SYSTEM FOR DETERMINING SEALING IN A WELLBORE

Abstract

A sealing system is provided for use in a wellbore (1) formed in an earth formation whereby a stream of fluid produced from the earth formation (6) flows through the wellbore to surface (3). The sealing system comprises a sealing device (18) arranged to seal a selected portion of the wellbore from the stream of produced fluid, a compound arranged to be absorbed by fluid from the earth formation entering the stream of produced fluid via the selected wellbore portion, and detection means (16) operable to detect said compound in the stream of produced fluid.

Description

The present invention relates to a sealing system for use in a wellbore formed in an earth formation whereby a stream of fluid produced from the earth formation flows through the wellbore to surface.

Wellbores for the production of hydrocarbon fluid generally are provided with one or more sealing systems such as, for example, a packer arranged to seal the annular space between a casing and a production tubing or between a production liner and the wellbore wall, and one or more cement layers between a casing and the wellbore wall or between casing sections of different diameter.

Generally casing sections are sealed to the wellbore wall by a layer of cement. However it is known that cement does not always provide the desired degree of sealing in view of shrinkage of the cement during curing.

As a result of such shrinkage micro-annuli may occur in the cement layer, which form an undesired migration path for fluid in the wellbore.

Further, it has been proposed to seal an annular space between a tubular element arranged in the wellbore, and a wall extending around the tubular element, such as the wellbore wall, by means of an annular sealing device in the form of a packer made of an elastomer material that swells upon contact with formation water or hydrocarbon fluid produced from the earth formation. The packer is fixedly connected to the outer surface of the tubular element before lowering into the wellbore, whereafter the tubular element, with the packer connected thereto, is lowered into the wellbore. When formation water and/or hydrocarbon fluid flows into the annular space, the elastomer material swells so that the packer expands and thereby seals the annular space. Although such method of sealing has provided good results, a problem is that the sealing device may not adequately seal after swelling of the elastomer material, that swelling of the elastomer has not yet completed, or the elastomer material may not be sufficiently exposed to water and/or hydrocarbon fluid to ensure adequate swelling of the elastomer material. Also, adequate sealing can be difficult if the space to be sealed has an irregular shape. For example, if the sealing device is to seal against the wellbore wall, adequate sealing can be hampered if the wellbore has washed-out sections which occurred during drilling of the wellbore.

EP 0816631 B1 discloses a wellbore system whereby a production conduit is provided with a coating including tracer material to be absorbed by produced fluid flowing entering the production conduit in a section of the wellbore between a pair of packer elements.

There is a need for an improved sealing system for use in a wellbore formed in an earth formation whereby a stream of fluid produced from the earth formation flows through the wellbore to surface.

In accordance with the invention there is provided a sealing system for use in a wellbore formed in an earth formation whereby a stream of fluid produced from the earth formation flows through the wellbore to surface, the sealing system comprising a sealing device arranged to seal a selected portion of the wellbore from the stream of produced fluid, a compound arranged to be absorbed by fluid from the earth formation entering the stream of produced fluid via the selected wellbore portion, and detection means operable to detect said compound in the stream of produced fluid.

With the system of the invention it is achieved that adequate sealing of the sealing device can be determined by determining whether or not said compound is present in the stream of produced fluid. Thus, if the detection means indicates that said compound is present in the stream of produced fluid, it can be concluded that fluid from the earth formation enters the stream of produced fluid via the selected wellbore portion, and that the sealing device is not properly sealing. Conversely, if the detection means indicates that said compound is not present in the stream of produced fluid, it can be concluded that the sealing device is properly sealing.

Suitably said compound is included in the sealing device, and the sealing device is arranged to be in contact with said fluid from the earth formation entering the stream of produced fluid via the selected wellbore portion.

In a preferred embodiment, the sealing device is movable between an active mode whereby the sealing device prevents fluid from the earth formation entering the stream of produced fluid via the selected wellbore portion, and an inactive mode whereby the sealing device allows fluid from the earth formation entering the stream of produced fluid via the selected wellbore portion.

