Method and Apparatus for Testing Wells Using Dual Coiled Tubing

The subject matter of the present invention relates to a method and apparatus for running a dual coiled tubing test string into a wellbore, pumping a kill fluid into an annular space located between the two coiled tubing strings, and performing a drill stem test.

Coiled tubing is increasing in popularity in connection with wellbore operations simply because it is easier and less expensive to lower a coiled tubing into a wellbore instead of a production tubing. For example, U.S. Pat. No. 5,287,741 to Schultz et al discloses a method for performing a drill stem test by lowering a coiled tubing and an attached drill stem test tool string into a production tubing string in a wellbore. The disclosure of U.S Pat. No. 5,287,741 to Schultz et al is incorporated by reference into the specification of this application. Although the Schultz patent indicates (in column 8, line 15) that the coiled tubing has no connections to leak, the coiled tubing may, nevertheless, separate thereby forming a hole. When the coiled tubing is carrying a formation fluid, the formation fluid may begin to leak through the hole in the coiled tubing. The Schultz patent fails to disclose any method or apparatus for protecting the coiled tubing and containing the leak of the formation fluid which is leaking through the hole in the coiled tubing. Consequently, a new drill stem test apparatus is needed which utilizes a coiled tubing instead of a production tubing to lower a drill stem test tool string into a wellbore, and which further includes a separate containment apparatus for preventing a formation fluid from leaking through a hole in the coiled tubing. When the new drill stem test apparatus is used in a wellbore, a new method for performing a drill stem test could be practiced in the wellbore.

Accordingly, it is a primary object of the present invention to provide a new drill stem test (DST) apparatus adapted to be disposed in a wellbore for performing a drill stem test.

It is a further object of the present invention to provide a new drill stem test (DST) apparatus adapted to be disposed in a wellbore for performing a drill stem test, the new DST apparatus including a first coiled tubing and a second coiled tubing enclosing the first coiled tubing and forming an annular space between the first coiled tubing and the second coiled tubing.

It is a further object of the present invention to provide a new drill stem test (DST) apparatus adapted to be disposed in a wellbore for performing a drill stem test, the new DST apparatus including a first coiled tubing and a second coiled tubing sealed at its end to an end of the first coiled tubing and enclosing the first coiled tubing thereby forming an annular space between the first coiled tubing and the second coiled tubing, the ends of the first and second coiled tubings adapted to be disposed in the wellbore, the first coiled tubing receiving the formation fluid.

It is a further object of the present invention to provide a new drill stem test (DST) apparatus adapted to be disposed in a wellbore for performing a drill stem test, the new DST apparatus including a first coiled tubing and a second coiled tubing sealed at its end to an end of the first coiled tubing and enclosing the first coiled tubing thereby forming an annular space between the first coiled tubing and the second coiled tubing, and a kill fluid disposed within the annular space between the first and second coiled tubings, the ends of the first and second coiled tubings adapted to be disposed in the wellbore, the first coiled tubing receiving the formation fluid.

It is a further object of the present invention to provide a new method for performing a drill stem test.

It is a further object of the present invention to provide a new method for performing a drill stem test, the new drill stem test method including the steps of lowering a dual coaxial coiled tubing into a wellbore and performing a drill stem test.

It is a further object of the present invention to provide a new method for performing a drill stem test, the new drill stem test method including the steps of lowering a first coiled tubing and a second coaxially disposed coiled tubing into a wellbore and performing a drill stem test.

It is a further object of the present invention to provide a new method for performing a drill stem test, the new drill stem test method including the steps of lowering a first coiled tubing and a second coaxially disposed coiled tubing into a wellbore, an annular space existing between the first coiled tubing and the second coiled tubing, filling the annular space with a kill fluid, and performing a drill stem test.

