US3054358A

US3054358A - Gas-lifting wells

Info

Publication number: US3054358A
Authority: US
Inventors: John W Merlyn; Robert N Tuttle
Original assignee: Shell Oil Co
Current assignee: Shell USA Inc
Priority date: 1959-07-24
Filing date: 1959-07-24
Publication date: 1962-09-18
Anticipated expiration: 1979-09-18

Description

P 1962 J. w. MERLYN ETAL 3,054,358

GAS-LIFTING WELLS Filed July 24, 1959 5:41:15!!!ivllllilllllllll lnlllvlll INVENTORS:

JOHN W. MERLYN ROBERT N. TUTTLE JMZM THEIR ATTORNEY Patented Sept. 18, 1962 3,054,358 GAS-LIFTING WELLS John W. Marlyn, Elk City, ()kla, and Robert N. Tuttle, River Edge, N.J., assignors to Shell Oil Company, a corporation of Delaware Filed July 24, 1959, Ser. No. 829,355 2 (Ilaims. (Cl. 103232) This invention pertains to gas lift systems for producing oil wells and the like and more particularly to an apparatus and method for controlling the injection of gas into the well in a gas lift system.

Gas lift systems have been used for many years for producing oil wells where the formation pressure has fallen too low to produce the well naturally. In such systems it is customary to inject the gas which has previously been raised to a relatively high pressure into the annular space between the well casing and the production tubing string. The gas is then admitted into the interior of the production tubing string below the level of the oil to raise the oil to the surface.

In the past it has been customary to control the admittance of gas into the annular space by using a clock timer and a diaphragm valve or a choke to control the injection cycle and the amount of gas injected. These systems have several disadvantages such as, spring wound clocks must be attended daily, gas may be injected into the annulus at higher pressures than are desirable for individual wells, the method of gas control must be changed when a different type of gas lift valves are used. In addition, the freezing of supply gas occurs in the choke because of pressure drop across the choke.

In another type of system, fluid controlled valves are used to control the flow of gas into the production tubing and gas is injected on a set time cycle. This system has a disadvantage in that the injection of the gas may commence prior to the closing of the downhole Valve and may continue after the gas pressure has risen to the desired level. Also, the valves used to control the flow of gas into the production tubing tend to remain open because the velocity of the excess gas flowing into the annular space creates higher pressures in the tubing holding the valve open. Thus, an excess amount of gas will be used for producing the well which will increase the gas oil ratio of the petroleum produced.

Accordingly, the principal object of this invention is to provide a novel system for controlling the injection of gas into a well in a gas lift system which both conserves the gas supply and eliminates freezing in the various parts of the system.

A further object of this invention is to provide a control system for controlling the injection of gas into the gas lift well which utilizes a delay means for delaying the injection of the gas for a predetermined time after the pressure in the annular space between the well casing and production string has fallen to a predetermined level.

The above objects and advantages of this invention are achieved by utilizing a pressure control switch which is disposed to control the flow of electrical current to the remainder of the system. The pressure control switch is re sponsive to the gas pressure in the annular space between the casing and the production string. The actual control system consists of a time delay device which is responsive to the closing of a pressure switch to actuate a gas injection valve in the system that controls the actual injection of gas into the annular space. The system thus delays the opening of the gas injection valve for a predetermined time after the pressure in the annular space has fallen to a predetermined level. This insures that the gas lift valve disposed at the bottom of the production tubing has had suflicient time to close and thus conserves gas. No choke or other means for reducing the flow of gas is utilized, the flow being completely controlled by the gas injection valve and thus no parts of the system are subject to freezing due to lower pressures.

The above objects and advantages of this invention will 5 be more easily understood from the following description when taken with reference to the attached drawing showing the gas lift system of this invention applied to an oil well.

In the attached drawing, the well is provided with a casing which projects down to the producing zone 13 of the well. A production tubing 11 is positioned in the central portion of the casing and its lower or open end is isolated from the casing by means of a packer 12. The top of the casing is closed by a suitable well cap 14 and the top end 15 of the production tubing is lead to suitable storage tanks and separating facilities not shown in the attached drawing. Thus, it can be seen that the annular space 16 between the production string 11 and casing 10 is sealed at both its upper and lower ends so as to enclose an annular space into which the supply gas may be injected and retained.

A gas lift valve 20 is disposed near the lower end of the production string 11 and is preferably of the type which operates on a pressure differential. More particularly, it should be of a type which opens to admit the gas from the annular space 16 into the production string when the oil level in the production string 11 rises to a predetermined height above the valve and closes when the gas pressure in the annular space 16 falls to a predetermined level. Many valves are available on the market which will fulfill these requirements. The gas inlet pipe 21 is connected to the top part of the casing 10 and is provided with a flow control valve 22 for controlling the injection of the gas into the annular space 16. The valve 22 is a motor operated valve and may be operated by any suitable means depending upon the remainder of the system. For example, the valve shown in the attached FIGURE is a pneumatic operated valve although electrically-operated valves or the like may also be used.

