GB2339583A - Method and apparatus for injecting fluid into wells - Google Patents

Description

2339583 1 1 "Method and Apparatus for Injecting Fluids into Wells" 2 3

This application relates to a method and apparatus for 4 injecting fluid into oil and gas wells.

6 In oil and gas wells, fluid production through 7 perforations in the casing can often be hampered by 8 build up of scale or wax in the formation and in the 9 perforations which limit the recovery of fluids from 10 the well. To address this problem, it has been common 11 practice for many years to inject chemicals into the 12 formation through the production tubing and 13 perforations in the casing in order to control 14 corrosion or the build up of scale and wax etc. 15 However, this only partially addresses the problems 16 since the deposition of scale or wax etc can re17 commence when all the injected fluid has been produced 18 from the well. 19 20 According to the present invention there is provided a 21 method for injecting fluid into a cased or lined oil or 22 gas well, the method comprising injecting the fluid 23 into the well, and passing injected fluid outside the 24 casing to a location adjacent the inlet for recovery of 25 fluids from the well.

2 1 The fluid injected into the well is preferably injected 2 via a fluid injection line separate from the production 3 tubing. The fluid injection line optionally injects 4 said fluid above a packer (or other sealing device) 5 which seals the annulus between the production tubing 6 and the casing from the inlet. In a particularly 7 preferred embodiment the fluid is injected between two 8 packers or other sealing devices. An optional check 9 valve in the injection line can maintain the integrity 10 of the pressure barrier. 11 12 The inlet for produced fluids from the wellbore is 13 preferably an area of perforated casing where the 14 produced fluids flow from the formation outside the 15 casing through the perforations therein and into the 16 production tubing. The fluid injected into the well is 17 preferably injected into the annulus between the 18 production tubing and the casing, and from there 19 typically passes through the casing via a suitably 20 controlled aperture into the formation. Typically, the 21 injected fluid passes along the outside of the casing 22 (optionally through a delivery sleeve) to an area 23 surrounding the perforations in the casing at the inlet 24 for produced fluids. At that point, the fluids 25 injected into the well typically pass through the 26 perforations with the fluids produced in the formation 27 and into the production tubing. In this manner, fluids 28 injected can be continuously injected while the well is 29 being produced allowing continuous treatment of the 30 well and formation. 31 32 optionally, the chemical is injected through the 33 formation in the vicinity of the main perforations and 34 thereby enables the method to treat the formation in 35 the area of the wellbore where formation damage may 36 occur and the pressure drop may induce scale and wax as 3 1 well as the perforations themselves. In the preferred 2 embodiment, the fluids injected pass into the formation 3 and then return to the wellbore via the perforations 4 thereby protecting both the formation and the 5 perforations from scale build up etc. 6 7 The annulus between the liner/casing and the production 8 tubing is preferably sealed from the inlet by a packer. 9 The aperture in the casing allowing injection of the 10 fluid into the formation is preferably sited above this 11 packer, and a second packer is optionally provided 12 above the fluid injection point so that between the two 13 packers an annular cavity is provided with an annular 14 row of exit points for injection of the fluid into the 15 formation. 16 17 Where the injection of fluid into the formation at a 18 point above the perforated inlets in the casing is 19 impractical, it is preferred that a sleeve surrounds 20 the casing for carrying the injected fluid to the 21 perforated inlet down the outside of the liner. This 22 can also be achieved by one or more external chemical 23 lines affixed to the outside of the liner/casing.

24 According to the invention there is also provided 26 apparatus for injecting fluid into an oil or gas well, 27 the oil or gas well having casing which lines the 28 borehole and production tubing for recovery of fluids, 29 the apparatus comprising a further conduit for passing injected fluid through the casing into the formation.

31 32 The further conduit preferably conveys the injected 33 fluid to a cavity having an aperture therein allowing 34 the fluid to pass through the casing to the formation.

