads to error due to not taking into account the density of the gas and which significantly affects the measurement of fluid flow, hydrostatic “weighing” is the environment of the compressed gas in the separator.

The second disadvantage of this method is that for determining the mass of fluid that fills the measuring capacity requires the constancy (or dimension), the square cross-section within the fill level [2], i.e. the shape of the tank should be close to the cylindrical within the permissible error in the measurement.

The technical task of the invention is to increase the measurement accuracy by eliminating the methodical error Δdue to the lack of accounting for the density of the gas, and eliminates the need to apply a measuring vessel, a cylindrical shape.

To solve this problem in the measurement of fluid flow in gas-liquid mixtures coming from oil wells, including the separation of a mixture of liquid and gas separator, the periodic accumulation of fluid in the tank of the separator and the displacement of gas by measuring the differential pressure when the liquid reaches the lower and upper fixed levels and time filling fixed amounts, additional measures absolute pressure and temperature of gas in the tank, and the mass flow rate is calculated from dependencies

where:

V1and V2- calibrated volume of the separator corresponding to the calibrated EIT is enum marks the height level H 1and H2;

g - free fall acceleration;

ρo- gas density at standard conditions;

T1T2- the value of the absolute temperature of the gas inside the separator when the level of marks H1and H2;

To=293K - is the absolute temperature at standard conditions;

Po=101.3 kPa - a value of absolute pressure at standard conditions;

Pa1and Ra2- the measured value of the absolute pressure in the separator at the moments t1and t2fill the separator liquid to calibrated levels H1and H2respectively;

P(t1), P(t2) - measured values of hydrostatic (differential) pressure at the moments t1and t2respectively;

τW=t2-t1- measured the time of filling of the separator liquid from mark H1to the level of H2.

The invention is illustrated in the drawing, in which figure 1 is a diagram of the device for measuring the average mass flow of the liquid.

To implement the method can be used in the device of known construction [1]. The device includes a separator 1 with inlet pipes 2 and 3 and the discharge pipe 4 with a three-way valve 5. A suction pipe 4 through the valve 5 is connected to the channel 6 output fluid channel 7 gas outlet of the separator 1. Separ the torus equipped with sensors 8 and 9 of the upper and lower levels, sensor 10 differential pressure sensors 11 and 12 temperature and pressure in the separator. The separator 1 may be a separator second stage, to which liquid and gas are fed to the individual tubes.

Field liquid and gas installation pre-selection of gas (or the first degree of separation) through the inlet pipe 2, and 3 received in the separator 1, where a further separation of gas from liquid.

While the valve 5 is in an intermediate position in which the channel 6 output fluid (residence permit) and channel 7 gas outlet (VG) communicate with the discharge pipe 4, the uncontrolled part of the liquid goes into the outlet pipe 4, which excludes the possibility of measurement of liquid flow.

At the time of switching of the valve from its initial position, “B”, when channel 6 (residence permit) is open, and channel 7 (VG) is closed, in the position “a”, when channel 6 is closed, and the channel 7 is open, the process of measurement of fluid flow, when the gas is diverted into the reservoir through the channel 7 and the pipe 4.

When the liquid level marks H1and H2sensors 9 and 8 signals to the controller. After the signal from the sensor 8, the controller gives a command to the switching valve 5 from position “A” to position “B”, and the rate of growth begins to decline.

After switching the valve 5 is replaced fluid in the outlet pipe 4.

Gave the e command is issued to switch the valve from position “B” to position “A” and the cycle of measurement of liquid flow is repeated.

According to the way the average mass flow rate of GWis calculated by the formula

where:

τW=t2-t1the time dimension GW;

V1- defined in the calibration volume of the separator, limited by marking the height level H1(H1measured from the zero level ONU);

V2- defined in the calibration volume of the separator between the marks of H1and H2;

g - free fall acceleration;

P(t1), P(t2- the value differential (hydrostatic) pressure points achievement level marks H1and H2determined by the signal from the pressure transducer 10;

ρo- gas density at standard conditions;

T1, T2- the value of the absolute temperature of the gas inside the separator when the level of marks H1and H2determined by the sensor 11;

Pa1Pa2- the value of the absolute pressure in the separator in moments of achievement level values of H1and H2determined by the sensor 12;

t1, t2- moments of achievement level marks the height H1and H2determined by the sensors, level switches 9 and 8.

