RU2483284C1 - Hydrostatic downhole densitometer - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: hydrostatic downhole densitometer comprises a body with two differential pressure sensors, which separate the inner cavity of the body into three chambers, two of which arranged at the body ends serve to receive pressure of environment, and a chamber arranged between differential pressure sensors is filled with a liquid with available physical properties. The chamber between differential pressure sensors is hydraulically connected with the environment via a hole in the side wall of the body with the help of a medium separator located inside the body with a movable partition.

EFFECT: increased accuracy of measurements and reduced diameter of a densitometer.

5 cl, 2 dwg

Description

The invention relates to instrumentation, and in particular to liquid and gas densitometers used in geophysical studies of oil, gas and hydrogeological wells. It can find application in the oil and gas industry and hydrogeology.

A well-known depth densitometer (USSR AS No. 450095 dated 11/15/74) containing a measuring system consisting of two bellows located at different heights, an auxiliary bellows and an electromechanical converter for linear displacements of the end face of the auxiliary bellows.

The disadvantage of the densitometer is the low measurement accuracy caused by the error in the operation of the electromechanical linear displacement transducer and the hysteresis of the deformation displacements of the measuring bellows.

Known pressure transmitter APR-2200D for measuring fluid density in open and closed containers (Intelligent hydrostatic pressure transmitter for measuring density APR-2200D, http: //www.aplisens.rn/catalog/APR-2200D.pdf). It contains a differential pressure sensor with two diaphragm pressure receivers that are remote for increasing the measurement base, which transmit pressure to the inputs of the differential sensor through tubes filled with a liquid with known physical properties.

The disadvantages of the device are:

- the presence of diaphragms that create errors when transmitting pressure to the inputs of a differential sensor, which reduces the accuracy of the measurements;

- a change in temperature and pressure of the liquid inside the tubes and diaphragm pressure receivers causes a change in its volume, as a result of which the diaphragms receive displacement; in the case of a temperature difference inside the tubes and diaphragm pressure receivers, the diaphragms have different movements, which leads to the appearance of an additional pressure difference on the sensor and a decrease in the measurement accuracy;

- large dimensions of the diaphragms; the possibility of downsizing is limited, as it causes a progressive increase in the stiffness of the diaphragms, which leads to a sharp decrease in the accuracy of measurements; the large dimensions of the diaphragms limit the scope of applications, for example, in pipes or wells of small diameter.

A known pressure transducer with a remote sealed diaphragm and correction loop and a method of measuring pressure (patent RU No. 2145703 from 02.28.1995).

The converter can be used as a densitometer of a liquid in a tank. In particular, it contains a differential pressure sensor with two remote diaphragm pressure receivers connected to the inputs of the differential pressure sensor with tubes filled with a liquid with known physical properties (Fig. 11). The converter has means for monitoring the temperature of the liquid in the tubes and remote pressure receivers (figure 10), which minimizes the error in measuring pressure when the temperature of the liquid in the tubes and receivers changes.

The disadvantage of the converter is the presence of diaphragms, which create additional errors when transmitting pressure to a differential pressure sensor.

Another disadvantage is the large dimensions of the diaphragms. The possibility of downsizing is limited, as it causes a progressive increase in the stiffness of the diaphragms, which leads to a sharp decrease in the accuracy of measurements. The large dimensions of the diaphragms limit the scope of applications, for example, in pipes or wells of small diameter.

A device is known for hydrostatically measuring the density of liquids flowing through a pipeline (USSR AS No. 197250 of 04/19/1966, prototype).

Although the device is intended for hydrostatic measurement of the density of fluids flowing through a pipeline, and not in a well, it is closest in essential features to the invention and is therefore selected as a prototype.

The device comprises a housing 2, in which two measuring elements are installed, consisting of dividers 9 and springs 10, which essentially are differential pressure sensors. The measuring elements divide the internal space of the housing into three chambers: an internal chamber 8 located between the measuring elements, and two end chambers 7 located at the ends of the device casing. All chambers are filled with liquid with known physical properties. Each chamber is hydraulically connected to its pressure source by means of diaphragm chambers 4, 5 and tubes 6, also filled with a liquid with known physical properties. The pressure difference between the end chambers and the inner chamber is converted to the movement of the corresponding measuring elements that act on the electromechanical summing transducer, the signal from which is supplied to the secondary device.

The disadvantage of this device is the presence of diaphragm chambers at the points of pressure selection, creating additional errors when transmitting pressure to the measuring elements.

Another disadvantage is associated with the difference in the temperature of the liquid inside the tubes and the associated diaphragm chambers. The temperature difference causes a different change in the volume of the liquid filling them, as a result of which the diaphragms move differently and create different additional pressure on the differential sensors, which leads to measurement errors.

The disadvantage is the large dimensions of the diaphragm cameras. The possibility of downsizing is limited, as it causes a progressive increase in the stiffness of the diaphragms, which leads to a sharp decrease in the accuracy of measurements. The large dimensions of the diaphragms limit the scope of applications, for example, in pipes or wells of small diameter.

