Hydrogas Lift System

Abstract

A power fluid is pumped downwardly through a power fluid tube toward the bottom of a well. The power fluid, due to pressure placed on the power oil fluid by a surface pump, forces the production fluid through a check valve and upwardly through a production fluid tube to the surface of the wall. Compressed gas is used to withdraw the power fluid from the power fluid tube so that the production fluid may again rise to the level of the production fluid tube and the pumping cycle is thereafter repeated. The power oil may also be removed by swabbing, rod pump, rotary pump, or any other form of artificial lift which may be applicable to the well.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to the pumping or lifting of a subsurface liquid by a liquid of a lower density. The lower density liquid is drawn toward the surface again by means of compressed gas. The compressed gas and the liquid are then separated at the surface and recycled in subsequent pumping operations. If another form of artificial lift is used, then the separator and gas compression system may be eliminated.

2. Description of the Prior Art

Prior art oil pumping systems oftentimes depend on natural oil pressure, artificial suction, or the injection of a gas or liquid to drive or draw petroleum to the surface. Typical of such systems is that disclosed in the Rich et al. U.S. Pat. No. 3,653,717 which depicts a system for lifting enriched solvents in solution mining wells by means of a liquid immiscible with, and lighter than, the solvent which is extracted.

There are several drawbacks to the prior art methods of operation. For instance, at great well depths, the efficiency and capacity decrease. Also, prior art systems often require the use of means to cope with high pressures at the surface. This often requires the installation of expensive, low-capacity equipment which renders such systems uneconomical. Moreover, many prior art systems cannot control the large drops in pressure that may occur in an oil well. A further problem with prior art systems is that when gas lift valves are used in cooperation with compressed gas to lift crude petroleum from a well, the crude will frequently emulsify and become a foam. Typically, the foam is of very light density and little crude is brought to the surface in this manner. It is difficult to separate compressed gas from the crude petroleum once the foam reaches the surface. The present invention provides an improved solution to these problems.

SUMMARY OF THE INVENTION

The present invention is designed to overcome the deficiencies of the prior art as described above. Also, a system has been provided that is rugged and simple and contains few moving parts. A principal advantage of the gas-hydraulic system described herein is that maintenance costs are kept to a minimum. The working environment of an oil field demands that all equipment have the capability to withstand rough daily punishment.

With this in mind, a system has been developed using both gas and a power fluid in an artificial lift system. A power fluid is pumped down a power fluid tube into an enclosed chamber at the bottom of the pipe string. The bottom of the chamber includes a check valve permitting the production fluid to enter the chamber when the pressure above the valve is lower than the pressure below the valve. As the power fluid is pumped into the chamber, production fluid is forced upwardly via a dip tube and through a discharge type check valve into a production tube. Compressed gas may be used to withdraw the power fluid or other conventional forms of artifical lift may be employed to evacuate the power oil from the power oil string.

A principal object of this system is to accomplish pumping from very deep wells with a high pumping efficiency.

Another object of this invention is to be able to control the well from the surface, thus eliminating the high cost of a work-over rig if one is necessary.

A further object is to develop a hydraulic pump with a relatively low surface pressure requirement and which is rugged and requires few moving parts.

A still further object of this invention is to increase the rate of production of an oil well while maintaining the pressure at the bottom of the well relatively constant.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, reference is made to the following description of representative embodiments thereof and to the accompanying drawings wherein:

FIG. 1 is a schematic depicting the hydrogas lift system at the end of the power fluid pump cycle when the power fluid in the power oil storage reservoir has reached the level of the low level control. The power fluid in the power fluid tubing is returned back to the power fluid reservoir via a separator by means of compressed gas introduced into the power fluid tubing; and

FIG. 2 shows the hydrogas lift system of FIG. 1 wherein the power fluid is in contact with the high level control on the power fluid reservoir. The pumping cycle is about to begin.

DESCRIPTION OF AN EMBODIMENT

In describing this invention, reference is made to both FIG. 1 and FIG. 2 wherein like elements are similarly numbered. FIG. 1 and FIG. 2 show the hydrogas lift system at different points in the lift. The system includes a production tube 10 and a power fluid tube 12 which fits inside and extends the entire length of a power string casing 14. At the bottom end of the production tube 10 there is a one-way discharge valve 16. The discharge valve 16 allows production fluid 58 to flow upwardly through the valve into the production tube 10 but does not allow production fluid 58 to flow back through the production tube.

