CA1240261A

CA1240261A - Fluid lift system

Info

Publication number: CA1240261A
Application number: CA000504541A
Authority: CA
Inventors: Linc Stefansson; Barry A. Mildenberer
Original assignee: Individual
Current assignee: Individual
Priority date: 1986-03-19
Filing date: 1986-03-19
Publication date: 1988-08-09

Abstract

ABSTRACT OF THE DISCLOSURE
Fluid is automatically removed from a gas well by providing tubing in the production casing which tubing is continually vented of a small quantity of gas causing liquid level to rise in the tubing. The liquid is trapped in the tubing by for example, a one-way check valve. The reduced gas pressure in the tubing signals a differential pressure switch to open a switching valve, which connects the casing to an actuator. The actuator opens a tubing production valve, whereupon a drift in the tubing pushes the liquid upwardly through the production valve. The drift then returns to a seat above the tubing check valve, so that the cycle can be repeated when the liquid level again rises in the casing.

Description

~4~61 This invention relates to a fluid lift system, primarily to a fluid lift system for removing fluid from gas or oil wells.
In general, a gas producing well includes an outer production casing with perforations therein which permit gas and liquid to enter the casing, and often with production tubing for carrying gas to the surface. Mortally, gas and possibly some of the liquid reach the surface. However, in low velocity wells, some or all of the liquid fails to reach the surface and accumulates in the tubular, or if no tubing, in the casing. Thus, a back pressure against the perforations is created which inhibits production.
The object of the present invention is to provide a solution to the problem described above by providing a relatively simple system for automatically removing unwanted liquids from wells.
Accordingly, the present invention relates to a fluid lift system for removing liquid from a gas well of the type including a production casing and tubing mounted co-axially in said casing, said system comprising above ground production valve means in said tubing; vent valve means in said tubing for venting gas from said tubing;
differential pressure switch means for sensing pressure ; differences between said casing and tubing for causing said vent valve means to open to reduce the pressure in said Jo I

tubing, whereby liquid rises in said tubing thereby further reducing gas pressure in said tubing; end switching valve means for operation by said pressure switch means in response to a predetermined reduced pressure in said tubing means for opening said production valve means, whereby liquid trapped in said tubing is discharged through said production valve means.
The invention will now be described in greater detail with reference to the accompanying drawing, which is a schematic flow diagram of a preferred embodiment of the system of the present invention.
Referring to the drawing, the system of the present invention is intended for use in a conventional gas well production casing 1, which has a closed top end 2 and perforations 3 permitting the flow of gas and liquid into the casing. During normal production gas and liquid enter the casing 1 and are discharged through a line 5 and a ball valve 6 or up-tubing, if the well is equipped with tubing. In a low velocity well, not all of the liquid reaches the surface, which results in an accumulation of the liquid in the well bore. Thus a back pressure is created which inhibits production.
In order to solve the problem of fluid accumulation in the casing 1, tubing 8 co-axial with and extending upwardly out of the casing 1 is used. A check valve 9 is .

I

provided in the bottom of the tubing 1 permitting the flow of fluid into the casing 1, but preventing -the backfill of liquid from the tubing 8 into the casing 1. In some instances, this check valve will be optional. A drift seat 10 in the tubing 8 above the valve 9 limits downward movement of a tubing drift 12, upward movement of which is limited by an above ground ported drift stop 13 which is spring mounted in a lubricator (not shown). A ball valve 14 is provided between the drift seat 12 and the drift stop 13. Flow of fluids in the top end of the tubing 8 is controlled by a production valve 16, which is opened and closed by a gas operated valve actuator 17.
In turn, the actuator 17 is operated by gas pressure from a three-way switching valve 20, which is connected to the top of the casing 1 by a line 21, a valve 22, and a pressure regulator 23 in a line 24. A line 26 extends from the valve 20 to the actuator 17. A line 28 extends from the valve 22 to a differential pressure switch 29. A pressure regulator 30 is provided in -the line 28, however this regulator is not required when a low pressure actuator is employed, in which case line 28 runs from regulator 23. The line 21 is also connected to the switch 29 by a line 32 containing a valve 33. A line 35 connects the switch 29 to the valve 20. The switch 29 is also connected to the tubing 8 above the valve 14 by a line 36, a pressure gauge 38, a I, ~4Q~6~