The objective of the invention is to increase the accuracy of measurements and reduce the diameter of the densitometer.

This is achieved by directly connecting the end chambers to the borehole medium without using remote tubes and diaphragm chambers and connecting the inner chamber to the borehole medium through an opening in the side wall of the casing using a media separator with a movable partition installed inside the device casing.

Figure 1 presents a General view of the hydrostatic borehole density meter in longitudinal section.

Figure 2 shows the hydraulic circuit of the hydrostatic borehole densitometer.

The hydrostatic borehole densitometer contains a housing 1 (Fig. 1), in which differential pressure sensors 2 and 3 are installed, dividing the internal cavity of the housing into three chambers. Chambers 4 and 5, located at the ends of the housing, are used to receive the pressure of the external environment, which enters them through the through channels in the housing 6 and 7, respectively. The chamber 8, located between the differential pressure sensors, is made in the form of a channel with a small cross section and is filled with a liquid with known physical properties. The chamber 8 is hydraulically connected to the external environment through a channel 9, a media separator with a movable partition 10 and an opening 11 in the side wall of the housing 1. A small cross section of the chamber 8 provides a small volume of liquid in this chamber, a small change in its volume with a change in pressure and temperature, and , therefore, reduces the design requirements of the media separator. The media separator with a movable partition can be made in various design options, including in the form of a bellows with a closed end, as shown in figure 1. A pressure sensor 12 and a temperature sensor 13 of the liquid in the chamber 8, as well as a sensor of the angle of inclination 14 of the axis passing through the centers of the differential pressure sensors to the vertical, are installed in the housing of the device.

The differential pressure transducer has an electronic circuit (not shown in the figures), which, based on signals from sensors 2, 3, 12, 13, 14, calculates the pressure difference in chambers 5 and 4 and calculates the density of the environment. It also writes the results of calculations and other necessary parameters to the device’s memory, if it is autonomous, or transfers it to the surface if the device descends into the well on a wireline cable.

Consider the operation of the hydrostatic borehole densitometer using the hydraulic circuit of the device shown in figure 2.

The diagram shows the housing of the density meter 15, filled with a liquid with known physical properties. At the upper and lower ends of the housing sensitive elements 16 and 17 of differential pressure sensors are shown. A media separator with a movable partition 18 is installed in the housing, through which the pressure of the external medium on the liquid inside the housing is transmitted.

The following notation is used in the diagram and in the text:

L is the nominal distance between the centers of the sensitive elements of the differential pressure sensors;

H is the vertical distance between the centers of the sensitive elements of the differential pressure sensors;

X is the vertical distance from the center of the sensing element of the upper differential pressure sensor to the center of the moving partition of the media separator;

α is the angle of deviation from the vertical axis connecting the centers of the sensing elements of differential pressure sensors;

ρ _B is the liquid density inside the densitometer case (not shown in the diagram);

ρ _H is the density of the medium surrounding the housing of the densitometer (not shown in the diagram);

g is the acceleration of gravity;

P1 _H - fluid pressure on the upper sensitive element from the outside of the housing;

P1 _B - fluid pressure on the upper sensitive element from the inside of the housing;

ΔP1 = P1 _H -P1 _B - pressure drop on the upper sensitive element;

P2 _H - fluid pressure on the lower sensitive element from the outside of the housing;

P2 _B - fluid pressure on the lower sensitive element from the inside of the housing;

ΔP2 = P2 _H -P2 _B - pressure drop on the lower sensitive element;

PX _H - fluid pressure on the movable partition from the outside of the housing;

PX _B - fluid pressure on the movable partition from the inside of the housing;

ΔP _P = PX _H -PX _B is the pressure drop across the movable partition.

We find the mathematical equation that connects the pressure drops across the differential pressure sensors with the pressure difference of the external environment acting on the upper 16 and lower 17 pressure sensors.

Based on the accepted notation, we determine the pressure PX _{H of an} external fluid with a density ρ _N on the movable partition 18 depending on the pressure P2 _Н. It is equal to the pressure P2 _N minus the gravitational pressure of the external fluid at the vertical drop H-X:

Given the pressure drop ΔP _P on the movable partition, we obtain:

The pressure P1 _{B is} expressed through PX _B , subtracting the hydrostatic pressure of the fluid inside the housing with a density ρ _V at the height difference X:

The pressure Р2 _{В is} determined through Р1 _В , adding the hydrostatic pressure of the liquid inside the body with a density ρ _В at the height difference Н:

Define the pressure drop ΔP1 = P1 _H -P1 _B using the expression (3):

The pressure drop ΔP2 = P2 _H -P2 _{B is} determined using equation (4):

ΔP2 = P2 _H -P2 _B = Р2 _Н -Р2 _Н + ρ _H g (HX) + ΔР _П + ρ _B gX-ρ _B gH =

ΔP _P -ρ _B g (HX) + ρ _H g (HX) = ΔP _P + (ρ _H -ρ _B ) g (HX),

or finally

Consider the difference ΔP1-ΔP2 using expressions (5) and (6):

Thus, as equation (7) shows, the pressure difference P1 _H -P2 _Н measured by the device in chambers 4 and 5 (Fig. 1) is equal to the difference in pressure drops ΔP1 and ΔP2 at the upper and lower differential pressure sensors 2 and 3 minus the hydrostatic differential fluid pressure in the chamber between the differential pressure sensors.

