WO2016156187A1

WO2016156187A1 - Method and system for operating a gas well

Info

Publication number: WO2016156187A1
Application number: PCT/EP2016/056518
Authority: WO
Inventors: Lubbertus Lugtmeier
Original assignee: Shell Internationale Research Maatschappij B.V.; Shell Oil Company
Priority date: 2015-03-27
Filing date: 2016-03-24
Publication date: 2016-10-06

Abstract

A wet gas production well (1) is during an initial phase operated by transporting gas via a production tubing (14) to a Christmas tree (22) with a gate valve (36) having a first gate (38,44), whereas during a subsequent phase the well is operated by: a) extending an inner tube(60) through the production tubing (14); b) replacing the first gate (38,44) by a second gate (66,68) with a flow opening of a diameter substantially equal to an inner diameter of the inner tube (60); c) closing an annular space (62) surrounding the inner tube (60) at an upper location thereof; d) lowering a plunger (82) into the inner tube (60); e) allowing a body of said liquid to accumulate in a portion of the inner tube (60) above the plunger (82); and f) injecting pressurised gas into the annular space (62), thereby pushing the plunger (82) and the body of liquid through the inner tube (60) to the Christmas tree (22).

Description

METHOD AND SYSTEM FOR OPERATING A GAS WELL

The present invention relates to a method and system for operating a gas well formed in an earth formation whereby liquid from the earth formation is susceptible of flowing into the well.

Early in the life of a gas well whereby also liquid (oil or water) is produced, the gas-to-liquid ratio and the velocities usually are high enough to keep the wellbore clear of liquids. The liquid typically is produced as a mist entrained in the gas stream. The high turbulence and velocity of the produced gas provides an efficient lifting mechanism for the liquid so that the well produces at steady flow rates. As the reservoir pressures declines and the flow rates decrease, the lifting mechanism generally changes. Liquid no longer is entrained in mist and starts to coalesce on the inner surface of the production tubing. The liquid still may move up and out of the well, but somewhat less-efficiently than in mist form.

As gas rates and velocities continue to drop, the effect of gravity on the liquid becomes more apparent.

Liquid coalesced on the tubing wall begins to stall, and gas flows through the center of the liquid. When enough liquid has accumulated, liquid slugs may form that inhibit gas flow. The well begins a cyclic process of unloading liquid, which commonly is referred to as "heading" or "slugging." Liquid that has collected on the tubing wall increases hydrostatic backpressure, restricts gas flow, and further decreases gas velocity.

US patent application 2012/193091 discloses a plunger lift control system for improving the output efficiency of an oil or gas well by a real-time reporting arrangement, whereby a tubing string is arranged within a well casing for receiving a plunger traveling there through. The plunger has a sound generating function so as to transmit a real time lower-end location signal from the plunger to a signal sensor and processor at the upper end of the tubing.

In the known system, formation gas that has accumulated in the annulus between the tubing string and the well casing pushes the plunger together with a volume of liquid through the tubing string to surface. However the known method cannot be used in wells where a production packer is present between the tubing string and the casing since the production packer prevents flow of formation gas into the annulus . US patent application 2004/216886 discloses a liquid lifting system in a wet gas production well, wherein a plunger is lowered into a small diameter coiled tubing inserted within a large diameter production, a liquid column is subsequently allowed to accumulate above the plunger and the plunger and liquid column are subsequently lifted to a Christmas tree by injecting pressurized gas into an annular space between the coiled tubing and production tubing. A drawback of the known method is that the plunger may get stalled in and thereby obstruct the Christmas tree.

It is an object of the invention to provide an improved method of operating a gas well, which overcomes drawbacks of the known methods.

In accordance with the invention there is provided a method of operating a gas well formed in an earth formation whereby liquid from the earth formation is susceptible of flowing into the well, wherein:

- during an initial phase of operation gas is transported via a production tubing to a Christmas tree having a gate valve with a first gate, and

- during a subsequent phase :

a) an inner tube is inserted into the production tubing; b) the first gate is replaced by a second gate with a flow opening of a diameter substantially equal to the inner diameter of the inner tube;

c) an annular space between the inner tube and the production tubing is closed at an upper location thereof; d) a plunger is lowered into the inner tube

e) a body of the liquid is allowed to accumulate in a portion of the inner tube above the plunger;

f) a volume of pressurised gas is injected into the annular space, and

g) the volume of pressurised gas is induced to push the plunger and the body of liquid through the inner tube to the Christmas tree.

In this manner it is achieved that gas production from the wellbore 2 is continued while also formation water is removed from the wellbore and that the plunger does not get stalled in the Christmas tree and that even for

applications where a production packer is arranged between the production tubing and the casing, pressurised gas accumulates in the annular space between the inner tube and the production tubing. The pressurised gas then pumps the plunger together with the body of water through the inner tube and the Christmas tree to surface.

