RU2224088C2 - Return valve for casing string - Google Patents

Abstract

FIELD: well mounting devices engineering. SUBSTANCE: return valve for casing string has body with the inside saddle, disk under the saddle with central passage and peripheral apertures, overlapped by a spring-loaded washer, and a ball lock lowered from the surface with capability of being pressed to the saddle during back movement of fluid. Disk is placed with capability of axial displacement. Upper outlet of central passage is provided with spring-loaded normally closed return valve with a rod for forming a pressurized cross connection. The return valve spring with a rod and washers are shared in the device. EFFECT: increased valve reliability. 4 dwg

Description

The invention relates to devices used for attaching oil and gas wells, and is intended to provide conditions for self-filling of the casing string with the borehole fluid during its descent, to reduce the hydrodynamic pressure on the borehole walls and to prevent the backflow of cement from the annulus into the column.

Known check valve for casing A.S. USSR 1328483, class E 21 B 33/14, in which the locking unit is placed with the possibility of axial movement between the ledges located above and below it.

The disadvantage of this valve is that it does not allow the casing to be filled with borehole fluid during descent.

Closest to the invention is a check valve for casing A.S. USSR 1218078, class E 21 B 34/10, adopted as a prototype, comprising a housing with a saddle located therein, a disk located under the saddle with a central channel and peripheral holes overlapped by a spring washer, and a ball valve discharged from the surface into the well to be pressed against the saddle with the reverse movement of the liquid.

The disadvantage of the valve is that it does not prevent the backflow of cement from the annulus into the column when the fluid velocity is low, insufficient to float the ball. The implementation of the ball valve with a bulk density lower than the density of the medium of the well is associated with a structural complication of the shutter or the need to assign a special material.

Another disadvantage of the valve is its low throughput for self-filling columns caused by the small diameter of the inlet throttle hole. This disadvantage is not eliminated by simply increasing the diameter of the inlet, since with a decrease in hydraulic resistance at the inlet to the string, there is a chance of overflow of the well fluid due to the inertia of the flow moving from the bottom up during the stops of the descent string. Moreover, the lower part of the side hole in the throttle in the device adopted as a prototype, through which the liquid enters, is made in such a way that its cross section decreases with an increase in the lag of the liquid level in the casing from its level behind the column. This is due to the fact that increasing differential pressure raises the sleeve. If in this situation the throttle hole becomes clogged with a solid particle, such as drilled rock, then the valve will shut completely and further descent of the column may lead to crushing of its walls.

The purpose of the invention is to increase the reliability of the valve.

This goal is achieved by the fact that the disk is placed with the possibility of axial movement, the upper outlet of the central channel is equipped with a spring-loaded normally closed non-return valve with a stem, which together with the washer and disk forms a tight jumper, while the spring of the non-return valve with the stem and washers is common.

The execution of the movable disk made it possible to forcefully lift the ball valve to the seat, regardless of the density of its material. This creates an additional positive effect - the limited rise of the liquid column in the well, which occurs along with the rise of the washer 4, will serve to drive various devices, for example control units, in a step cementing clutch.

Installing a normally closed non-return valve in the central channel will allow you to block the entire cross section of the disk and provide the conditions for lifting the ball valve even with a slight movement of the liquid from the bottom up. And the implementation of this valve spring-loaded opens up the possibility of adjusting the amount of fluid passage into the string in direct proportion to the pressure drop, preventing the level in the casing from lagging behind the level behind the string and ensuring that the valve closes when these levels are aligned, preventing fluid overflow through the top of the casing.

And finally, a non-return valve introduced into the device instead of the throttle reduces the likelihood of clogging of the passage by solid particles in the well fluid. In the case of a tendency to clogging the passage in the valve, a pressure rise occurs, which increases the degree of opening of the valve and ensures the removal of solid particles outside the passage.

Figure 1 shows the check valve in its original position.

Figure 2 is the same in the process of filling the casing during its descent.

Figure 3 - in the process of direct circulation through the valve.

Figure 4 - check valve at the time of sealing the column from the reverse movement of fluid from the annulus to the column.

Arrows indicate the direction of fluid movement.

The check valve contains a housing 1 (Fig. 1) with a seat 2 placed therein and a ball valve (ball) 3 (Fig. 3), discharged from the surface. In addition, the valve contains a disk 4 located under the saddle (Fig. 1), in which the central channel 5 and peripheral openings 7 overlapped by the spring washer 6 are made. The ball valve 3 (Fig. 4) is mounted so that it can be pressed against the saddle 2 during reverse fluid movement . The disk 4 is placed with the possibility of axial movement. The upper outlet of the Central channel is equipped with a spring-loaded normally closed check valve 8 (Fig. 1) with a stem 9, which ensures, together with the washer and disk, the formation of a tight jumper. The spring 10 of the check valve 8 with the stem 9 and the washer 6 is common.

The device operates as follows.

The pressure drop that occurs when the casing is lowered raises the check valve 8 (figure 2). Downhole fluid enters the column through the Central channel 5, without creating significant resistance. As a result of this, the dynamic pressure on the borehole walls decreases. Moreover, the higher the descent speed, the wider the central channel opens.

During the descent column stop, the liquid levels in the column and behind the column tend to level out. But as they equalize, the pressure drop in the central channel will decrease and at a certain value, for which the spring 10 is designed, the valve 8 will close, stopping the further rise in the liquid level in the column and thereby preventing liquid overflow through the mouth.

When the drilling fluid or cement is injected into the casing, the fluid stream squeezes the washer 6 (Fig. 3) and passes through the peripheral holes 7. Ball 3 (ball valve), dropped from the surface into the well, reaches the valve and sits on the bowl-shaped surface of the non-return valve, obstructing fluid flow.

After the termination of the injection of fluid into the well, the spring 10 overlaps the peripheral holes 7 with the washer 6, as a result of which the washer with the disk 4 and the check valve 8 forms a tight jumper across the entire cross section of the valve. Therefore, when even a slight reverse movement of fluid from the annulus to the column occurs, the disk 4 rises and presses the ball valve 3 against the seat 2 (Fig. 4), providing reliable sealing of the casing. Moreover, the limited rise of the liquid column in the borehole, which occurs together with the rise of the disk 4, can serve to drive various devices whose operation is based on the use of this movement, for example, step cementing couplings.

Technical and economic efficiency of the device is provided by the following main advantages of it:

- the performance of the sealing unit does not depend on its bulk density (buoyancy), which increases the reliability of the valve and reduces its cost;

- facilitated filling the casing during the descent, thereby reducing the crushing pressure on the walls of the casing;

- reduced hydrodynamic pressure on the walls of the well exerted by the descent casing.

Claims (1)

A check valve for a casing string, comprising a housing with a seat located therein, a disk located under the saddle with a central channel and peripheral openings blocked by a spring washer, and a ball valve discharged from the surface into the well, which can be pressed against the seat during fluid reverse movement, characterized the fact that the disk is placed with the possibility of axial movement, the upper output of the central channel is equipped with a spring-loaded normally closed non-return valve with a stem, providing together with formation of a tight jumper with the disk and the disk, while the spring of the check valve with the stem and washers is common.

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