One lead 39* of a suitable power supply 30 is coupled to the time delay and valve control system through a pressure-operated switch 31 while the other lead 38 is grounded. The power supply 30 may be either an alternating current or a direct current power supply depending upon the availability. The pressure operated switch 31 is responsive to the gas pressure in the annular space 16 and coupled thereto by tubing 32. Thus, the switch 31 is disposed to control the flow of power from the power supply 30 to the remainder of the time delay and valve control system.

The lead 33 from the pressure-operated switch 31 is coupled to pair of

switch arms

34 and 35 which move in unison and have associated

contacts

36 and 37, respectively. The contacts 36 is coupled to a time delay device 55 40 which is shown as being a timer motor although other devices such as time delay relays could also be used.

The time delay device should be designed to return the

switch arms

34 and 35 to a position in which the switch arms 34 closes on contact 36 when the pressure switch 31 60 opens. The contact 37 is coupled to one end of a solenold 41 whose other end is coupled to the ground lead 38. The solenoid 41 is utilized to operate a pilot valve 42 which controls the flow of compressed air to the pneumatic cylinder 43 on the flow control Valve 22.

As shown in the attached figure, the switch arm 34 is closed to 36 and 35 is open when the pressure-operated switch 31 is open. This is the position of the circuit at the end of a gas injection cycle. When the pressure in the annular space 16 of the well falls to a prede- 70 termined level the pressure responsive switch 31 will close thus energizing the time delay means 40. The time delay means will operate and after the predetermined time injection of gas into the annular space 16. The injection of the-gas will continue until the pressure in the annular space 16 rises to a predetermined value to open the pressure responsive switch 31. When the switch opens the circuit will be de-energized and the time delay'device 49 will cease to operate and the

switch arms

34 and 35 will move to their opposite position with the switch arm 34 in contact with the contact 36 and switch arm 35 open.

The system will then remain in this position until the gas pressure in the annular space 16 again falls to the predetermined value when the cycle will again be repeated.

1 From the above description it is easily appreciated that the gas injection cycle is controlled directly by the pressure in the annular space 16 without the use of chokes, diphragm valves or timer means of prior devices. Thus, there is no possibility of the gas freezing as it flows through the choke device due to a large pressure drop. The utilization of the time delay means 48 insures that the gas lift valve 20 will have sufficient time to close priorto the injection of gas thereby preventing high gas oil ratios which occur in other means of controlling gas wherein the valve remains open due to the high velocity of the gas flowing through the valve.

While but one gas lift valve is shown, a plurality could disposed along the production strings at various levels as is well known in the art. Also, other types of flow control valves 22 could also be used as well as different types or time delay means 40. The important features of this invention are the use of pressure in the annular space 16 to control the injection of gas and the time delay means 40 to delay the injection of the gas for a predetermined time after the pressure in the annular space 16 has fallen to the predetermined level. These two features eliminate the difiiculties of prior devices and in addition conserve the gas supply by delaying its injection until the downhole valve has closed.

f, Accordingly this invention should not be limited to the details shown and described but only to its broad spirit and scope.

. We claim as our invention:

said production tube; a motor operated flow control valve disposed in said line to control the flow of gas to the annular space; a pressure responsible switch operably connected to said annular space and disposed to control the flow of electrical energy to a control system, said switch being adjusted to energize said control system when the gas pressure in the annular space falls to a predetermined value and to de-energize the control system when the gas pressure rises to a predetermined value; said flow control valve being opened by an operating signal from said control system; a delay means coupled to said pressure operated switch and said control system, said delay means being actuated by the energizing of the control system to provide said operating signal for said flow control valve a predetermined time after the energization of the control system and said control system in addition providing a closing signal for said flow control valve when de-energized said control valve being closed by said closing signal.

2. A system for controlling the admission of pressurized gas to the annular space between the casing and production tubing of a Well having a gas lift producing system comprising: a well having an outer casing and an inner production tube; a source of pressurized gas connected by a line to the annular space between said casing and said production tube; a motor operated flow control valve disposed in said line having access to the V annular space; a pressure switch operably connected to 1.'A system for controlling the admission of gas to a well in a gas liftsystem for producing an oil well comprising: a well having an outer casing and an inner production tube; a source of pressurized gas connected said annular space and responsive to the pressure in the annular space to close at a first pressure and open at a second pressure being higher than said first pressure a time delay device coupled to said switch; said switch being disposed to couple and uncouple said time delay device toa' source of power; a solenoid valve, said time delay device being coupled to said solenoid valve said solenoid valve being disposed to control the motive power supplied to said motor valve, said time delay means bei-ng disposed to open said solenoid valve a predetermined time after said pressure switch closes and maintain the solenoid valve open until the pressure switch closes.

ReferencesCited in the file of this patent UNITED STATES PATENTS "1,025,727 Wells Q 'May 7, 1912 "1,822,645 Crane Sept. 8, 1931 2,316,494 Tipton -i Apr. 13, 1943 2,326,442 DeVWit Aug. 10, 1943 2,339,487 King Jan. 18, 1944 2,434,027 Whittington Jan. 6, 1948 2,642,812 Robinson June 23, 1953