RU2487993C2 - Method of gas separation - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: method of free gas separation by turning of liquid-gas mixture upflow and its passage through semi-transparent separation surface. Separation surface contains vertical slots. Pressure gradients are created perpendicular to separation surface.

EFFECT: ensuring of identical rate of volume flow for movement of liquid-gas mixture.

3 cl, 1 dwg

Description

The invention relates to the field of oil production from oil wells by a mechanized method, namely oil production by electric centrifugal pump or sucker rod pump.

The main complicating factor in oil production by various deep pumps is the presence of dissolved gas in it (the value of the volume of dissolved gas in a unit volume of oil is called the gas factor or gas saturation, and depends on the field, productive formation - we denote it by G, m ³ / m ³ ), which at pressures below the saturation pressure begins (the value of which depends on the field, reservoir, denoted by Rn, [1]) to be released into free associated gas. The volume fraction of free gas in a gas-liquid mixture is called gas content. The presence of free gas at the intake of the downhole pump complicates the production of oil, leading to destabilization of the operating modes of the pump and ultimately to failure of the entire pumping unit, reducing the economic efficiency of the method of operating an oil well. To combat the harmful effects of free gas on the deep pump, various types of separators (gas separators) for electric centrifugal pump units (ESPs), gas anchors for sucker rod pumps (SHGN), etc., which must pass the gas-liquid mixture away from the intake of the pump unit, were created free gas into the annulus of an oil well and help stabilize the operating mode of the deep well pump. The separators are characterized by the so-called separation coefficient - the ratio of the volume of free gas withdrawn from the pump intake to the entire volume of free gas in the gas-liquid mixture at the pump intake and is indicated by the letter σ [1].

$$\sigma =\frac{V_c}{V_0}(\mathrm{one})$$

Where

V _c - the amount of free gas discharged by the separator beyond the pump intake,

V ₀ - the total amount of free gas at the pump intake. All these separators are of a centrifugal principle of operation (separators of the MGN-5L type - Russian-made by Lyapkov PD, “RGV”, “KGV” by ODI [2]). Due to the large difference in laboratory conditions, the gas density (1 kg / m ³ ) and oil density (700-800 kg / m ³ ), such separators can obtain a separation coefficient of at least 0.5 (50%). The centrifugal force in the centrifugal separator depends on the following:

$$F=\mathrm{<figure-callout\; id="2"\; label="m\; V"\; filenames="00000008.png"\; state="\{\{state\}\}">m\; </figure-callout>}{V}^{}{}^2/R,(2)$$

where m is the mass of the particle, some selected oil element with gas (or the mass of a unit volume of oil, which is called the oil density), V is the linear speed of rotation of the "particle" of oil in the separator, equal to the linear speed of the elements of the electric centrifugal gas separator, R is the radius of rotation of the pieces oil.

With the same radius and linear speed of rotation, the centrifugal force acting on the "element" of the oil depends on the density. If in the "element" of oil with density p _n there is a free gas bubble with density p _g , then the ratio of centrifugal forces per oil element F _n and gas element F _g differ

$$F_n/F_g={\mathrm{<figure-callout\; id="2"\; label="m\; n\; V"\; filenames="00000008.png"\; state="\{\{state\}\}">m\; </figure-callout>}}_n{V}^{}{}^2/R:m_g{V}^2/R=m_n/m_n(3)$$

In an electric centrifugal pump under pressure (called pressure at the pump inlet) 30-60 atmospheres, the oil density differs from the gas density in free gas bubbles in the same oil no more than 4-5 times (for example, the average oil density is 700-800 kg / m ³ , at the same time, the gas density is equal to 145-150 kg / m ³ ). In laboratory conditions, when the density of a liquid (oil) differs by several hundred times from the density of gas bubbles (air or methane), relation (3) becomes significant and, therefore, in laboratory conditions centrifugal separators give a good separation coefficient.

However, in an oil field, at great depths and under a pressure of 30-60 at. the difference in the densities of gas (about 150 kg / m ³ ) and liquid (about 750 kg / m ³ ) the separation coefficient of these separators is not more than 0.18 (18%) [3].

Gravity separators for electric centrifugal pumps (ESPs) are also known, in which gravity is used for separation when turning the upward flow of the gas-liquid mixture and passing the gas-liquid mixture through the translucent separation surface. For example, in the module of a submersible centrifugal pump according to the patent RU 2215907, the decrease in the content of free gas is performed by passing a stream of gas-liquid mixture through the openings of the grid.

The closest analogue is a method for separating a gas anchor (V. Kretz, Fundamentals of oil and gas business: a training manual / V. G. Krets, A. V. Shadrina. - Tomsk: Tomsk Polytechnic University Publishing House, 2010, p. 126, Fig. 11.5), in which, when the gas-liquid flow changes by 180 °, gas bubbles under the influence of the Archimedean force float and partially separate into the annulus, and the liquid through the holes enters the central pipe to receive the pump. However, according to the laws of hydromechanics, the movement of the gas-liquid flow through the holes is not the same: the highest speed is in the holes close to the pump intake (since there is more pressure drop in them), and the lowest speed is in the holes remote from the pump intake (since there is a pressure drop in them smaller). As a result of this, separation does not occur at the highest speeds. Thus, although gravity separators are the most economical (there are no rotating units and parts), due to the uneven speed of movement through the separation surface, they have a low separation coefficient (not more than 10%) and, therefore, have not been widely used.