To enable easy activation of the sealing device, the sealing device preferably includes a swellable material which swells upon contact with a selected fluid, and wherein the sealing device moves from the inactive mode to the active mode by swelling of the swellable material.

Suitably said swellable material includes an elastomer, and the selected fluid comprises, for example, fluid produced from the earth formation.

The system of the invention can include a plurality of said sealing devices, a plurality of said selected wellbore portions, and a plurality of said compounds, wherein for each said selected wellbore portion a respective one of the sealing devices is arranged to seal the selected wellbore portion from the stream of produced fluid, and a respective one of said compounds is arranged to be absorbed by fluid from the earth formation entering the stream of produced fluid via the selected wellbore portion, and wherein the detection means is operable to detect each said compound in the stream of produced fluid.

To allow easy determination if one or more sealing devices are leaking, suitably said compounds have mutually different characteristics detectable by the detection means. Thus, in case of leakage of fluid past a sealing device, the detection means is capable of determining which sealing device is leaking.

Preferably said compound is selected from a Halogen substituted carboxylic acid and a Halogen substituted alcohol, for example a Halogen substituted decanoic acid or a Halogen substituted decanol.

More preferably said compound is selected from a Chloro substituted carboxylic acid and a Chloro substituted alcohol, for example a Chloro substituted decanoic acid or a Chloro substituted decanol.

The invention will be described hereinafter in more detail, and by way of example, with to the accompanying drawings in which:

FIG. 1 schematically shows an embodiment of the system of the invention whereby swellable packers are arranged in a wellbore;

FIG. 2 schematically shows the system of FIG. 1 after swelling of some of the swellable packers.

In the Figures, like components are provided with like reference numerals.

Referring to FIG. 1 there is shown a wellbore 1 having an upper section 2 extending from surface 3 substantially vertically downward, and a lower section 4 extending substantially horizontally into a reservoir zone 6 of earth formation containing hydrocarbon fluid. Instead that the lower section 4 extends substantially horizontally, the lower section 4 may alternatively extend inclined or even vertically. The lower wellbore section 4 intersects a number of natural fractures 8 present in the earth formation 6, which are in fluid communication with a formation zone (not shown) containing water.

The wellbore 1 is provided with a casing 10 extending from surface 3 to near the lower end of the upper (vertical) wellbore section 2, and a tubular element in the form of a production conduit 12 extending from surface through the casing 10 and into the lower (horizontal) wellbore section 4. A production packer 13 is arranged at the lower end of casing 10 to seal the annular space between the production conduit 12 and the casing 10. The production conduit 12 has a plurality of fluid inlet openings 14 located in the lower wellbore section 4. Furthermore, the production conduit 12 is at its upper end connected to a production facility 16 at surface 3 for receiving and further transporting hydrocarbon fluid produced from the earth formation 6.

The production conduit 12 is provided with a series of annular packers 18a, 18b, 18c, 18d, 18e, 18f spaced at selected intervals along the portion of the production conduit 12 extending in the lower wellbore section 4, whereby each packer comprises an elastomer material susceptible of swelling upon contact with water from the earth formation. Each packer 18a, 18b, 18c, 18d, 18e, 18f, before swelling of its elastomer material, leaves an annular clearance 20 between the packer and the wellbore wall 22. Upon swelling of the elastomer material, the packer 18a, 18b, 18c, 18d, 18e, 18f radially expands against the wellbore wall 22 so that the annular clearance 20 that was originally present between the packer and the wellbore wall 22, thereby vanishes.

Each packer 18a, 18b, 18c, 18d, 18e, 18f is at its outer circumference provided with bands 24 of a tracer material in the form of a compound adapted to be absorbed by fluid flowing along the packer, the fluid being either produced hydrocarbon fluid or water. Preferred tracer materials are, for example, Chloro-substituted decanoic acid or Chloro-substituted decanol. Further, the tracer materials of the various packers 18a, 18b, 18c, 18d, 18e, 18f have mutually different characteristic parameters, so that the characteristic parameter of the tracer material of a respective packer uniquely defines the respective packer.