Formula (1) is derived based on the following considerations.

The pressure difference P(t) in the “ + ” and the negative” camera sensor 10 is expressed by the formula

where:

ρWand ρgthe density of the liquid and gas;

N is a value below the height level at an arbitrary time t;

P+and R-- the value of the absolute pressure in the “plus” and “minus” camera sensor 10, expressed by the formula

where:

HA- mark height of the sampling point “negative” pressure (assuming that the pulse tube To the “minus chamber” filled with gas with a density of ρg);

Pathe absolute pressure in both chambers of the sensor.

Formula (2) obtained by subtracting the left and right parts of equations (3) and (4).

The density of liquid ρWis expressed by the formula obtained by the conversion formula (2):

Using formula (5) eliminates truncation error Δabove.

The process of filling of the separator liquid is described by the following formulas.

At time t1volume V1filled liquid mass m1.

where ρ1=ρ(t1- the density of the fluid in the volume V1at time t1.

At time t2the volume of the separator (V1+V2) filled with a fluid with mass m1(t1)+m2(t2), where m2 2- weight of fluid in the volume V2at time t2

where ρ2- the average density of the fluid in the volume (V1+V2).

Weight gain liquid Δm on the interval t2-t1will be:

Mass ow rate (average value) is expressed by the formula

From the formula (7) mass m2(t2) is expressed by the formula

Substituting the expression m1(t1from formula (6) in formula (10), we obtain:

Substituting the expression m2(t2from formula (11) in formula (9), we obtain:

Using formulas (5) to obtain the formula for ρ1and ρ2-

where ρr1- gas density at time t1and ρr2- gas density at time t2.

Substituting the expression ρ1and ρ2from formulas (13) and (14) into formula (12), we obtain:

Express ρr1and ρr2through the gas density at standard conditions ρo(at temperature To=293K and pressure Po=101.3 kPa).

To do this, use the equation comp is being a real gas [3. Accion and other Molecular physics, M., Nauka, 1976, S. 478].

where:

m is the mass of gas in the volume V at the absolute temperature T and absolute pressure Pand;

R - universal gas constant;

Z is the compressibility factor, taking into account the difference between the properties of real gas from ideal.

From equation (16) gas density ρ in real terms is expressed by the formula

Gas density ρoin standard conditions, RoTousing formula (16) is expressed by the formula

Dividing each other left and right parts of equations (17) and (18), after identical transformations get the well-known formula

Using formula (19), we obtain formulas for ρr1and ρr2-

Substituting the expression ρr1and ρr2from formulas (20) and (21) into the formula (16), we obtain the desired formula (1). The proposed method does not require permanence ρWon the interval t2-t1that can be seen from formulas (6) and (7).

Method of measurement of liquid flow in gas-liquid mixtures coming from oil wells, including the separation of a mixture of liquid and gas separator, the PE jdicheskoe accumulation of fluid in the tank of the separator and the displacement of gas by measuring the differential pressure when the liquid reaches the lower and upper fixed levels and time filling fixed volume and calculating the mass flow of the fluid, characterized in that it further measure absolute pressure and temperature of gas in the tank, and the mass flow rate is calculated from dependencies

where V1and V2- calibrated volume of the separator corresponding to the calibrated values marks the height level H1and H2;

g - free fall acceleration;

ρ0- gas density at standard conditions;

T1T2- the value of the absolute temperature of the gas inside the separator when the level of marks H1and H2;

T0=293 K is the value of the absolute temperature at standard conditions;

P0=101.3 kPa - a value of absolute pressure at standard conditions;

Pa1and RA2- the measured value of the absolute pressure in the separator at the moments t1and t2fill the separator liquid to calibrated levels H1and H2respectively;

P(t1), P(t2) - measured values of hydrostatic (differential) pressure at the moments t1and t2respectively;

τW=t2-t1- measured the time of filling of the separator liquid from mark H1to the level of H2.



 

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