The aim of the invention is to increase the separation coefficient of the separator.

For this, the method of separating free gas at the intake of a deep pump for oil production by rotating the upward flow of the gas-liquid mixture and passing the gas-liquid mixture through the translucent separation surface is characterized in that the separation surface containing vertically located slots is placed vertically and pressure gradients are created perpendicular to the separation surface in such a way as to ensure the flow of the gas-liquid mixture with the same space velocity. As a result of the redistribution of pressure drops, the velocity of the gas-liquid mixture on all slits, as well as the upper and lower parts of the slots become the same and decrease, therefore, the velocity of the gas bubble near the slit in the vertical direction under the action of the Archimedean force becomes greater than the speed of the horizontally directed gas-liquid mixture, leading to bubble lag and increased separation.

In the particular case, pressure gradients are created using calibrated holes at the pump inlet.

In another particular case, to increase the separation of the gap on the surface of the separation is performed with a width mainly less than the diameter of the bubbles.

Figure 1 shows the implementation diagram of the proposed method of gas separation, which made the following notation:

1 - pipe of radius R, muffled from the bottom and connected (not shown) with the upper end to the pump intake,

2 - the direction of movement of the mixture at the pump intake,

3, 4 and 5 - calibrated holes of radii R ₁ , R ₂ and R ₃ ,

6 - separation surface area S,

7 - speed W _{n the} ascent of gas bubbles that have not passed through the slots 13,

8 - speed W _{c the} movement of the gas-liquid mixture on the surface 6,

9, 10 and 11 - the velocity of the gas-liquid mixture at the level of holes 3, 4 and 5,

12 - speed W _{0 the} movement of the gas-liquid mixture in an upward flow to the surface 6,

13 - slits of width d ₀ on the surface 6.

The proposed separation method is as follows. At the pump inlet, a nozzle 1 of radius R, which is muffled from below, with calibrated holes 3, 4, and 5 on the side surface of the working pump creates pressure gradients perpendicular to the axis of the nozzle 1.

The pressure gradients should ensure the movement of the gas-liquid mixture with the same volumetric velocity (volumetric velocity 9 is equal to the volumetric velocity 10 and equal to the volumetric velocity 11). On the path of space velocities, a vertical separation surface 6 is established perpendicular to the direction of flows with vertically arranged slots 13. The direction of the upward gas-liquid flow on the cylindrical separation surface 6 is changed by 90 ° under the influence of a pressure gradient. If the linear velocity in the upward flow is W ₀ , then on the separation surface this velocity will decrease and become equal to:

$$W_c=\frac{W_0}{S}(\mathrm{four})$$

where S is the surface area of the slots on the separation surface.

The velocity vector c will be equally directed with the pressure gradient vector, i.e. the direction of the velocity vector W _s will be perpendicular to the plane of calibrated holes 3, 4 and 5. It is possible to select the area S so that the speed 8 W _s becomes much less than the linear velocity o in the upward flow of the gas-liquid mixture

$$W_c<W_0(5)$$

and so that the horizontal velocity of the gas-liquid mixture (as well as gas bubbles) becomes less than the speed of ascent of gas bubbles.

$$W_c\le W_n(6)$$

When the gas-liquid mixture is rotated due to the low velocity of the "drift" of the bubbles toward the separation surface 6, the Archimedean force will cause the bubbles to move in the upward direction. The deceleration of gas bubbles and the approach to the separation surface 6 of other bubbles according to the laws of mechanics of the movement of gas-liquid mixtures will lead to coagulation - coalescence and coarsening of gas bubbles, which will increase the value of the acting Archimedean force, and therefore, the value of the speed of upward movement of gas bubbles.

On the other hand, gas bubbles with a diameter of d _p moving horizontally towards the slit 13, due to their diameters and slit width d _o , cannot pass through the slit 13 and will be forced into the space in front of the cylindrical separation surface 6 by other bubbles approaching the slit .

$$d_{\mathrm{about}}<d_P(7)$$

Thus, the surface 6 passes a homogeneous liquid through the slots 13 (oil + associated water) and the separated homogeneous mixture will enter the holes 3, 4 and 5. A decrease in the mixture of gas bubbles stabilizes the supply of ESP, SHGN. The separation coefficient of the bubble separator will be closer to 100%. Literature:

1. Mishchenko I.T. Downhole oil production. Publishing House "Oil and Gas" Russian State University of Oil and Gas. I.M. Gubkina. M. 2003. p. 424, 474.

2. Surgutneftegas. Workshop on PNS technology. Tulsa. Oklahoma, 15.X. 1995.

3. Khusainov Z.M., Usmanov I.Sh., Gareev A.A. On the issue of gas separation. Oilfield business, No. 2, 2000, Pages 21-22.

Claims (3)

1. The method of separation of free gas at the reception of a deep pump for oil production by turning the upward flow of the gas-liquid mixture and passing the gas-liquid mixture flow through the translucent separation surface, characterized in that the separation surface containing vertically located slots is placed vertically, and gradients are created perpendicular to the separation surface pressure in such a way as to ensure the flow of the gas-liquid mixture with the same space velocity. 2. The method according to claim 1, characterized in that the pressure gradients are created using calibrated holes at the pump inlet. 3. The method according to claim 1, characterized in that the cracks on the separation surface are made with a width mainly less than the diameters of the bubbles.

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