It is significant that neither the pressure drop across the movable partition ΔР _П , nor the position of the movable partition relative to the differential sensors (coordinate X) in any way affect the measurement result.

In equation (7) is included _in the current density ρ fluid in the chamber between the differential pressure sensors. It depends on its physical properties, the magnitude of the absolute pressure in the liquid and its temperature. Liquid pressure and temperature can vary widely during the operation of the device. Therefore, it is necessary at each measurement to determine these values and calculate the current density of the liquid inside the device. The fluid pressure in the chamber between the differential pressure sensors is measured by a pressure sensor 12.

The pressure sensor 12 may be absent if the densitometer is part of a complex device in which an external pressure sensor is present, since the pressure in the chamber 8 differs slightly from the pressure of the external medium. The difference is mainly determined by the pressure drop across the movable partition 10, which cannot be higher than the measurement limit of the differential pressure sensor, otherwise it will be damaged. As theoretical estimates show, to ensure high accuracy of the densitometer with a measuring base of 1 meter, the measurement limits of differential pressure sensors should not exceed 1 atmosphere. If the pressure in the chamber 8 is estimated based on the readings of the ambient pressure sensor, then an error in one or less atmospheres will cause a slight error in determining the density of the liquid filling the chamber 8, due to its low compressibility, and it will not significantly affect the accuracy of density measurement the external environment.

When operating the densitometer in vessels or vertical wells, the device may lack a sensor 14 of the angle of inclination to the vertical axis passing through the centers of the differential pressure sensors.

If the temperature of the medium in which the densitometer operates is known, then there may be no temperature sensor 13 of the liquid in the chamber 8.

Knowing the pressure difference between the levels of the upper and lower pressure sensors, it is possible to determine the density ρ _{N of} the environment, provided that the speed of the medium relative to the device and the well is zero. Otherwise, it is necessary to take into account the additional pressure drop caused by the forces of friction of the medium against the wellbore and the body of the device, as well as the dynamic pressure drop if the flow rate of the medium in the areas of differential pressure sensors is not the same.

Since the pressure drop between the sensing elements 17 and 16 is equal to the hydrostatic pressure drop in the external environment between the levels of location of these elements, taking into account (7) we have the relation:

P2 _H -P1 _H = ΔP2-ΔP1 + ρ _B gH = ρ _H gH.

From it follows:

The vertical distance H between the centers of the sensitive elements can be expressed in terms of the nominal distance L between them and the angle α of the inclination of the axis passing through the centers of the sensitive elements to the vertical H = L. Substituting this expression in (7) and (8), we obtain:

Equation (9) is used to calculate the pressure difference between the levels of the lower and upper pressure sensors, and expression (10) is used to calculate the density of a liquid or gas in the environment.

To ensure the operation of the device, its electronic circuit must perform the following functions:

- determine the effective pressure drops on the differential pressure sensors;

- determine the absolute pressure of the liquid in the chamber between the differential pressure sensors and its temperature;

- calculate the current density of the liquid in the chamber between the differential pressure sensors;

- determine the angle of inclination of the axis passing through the centers of the differential pressure sensors to the vertical;

- determine the pressure drop between the levels of the lower and upper pressure sensors according to the formula (9);

- determine the density of a liquid or gas in the external environment by the formula (10);

- write down the measurement results and other necessary parameters in the device memory or transfer them to the surface via a wireline cable.

Claims (5)

1. A hydrostatic borehole densitometer, comprising a housing with two differential pressure sensors separating the internal cavity of the housing into three chambers, two of which located at the ends of the housing serve to receive environmental pressure, and the chamber located between the differential pressure sensors is filled with liquid known physical properties, characterized in that the chamber between the differential pressure sensors is hydraulically connected to the external environment through an opening in the side wall of the housing using located inside the housing of the media separator with a movable partition. 2. The hydrostatic borehole densitometer according to claim 1, characterized in that the chamber between the differential pressure sensors is made in the form of a small cross-section channel. 3. The hydrostatic borehole densitometer according to claim 1, characterized in that it comprises a liquid temperature sensor located in the chamber between the differential pressure sensors. 4. The hydrostatic borehole densitometer according to claim 1, characterized in that it comprises a pressure sensor and a liquid temperature sensor located in the chamber between the differential pressure sensors. 5. The hydrostatic borehole densitometer according to claim 1, characterized in that it contains a sensor for the angle of inclination of the axis passing through the centers of the differential pressure sensors to the vertical.

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