metering valve 39, a scrubber bottle 40~ a line 41 and a needle valve 43. The tubing is vented through metering valve 45, either to atmosphere or back to the production line. A
regulator, orifice and gauge (not shown) can employed in lieu of valve 45. A volume bottle 46 is provided in the line 36 between the gauge 38 and the metering valve 39. The bottom of the bottle 46 can be drained to atmosphere through a valve 47 to dump accumulated liquids. The bottom f the scrubber bottle 40 is also connected to the tubing 8 by a line 49 and a one-way check valve 50. The scrubber bottle 40 can also be drained to atmosphere via the line 49 and a ball valve 52.
OPERATION
During normal operation of the well, gas and liquid enter the casing 1 through the perforations 3. Gas and some liquid reaches the surface, and is withdrawn through the line 5 and the valve 6 or up-tubing. In low velocity wells, some or all of the liquid fails to reach the surface, and accumulates in the annuls between the casing 1 and the tubing 8. The accumulated liquid exerts a back pressure on the perforations which inhibits or stops production. In order to remove trapped liquid, with the valves 14 and 43 open, the valve 45 is opened to vent a small quantity (generally less than 0.5 MCFD) of gas from the tubing 8. Thus, gas pressure in the tubing is reduced, permitting liquid to rise in the tubing 8 where the liquid it trapped by the check valve 9.

' owe The gas pressure in the tubing 8 is further decreased by the - hydrostatic pressure of the liquid in the -tubing. After the tubing gas pressure has decreased to a predetermined level, which varies depending on well conditions, -the differential switch 29 opens the valve 20 to cause gas flow through the lines I 24 and 26 to the actuator 17. Reduced pressure in the tubing 8 is detected by the switch 29 by virtue of tune connection between the tubing 8 and the switch 29 through the scrubber bottle 40, the valve 39 and the line 36. The actuator 17 opens the valve 16, so that the pressure in the annuls between the casing 1 and the tubing 8, and the formation pressure can drive the tubing drift 12 upwardly from the seat 10. Thus, the liquid is driven through the valve 16 to a tank, pit or production line. The tubing drift 12 is stopped by the drift stop 13.
At this time, the pressures in the casing 1 and tubing 8 are essentially the same. The switch 29 causes the valve 20 to close, and venting of the line 26 to atmosphere which results in closing of the valve 16. The drift 12 drops down onto the tubing seat 10 until the liquid level in the tubing again rises to a predetermined level, triggering a repetition of the process described above.
It will be appreciated that a pressure/time delay is required for equalizing pressures between the scrubber bottle and the volume bottle 46. The delay can be adjusted by -, adjusting the metering valve 39. Such a delay is required to prevent closing of the valve 16 before all the liquid in the tubing 8 is dumped. The time delay ensures that tune switch 29 does not close the valve 20, and consequently the valve 16 until the tubing 8 it properly purged of liquid.
By varying the setting of the differential pressure switch 29, the pressure acting on the switch from the casing 1, and consequently the reduction in gas pressure in the tubing 8 required to operate the switch 29 and to open the valve 20 can be varied. The pressure regulator 23 merely regulates the pressure acting on the actuator 17 through the switching valve 20.
For wells which are subject to erratic liquid production or which are frequently removed from production, lo an electrically operated venting valve 45 can be used in conjunction with a bottom hole liquid sensor (not shown).
Such an arrangement could be used to vent tubing gas at a greater rate in order to prevent liquid over loading. The liquid level sensor is installed in the annuls between the casing 1 and the tubing 8 near the bottom of the tubing on a dual conduit electrical line. The sensor triggers the venting valve 43 to vent gas at a faster rate when liquid reaches a predetermined level, so that liquid is drawn faster into the tubing 8.
In a further embodiment, or variation of the subject ~Q~6~.

