Chemical Injector for Wells

Abstract

A fluid injection sub for a well creates eduction to draw well fluid into a mixing chamber and discharge the well fluid mixed with an injection fluid pumped down a string of tubing to the sub. The injection sub has a well fluid intake passage leading from an exterior of the housing to the mixing chamber. The injection sub also has a mixed fluid discharge passage extending from the mixing chamber to the exterior of the housing for discharging the mixed fluid exterior of the housing. A nozzle at the lower end of the mixing chamber discharges the injection fluid into the mixing chamber.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to provisional application 61/387,876 filed Sep. 29, 2010.

FIELD OF THE DISCLOSURE

This disclosure relates in general to an injector to inject chemicals into a well and in particular to facilitate the removal of water from gas wells by injecting a foaming agent.

BACKGROUND OF THE DISCLOSURE

Many gas wells are drilled in gas bearing shale formations. Often the gas well has an upper vertical portion leading to a horizontal portion. In one technique for completing these wells, the operator perforates the shale formation through the casing and employs hydraulic fracturing to create cracks and fissures in the shale formations. During hydraulic fracturing, a fracturing fluid is pumped down the casing at high pressure. After the fracturing process has been completed, the well will be loaded with fracturing fluid that must be removed. The formation pressure of the gas may be inadequate to blow the fracturing fluid from the well. Swabbing can be employed to remove the fracturing fluid from the vertical portion of the well, enabling the gas to begin producing.

Also, after the well begins producing, often liquids, both water and hydrocarbons, will be produced along with the gas. These liquids tend to accumulate in the well, impeding the flow of gas. Various techniques are employed to remove the liquids, including installing a submersible pump.

Hydrocarbon producing wells also have many other problems that develop overtime. Salt can accumulate which builds up in the production tubing and impedes well fluid flow. Paraffin can build up within the production tubing. Corrosion and scale occur in some wells. Operators have deployed chemicals for these various problems by pumping or gravity feeding the chemicals into the well. One type of chemical is a foaming agent that creates foam when mixed with the well fluid.

SUMMARY

A fluid injection apparatus for a well has a housing with a tubing mounting mechanism for securing the housing to a string of tubing to lower the housing into a well. A tubing intake in the housing is in fluid communication with an interior of the tubing. A mixing chamber is located in the housing. An injection fluid inlet passage extends from the tubing intake to a lower end of the mixing chamber for discharging an injection fluid pumped down the tubing into the mixing chamber. A well fluid intake passage leads from an exterior of the housing to the mixing chamber. The well fluid intake passage has an entrance selected to be below a liquid level in the well, so that well fluid is induced to flow into the mixing chamber where it mixes with the injection fluid being pumped down the tubing, creating a mixed fluid. A mixed fluid passage extends from the mixing chamber to the exterior of the housing for discharging the mixed fluid exterior of the housing.

A nozzle may be at an end of the injection fluid inlet passage opposite the tubing intake and joining the mixing chamber. The nozzle has a flow area smaller than a flow area of the mixing chamber.

A check valve may be located in the injection fluid inlet passage between the tubing intake and the mixing chamber. The check valve is biased to a closed position that prevents flow from the tubing intake to the mixing chamber unless a selected pressure of the injection fluid is reached.

The entrance of the well fluid intake passage is at an elevation below the mixing chamber. The mixed fluid passage has an outlet at an elevation above the mixing chamber.

A seal carried within an upper portion of the housing seals around the tubing. Gripping members carried by the housing grip an outer diameter of the tubing.

The injection fluid intake passage may include a plenum located below and in fluid communication with the mixing chamber. An upper injection fluid intake passage portion joins the tubing intake and extends within the housing alongside the mixing chamber to the plenum.

The tubing intake may include an intake chamber for receiving fluid discharged by the tubing. The tubing intake may also include a throat passage of smaller diameter than the intake chamber and extending downward from the intake chamber. In addition, optionally, a diverging passage extends downward from the throat passage and is in fluid communication with the injection fluid passage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view illustrating a well having an injection system in accordance with this disclosure.

FIG. 2 is a cross-sectional view of the injector sub of the system of FIG. 1.

FIG. 3 is a cross-sectional view of the injector sub of FIG. 2, showing a chemical being injected into the injector sub and well fluid being drawn into the sub.