36 An embodiment of the invention will now be described by 4 1 way of example and with reference to the accompanying 2 drawings, in which:

3 4 Fig. 1 shows a schematic representation of a well employing an embodiment of the invention; 6 Fig. 2 shows a schematic view of a well employing 7 a second embodiment; 8 Fig. 3a and b show plan sectional and side views 9 respectively of a liner and external. sleeve of the Fig. 2 embodiment; and 11 Fig. 4 is a schematic illustration of a wellbore 12 employing a third embodiment of the invention.

13 14 Referring now to the drawings, Fig. 1 shows a cased wellbore having a liner 10 cemented in the wellbore in 16 an oil producing formation. The liner 10 is perforated 17 at lop to allow ingress from the formation into the 18 liner 10 of produced fluids from the well. Production 19 tubing 15 is provided for conveying the produced fluids to the wellhead, as is conventional, and is sealed to 21 the liner 10 by a packer 17 which seals the annulus 22 between the production tubing 15 and the liner 10 at a 23 location above the perforations lop in the liner 10.

24 A fluid injection line 20 extends downhole from the 26 wellhead to inject fluids into the area of the annulus 27 above the packer 17 such that the fluids injected 28 through injection line 20 pass into the annulus between 29 packer 17 and a second packer 18 located above the outlet of the fluid injection line 20. A check valve 31 20v is provided in the line 20 to maintain pressure 32 integrity in the line 20. Thus the injection line 20 33 discharges fluid into a cavity 19 in the annulus 34 between the production tubing 15 and the liner 10, and between the packers 17 & 18. The cavity 19 has a 36 perforation in the liner wall 19p to allow egress of 1 injected fluid from the cavity 19 into the formation 2 near the main perforations lop. Therefore, fluid 3 injected into the cavity 19 through injection line 20 4 passes through the perforation 19p into the formation 5 and diffuses vertically and horizontally through the 6 formation. Vertical diffusion of the injected fluids 7 downwards towards the main perforations lop results in 8 re-uptake of injected fluid through the main 9 perforations lop and subsequently through the 10 production tubing 15 back to the wellhead. 11 12 Fluid injected can comprise corrosion, wax or scale 13 inhibitors etc which by the method of the invention can 14 be injected so as to diffuse through the formation on a 15 continuous basis via injection through the wellbore 16 itself and protect the formation and the main 17 perforations lop from wax or scale build up. It will 18 be appreciated that the particular nature of the 19 chemical being injected is unimportant, and various 20 different fluids can be injected into the formation by 21 the present invention in order to alter the 22 characteristics of the well. Liquids or gases could 23 conceivably be injected, and inactive fluids such as 24 water could also be injected in addition to active 25 chemicals such as scale and wax inhibitors. 26 27 Fig. 2 shows a modification to the first embodiment 28 which utilises an external sleeve 25 surrounding the 29 liner 10 around the area of the packers 17, 18 and the 30 main perforations lop. The sleeve 25 defines in its 31 annulus a pre-formed fluid path for injected fluid 32 through the injection line 20 which egresses the 33 chamber 19 through perforation 19p so as to direct the 34 injected fluid straight to the main perforations lop in 35 order principally to prevent scale and wax build up in 36 the perforations lop. The perforation 19p in the 6 1 cavity 19 can be formed by a controlled explosion so as 2 not to perforate the cement surrounding the liner 10. 3 4 In other embodiments of the invention, the perforation 5 19p can be selected to be a very deep penetrating 6 perforation through the liner 10, cement and 7 surrounding formation so as to provide a fluid path 8 deep into the formation. Different sizes of initial 9 perforation 19p can be selected in accordance with the 10 vertical and horizontal permeabilities of the fluid 11 being injected in the particular formation, so as to 12 achieve desirable characteristics which may change from 13 time to time without departing from the scope of the 14 invention. For example, if a fluid to be injected has 15 a high vertical permeability in the formation then it 16 may be desired to make perforation 19p very deep so as 17 to inject the fluid deep into the reservoir and thereby 18 treat a greater area of the reservoir than would be 19 achieved with a shallower initial perforation. 20 Likewise, several different perforations can be made in 21 the wall of the liner 10 in the area of the cavity 19 22 so as to distribute injected fluid evenly throughout 23 the reservoir or alternatively concentrate it if 24 required. In particular, perforations can be made at 25 different circumferential spacings around the 26 circumference of the liner, and/or can comprise one or 27 more perforations axially displaced along the liner 10. 28 29 The initial perforation 10p can be made by a variety of 30 different initiation methods such as pressure and 31 electrical power and shock. The particular initiation 32 method selected can depend on the well configuration. 33 Treatment fluids which are suitable can include scale 34 inhibitor, acid, corrosion inhibitor, wax inhibitors 35 and the like. The fluid generally flows through the 36 upper perforation, the formation and on to the lower 7 1 perforations to treat as much of the formation and 2 production equipment as possible. 3 4 This allows treatment fluids to be applied to the 5 outside of the well through the wellbore itself and on 6 a continuous basis without interrupting production. 7 The treatment fluid can be injected under pressure at a 8 variety of sites and can be directed to treat the 9 perforations and damage zone near the wellbore. 10 Certain embodiments with the treatment delivery sleeve 11 can provide a direct conduit for the treatment fluid to 12 the perforations where this is desired. 13 14 Modifications and improvements can be incorporated 15 without departing from the scope of the invention.