It is a further object of the present invention to provide a new method for performing a drill stem test, the new drill stem test method including the steps of lowering a first coiled tubing and a second coaxially disposed coiled tubing into a wellbore, the second coiled tubing being sealed at one end to an end of the first coiled tubing and enclosing the first coiled tubing thereby forming an annular space between the first and second coiled tubing, the ends of the first and second coiled tubings being lowered into the wellbore; filling the annular space between the first and second coiled tubings with a kill fluid; and receiving a formation fluid into the end of the first coiled tubing.

These and other objects of the present invention are accomplished by providing a new drill stem test apparatus adapted to be disposed in a wellbore. When the new drill stem test apparatus is disposed in the wellbore, a new method for performing a drill stem test may be practiced.

The new drill stem test apparatus includes a dual coaxial coiled tubing adapted to be disposed in the wellbore. The dual coaxial coiled tubing includes a first coiled tubing, and a second coiled tubing surrounding and enclosing the first coiled tubing and forming an annular space between the first coiled tubing and the second coiled tubing. A first end of the second coiled tubing is sealed to a first end of the first coiled tubing. Although the first ends of the first and second coiled tubing are adapted to be disposed in a wellbore, the first end of the first coiled tubing is the only tubing which receives a formation fluid from a formation penetrated by the wellbore. A second end of the first coiled tubing is connected to a formation fluid valve via a coiled tubing reel, and a second end of the second coiled tubing is connected to a kill fluid valve via the coiled tubing reel. The new method for performing a drill stem test includes the steps of lowering the first end of the aforementioned dual coaxial coiled tubing into a wellbore, the first end of the first coiled tubing being adapted to receive the formation fluid from the formation. The kill fluid valve is opened. When the kill fluid valve is opened, a kill fluid begins to flow into the annular space between the first coiled tubing and the second coiled tubing. The kill fluid cannot leak out of the first end of the first and second coiled tubing because the first end of the second coiled tubing is sealed to the first end of the first coiled tubing. When the kill fluid fills the annular space and is pressurized to a predetermined pressure, the formation fluid valve, connected to the second end of the first coiled tubing, is opened. As a result, the formation fluid which is flowing into the first end of the first coiled tubing begins to flow uphole through the first coiled tubing and through the formation fluid valve. If the first coiled tubing separates and forms a hole, the formation fluid in the first coiled tubing will attempt to leak out of the hole in the first coiled tubing and into the annular space. However, the pressurized kill fluid which is present in the annular space between the first and second coiled tubing will prevent the formation fluid from leaking out of the hole from the interior of the first coiled tubing into the annular space. Consequently, the formation fluid will continue to flow uphole uninterrupted through the first coiled tubing and through the formation fluid valve.

Further scope of applicability of the present invention will become apparent from the detailed description presented hereinafter. It should be understood, however, that the detailed description and the specific examples, while representing a preferred embodiment of the present invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become obvious to one skilled in the art from a reading of the following detailed description.

A full understanding of the present invention will be obtained from the detailed description of the preferred embodiment presented hereinbelow, and the accompanying drawings, which are given by way of illustration only and are not intended to be limitative of the present invention, and wherein:

FIG. 1 illustrates a first embodiment of the new drill stem test method and apparatus of the present invention including the new dual coaxial coiled tubing string disposed in a wellbore.

FIG. 2 illustrates a second embodiment of the new drill stem test method and apparatus of the present invention;

FIG. 3 illustrates an exploded section of a portion of the dual coaxial coiled tubing of FIG. 2 illustrating the inner coiled tubing, the outer coiled tubing, a sealing element, and the annular space between the inner and outer coiled tubing;

FIG. 4 illustrates a third embodiment of the new drill stem test method and apparatus of the present invention; and

FIG. 5 illustrates an exploded section of a portion of the dual coaxial coiled tubing of FIG. 4 illustrating the inner coiled tubing, the outer coiled tubing, a sealing element, and the annular space between the inner and outer coiled tubing;

Referring to FIG. 1, a new drill stem test apparatus in accordance with a first embodiment of the present invention is illustrated.