DETAILED DESCRIPTION OF THE DISCLOSURE

Referring to FIG. 1, an injection system 11 is employed in this example to facilitate the production of gas in a well. The well includes a casing 13 that optionally may have a vertical portion 13a and an inclined or horizontal portion 13b. Horizontal portion 13b has perforations 15 into which well fluid 17 flows. Well fluid 17 includes gas 19 as well as liquid 21; principally water, but possibly condensate or liquid hydrocarbons. Depending upon the formation pressure of the well, liquid 21 will flow partially up the vertical portion 13a of casing 13, reaching a level 22. Gas 19 will flow from perforations 15 into horizontal portion 13b and up casing vertical portion 13a to the surface. The liquid 21 flowing through perforations 15 begins to build up within casing horizontal portion 13b. Gas 19 may still continue to flow as it will bubble through liquid 21 and up casing 13. However, the buildup of liquid 21 impedes the amount of gas that can be produced. A significant level of liquid 21 in casing vertical portion 13a could stop the flow of gas from perforations 15.

Casing 13 is supported at the surface by a casing hanger 23 and seal. Hanger and seal 23 engage a wellhead member 25 located at the surface. Wellhead member 25 serves as a production tree and has a lateral flow port with a wing valve 27 for flowing gas to production facilities.

A chemical injector 29 is suspended in casing vertical portion 13a. Injector 29 is a tubular sub that preferably has a lower portion submerged within liquid 21 and an upper portion above level 22. Injector 29 may have a weight bar 30 connected to its lower end to provide additional weight for lowering it into casing 13. In this example, injector 29 is much smaller in diameter than the inner diameter of casing 13. For example, it may be only about 1.8 inches in outer diameter while the inner diameter of casing 13 would typically be greater than five inches. There is no packer or seal utilized in this example for sealing the annular space between injector 29 and casing 13.

The weight of injector 29 is supported by a small capillary tube 31 that extends upward to wellhead 25. Tube 31 is employed to lower injector 29 into casing 13 as well as pump a chemical down. Tube 31 is preferably a metal tube, such as stainless steel, of dimensions that may be in a range from 0.25 to 0.375 inches in outer diameter. A tubing hanger 33, shown schematically, supports tube 31 and injector 29. Tubing hanger 33 mounts to or within wellhead member 25 and may be of a type for supporting a string of tubing in the well. In this example, production tubing is not employed; rather gas 19 flows up casing 13. Alternately, production tubing could be installed, in which case injector 29 would be lowered through the production tubing to a point within casing 13 below the production tubing. Gas 19 would flow up the production tubing in that instance.

Tube 31 extends through tubing hanger 33 and over to a pump 35, which may be a conventional type, such as a positive displacement pump. Pump 35 has its intake within a reservoir or accumulator 37 that contains an injection fluid chemical 36, which in this example comprises a liquid foaming agent. The foaming agent may be a conventional type utilized to provide foam within wells, such as a surfactant. A controller 39 controls the operation of pump 35. Pump 35 has the capability of applying a significant amount of pressure, such as 5000 psi greater than the pressure of the well where injector 29 is located.

Referring to FIG. 2, injector 29 includes a housing 41, which may be formed of several components secured together. Housing 41 has a head member 43 with a vertical tube passage 45 extending through it. Tube 31 extends through tube passage 45 and is sealed by a tube seal 47. A seal nut 49, when tightened, energizes tube seal 47 to seal around tube 31. A set of tube slips 51 is mounted below tube seal 47. Tube slips 51 comprise gripping members with teeth on the inner sides that grip tube 31 to support the weight of injector 29. A slips nut 53 when tightened causes tube slips 51 to tightly grip the outer diameter of tube 31.

An intermediate housing member 55 is secured by threads to head member 43. Intermediate housing member 55 has a tube intake chamber 57 in fluid communication with the interior of tube 31 for receiving injection fluid. A smaller diameter or throat portion 59 joins a lower end of tube intake chamber 55. A valve seat 60 joins the throat portion 59. Valve seat 60 is conical and diverges outward in this example. Pump down tube 31 passes into tube intake chamber 57 and terminates above throat portion 59. A check valve 61 mounts below throat portion 59 for engaging valve seat 60. Check valve 61 is upwardly spring biased to a closed position and can be set to open at a selected pressure from tube 31. When the pressure of the fluid flowing down tube 31 is below the selected pressure, check valve 61 will be closed.