A dual packing 18 is provided at the bottom of the power fluid tube 12 in order to contain the compressed gas stored within the power string casing 14 and to support the power fluid tube 12 and the production tube 10. A similar packing is shown at the top of the well as element 20. The packings 18 and 20 are designed to prevent the compressed gas 22 from leaking from the well casing 14.

A one-way standing check valve 24 is shown at a location below discharge valve 16. The packing is provided about the standing valve 24 to form a pressure-tight chamber 26 between the packing 18 and the standing valve 24. A series of gas lift valves 28 are placed at intervals along the power fluid tubing 12. Conventional gas lift valves such as the CM2FS-RC type made by the MACCO Oil Tool Company, Inc. are satisfactory for this type of operation. Gas lift valves are valves which permit a compressed gas to enter a pipe string when the differential pressure between the fluid in the pipe string and the compressed gas reaches a predetermined point. In this particular application, compressed gas may enter the pipe string at the end of the pumping cycle when triplex pump 36 shuts off. The gas lift valves allow the compressed gas 22 inside the casing 14 to flow into the power fluid tubing 12 at the end of the pump cycle thereby returning power fluid 30 to a separator 32 and then to a power fluid reservoir 34.

The power fluid reservoir stores the power fluid 30 and the now decompressed gas 22 is returned to the compressor 46 for recompression. A triplex type pump 36, driven by an electric motor 38, is connected to the bottom discharge line 40 from the power fluid reservoir 34. The pump 36 powers the fluid 30 downwardly through the power fluid tubing 12.

Mounted within the power fluid reservoir 34 is a high level control 48 and a low level control 50. Controls 48 and 50 are sensitive to the fluid level in the power fluid reservoir. They, in turn, control the opening and closing of motor valve 44 and the operation of electric motor 38 which drives triplex pump 36.

A dip tube 52 extends from the bottom of production tube 10 into production fluid 58. Discharge valve 16 is located at the lower end of dip tube 52. Another one-way check valve 54 is mounted on the discharge port 56 of the triplex pump 36. Valve 21 prevents compressed gas 22 and power fluid mixture from returning to the pump 36.

DESCRIPTION OF OPERATION

FIG. 2 shows a hydrogas lift system immediately after to the beginning of the power fluid pump cycle. Prior to this stage, power fluid 30 is entering reservoir 34. When the level of power fluid reaches the high level control 48, motor valve 44 is caused to close and motor 38 is energized and pump 36 is operated. By action of pump 36, the power fluid 30 from reservoir 34 is driven through check valve 54 and downwardly through power fluid tube 12. It is, of course, understood that power fluid 30 is of a lower density than that of production fluid 58. Typically, power fluid 30 is an oil rated about 55 gravity crude. As a result of the pumping action, power fluid 18 will fill the chamber 26 between packing 18 and standing valve 24. As chamber 26 is filled with power fluid 18, production fluid 58 trapped within the chamber is displaced and forced to flow through discharge valve 16 of production tube 1 and towards the surface. At this time, standing valve 24 is closed because the pressure above the valve is higher than the pressure below it. Similarly, discharge valve 16 is caused to open because the pressure below it is higher than the pressure above it.

After a predetermined amount of power fluid 38 is pumped out of reservoir 34, the low level control 50 is tripped. The low level control 50, in turn, de-energizes electric motor 38, pump 36 stops, and the motor valve 44 is opened. This stage of the operation is shown at FIG. 1.