The invention also relates to a system for operating a gas well formed in an earth formation whereby liquid from the earth formation is susceptible of flowing into the well, wherein a production tubing extends in the well for transporting gas from an inflow section of the well to a Christmas tree with a gate valve having a first gate during an initial phase of operation, the system comprising during a subsequent phase of operation:

an inner tube which extends through the production tubing and provides fluid communication between the inflow section and the Christmas tree at surface;

closure means for closing an annular space between the inner tube and the production tubing at an upper location thereof;

a plunger adapted to be lowered into the inner tube so as to allow a body of said liquid to accumulate in a portion of the inner tube above the plunger;

means for inducing a volume of gas that has entered the annular space to push the plunger and the body of liquid through the inner tube to the production facility at surface; and

the Christmas tree has a second gate with a flow opening of a diameter substantially equal to the inner diameter of the inner tube.

Suitable optional features of the method and system according to the invention are described in the sub-claims and a summary is provided in the accompanying abstract.

The invention will be described hereinafter in more detail and by way of example with reference to the

accompanying schematic drawings in which:

Fig. 1 shows an exemplary embodiment of a system for use during an initial phase of operation of the method of the invention;

Fig. 2 shows an assembly of a wellhead and a Christmas tree of the system of Fig. 1;

Fig. 3 shows the exemplary embodiment after being adapted for use during a subsequent phase of operation of the method of the invention;

Fig. 4 shows the assembly of wellhead and Christmas after during the subsequent phase of operation; and

Fig. 5 shows a detail of a lower section of the gas well during the subsequent phase of operation.

In the detailed description and the figures, like reference numerals relate to like components.

Referring to Fig. 1 there is shown a gas well 1 whereby a wellbore 2 extends into an earth formation 3 to a hydrocarbon gas containing reservoir zone 4 of the earth formation. The wellbore 2 is provided with a casing 6 extending from a wellhead 8 at surface 10 to a lower section 12 of the wellbore. A production tubing 14 extends from the wellhead 8 through the casing 6 whereby an annulus 16 is formed between the casing 6 and the production tubing 14. The annulus 16 is closed in the lower wellbore section 12 by means of a production packer 18. The production tubing 14 is at the upper end thereof in fluid

communication with a flow channel 20 (Fig. 2) of a

Christmas tree 22 arranged on top of the wellhead 8. A conduit 24 provides fluid communication between the flow channel 20 and a production facility 26 at surface 10. The open lower end of production tubing 14 is in fluid

communication with the reservoir zone 4 via perforations 28 in the casing 6 and the surrounding rock formation.

Referring to Fig. 2 there is shown in more detail a portion of the wellhead 8 and Christmas tree 22 assembly during the initial phase of operation. The production tubing 14 is suspended on a tubing hanger 30 in a tubing head 32. The tubing hanger 30 is internally provided with a landing nipple profile 34. The Christmas tree 22 is provided with gate valves in the form of a lower master valve 36 having a gate 38 arranged in a housing 40, and an upper master valve 42 having a gate 44 arranged in a housing 46. Gate 38 has a central opening 47 and gate 44 has a central opening 48. Housing 40 has a central bore 50, and housing 46 has a central bore 52. Seal rings 54 are provided to seal gate 38 relative to housing 40, and to seal gate 44 relative to housing 46. The flow channel 20 is defined by the central bores 50, 52, the central openings 47, 48, and the spaces enclosed by the seal rings 54, all being of a diameter Di.

Referring further to Fig. 3 there is shown the wellbore 2 during the subsequent phase of operation whereby an inner tube in the form of coiled tubing 60 has been extended through the production tubing 14. The coiled tubing has an inner diameter D₂ which is smaller than Di. An annular space 62 is formed between the coiled tubing 60 and the production tubing 14. The coiled tubing has an open lower end in fluid communication with the reservoir zone 4 via the perforations 28.

Referring further to Fig. 4 there is shown in more detail the assembly of wellhead 8 and Christmas tree 22 during the subsequent phase of operation. The coiled tubing 60 is suspended on a landing nipple 63 latched into the landing nipple profile 34 of the tubing hanger 30 whereby a seal member (not shown) is provided to seal the landing nipple 63 gastight to the tubing hanger 30. The flow channel 20 of the Christmas tree 22 now has a diameter equal to the inner diameter D₂ of the coiled tubing 60. This has been done by replacing gates 38, 44 with gates 66, 68 of flow opening diameter D₂, by replacing the seal rings 54 with seal rings 70 of inner diameter D₂, and by arranging tubular seal ring extensions 72, 73, 74 of inner diameter D₂ into the central bores 50, 52.

Referring further to Fig. 5 there is shown in more detail a lower portion of the wellbore 2 during the subsequent phase of operation whereby a plunger 82 is positioned in the coiled tubing 60. The plunger 82 has an outer diameter slightly smaller than D₂ thus allowing the plunger 82 to move in axial direction through the coiled tubing 60 and through the flow channel 78 of the Christmas tree 22. Furthermore, the plunger 82 is provided with a check valve 84 allowing liquid to flow in upward direction through the plunger and preventing liquid to flow in downward direction through the plunger. The coiled tubing 60 includes at the lower end thereof a bumper sub 84 onto which the plunger 82 may land when moving downwardly through the coiled tubing.