invention, reference is made to the drawing and in particular with regard to the system shown in dotted outline.
In cases of extreme muddy or high pressure conditions it is possible to use a pneumatically operated valve H in place of choke 43. A fluid line A is run from the casing to switching valve B, through line C to metering value D, through line E to scrubber bottle 40. A fluid line F
interconnects line 26 with switch valve B, and a fluid line I
interconnects line 26 to actuator valve I.
The system operates as before with the actuator valve in the open position, and switching valve in the closed position. When the system goes into the 'dump" mode, line 26, through line I closes valve H, at the same time, line 26, through line F opens switching valve "B" allowing gas to flow from the casing through metering valve "D" into the scrubber bottle and escape through check valve 50 to tubing 8 and to dump line.
When drift 12 hits top closing port 12, gas pressure from the casing will build up in the scrubber bottle since tubing 8 is now also pressurized up. When the build-up of pressure closes differential switching valve 29 and 3-way switching valve 20, line 26 is vented-off, opening actuator valve H and closing switching valve B. System then goes into next cycle.
As will be appreciated, the system as disclosed ~:402~i~

would be operable in the same manner as a well which is "open-hole" completed rather than cased and perforated or in a well with a conventional "slotted" line.
Thus, there has been described a relatively simple, automatic system for lifting liquid from a gas well. In its simplest form, the system can be left virtually unattended for long periods of time. The frequency of gas venting and liquid removal is dictated only by the quantity of liquid produced in the well, and may be several times per hour or once every several days.

. I,

Claims

THE EMBODIMENTS OF AN INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A fluid lift system for removing liquid from a gas well of the type including a production casing and tubing mounted co-axially in said casing, said system comprising above ground production valve means in said tubing; vent valve means in said tubing for venting gas from said tubing;
differential pressure switch means for sensing pressure differences between said casing and tubing for causing said vent valve means to open to reduce the pressure in said tubing, whereby liquid rises in said tubing to above said check valve means thereby further reducing gas pressure in said tubing; and switching valve means for operation by said pressure switch means in response to a predetermined reduced pressure in said tubing means for opening said production valve means, whereby liquid trapped in said tubing is discharged through said production valve means.

2. A fluid lift system according to claim 1 including check valve means in the bottom of said tubing for trapping liquid in said tubing, and wherein said vent valve means is located between said check valve means and said production valve means.

3. A fluid lift system for removing liquid from a gas well of the type including a production casing and tubing mounted co-axially in said casing, said system comprising check valve means in the bottom of said tubing for trapping liquid in said tubing; above ground production valve means in said tubing; vent valve means in said tubing between said check valve means and said production valve means for venting gas from said tubing; differential pressure switch means for sensing pressure differences between said casing and tubing for causing said vent valve means to open to reduce the pressure in said tubing, whereby liquid rises in said tubing to above said check valve means thereby further reducing gas pressure in said tubing; and switching valve means for operation by said pressure switch means in response to a predetermined reduced pressure in said tubing means for opening said production valve means, whereby liquid trapped in said tubing is discharged through said production valve means.

4. A fluid lift system according to claim 1 or claim 3, including drift seat means in said tubing above said check valve means; ported drift stop means in said tubing between said production valve means and said vent valve means; and tubing drift means for movement between said drift seat means and drift stop means for driving liquid from said tubing when said production valve means is open.

5. A fluid lift system according to claim 1 or claim 3, including volume bottle means in fluid communication with said tubing and with said differential switch means for causing a time delay between the open and closing of said production valve means to ensure that a maximum quantity of the liquid is discharged from said tubing before such closing.