CA1287566C

CA1287566C - Injection mandrel

Info

Publication number: CA1287566C
Application number: CA000559598A
Authority: CA
Inventors: John R. Gordon; Dale V. Johnson
Original assignee: Exxon Production Research Co
Current assignee: ExxonMobil Upstream Research Co
Priority date: 1987-04-03
Filing date: 1988-02-23
Publication date: 1991-08-13
Anticipated expiration: 2008-08-13
Also published as: NO881338D0; GB2202880A; GB2202880B; NO881338L; GB8807792D0; MY103068A; USH635H

Abstract

ABSTRACT

An injection mandrel and method for introducing treating fluids into a well comprise a center pocket mandrel having a check valve in fluid communication with treating fluid in the annulus of the well and with a chemical injection valve in the mandrel. Treating fluid is pumped through the check valve and the chemical injection valve into the produced fluids in the mandrel, while reverse flow is prevented. In anther embodiment a dip tube communicating with the injection valve pocket places treating fluid at a preselected location in the well.

Description

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- INJECTION MANDREL

BACKGROUND OF THE INVENTION

The invention relates generally to subsurface well treating apparatus and operations. In particular, the invention relates to an injectlon mandrel and method for circulating well treating fluids into subsurface wells to treat produced fluids from subsurface earth formations.
In order to complete oil and gas wells, subsurface earth formations are perforated to bring the wells into production. The fluids produced may subject the subsurface and surface equipment to corrosion from a variety of chemical agents present in the fluids~ To combat this corrosion, a number of `~ 15 well-known corrosion inhibitors may be circulated through the wellbore to reduce or prevent the undesirable effects of the corrosive agents.
Produced fluids also may contain salts and other dissolved and undissolved solids which can precipitate and deposit on the surface of the production tubing or in the perforations in the subsurface earth formation. As deposits build, production flow becomes restricted. To combat this :: .
problem, one or more of a number of well-known solvents may be circulated~through the well to dissolve any flow restricting deposits and to prevent deposits from recurring. `

Apparatus and methods are known to circulate such :`
treatiDg fluids through wells at various depths in the wells.

Side-pocket mandrels may be utilized for this purpose. A

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12~ 5~i treating fluid is injected into the annulus of a well above a packer assembly, through ports in the side-pocket of the mandrel, through a chemical injection valve set in the side-pocket, and into contact with the produced fluids flowing out of the well. Once the fluids have been treated, they flow through the mandrel and production tubing to the surface for recovery.
Side-pocket mandrels suffer from several shortcomings when used for the above purpose. First, side-pocket mandrels require complicated kickover tools to set and retrieve chemical injection valves in their side valve pocket. Current kickover tools require involved wireline operations which are typically not practical at depths below about 15,000 feet. Second, the construction of a side-pocket mandrel does not permit `~ 15 circulation of the treating fluid below the packer assembly because the mandrel does not extend below the packer. Third, side-pocket mandrels allow untreated, often corrosive, produced fluids into the upper annulus of the well above the packer assembly when the chemical injection valve is not in place. In the annulus, such produced fluids could damage the tubing, casing and other equipment, such as a subsurface safety valve.
Other designs have also been proposed, but these designs suffer from the same or other shortcomings. The other shortcomings include limitations on the ability to circulate treating fluids at any desired depth in a well, limitations on conduc.lng periorating, logging or other oper6tion6 without '` : ' : .

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~ 2~7~6~i having to pull the mandrel from the well, and limitaticns on flow through the mandrel, which may cause pressure losses and erosion problems.
Ideally, an apparatus for treating produced fluids in a wellbore will have the following characteristics. The annulus, the space between the production tubing and the casing, above the packer should be effectively isolated from produced fluids.
The apparatus should be capable of circulating treating fluids across the perforations or at any other preselected depth. The apparatus should be capable of being routinely set and operated at total depths in excess of 15,000 ft. There should be a capability for conducting workover operations through the apparatus. Restrictions to flow should be minimized.