In FIG. 1, a dual coaxial coiled tubing 10 is wound upon a coiled tubing reel 12. The dual coaxial coiled tubing 10 includes an inner coiled tubing 10a and an outer coiled tubing 10b which encloses the inner coiled tubing 10a thereby forming an annular space 10c between the inner coiled tubing 10a and the outer coiled tubing 10b. When the dual coaxial coiled tubing 10 is rolled off the coiled tubing reel 12, a first end 12 of the dual coaxial coiled tubing 10 is disposed in a wellbore which is lined with a casing 16. The casing 16 penetrates an earth formation 14 traversed by the wellbore. A second end 18 of the dual coaxial coiled tubing 10 is wound upon the coiled tubing reel 12. The second end 18 is connected to a pipe 20. The pipe 20 is connected to a 31/2 inch kill fluid valve 22 which is associated with a kill pump 24 and a 2 inch formation fluid valve 26 which is associated with a formation fluid pump 28. The kill fluid valve 22 is adapted to open a flow line between the pipe 20 and the annular space 10c which is disposed between the inner and outer coiled tubings 10a and 10b. However, the formation fluid valve 26 is adapted to open a flow line between an interior of the inner coiled tubing 10a and the pipe 20. When the kill fluid valve 22 is opened, the kill pump 24 will pump a kill fluid into the annular space 10c disposed between the inner coiled tubing 10a and the outer coiled tubing 10b. The kill fluid is heavier than the expected formation fluid which will flow from the formation 14 through the interior of the inner coiled tubing 10a. As a result, if a hole is formed in the inner coiled tubing 10a, the kill fluid, being heavier than the formation fluid, will prevent the formation fluid from leaking out of the hole from the interior of the inner coiled tubing 10a into the annular space 10c. However, when the formation fluid valve 26 is opened, a formation fluid flowing within the interior of the inner coiled tubing 10a will flow out of the inner coiled tubing 10a and through the pipe 20 in the direction of the arrow 30. The first end 12 of the dual coaxial coiled tubing 10 includes an end 10b1 of the outer coiled tubing 10b, an end 10a1 of the inner coiled tubing 10a, and a sealing element 10d which seals the end 10b1 of the outer coiled tubing 10b to the end 10a1 of the inner coiled tubing 10a. The sealing element 10 d may comprise either a polished rod or a sealing slip joint. When the sealing element 10d seals the end 10b1 to the end 10a1 of the outer and inner coiled tubings, if a formation fluid begins to flow from a plurality of perforations 14a in the formation 14, the formation fluid cannot enter the annular space 10c disposed between the inner and outer coiled tubings 10a and 10b. In FIG. 1, a drill stem test string 32 protrudes from an end of the sealing element 10c. In our example shown in FIG. 1, the drill stem test string 32 actually forms a part of the inner coiled tubing 10a. However, the inner coiled tubing 10a which comprises the drill stem test string 32 of FIG. 1 could easily be connected to a number of other drill stem test tools, such as the tools shown in FIG. 1B of U.S. Pat. No. 5,287,741 to Schultz et al. These other tools would include a reverse circulating valve, a tester valve, a sampler, a gauge carrier, and/or a straddle packer. In FIG. 1, the dual coaxial coiled tubing 10 also includes an injector head 34, an upper stripper 36, a lower stripper 38, a quick connector 40, an upper coiled tubing blowout preventer 42, a coiled tubing annular blowout preventer 44, a lower coiled tubing blowout preventer 46, a swab valve 48, a hydraulic master valve 50, a manual master valve 52, and a hydraulic subsurface safety valve 54. When the kill fluid valve 22 is opened, the kill fluid will be pumped by kill pump 24 into the entire length of the annular space 10c, disposed between the inner and outer coiled tubings 10a and 10b of FIG. 1.