The production facility 16 at surface is provided with a detection device (not shown) for detecting tracer material from the bands 24 in the stream of fluid produced from the earth formation. The detection device is adapted to recognize the different characteristic parameters of the tracer materials of the various packers 18a, 18b, 18c, 18d, 18e, 18f, and thereby to determine whether or not tracer material pertaining to a specific packer is present in the stream of produced fluid.

Suitably the detection device is selected from a gas chromatography mass spectrometer, a gas chromatography electron capture detector, a high performance liquid chromatography-mass spectrometer, a high performance liquid chromatography-fluorescence detector, an atomic adsorption spectrometer, an atomic emission spectrometer, an inductive coupled plasma mass spectrometer, an immunological detection device, an electron microscope, and a light microscope.

In FIG. 2 is shown the wellbore 1 of FIG. 1 after swelling of the elastomer material of packers 18a, 18c whereby these packers 18a, 18c seal against the wellbore wall 22.

During normal operation, hydrocarbon fluid flows from the earth formation 6 into the lower wellbore section 4, and thence via the inlet openings 14 into the production conduit 12 through which the stream of produced fluid flows to the production facility 16 at surface. At the start of oil or gas production, the annular packers 18 are in their unexpanded state so that the produced hydrocarbon fluid freely flows through the annular clearances 20 around the respective packers 18. The hydrocarbon fluid thereby comes into contact with the bands 24 of tracer material so that, as a result, tracer material from the bands 24 enters into the stream of produced hydrocarbon fluid and flows with the stream to the production facility 16 at surface. The detection device at the production facility 16 detects the presence of tracer material in the stream of produced hydrocarbon fluid, and recognizes the different characteristic parameters of the tracer materials of the various packers 18. The detection device then generates a signal indicating the respective packer(s) 18 from which the detected tracer material originates.

After some time of continued oil or gas production, formation water may enter the wellbore 1, for example via the natural formation fractures 8, which are in communication with the water-bearing zone. Also, formation water may enter the wellbore 1 due to ‘water-coning’ as a result of depletion of the reservoir zone 6.

Such produced formation water flows along one or more of the respective packers 18 and thereby induces swelling of the elastomer material of such packers 18. During initial swelling of the elastomer material of each packer 18 that is exposed to formation water, tracer material from the bands 24 of the respective packer 18 continues to be absorbed by the stream of fluid produced from the wellbore 1. Upon swelling of the elastomer material, the respective packer 18 gradually expands towards the wellbore wall 22 so that, ultimately, the packer 18 becomes pressed against the wellbore wall 22 and the annular clearance 20 around the packers 18 vanishes.

Thus, each expanded packer 18 seals against the wellbore wall 22 and thereby prevents further flow of produced fluid along the respective bands 24 of tracer material of the expanded packer 18. Consequently, for each expanded packer 18, tracer material from the expanded packer 18 is then no longer present in the stream of produced fluid, and hence the detection device no longer generates a signal indicating the respective packer 18 from which the detected tracer material originates. The presence and/or absence of such signals from the detection device enables the operator to determine which packers 18 are sealing against the wellbore wall 22, and which are not.

Once it has been determined in which section of the production conduit 12 formation water enters the stream of produced fluid, the inlet openings 14 of such section of the production conduit 12 can be closed. For example, if formation water enters into the stream of produced fluid through the inlet openings 14 of a section of the production conduit 12 located between the expanded packers 18a and 18c, an expandable tubular element (not shown) can be lowered into such section of the production conduit 12, and subsequently be expanded against the inner surface of the production conduit 12 so as to close the inlet openings 14 of said conduit section. Formation water entering the portion of the wellbore 1 between expanded packers 18a and 18c, then no longer can flow into the production conduit 12.