SUMMARY OF THE INVENTION

The present invention is a mandrel and method for ` circulating a treating fluid in a well. Preferably, the mandrel is a center-pocket mandrel.
The injection mandrel preferably comprises a body having a longitudinal flow conduit therethrough, a valve pocket in the body substantially axially aligned with the bore of the well and the production tubing and adapted to receive a removable chemical injection valve, a check valve mounted on the body, and a conduit for permitting fluid communication between the check valve and ~he chemical injection valve. The body is adapted to be attached to a production tubing string. It may be put in the well through and engaging a packer assembly.

, ~ ~37~66 With a chemical injection valve set in the valve pocket, treating fluid is injected into the annulus of the well above the packer assembly. This treating fluid flows from the annulus, through the check valve into the va]ve pocket, through the chemical injection valve and into contact with the formation fluid from the lower interval of the well. The treated formation fluid flows upwardly through the mandrel and the tubing string to the surface for recovery. The check valve - prevents formation fluids from entering the annulus.
The chemical injection valve may be removed using standard wireline tools and workover operations can be conducted through the valve pocket, since it is substantially aligned with the well tubing bore.
In order to inject treating fluids at any preselected depth below the mandrel~ a dip tube may be connected to the lower end of the injection valve housing. Treating fluids from the annulus may then be pumped through the dip tube to the desired depth for injection into the formation fluids.
The present invention allows chemical injection valves to be routinely set and retrieved at depths much greater than 15,000 feet and precludes entry of the untreated producing fluids into the upper annulus above the packer assembly.
Treating fluids may be circulated in the well at any desired depth, and allows a variety of workover and loggin& tools to be run through the apparatus when the chemical injection valve is removed, so that other downhole operations may be conducted without removing the tubing from the well.

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Embodiments of the inventlon will now be described with reference to the accompanying drawings, wherein:
Figs. 1, lA and lB are schematic elevational views of a first embodiment of an injection mandrel embodying the present invention.
Fig. 2 is a longitudinal section of the first embodiment of the injection mandrel embodying the present invention.
Fig. 3 is a longitudinal section of the first embodiment of the injection mandrel embodying the present invention, includlng a dip tube.
Fig. 4 is a detailed longitudinal section of a second embodiment of an injection mandrel embodying the present invention; Fig. 4A illustrates the upper hal~ of an injection mandrel; and, Figure 4B illustrates the lower half of the same injection mandrel.
Fig. 5 is a horizontal section of the second embodiment of the injection mandrel taking along line 5-5 of Fig. 4B.
Fig. 6 is a horizontal sectlonal view of the first embodiment of the injection mandrel taken along line 6-6 of Figs. 2 and 3.
Fig, 7 is a horizontal sectional view of the first embodiment of the injection mandrel taken along line 7-7 of Fig. 2, ~

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~ ~7S~i6 DETAILED DESCRIPTION

Referring now to the drawings in more detail, particularly to Figs. 1, lA and lB, there is illustrated a schematic elevational view of an injection mandrel in accordance with the present invention. Preferably, the mandrel is a center pocket mandrel. A well 10 is shown in which a casing 11 has been cemented, indicated at 12, and perforated in a producing sone 13. At the surface a Christmas tree 14 is mounted on a wellhead 15 on top of the casing 11. A tubing string 20 is suspended from the wellhead 15. A valved conduit 21 is connected to the upper end of the tubing string 20 and a second valved conduit 22 is connected into the wellhead 15 to communicate with the annulus between the inside of the casing and the outside of the tubing string. A center pocket mandrel, 24a in Fig. lA and 24b in Fig. lB, is connected to the tubing string 20. A packer assembly 26 seals off and divides the well 10 into an annulus 14 between the casing ll and the tubing string 20 (and between the casing ll and center pocket mandrels 24a and 24b) and a lower interval 23 below the packer assembly 26.
Fluids from the producing zone 13 may contain corrosive agents such~as hydrogeD sulfide, carbon dioxide or water which can damagq the casing string 11, tubing 20 and other subsurface ` 25 and surEace equipment. To combat this corrosion problem, a suitable corrosion inhibitor may be injected into the well.
Sui tble corrosion inhibitors are vel: know~ in the ~rt.

