Gas lift method

Abstract

A method is provided comprising the steps of: providing a production tubing to a production interval in a wellbore; providing a check valve in the production tubing at a lower end of the production tubing, the check valve effective to permit flow into the production tubing but not permit flow from the production tubing through the check valve; allowing liquids from the formation to flow into the production tubing; and after liquids from the formation have entered the production tubing, pressuring the production tubing with gas from below the level of the liquids from the formation and thereby forcing at least a portion of the liquids from the formation to the surface; and discontinuing pressuring the production tubing to allow liquids from the formation to again enter the production tubing.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to a method and apparatus for lifting liquids from a wellbore.

BACKGROUND TO THE INVENTION

[0002] When hydrocarbon formations do not have sufficient pressure to cause produced water and oils to flow to the surface, the liquids can be removed from wellbores by, for example, pumps, or by gas lifts. Pumps can be downhole electric pumps or sucker-rod pumps that lift liquids by a pump rod that extends from the surface. Gas lifts utilize injection of gas into a production tubing to reduce the static head to which hydrocarbons in the formation are exposed, and thereby facilitating flow of those hydrocarbons into the borehole; or they operate at sufficient pressure and rate to cause a piston-like displacement of wellbore fluids above a standing value. Gas lifts involve injecting gas into the wellbore below the liquid hydrocarbon producing formation. The upward flow of gas reduces the density of the wellbore contents and therefore both reduces backpressure on the formation, and lifts produced wellbore liquids to the surface. Pumps can be relatively expensive, and particularly difficult to apply in horizontal wellbores. Gas lifts, depending on the amount of pressure available in the wellbore, and the availability of higher pressure gas, and other design limitations, can be a preferred method to lift hydrocarbons from wellbores.

[0003] U.S. Pat. Nos. 5,522,418, and 5,743,717 for example, discloses a valve for control of a gas lift operation. This valve is operated by gas pressure which can be applied and controlled through a conduit from the surface by applying a differential pressure between the gas supply and the wellbore. The method patent '418 applies a back pressure to the formation because of the pressure required to force the flow of gas and liquids up the wellbore.

[0004] It would be preferable to have an apparatus and method wherein the pressure on the formation was maintained at a minimal level but a simple gas lift method could be utilized, and wherein only commercially available equipment is required. It is therefore an object of the present invention to provide such an apparatus and method.

SUMMARY OF THE INVENTION

[0005] This object is accomplished by a method comprising the steps of: providing a production tubing to a production interval in a wellbore; providing a check valve in the production tubing at a lower end of the production tubing, the check valve effective to permit flow into the production tubing but not permit flow from the production tubing through the check valve; allowing liquids from the formation to flow into the production tubing; and after liquids from the formation have entered the production tubing; injecting gas into the production tubing at a point below the level of the liquids from the formation and thereby forcing at least a portion of the liquids from the formation to the surface; and discontinuing injection of the gas to allow liquids from the formation to again enter the production tubing. The gas is preferably injected from a coiled tubing ran within the production tubing to the vicinity of the check valve. The method and apparatus of the present invention is preferably applied to a horizontal wellbore wherein the production tubing can extend along the horizontal section of the wellbore and fill with a considerable volume of liquids without adding significant back pressure to the formation. The gas may be injected either based on a detected liquid level, or based on a time interval.

BRIEF DESCRIPTION OF THE FIGURES

[0006] The FIGURE is a cross section view of a horizontal well equipped to utilized the method of the present invention.

DESCRIPTION OF A PREFERRED EMBODIMENT

[0007] Referring now to the FIGURE, a cross sectional view of a wellbore equipped to practice the present invention is shown. A check valve 101 is shown as a ball type valve, with a ball 106 that seats on a circular hole 107 when pressured from the inside of a production tubing 102, but is contained by, for example, a screen 108, when pressured from outside of the production tubing, thereby permitting flow to pass through the check valve and into the production tubing when the production tubing has less pressure in it than in the wellbore surrounding the production tubing. A ball type valve is show, but many types of check valves are known and useful in the practice of the present invention. A casing 103 is shown cemented into a borehole with cement 105 to secure the casing. Wellbores are typically cemented by flowing cement through the inside of the casing followed by a plug 121 to separate the cement from a fluid used to move the plug and cement. The plug is typically caught at the bottom of the casing and remains in the completed well. The casing and cement are perforated with perforations 104 to provide communication between the inside of the casing and a hydrocarbon bearing formation 109. The hydrocarbon bearing formation is below an overburden 110 through which the wellbore passes. A simplified well head 111 is shown at the surface 112. A gas tubing 113 extends from the surface, through a packer 114 into the production tubing to near the check valve. The production tubing is shown with a tee 116 to provide for the packer and an outlet 115 for produced oil and carrier gas. A gas control valve 117 is accessible at the surface outside of the production tubing. The control valve will intermittently pressure the inside of the production tubing with gas to pressure out hydrocarbon liquids that flow from the formation into the casing and into the production tubing. Timing of the control valve movement may be determined by, for example, trial and error to maximize average liquid production. Alternatively, a liquid level sensor 118 may be placed in the production tubing and the carrier gas provided starting when a liquid level is detected. The liquid level may be detected by sonic or pressure pulse measurements from the surface, or by measuring the pressure difference between a dip tube inserted into the liquid from the surface and the production tube.