A lower housing member 63 secures by threads to intermediate housing member 55. Lower housing member 63 has a cylindrical cavity 64 with a closed base or bottom 66. A cylindrical mixing member 65 is located within cavity 64. Lower housing member 63 has one or more well fluid intake ports 67 (two shown) that are preferably angled upward and inward. Well fluid intake ports 67 are intended to be below liquid level 22. Lower housing member 63 also has one or more mixed fluid outlet ports 69 (two shown). Mixed fluid outlet ports 69 may angle upward and outward and are preferably located above liquid level 22.

Mixing member 65 has at least one injection fluid passage 71 (two shown) extending from its upper end to its lower end. Injection fluid passages 71 are parallel to the axis of injector 29 and spaced circumferentially apart from each other around the axis of injector 29. The upper ends of injection fluid passages 71 are open when check valve 61 is open and closed when check valve 61 is closed. The lower ends of injection fluid passages 71 lead to a plenum 73 located between lower housing bottom 66 and the bottom of mixing member 65.

A nozzle 75 mounts to the bottom of mixing member 65 and points upward. Nozzle 75 is shown as a two-piece member secured by a retainer ring 76. Other configurations for nozzle 75 are feasible. Nozzle 75 has a passage 77 extending through it that is in communication with plenum 73.

Mixing member 65 has at least one and preferably more than one well fluid intake passages 79. Well fluid intake passages 79 register with a gallery 80, which is an annular groove surrounding mixing member 65. Gallery 80 is in communication with well fluid intake ports 67 in lower housing 63. Well fluid intake passages 79 extend inward and upward. Mixing member 65 also has at least one mixed fluid discharge passage 81, and two are shown. Mixed fluid discharge passages 81 also extend to a gallery surrounding mixing member 65 so that they will register with mixed fluid outlet ports 69. The inclination of mixed fluid outlet ports 69 and mixed fluid discharge passages 81 are the same in this example. Mixed fluid discharge passages 81 extend upward and outward from an upper portion of a central throat or mixing chamber 83 within mixing member 65. Mixing chamber 83 is simply a cylindrical passage without any elements within in it. The inclinations of well fluid intake passages 79 are also the same as inclinations of well fluid intake ports 67 in this example. Well fluid intake passages 79 extend to a lower portion of mixing chamber 83 below injection fluid discharge passages 81. The outlet of nozzle 75 is located within a lower portion of mixing chamber 83, thus is in communication with fluid flowing into well fluid intake passages 79. Annular seals 85 extend around mixing member 65 and are positioned to seal to the inner diameter of lower housing member 63 above and below each gallery 80.

The cumulative flow area of the well fluid intake passages 79 is preferably greater than the flow area of mixing chamber 83. Also, preferably the cumulative flow area of the mixed fluid discharge passages is greater than the flow area of mixing chamber 83. The flow area of nozzle 75 is less than the flow area of mixing chamber 83.

In operation, the operator will lower injector 29 on tube 31 and secure tube 31 with tubing hanger 33. If wellhead pressure exists, the operator may need to employ a lubricator and other pressure control equipment. The operator will position injector 29 with its outlet ports 69 above liquid level 22 and intake ports 67 below liquid level 22.

Controller 39 will be set to periodically turn on pump 35 to inject a chemical 36, which in this example, comprises a foaming agent. The intermittent initiation of pump 35 and the shutting off of pump 35 may be based on a timer or on a sensing mechanism to sense the level 22 of liquid. Once pump 35 is turned on, it will pump liquid foaming agent 36 down tube 31. When the pressure from pump 31 reaches a preset amount, such as 1500 psi, it will cause check valve 61 (FIG. 2) to open. The preset amount is selected to be above the well pressure at well fluid inlet ports 67 of injector 29. Then, as illustrated in FIG. 3, liquid foaming agent will pass down injection fluid passages 71 into plenum 73 and up nozzle 75. Preferably controller 39 (FIG. 1) will continue to cause pump 35 to operate until the pressure at the lower end of tube 31 increases significantly above the well pressure at injector 29, such as to 6500 psi.