At this point, gas lift valves 28 open and the compressed gas 22 within the casing 14 flows into the power fluid tube 12 causing the power fluid 30 within the tube to rise through motor valve 44 and the by-pass line into separator 32. In operation, the gas lift valves would not all operate simultaneously but rather would be operated in sequence with the valve or valves closest to the surface opening first and with the lower valve sequentially opening as the differential pressure between the power fluid and the compressed gas reaches the predetermined point at which the particular selected gas lift valve will operate. The gas lift valves do not have to be located equidistant from one another along the power fluid string. In fact, it is preferred that the gas lift valves be located closer to one another the deeper those valves are located on the power fluid string. The purpose of placing the gas lift valves closer to each other at deeper depths is to give added boosting power where it is needed. The deeper valves have to provide more power because they must lift not only the increment between themselves and the nearest valve up the string, but they must also lift all of the foam and residue in the power string located between the next uppermost valve and the surface of the well. The compressed gas and power fluid mixture does not flow back into pump 36 because check valve 54 is closed. The compressed gas 22 displaces power fluid 30 and causes its withdrawal from chamber 26. As power fluid 30 is withdrawn from chamber 26 an equal volume of production fluid 58 is drawn through one-way standing check valve 24 to replace the power fluid that has been withdrawn. The pressure within chamber 26 at this time is lower than during the pump cycle and discharge valve 16 is closed due to the higher pressure of the production fluid 58 within tube 10. The compressed gas and power fluid mixture flows into separator 32 where it is segregated. The compressed gas 22 is returned to casing 14 by means of compressor 46, and power fluid 30 is returned to power fluid reservoir 34. As the power fluid 30 is returned to the power fluid reservoir, the level of the power fluid 30 rises. When a sufficient amount of the power fluid 30 is withdrawn from chamber 26, the level of the power fluid in power fluid reservoir 34 will again reach the high level control 48. At this point, the pump cycle as shown in FIG. 2 begins again. Each operation of the pump cycle causes a pre-determined increment of production fluid 58 to flow up production tube 10. Repeated pumping eventually causes this increment to reach ground level.

While gas lift valves have been shown as a preferred means of removing the power oil from the power oil string, it is clear that there are many other ways of performing the same function. For instance, it would be further possible to withdraw the power oil by means of a swab which is drawn up the power oil string at predetermined intervals. Also, a rod pump or a rotary pump or any other form of artificial lift may be used to withdraw the power oil.

Other modifications of the described embodiment may be obvious to one of ordinary skill in the art. For instance, separator 32 which has been shown in FIGS. 1 and 2 to be of the conventional, horizontal variety, may be vertical instead. Also, it is clear that this application is not intended to be limited to the production of petroleum. This method instead may be employed to lift any type of suitable production fluid by means of a lighter power fluid.

In a general manner, while there has been described an effective and efficient embodiment of the invention, it should be well understood that the invention is not limited to such an embodiment, as there might be changes made in the arrangement, disposition, and form of the parts without departing from the principle of the present invention as comprehended within the scope of the accompanying claims.

Claims

I claim:

1. A system for lifting a production fluid comprising,

a well casing,

a power fluid tube and a production tube within said well casing,

said production tube including a first one-way valve for allowing the production fluid to pass only in the upward direction through the production tube,

a second one-way valve located in said well casing below said first one-way valve for allowing said production fluid to pass only in the upward direction,

a compressor for forcing a gas through said well casing,

a reservoir for storing a power fluid,

a pump disposed between said reservoir and said power fluid tube for driving said power fluid from said reservoir through said power fluid tube, said power fluid causing said production fluid to be forced upwardly through said production tube,

first means for displacing said power fluid with said gas after a predetermined amount of power fluid has been pumped from said reservoir, and

wherein said first means includes a gas lift valve means for passing said gas from said well casing to said power fluid tube, said gas forcing said power fluid back through said power fluid tube.

2. A system for lifting a production fluid comprising,

a well casing,

a power fluid tube and a production tube within said well casing,

said production, tube including a first one-way valve for allowing the production fluid to pass only in the upward direction through the production tube,

a second one-way valve located in said well casing below said first one-way valve for allowing said production fluid to pass only in the upward direction,

a compressor for forcing a gas through said well casing,

a reservoir for storing a power fluid,

a pump disposed between said reservoir and said power fluid tube for driving said power fluid from said reservoir through said power fluid tube, said power fluid causing said production fluid to be forced upwardly through said production tube,

first means for displacing said power fluid with said gas from said compressor after a predetermined amount of power fluid has been pumped from said reservoir,

a second means for separating said gas and power fluid,

a bypass line connecting said second means to said power fluid tube,

a control means for selectively operating said pump, said control means being responsive to the level of power fluid in said reservoir,

a bypass valve in said bypass line selectively opened and closed by said control means, and

wherein said control means is responsive to a predetermined high level and a predetermined low level of said power fluid in said reservoir, said control means causing said pump to energize and said bypass valve to close upon said power fluid attaining said predetermined high level and said control means causing said pump to de-energize and said bypass valve to open upon said fluid attaining said predetermined low level.

3. A system for lifting said production fluid of claim 2 wherein said power fluid is introduced into said well casing above said second one-way valve by said pump at a pressure sufficient to close said second one-way valve.