Referring to FIGS. 2 and 3, the new drill stem test apparatus in accordance with a second embodiment of the present invention is illustrated. FIG. 2 illustrates a dual coaxial coiled tubing string, in accordance with a second embodiment of the present invention, disposed in a wellbore for use during the practice of a new method, also in accordance with the present invention, for performing drill stem test. FIG. 3 illustrates an exploded section of a portion of the dual coaxial coiled tubing of FIG. 2 illustrating the inner coiled tubing, the outer coiled tubing, a sealing element, and the annular space between the inner and outer coiled tubing. In FIGS. 2 and 3, the element numerals used in FIG. 1 will be used in FIGS. 2 and 3 wherever possible.

In FIGS. 2 and 3, the second embodiment of the new drill stem test apparatus of the present invention is basically the same as the first embodiment shown in FIG. 1. The second end 18 of the dual coaxial coiled tubing 10 is wound upon the coiled tubing reel 12 as shown in FIG. 1 and the first end 12 of the dual coiled tubing 10 is situated in the casing string 16 of the wellbore. The drill stem test apparatus of FIG. 2 also includes the injector head 34 and the coiled tubing blowout preventors 42/46. As best shown in FIG. 3, the outer coiled tubing 10b encloses the inner coiled tubing 10a and forms an annular space 10c between the outer and inner coiled tubing. In FIG. 2, the annular space 10c is connected to the kill fluid valve 22. When the kill fluid valve 22 is opened, a pressurized kill fluid begins to flow into the annular space 10c between the outer and inner coiled tubing 10b and 10a, respectively. However, in FIG. 3, the first end 12 of the dual coaxial coiled tubing 10 includes an outer coiled tubing end 10b1 and an inner coiled tubing end 10a1, the two ends 10b1 and 10a1 being sealed together by the sealing element 10d. The sealing element 10d can be either a sliding seal assembly, polished rod, or a welded joint. Therefore, when the kill fluid valve 22 is opened and the kill fluid begins to flow into the annular space 10c, in view of the sealing element 10d of FIG. 3, the kill fluid will not flow out of the first end 12 of the dual coiled tubing 10. The kill fluid between the inner and outer coiled tubing 10a and 10b can be used in the following manner: (1) fill the annular space 10c with the kill fluid and remove all air; monitor the kill fluid with a pressure readout at the surface of the wellbore to determine if there is any indication of a leak in the inner coiled tubing 10a, or (2) fill the annular space 10c with the kill fluid and pressurize the kill fluid to a desired, predetermined pressure to reduce the burst stress on the inner coiled tubing 10a; continue to monitor the kill fluid to determine if a hole in the inner coiled tubing 10a produces a leak from the inner coiled tubing; if a leak from the inner coiled tubing 10a occurs, increase the pressure of the kill fluid in the annular space 10c to control the leak. When formation fluid is produced from the perforations 14a in the formation, the formation fluid will be forced to enter the drill stem test string 32 of FIG. 3, which in the example of FIGS. 2-3, consists of the first end 12 of the inner coiled tubing 10a. However, recall again that the end of the inner coiled tubing 10a of the drill stem test string 32 of FIG. 3 could easily be connected to other drill stem test tools, such as a reverse circulating valve, a tester valve, a sampler, a gauge carrier, and/or a straddle packer.

Referring to FIGS. 4 and 5, the new drill stem test apparatus in accordance with a third embodiment of the present invention is illustrated. FIG. 4 illustrates a dual coaxial coiled tubing string, in accordance with a third embodiment of the present invention, disposed in a wellbore for use during the practice of a new method, also in accordance with the present invention, for performing drill stem test. FIG. 5 illustrates an exploded section of a portion of the dual coaxial coiled tubing of FIG. 4 illustrating the inner coiled tubing, the outer coiled tubing, a sealing element, and the annular space between the inner and outer coiled tubing. In FIGS. 4 and 5, the element numerals used in FIG. 1 will be used in FIGS. 4 and 5 wherever possible.