The high pressure foaming agent being injected out of nozzle 75 flows through mixing chamber 83 and out outlet passages 81 and outlet ports 69. The discharge of nozzle 75 causes a dynamic pressure drop. This flow operates on a venturi principle, inducing the flow of well fluid 17 into mixing chamber 83 through inlet ports 67 and intake passages 79. The well fluid 17 and foaming agent 36 mix within mixing chamber 83 and discharge out mixed fluid outlet ports 69 above liquid level 22. The mixing of foaming agent 36 with well fluid 17 creates a foaming action as illustrated in FIG. 3. The foam facilitates the production of gas by lowering liquid level 22 and reducing the hydrostatic head in casing 13 by lightening the column of fluid in casing 13. Some of the gas 19 will flow up casing 13 without entering injector 29, and some gas will flow into injector 29 along with liquid 21. Foaming agent 36 mixed with liquid 21 and propelled by the upward flow of gas 19 flows up casing 13 to wellhead 25. At the surface, separation equipment, not shown, removes foaming agent 36 and liquid 21 from gas 19, which is then further processed. Because liquid 21 becomes a foam that flows up casing 13, the process removes liquid from casing 13.

Controller 39 may be preset to turn off the pump 35 and the injection of foaming agent 36 for a selected time. During this off duty time, liquid level 22 will gradually build back up. Controller 39 will then turn on pump 35 for another cycle.

Injector 29 could also be utilized in wells to inject chemicals other than foaming agents. Injector 29 could be employed in wells that produce oil rather than significant amounts of gas. The various chemicals could be employed not only to remove fluid from the well, but also treat salt accumulations, paraffin build-up and corrosion and scale.

While the disclosure has been shown in only one of its forms, it should be apparent to those skilled in the art that it is not so limited but is susceptible to various changes without departing from the scope of the disclosure.

Claims

1. A fluid injection apparatus for a well, comprising:

a housing;

a tubing mounting mechanism associated with the housing for securing the housing to a string of tubing to lower the housing into a well;

a tubing intake in the housing in fluid communication with an interior of the tubing;

a mixing chamber located in the housing;

an injection fluid inlet passage extending from the tubing intake to a lower end of the mixing chamber for discharging an injection fluid pumped down the tubing into the mixing chamber;

a well fluid intake passage leading from an exterior of the housing to the mixing chamber, the well fluid intake passage having an entrance selected to be below a liquid level in the well, so that well fluid is induced to flow into the mixing chamber where it mixes with the injection fluid being pumped down the tubing, creating a mixed fluid; and

a mixed fluid passage extending from the mixing chamber to the exterior of the housing for discharging the mixed fluid exterior of the housing.

2. The apparatus according to claim 1, further comprising:

a nozzle at an end of the injection fluid inlet passage opposite the tubing intake and joining the mixing chamber, the nozzle having a flow area smaller than a flow area of the mixing chamber.

3. The apparatus according to claim 1, further comprising:

a check valve in the injection fluid inlet passage between the tubing intake and the mixing chamber, the check valve being biased to a closed position that prevents flow from the tubing intake to the mixing chamber unless a selected pressure of the injection fluid is reached.

4. The apparatus according to claim 1, wherein the entrance of the well fluid intake passage is at an elevation below the mixing chamber.

5. The apparatus according to claim 1, wherein the mixed fluid passage has an outlet at an elevation above the mixing chamber.

6. The apparatus according to claim 1, wherein the tubing mounting mechanism comprises:

a seal carried within an upper portion of the housing for sealing around the tubing; and

a plurality of gripping members carried by the housing to grip an outer diameter of the tubing.

7. The apparatus according to claim 1, wherein the injection fluid intake passage comprises:

a plenum located below and in fluid communication with the mixing chamber; and

an upper injection fluid intake passage portion joining the tubing intake and extending within the housing alongside the mixing chamber to the plenum.

8. The apparatus according to claim 1, wherein the tubing intake comprises:

an intake chamber for receiving fluid discharged by the tubing;

a throat passage of smaller diameter than the intake chamber and extending downward from the intake chamber;

a diverging passage extending downward from the throat passage; and

wherein an upper end of the injection fluid passage is in fluid communication with the diverging passage.