8

Claims (1)

1 Claims

2 3 1 A method for injecting fluid into a cased or lined 4 oil or gas well, the method comprising injecting the fluid into the well, and passing injected fluid outside 6 the casing to a location adjacent the inlet for 7 recovery of fluids from the well.

8 9 2 A method according to claim 1, wherein the injected fluid is recovered through the inlet.

11 12 3 A method according to any preceding claim, wherein 13 the injected fluid is injected via a fluid injection 14 line separate from production tubing.

16 4 A method according to any preceding claim, wherein 17 the injected fluid is injected at a position spaced 18 from the inlet, and a sealing device is disposed 19 between the injection position and the inlet.

21 5 A method according to any preceding claim, wherein 22 the fluid is injected between two packers or other 23 sealing devices.

24 G A method according to any preceding claim, wherein 26 the injected fluid is injected into the annulus between 27 the production tubing and the casing, and from there 28 passes through the casing via an aperture into the 29 formation.

31 7 A method according to any preceding claim, wherein 32 the injected fluid passes along the outside of the 33 casing to an area surrounding the perforations in the 34 casing at the inlet for produced fluids.

36 8 A method according to claim 7, wherein the fluids 9 1 injected into the formation are recovered through the 2 inlet with the fluids produced in the formation.

3 4 9 A method according to any preceding claim, wherein fluids injected through the casing are conveyed along 6 the outside of the casing by a conduit outside the 7 casing to the area surrounding the inlet.

8 9 10 A method according to claim 9, wherein the conduit is a sleeve surrounding the casing.

11 12 11 A method according to claim 9, wherein the conduit 13 comprises one or more tubes on the outside of the 14 casing.

16 12 Apparatus for injecting fluid into an oil or gas 17 well, the oil or gas well having casing which lines the 18 borehole and production tubing for recovery of fluids, 19 the apparatus comprising a conduit for passing injected fluid through the casing into the formation for 21 recovery through an inlet of the casing.

22 23 13 Apparatus according to claim 12, wherein the 24 conduit comprises an aperture through the casing.

26 14 Apparatus according to claim 12 or 13, comprising 27 an external conduit guiding injected fluid along the 28 outside of the casing.

29 15 Apparatus according to any one of claims 12-14, 31 wherein the injected fluid is injected via a fluid 32 injection line separate from production tubing.

33 34 16 Apparatus according to any one of claims 12-15, wherein the injected fluid is injected at a position 36 spaced from the inlet, and a sealing device is disposed between the injection position and the inlet.

2 3 17 Apparatus according to any one of claims 12-16, 4 wherein the fluid is injected between two packers or other sealing devices.

6