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The fluids from the producing zone 13 may also contain salts or other dissolved and undissolved solids which can precipitate and deposit in the perforations or tubing string 20, reducing production. To combat this problem, a suitable solvent may be injected into the well to dissolve the deposits. Such solvents are also well known in the art.
As illustrated in Figs. lA and lB, the center pocket mandrels 24a and 24b are provided for these and for other operations in which;it is desired to circulate a treating fluid from the annulus 14 of the well 10 into contact with the formation fluid in the lower interval 23. The present invention is, therefore, not limited in scope solely to the use of corrosion inhibitors or solvents.
Referring to Figs. 1 and lA, a suitable treating fluid is pumped through the valved conduit 22 and injected into the annulus 14. From the annulus 14, the treating fluid enters the center pocket mandrel 24a through a check valve, described hereinaEter, flows into the valve pocket in the valve housing of the center pocket mandrel 24a and into the bore of the mandrel to contact the formation fluids from lower interval 23. The treated formation fluld is circulated upward through the flow conduit 25 and to the tubing string 20 and the surface for recovery through the valved conduit 21.
If it is desired to treat formation fluids at a depth below the packer assembly 26, for example at the depth of producing zone 13, the modified center pocket mandrel 24b of Fi~. IB may b- u.ilized. The Elow of tre=tin~ Eluid is tùe eame ,:

~ 2~375~i as described above1with the following exception. A dip tube 25 is connected to the valve pocket. The dip tube extends below the mandrel into the producing zone 13.
Specific embodiments of injection mandrels in accordance with the present invention are show~ in greater detail in Figs. 2-7. It should be noted that the embodiments comprise many common elements, some identical in construction and others similar but modified for the specific embodiment.
The identical elements of the various specific embodiments have common numbering throughout this detailed discussion. The similar but non-identical elements will also have common numbering including a letter identifier for the particular embodiment.
Referring to Fig. 2, there is illustrated in detail a center pocket mandrel in accordance with the invention and corresponding to the embodiment depicted in Fig. lA. The center pocket mandrel 30 comprises a tubular body 32, an exterior check valve 34, a conduit 36 for fluid communication between the check valve 34 and a valve housing 33 defining a valve pocket 38 in the body 32. A removable chemical injection valve 40 is set in the valve pocket 38 for permitting fluid communication from the valve pocket 38 into the formation fluid. The lower end of the chemical injection valve is preferably recessed in, or enclosed by, the valve housing to create a dead space to thereby reduce wear and corrosion of the injection valve by the produced fluids flowing upwardly through the mandrel. A longitudinal flow conduit 42 through the mandrel body 32 transmits treated formation fluid through the mandrel 30 and tubing string 20 `,~ .

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(Fig. lA) Eor collection at the surface. The flow conduit 42 is defined by the inner surface of the body 32 and the outer surface of the valve housing 33 that is attached to the ;nner surface of the mandrel body 32.
The body 32 has threaded ends 44, 94 for connection to the tubing string 20, a lower section 46 for the chemical injection valve 40, and a tapered upper section 48 between the lower section 46 of the body and the upper threadéd end 44. The tapered upper section of the body reduces turbulence in the produced fluid flow to minimize wear on the mandrel at this point.
A mounting lug 58 having a slanted upper surface 60 is connected to the inside surface of the body 32 and the exterior of the valve housing 33, with the slanted upper surface 60 above the top of the valve housing 33. The lug 58 provides additional support for the valve housing 33 and the slanted upper surface 60 directs chemical injection valves 40 (or downhole tools) into or through the valve pocket 38. The valve housing 33 has an inwardly beveled upper edge 62 for the same purpose.
The treating fluid conduit 36 is moun~ed to the exterior wall of the lower body section 46. The conduit 36 comprises a flow passage from the check valve 34, through a fluid port 66 through the mandrel body, and into,the valve pocket 38.; Referring to Figs. 2 and 7, it can be seen that the conduit 36 may comprise a tube welded or otherwise mounted to the exterior wall of the lower body section 46 on the side adjacent the valve housing 33.