[0008] The conduit through which the hydrocarbon liquids are pressured to the surface is referred to herein as a production tube, but any conduit or volume which can be separated from a volume that is directly in communication with the formation may be used. As used herein, production tubing includes the broader range of possibilities. For example, if the horizontal well is cased through a low point, and then sloped upward through a horizontal open hole completion, a check valve could be placed at the end of the casing, and the casing used as the conduit to the surface through which the hydrocarbon liquids are forced by the injected gas.

[0009] The duration of the carrier gas could optionally be set by a sensor that detects when the fluids exiting the well head contain either no liquids or reach a certain level of liquids that is indicative of the majority of the liquids in the production tubing having been removed.

[0010] After the carrier gas has been discontinued, it is preferable to block the production flow line at the surface with valve 119 and, and to vent the production tubing through vent 120 to minimize pressure in the production tubing for filling the production tubing with liquids from the casing.

[0011] A packer may optionally be present between the casing and the production tubing above the perforated section of the casing, and the completion may also be an open hole completion rather than the cased completion shown in the FIGURE.

[0012] The gas used to pressure the liquids from the production tubing may be natural gas, or gas from a higher pressure formation. The gas may contain carbon dioxide, nitrogen, methane, ethane or higher aliphatics, or combinations of these with other components. Components such as hydrogen sulfide may also be present. The gas could be recompressed and reused after separation from the hydrocarbon liquids.

[0013] A horizontal wellbore is particularly suited for the practice of the present invention because a minimal liquid head on the formation could be maintained with the present invention.

Claims

1. A method comprising the steps of:

providing a production tubing to a production interval in a wellbore;

providing a check valve in the production tubing at a lower end of the production tubing, the check valve effective to permit flow into the production tubing but not permit flow from the production tubing through the check valve;

allowing liquids from the formation to flow into the production tubing; and after liquids from the formation have entered the production tubing;

injecting gas into the production tubing at a point below the level of the liquids from the formation and thereby forcing at least a portion of the liquids from the formation to the surface; and

discontinuing injection of the gas to allow liquids from the formation to again enter the production tubing.

2. The method of

claim 1 further comprising the step of injecting gas through a gas tubing that extends from the surface inside of the production tubing.

3. The method of

claim 2 wherein the gas tubing is a coiled tubing.

4. The method of

claim 2 wherein the gas tubing extends to near the check valve in the production tubing.

5. The method of

claim 4 wherein the check valve is attached to an end of the production tubing.

6. The method of

claim 4 wherein the check valve is attached to the end of the coiled tubing.

7. The method of

claim 5 wherein the check valve is seated into a nipple at or near the bottom of the production tubing.

8. The method of

claim 6 wherein the check valve is seated into a nipple at or near the bottom of the coiled tubing.

9. The method of

claim 1 further comprising the step of blocking the production tubing at the surface, and then reducing the pressure within the production line to allow liquids from the formation to enter the production tubing.

10. An apparatus for production of liquid hydrocarbons from a wellbore to a gathering system at an accessible surface, the apparatus comprising:

a production tubing extending from the surface into the wellbore;

a check valve connected to an end of the production tubing inside of the wellbore, the check valve effective to permit flow from the wellbore outside of the production tubing into the production tubing but not allowing flow out of the production tubing into the wellbore;

a gas tubing extending from the surface to near the check valve, inside of the production tubing; and

a control system to intermittently inject gas into the production tubing from the gas tubing and thereby lift liquids from inside of the production tubing to the surface.

11. The apparatus of

claim 10 further comprising a vent effective to reduce pressure within the production tubing when the gas is not being injected.