During the initial phase of operation, hydrocarbon gas from the reservoir zone 4 flows via the perforations 28 into the wellbore 2, and from there via the production tubing 14 and the flow channel 20 of the Christmas tree 22 to the production facility 26 at surface. After a period of continued gas production the reservoir zone may become depleted whereby the gas pressure in the reservoir

decreases. Simultaneously an increasing amount of formation water may flow into the wellbore 2. If the reduced gas pressure is insufficient to transport formation water that has accumulated in the lower wellbore section via the production tubing 14 to surface, it may be decided to operate the gas well in the subsequent phase of operation described below.

During the subsequent phase of operation, the coiled tubing 60 is lowered into the production tubing 14 whereby the landing nipple 63 latches into the landing nipple profile 34 of the tubing hanger 30. The Christmas tree 22 is adapted by replacing gates 38, 44 with gates 66, 68, by replacing seal rings 54 with seal rings 70, and by

positioning the tubular seal ring extensions 72, 73, 74 into the central bores 50, 52.

In a next step the well is closed at surface, and the plunger 82 is inserted into the coiled tubing 60 and allowed to fall through the coiled tubing until landing on the bumper sub 85. Hydrocarbon gas and water from the earth formation are then allowed to enter the wellbore 2 whereby water accumulates in the lower wellbore section 12, and a volume of hydrocarbon gas accumulates in the annular space 62 between the coiled tubing 60 and the production tubing 14. As a result water also enters into the coiled tubing 60 via the open lower end thereof, whereby the check valve 84 of the plunger 82 allows a volume of water to accumulate above the plunger 82. When the gas pressure in the annular space 62 has become sufficiently high, the well is opened at surface. The volume of pressurised gas in the annular space 62 then pushes the plunger 82 together with the volume of water through the coiled tubing 60 to surface. Since the flow channel 20 of the Christmas tree has been adapted to the inner diameter D₂ of the coiled tubing, it is ensured that the plunger 82 together with the volume of water is pushed into the flow channel 20. The plunger 82 is received in a chamber (not shown) at the upper end of the flow channel 20, and the volume of water is discharged into a water reservoir (not shown) . The stream of hydrocarbon gas behind the plunger 82 flows via the conduit 24 to the production facility 26. In addition, hydrocarbon gas that has accumulated in the annular space 62 may be allowed to flow to the production facility 26 via a dedicated flowline and valve assembly (not shown) .

In this manner it is achieved that gas production from the wellbore 2 is continued while also formation water is removed from the wellbore.

The cycle of closing the well 1, dropping the plunger 82, allowing hydrocarbon gas to accumulate in the annular space 62, allowing a volume of formation water to

accumulate in the coiled tubing 60, and opening the well 1 is repeated continuously during the subsequent phase of operation .

Claims

C L A I M S

1. A method of operating a gas well formed in an earth formation whereby liquid from the earth formation is susceptible of flowing into the well, wherein:

- during a subsequent phase :

a) an inner tube is inserted into the production tubing; b) the first gate is replaced by a second gate with a flow opening of a diameter substantially equal to an inner diameter of the inner tube;

f) a volume of pressurised gas is injected into the annular space; and

2. The method of claim 1, wherein steps (d) - (g) are repeated during the second phase of operation and the second gate is created by inserting into the gate valve a tubular insert having an inner diameter substantially equal to the inner diameter of the inner tube.

3. The method of claim 1, wherein the first gate is sealed to a housing of the Christmas tree by at least one primary seal ring, and wherein the method comprises during the subsequent phase of operation replacing each primary seal ring by a respective secondary seal ring with a flow opening of a diameter substantially equal to the inner diameter of the inner tube.

4. The method of any one of claims 1-3, wherein the Christmas tree includes a valve for selectively preventing fluid communication between the inner tube and a surface production facility, and wherein step (f) comprises opening said valve so as to induce the volume of pressurised gas to push the plunger and the body of liquid through the inner tube to the production facility.

5. The method of any one of claims 1-4, wherein said volume of pressurised gas flows from the earth formation into the annular space via an open lower end of the annular space .

6. A system for operating a gas well formed in an earth formation whereby liquid from the earth formation is susceptible of flowing into the well, wherein a production tubing extends in the well for transporting gas from an inflow section of the well to a Christmas tree with a gate valve having a first gate during an initial phase of operation, the system comprising during a subsequent phase of operation:

7. The system of claim 6, wherein during the first phase of operation a primary seal ring seals the first gate to a housing of the Christmas tree, and is replaced at the beginning of the second phase of operation by a e secondary seal ring with a flow opening of a diameter substantially equal to the inner diameter of the inner tube.

8. The system of claim 7, wherein the second gate is created by inserting into the gate valve a tubular insert having an inner diameter substantially equal to the inner diameter of the inner tube.

9. The system of any one of claims 6-8, wherein the Christmas tree includes a valve for selectively preventing fluid communication between the inner tube and a production facility .

10. The system of any one of claims 6-9, wherein the production tubing extends through a casing whereby an annulus is formed between the production tubing and the casing, said annulus being closed at a lower end thereof by a production packer.