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The check valve 34 allows fluid to flow from the amlulus 14 of the well 10 through the conduit 36 and into the valve pocket 38, but precludes fluid flow in the opposite direction. The check valve 34 may be any of the well known one-way or check valves commonly used in injection operations.
The preferred choice is a unit consisting of two ball and seat check valves in series. Ball and seat valves will allow fluid flow when the pressure in annulus 14 rises to a preselected value in excess of the fluid pressure in the valve pocket 38.
Spring loaded check valves may also be used. Such one-way valves and valve arrangements are well-known to those skilled in the art. The set point of the check valve will need to be selected so that the check valve will permit flow into the mandrel when there is a preselected differential pressure between the fluid in the annulus and the fluid in the mandrel.
The check valve 34 is connected to one end of the conduit on the exterior wall of the lower body section 46 at a point below the fluid port 66. Alternatively, at least a part of the conduit should be below the port 66. These arrangements will form a gas trap in the conduit 36, preventing produced fluids, such as corrosive gases, from entering the conduit and minimizing the chances of damage to the check valve 34.
Once the treating fluid has entered the valve pocket 38, it flows through ports 70 into a longitudinal bore 68 in the chemical injection valve 40. The longitudinal bore 68 houses one or more one-way or check valves 72 which allow the treating fluid to flow through an opening 73 in the end of the chemical injection valve 40 and into contact with the formation ~ ~'756~;

fluids. The check valves 72 may be of any of the types cor~nonly used in injection operations and fam;liar to those skilled in the art. The preferred choice is again a ball and seat arrangement which may be used singly or in series plurality.
The injection valve 40 is inserted and removed from the valve housing 33 by standard wireline operations. The injection valve 40 is provided with a fishing neck 74 for attachment to a wireline and a locking assembly 76 which is used to secure chemical injection valve 40 in place in the valve housing 33.
10 The fishing neck 74 and locking assembly 76 may be any one of the number of well known arrangements familiar to those skilled in the art. The locking assembty 76 is provided with dogs 78 which, when inserted into inner tube 52, rest on shoulders 80 thereof to secure the valve 40 in place in the valve housing 33.
Above and below ports 70, the chemical injection valve 40 is provided with fluid seals 82, which may comprise any of the number of well known fluid seals such as, for example, chevron seals or o-rings. As the chemical injection valve 40 is inserted into the valve pocket 38, fluid seals 82 contact 20 shoulders 84 on the interior wall of the valve housing to form a fluid seal. This seal insures treating fluid will flow through the ports 70 and out of the chemical injection valve 40.
Deflector lugs 92 are provided on the e~terior wall of lower body section 46 aligned with the check valve 34 to prevent 25 the valve from contacting the casing 11 or any obstructions in the well 10 when the injection mandrel is run into the well.
Similar deflector surfaces 93 are provided adjacent the upper and lower ends of the conduit.

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The end of the lower hody 46 has threads 94 for engaging a packer assembly 26 or for connection to tubing or other downhole tools (not shown) which may be attached to the center pocket mandrel 30.
Referring now to Fig. 1, lA and 2, in the operation of the apparatus of Fig. 2, the center pocket mandrel 30 is inserted into a well 10 connected to the end of tubing string 20 and engaging the packer assembly 26. The check valve 34 is positioned above the packer assembly 26.
The chemical injection valve 40 may be in place when the mandrel is run into the well 10. Alternatively a wireline (not shown) may be attached to the fishing neck 74 and the chemical injection valve 40 lowered into the well through the tubing string 20.
The chemical injection valve 40 is then set in the valve housing using standard wireline methods. The chemical injection valve 40 is preferably constructed so that when dogs 78 are seated, the injection valve ports 70 will be adjacent the treating fluid port 66. Once the chemical injection valve 40 is in place and secured within the valve pocket 38, the wireline is removed in the usual manner.
The desired treating fluid is then introduced into the annulus 14 of the well. The fluid pressure in the annulus may .. ..
then be increased until it is at the,preselected value in excess of the Eluid pressure in the valve pocket 38. The treating fluid from the annulus then flows through the check valve 34, the conduit 36 and the fluid port 66 into the valve pocket 38.