Instead of applying a production conduit having inlet openings in each conduit section between adjacent packers, a production conduit can be applied that has inlet openings in only one, or some, conduit sections between adjacent packers. Thus, the production conduit then has one or more sections without inlet openings between adjacent packers, and consequently formation fluid cannot enter the production conduit after full expansion of such adjacent packers.

Instead of applying elastomer material that swells upon contact with water from the earth formation, the packers can be made of any other suitable material that swells upon contact with formation water.

Also, the packers can include elastomer material, or any other suitable material, that swells upon contact with hydrocarbon fluid. In such application, the packers expand against the wellbore wall upon contact with hydrocarbon fluid, and thereby provide zonal isolation between formation layers at various depths along the wellbore.

Claims

1. A sealing system for use in a wellbore formed in an earth formation whereby a stream of fluid produced from the earth formation flows through the wellbore to surface, the sealing system comprising a sealing device arranged to seal a selected portion of the wellbore from the stream of produced fluid, a compound arranged to be absorbed by fluid from the earth formation entering the stream of produced fluid via the selected wellbore portion, and detection means operable to detect said compound in the stream of produced fluid, wherein the sealing device is arranged to be in contact with said fluid from the earth formation entering the stream of produced fluid via the selected wellbore portion, characterized in that said compound is included in the sealing device.

2. The sealing system of claim 1, wherein the sealing device is movable between an active mode in which the sealing device prevents fluid from the earth formation entering the stream of produced fluid via the selected wellbore portion, and an inactive mode in which the sealing device allows fluid from the earth formation entering the stream of produced fluid via the selected wellbore portion.

3. The sealing system of claim 2, wherein the sealing device includes a swellable material that swells upon contact with a selected fluid, and wherein the sealing device moves from the inactive mode to the active mode by swelling of the swellable material.

4. The sealing system of claim 3, wherein said swellable material includes an elastomer.

5. The sealing system of claim 3, wherein the selected fluid comprises fluid produced from the earth formation.

6. The sealing system of claim 5, wherein the stream of produced fluid flows through a conduit extending in the wellbore, and wherein the sealing device is an annular sealing device arranged between said conduit and one of the wellbore wall and another conduit extending in the wellbore.

7. The sealing system of claim 6, wherein the sealing device is a packer arranged to seal an annular space between the conduit and the wellbore wall.

8. The sealing system of claim 1, wherein said compound is selected from the group consisting of organic materials, inorganic materials, radioactive materials, and biochemical materials.

9. The sealing system of claim 8, wherein said compound is selected from the group consisting of Halogen substituted carboxylic acids and Halogen substituted alcohols.

10. The sealing system of claim 9, wherein said compound is selected from the group consisting of Halogen substituted decanoic acids and Halogen substituted decanols.

11. The sealing system of claim 9, wherein said compound is selected from the group consisting of Chloro substituted carboxylic acids and Chloro substituted alcohols.

12. The sealing system of claim 11, wherein said compound is selected from the group consisting of Chloro substituted decanoic acids and Chloro substituted decanols.

13. The sealing system of claim 1, wherein the detection means is a gas chromatography mass spectrometer, a gas chromatography electron capture detector, a high performance liquid chromatography-mass spectrometer, a high performance liquid chromatography-fluorescence detector, an atomic adsorption spectrometer, an atomic emission spectrometer, an inductive coupled plasma mass spectrometer, an immunological detection device, an electron microscope, a light microscope.

14. The sealing system of claim 1, comprising a plurality of said sealing devices, a plurality of said selected wellbore portions, and a plurality of said compounds, wherein for each said selected wellbore portion a respective one of the sealing devices is arranged to seal the selected wellbore portion from the stream of produced fluid, and a respective one of said compounds is arranged to be absorbed by fluid from the earth formation entering the stream of produced fluid via the selected wellbore portion, and wherein the detection means is operable to detect each said compound in the stream of produced fluid.

15. The sealing system of claim 14, wherein said compounds have mutually different characteristics detectable by the detection means.

16. (canceled)