9. A fluid injection apparatus for a well, comprising:

a string of tubing adapted to be suspended in a well;

a housing having an upper portion and a lower portion;

a tubing mounting mechanism associated with the upper portion of the housing for securing the housing to the string of tubing;

a tubing intake in the upper portion of the housing in fluid communication with an interior of the tubing;

a mixing member having a cylindrical exterior and located within a cylindrical interior of the lower portion of the housing;

a mixing chamber located in the mixing member;

an injection fluid inlet passage extending from the tubing intake through the mixing member alongside the mixing chamber to a lower end of the mixing chamber for discharging an injection fluid pumped down the tubing into the mixing chamber;

at least one well fluid intake passage leading through the lower portion of the housing and through the mixing member to the mixing chamber, the well fluid intake passage having an entrance below the mixing chamber and selected to be below a liquid level in the well, so that well fluid is induced to flow into the mixing chamber where it mixes with the injection fluid being pumped down the tubing, creating a mixed fluid; and

at least one mixed fluid passage extending upward and outward from the mixing chamber through the mixing member and through the lower portion of the housing for discharging the mixed fluid exterior of the housing and above the entrance of the well fluid passage.

10. The apparatus according to claim 9, wherein an outer diameter of the tubing is in a range from 0.25 to 0.375 inches.

11. The apparatus according to claim 9, further comprising:

a nozzle at an end of the injection fluid inlet passage opposite the tubing intake and joining the mixing chamber, the nozzle having a flow area smaller than a flow area of the mixing chamber.

12. The apparatus according to claim 9, further comprising:

a check valve in the injection fluid inlet passage between the tubing intake and the mixing chamber, the check valve being biased to a closed position that prevents flow from the tubing intake to the mixing chamber unless a selected pressure of the injection fluid is reached.

13. The apparatus according to claim 9, wherein the tubing mounting mechanism comprises:

a seal carried within the upper portion of the housing that seals around the tubing; and

a plurality of gripping members carried by the housing that grip an outer diameter of the tubing.

14. The apparatus according to claim 9, wherein the injection fluid inlet passage comprises:

a plenum located between a base of the lower portion of the housing and a bottom of the mixing member in fluid communication with the mixing chamber; and

an upper injection fluid inlet passage portion joining the tubing intake and extending within the housing alongside the mixing chamber to the plenum.

15. The apparatus according to claim 9, wherein the tubing intake comprises:

an intake chamber for receiving fluid discharged by the tubing;

a throat passage of smaller diameter than the intake chamber and extending downward from the intake chamber;

a diverging passage extending downward from the throat passage; and

wherein an upper end of the injection fluid inlet passage is in fluid communication with the diverging passage.

16. The apparatus according to claim 9, wherein:

said at least one well fluid intake passage comprises a plurality of the well fluid intake passages; and

said at least one mixed fluid discharge passages comprises a plurality of the mixed fluid discharge passages.

17. The apparatus according to claim 16, wherein:

a total flow area of the well fluid intake passages exceeds a flow area of the mixing chamber; and

a total flow area of the mixed fluid discharge passages exceeds the flow area of the mixing chamber.

18. A method of removing liquid from a gas producing well, comprising:

providing an injection sub having a mixing chamber, an injection passage leading to a lower end of the mixing chamber, a well fluid intake passage leading from an exterior of the sub to the mixing chamber and a mixed fluid discharge passage leading from the mixing chamber to an exterior of the sub;

connecting the injection sub to a string of tubing and lowering the sub into the well to a point wherein an entrance of the well fluid intake passage is below a liquid level in the well;

pumping a foaming agent down the tubing and through the injection fluid intake passage into and through the mixing chamber and out the mixed fluid discharge passage into the well;

in response to the flow of foaming agent into the mixing chamber, inducing well fluid to flow into the well fluid intake passage and mix with the foaming agent in the mixing chamber as the foaming agent flows out the mixed fluid discharge passage; and

wherein the mixing of the foaming agent with the well fluid creates a foam that migrates up the well in an annulus surrounding the tubing.

19. The method according to claim 18, wherein the well fluid is induced to flow into the well fluid intake passage by creating a lower dynamic pressure within the mixing chamber than a hydrostatic pressure of the well bore fluid at an entrance of the well fluid intake passage.

20. The method according to claim 18, wherein the sub is lowered to a level that positions an outlet of the mixed fluid discharge passage above the liquid level.