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As the fluid pressure rises above the ~luid pressure in the lower interval 23, the treating flu;d in the valve pocket flows through the ports 70, the longitudinal bore 68 and the check valves 72 of the chemical injection valve 40 and into contact with the formation fluid. The check valves 72 in the chemical injection valve 40 prevent flow in the opposite direction.
Formation fluid from lower interval enters the center pocket mandrel 30 through the end 96 of the lower body 46 and contacts the treating fluid exiting the chemical injection valve 40. The treated formation fluid then flows upwardly through flow conduit 42 and the tubing string 20 to the surface for recovery.
A modification of the center pocket mandrel described above is illustrated in Fig. 3 and corresponds to the embodiment depicted in Fig. lB. The center pocket mandrel 30a illustrated in Fig. 3 and the center pocket mandrel 30 illustrated in Fig. 2 are nearly identical in construction. The difference is the construction of the valve housings 38a. The operation of the center pocket mandrels 30a and 30 is also nearly identical. The following discussion will cover the differences between the two embodiments, and reference may be had to the prior discussion of the center pocket mandrel for other details.
Referring to Fig. 3, the valve housing 33a is connected to dip tube 98 by threads, welding or any suitable means. The ; dip tube 98 is threaded 100 for connection to additional joints of dip tubing to extend the dip tube 98 to any preselected depth. This allows treating fluid to be injected directly into .

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the lower intervat 14 at any point below the packer assernbly 26 (Fig. lB~ such as at the depth of the perforations in the producing zone 13.
The treated formation fluid enters the flow conduit 42a of center pocket mandrel 30a through the opening 96 at the base of the lower body 46. Upon entering center pocket mandrel 30a, this fluid flows upwardly through flow conduit ~2 and tubing string 20 to the surface for recovery.
A second embodiment of a center pocket mandrel in accordance with the present invention is illustrated in Fig. 4.
This embodiment is useful in operations where the diameter of the casing 11 (Fig. lA) is such that a center pocket mandrel with a smaller outside diameter should be used.
The center pocket mandrel 30b in Fig. 4 and 7, and the center pocket mandrel in Figs. 2 and 6 are nearly identical in construction except for the placement of their conduits 36 and 36b. The operation of the center pocket mandrels 30b and 30 is also essentially identical. The discussion below will therefore relate only the differences between the two embodiments, and reference may be had to the prior discussion for other construction and operation details.
The mandrel of this embodiment requires a special lower body section 46b. The lower body section is preferably attached to the mandrel housing 46 by welding 47. A port 49 is machined through the lower body to connect the conduit 36 and a check valve manlfold 51. The manifold is threaded or otherwise adapted to accept a check valve 34.

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Referring to Fig. ~, conduit 3~b is mounted inside the lower body section ~6 between the outer surface of the valve housing 33 of the inside surface of the body ~6. The check valve 34 is in fluid communication with the conduit and is 5 mounted on the outer surface of the mandrel body 46. Referring to Figs. 4 and 5, the conduit 36b extends through the flow conduit 42b and into the valve pocket 38 through the fluid port 66b. The rest of the details of this embodiment are the same as in the embodiment described above. By routing the 10 treating fluid conduit through the inside of the mandrel, a smaller diameter mandrel is possible.
; The mandrels of the present invention provide effective tools for injecting treating fluids into wells to treat fluids from producing formations. The ability to insert and remove 5 chemical injection valves by standard wireline procedures allows the center pocket mandrel to be set at depths where side-pocket and other mandrels could not practically be used. ~se of a dip tube allows the center pocket mandrel to be set at a selected depth while permitting injection of treating fluid into the well 20 at any depth below the center pocket mandrel.
The exterior check valve (and the chemical injection valve)~prevent formation fluid from entering the annulus of the well above the packer assembly. This is important to maintain the integrity of any subsurface safety valves in the tubing 25 string and to minimize potential problems due to pressure leakage.