In FIGS. 4 and 5, the drill stem test apparatus of FIG. 4 is basically the same as the drill stem test apparatus of FIGS. 2 and 3. However, the major difference between the drill stem test apparatus of FIGS. 2 and 4 relates to the location of the sealing element 10d. In FIG. 2, the sealing element 10d was located adjacent to the drill stem test string 32 (the end of the inner coiled tubing 10a) and adjacent to the perforations 14a in the formation. However, in FIG. 4, the sealing element 10d is located adjacent the first end of the inner coiled tubing 10a which is located just below the blow out preventors 42/46; however, in FIG. 4, the first end 12 of the outer coiled tubing 10b extends far beyond the first end of the inner coiled tubing 10a.

In FIG. 4, the new drill stem test apparatus includes the dual coaxial coiled tubing 10 disposed in a wellbore for performing a new drill stem test. As shown in FIG. 5, the dual coaxial coiled tubing 10 includes the inner coiled tubing 10a which is enclosed by the outer coiled tubing 10b, and the annular space 10c disposed between the inner and outer coiled tubing. The second end 18 of the dual coaxial coiled tubing 10 is wound on the coiled tubing reel 12 and the first end 12 of the dual coiled tubing 10 is disposed in the wellbore. As mentioned earlier, the drill stem test apparatus also includes the injector head 34 and the blowout preventors 42/46. When the kill fluid valve 22 is opened, a pressurized kill fluid enters the annular space 10c, which is best shown in FIG. 5. However, the sealing element 10d of FIG. 5 will prevent the kill fluid in the annular space 10c from spilling out the annular space 10c and out of the end of the outer coiled tubing. When the formation fluid from the perforations 14a enter the outer coiled tubing 10b, and when the formation fluid valve 26 is opened, the formation fluid in the inner coiled tubing 10a will flow uphole within the inner coiled tubing 10a and through the formation fluid valve 26. If a hole forms in the inner coiled tubing 10a, the formation fluid will not leak from the interior of the inner coiled tubing 10a and through the hole into the annular space 10c because the pressurized kill fluid, which is located in the annular space 10c, will prevent the formation fluid from leaking through the hole. The formation fluid will continue to flow through inner coiled tubing 10a and through the formation fluid valve 26.

The new drill stem test method of the present invention will be described below in the following paragraphs with reference to the new drill stem test apparatus of the present invention which is shown in FIGS. 1 through 5 of the drawings.

The new drill stem test apparatus of the present invention is set up in the wellbore in the manner shown, for example, in FIG. 1. The dual coaxial coiled tubing string, consisting of two concentrically disposed coiled tubing strings separated by an annular space 10c, is wound off the coiled tubing reel 12 and a first end is disposed in a wellbore lined by a casing 16. The kill fluid valve 22 is opened, but the formation fluid valve 26 remains closed. A kill fluid, which is heavier than the expected formation fluid, begins to flow from the kill fluid valve 22 and into the annular space 10c between the outer coiled tubing 10b and the inner coiled tubing 10a. The sealing element 10d will prevent the kill fluid in the annular space 10c from spilling out the other end of the annular space 10c and out of the dual coaxial coiled tubing 10 and into the wellbore. The kill fluid is pressurized to a predetermined pressure. Then, the formation fluid valve 26 is opened. Formation fluid from the perforations 14a in the formation begins to flow into the first end 12 of the inner coiled tubing 10a. Since the formation fluid valve 26 is opened, the formation fluid will flow through the inner coiled tubing 10a and through the formation fluid valve 26 at the surface of the wellbore. Assume that a hole forms in the wall of the inner coiled tubing 10a. The formation fluid inside the inner coiled tubing 10a will attempt to leak out of the hole and into the annular space 10c. However, since the pressurized kill fluid is located in the annular space 10c and since it is heavier than the formation fluid, the kill fluid in the annular space 10c will prevent the formation fluid in the inner coiled tubing 10a from leaking out from the interior of the inner coiled tubing 10a, through the hole, and into the annular space 10c. The flow of the formation fluid in the inner coiled tubing 10a will not be interrupted; rather, the formation fluid will continue to flow out of the formation fluid valve 26.

The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.