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The center pocket mandrels of the present lnvent;on permit other downhole operations to be conducted below the mandrel by removing the chemical injection valve from the valve housing. A number of downhole tools such as well logging or perforating guns can be lowered through the valve pocket to conduct operations below the mandrel.
Many modifications and variations may be made in the techniques and structures described herein and depicted in the accompanying drawings without departing substantially Erom the concept of the present invention. In particular, it is recognized it is possible to modify a side pocket mandrel to include the check valve and certain other features of the invention and thereby practice the invention. Accordingly, it should be understood that the form of the invention described and illustrated herein is exemplary only, and is not intended as a limitation on the scope thereof.

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Claims

1. An injection mandrel for circulating treating fluid from a supply of such fluid in the annulus of a well through a separate chemical injection valve having a lower end and into a fluid produced from said well, comprising:

a body adapted to be connected in a tubing string, said body having a longitudinal flow conduit therethrough for the produced fluid and a port through the body communicating with the annulus of the well;

a longitudinal valve housing within the body and in fluid communication, through a lower end thereof, with the flow conduit in the body and also in communication with the port through the body, said valve housing defining a valve pocket in the valve housing adapted to receive said separate chemical injection valve; and a check valve connected to the body and responsive to the fluid pressure communicating between the fluid in said conduit and the fluid in said annulus, said check valve permitting flow of the treating fluid from the annulus to the valve pocket through the port in the body, and for preventing reverse flow, whereby when a chemical injec-tion valve is in the valve pocket, treating fluid may be flowed through the check valve and the chemical injection valve into contact with the produced fluid and when there is no chemical injection valve in the pocket, the check valve prevents flow of produced fluids through the check valve into the annulus of the well.

2. An injection mandrel as claimed in Claim 1, wherein the body further comprises a treating fluid conduit having ends respectively connected to the body and to the check valve so as to provide fluid communication between the check valve and the port.

3. An injection mandrel as claimed in Claim 2, wherein at least a portion of the treating fluid conduit is below the port, thereby defining a gas trap above the check valve.

4. An injection mandrel as claimed in Claim 2, wherein the conduit between the check valve and the port is inside the body of the mandrel.

5. An injection mandrel as claimed in Claim 1, wherein the injection mandrel is a center pocket mandrel having the valve pocket substantially axially aligned with the longitudinal axis of the tubing string.

6. An injection mandrel as claimed in Claim 1, wherein the valve housing has a length sufficient to enclose the lower end of said separate chemical injection valve in the valve housing.

7. An injection mandrel as claimed in Claim 1, further comprising a dip tube connected to the valve housing and extending therefrom, in a downward direction, a preselected distance to deliver treating fluid from a valve pocket to a point a preselected distance from the valve pocket.

8. An injection mandrel as claimed in Claim 1, further comprising a mounting lug connected to the inside surface of the body of the mandrel and to the valve housing.

9. An injection mandrel as claimed in Claim 1,2,3,4,5,6,7 or 8 wherein the body of the mandrel has an upper end, including an upper section adjacent the upper end of the body, having an inner surface tapered upwardly and inwardly toward the upper end of the body.

10. A method for treating a well having a tubing string therein, an injection mandrel in the tubing string, an annulus around the tubing string and injection mandrel, and a check valve connected to the mandrel and in fluid communication between the tubing string and the annulus of the well, said check valve being responsive to the fluid pressure communicating between the tubing string and the well annulus for permitting flow from the annulus into the tubing string, said method comprising the steps of:

introducing a volume of treating fluid into the annulus of the wall, establishing fluid communication between the check valve and the volume of treating fluid in the annulus, increasing the pressure in the annulus relative to the pressure on the tubing string; and flowing the treating fluid through the check valve and into the injection mandrel and tubing string when the differential in pressure between the annulus and the tubing string reaches a preselected value, the check valve preventing reverse flow into the annulus.

11. A method as claimed in Claim 10, including the step of flowing treating fluid from the annulus through a dip tube in fluid communication with the check valve to a preselected point in the well remote from the injection mandrel.