Method of perforating a new zone

Abstract: A new sub-surface zone 406 of an existing production well (10) is perforated by shutting down production of the well through a production tubing bore (32) and running a coiled tubing test string (400) down into the production tubing string (26). The coiled tubing test string includes a perforating gun (402) and optionally a test packer (54). The gun (402) is fired adjacent the new zone (406) to make perforations (408) therein, and the coiled tubing string (400) is removed and production resumed.

Description: The present invention is directed to a method of perforating a new zone in an existing production well. It is often desirable to perform flow tests to evaluate the performance of a well. A flow test can be performed at various stages in the development and life of a well. For instance, a flow test may be performed while the well is being drilled, before casing is set. A flow test may also be performed on a new or exploratory well in which casing has been set, but completion operations have not been undertaken. Finally, it is sometimes desirable to test a well which has been completed and placed on production for some time. In this last instance, tests on wells which contain production tubing are usually less comprehensive or are much more expensive than tests conducted on wells prior to the installation of production tubing. This is because conventional flow testing equipment cannot be run through the production tubing, and thus either modified tests must be utilized or the production tubing must be removed from the well so conventional testing equipment can be placed in the well. Conventional testing equipment typically utilizes drill stem test tools which are conveyed on drill pipe, threaded tubing, electric line, or slick line. According to the present invention there is provided a method of perforating a new subsurface zone of a production well, said well having a casing set in a borehole intersecting said new subsurface zone and a pre-existing subsurface zone said casing having a casing bore and having pre-existing perforations communicating said casing bore with said pre-existing subsurface zone, said well further having a production tubing string received within said casing and having a production tubing bore, and a production packer sealing between said casing bore and said production tubing string above said pre-existing perforations, said well having previously been on production by flowing well fluid from said pre-existing subsurface zone through said pre-existing perforations and through said production tubing bore, said method comprising: (a) shutting down production of said well through said production tubing bore; (b) leaving said production tubing string in place in said well and running a coiled tubing test string downward into said production tubing string, said coiled tubing test string including a coiled tubing string and a perforating gun carried by said coiled tubing string; (c) placing said perforating gun adjacent said new subsurface zone; (d) firing said perforating gun and thereby forming new perforations communicating said casing bore with said new subsurface zone; (e) after step (d), removing said coiled tubing test string from said production tubing; and (f) resuming production of said well up through said production tubing bore. In order that the invention may be more fully understood, reference is made to the accompanying drawings, wherein: FIGS. 1A-1B comprise an elevation sectioned schematic view of a production well having coiled tubing test string in place therein for conducting draw-down and build-up testing on the production well. FIG. 1A shows the upper portion of the well and FIG. 1B shows the lower portion of the well. The coiled tubing test string shown in FIG. 1B is not for use in the method according to the present invention. FIG. 2 is a view similar to FIG. 1B showing an alternative form of the coiled tubing test string. The upper portions of the well of FIG. 2 are identical to that shown in FIG. 1A. The coiled tubing test string shown in FIG. 2 is not for use in the method according to the present invention. FIG. 3 is another view similar to FIG. 1B showing another alternative arrangement for a coiled tubing test string. Again, the upper portions of the well of FIG. 3 are identical to that shown in FIG. 1A. The coiled tubing test string shown in FIG 3 is not for use in the method according to the present invention. FIG. 4 is another view similar to FIG. 1B showing one embodiment of the coiled tubing test string which is similar to that of FIG. 1B with the addition of a perforating gun located between the upper and lower packer elements of the straddle packer. The coiled tubing test string shown in FIG. 4 is for use in the method according to the present invention. FIG. 5 shows another embodiment for a coiled tubing test string similar to that of FIG. 2 and including a production screen and perforating gun with an optional bridge plug located therebelow. The coiled tubing test string shown in FIG. 5 is for use in the method according to the present invention. FIG. 6 shows another embodiment for a coiled tubing test string which is similar to that of FIG. 3 and which has a perforating gun and a production screen added thereto below the inflatable packer. The coiled tubing test string shown in FIG. 6 is for use in the method according to the present invention. Referring now to the drawings, and particularly to FIG. 1A, a well is shown and generally designated by the numeral 10. The well 10 is formed by drilling a borehole 12 down through the earth's surface 14 to intersect a subsurface formation 16. The well 10 includes a casing 18 set within the borehole 12 and cemented in place therein by cement 20. The casing 18 has a casing bore 22. Casing 18 has a plurality of perforations such as 24 extending therethrough and communicating the casing bore 22 with the subsurface formation 16. A production tubing string 26 is concentrically received within the casing 22. A production packer 28 seals between the casing bore 22 and the production tubing string 26 near a lower end 30 of production tubing string 26. The production packer 28 is located above the perforations 24 so that when the well 10 is in production, formation fluid from the subsurface formation 16 flows inward through the perforations 24, then in through the open bottom end 30 of production tubing string 28 and up through a production tubing bore 32. The upper end of the well 10 includes a conventional well head schematically illustrated at 34 for controlling flow of fluids through the production tubing 26. When it is desired to evaluate the performance of the well 10 by conducting flow tests thereon the production of well fluids up through the production tubing bore 32 is shut down by closing appropriate valves on the wellhead 34. Then, while leaving the production tubing string 26 in place within the well 10, a coiled tubing test string generally designated by the numeral 36 is run downward into the production tubing string 26. The coiled tubing test string includes a coiled tubing string 38 which is continuously inserted down into the production tubing string 26 with a coiled tubing injector apparatus 40. The coiled tubing is previously stored on a large reel 42 before being unreeled and inserted into the well 10. The coiled tubing test string 36 includes a plurality of tools carried by the coiled tubing string 38 on its lower end. Those tools as schematically illustrated in FIG. 1B include a reverse circulating valve 46, a tester valve 48, a sampler 50, a gauge carrier 52, and a straddle packer generally designated by the numeral 54. The straddle packer 54 includes upper and lower inflatable packer elements 56 and 58, respectively, and includes a screen 60 having a plurality of flow ports 62 therein which communicate the interior of the coiled tubing test string 38 with the interior of casing 18 between the upper and lower packer elements 56 and 58. The coiled tubing test string 36 may also carry a number of joints of conventional threaded pipe, schematically indicated at 44, above circulating valve 46. The threaded pipe will better withstand the higher hydrostatic pressures in the deeper portions of well 10. The coiled tubing test string 36 with the various tools just described attached thereto is run down through the production tubing bore 32 with the upper and lower packer elements 56 and 58 in an uninflated position. Due to the lower collapse resistance of coiled tubing as compared to threaded joint tubing, precautions must be taken to prevent collapse of the coiled tubing when producing well fluids up through the coiled tubing. To prevent hydrostatic pressure in the well from collapsing the coiled tubing, the coiled tubing should be allowed to fill with well fluid as it is run into the well. Then prior to testing the well, the well fluid can be flushed from the coiled tubing with nitrogen gas. When the straddle packer 54 is in the position generally shown in FIG. 1B, the upper and lower packer elements 56 and 58 are inflated to seal against the casing bore 22 above and below the perforations 24, respectively. Formation fluid from the subsurface formation 16 may then communicate through the perforations 24 and through the flow ports 62 with the interior of the coiled tubing test string 38. Then, the tester valve 48 can be opened to selectively flow the well fluid from the subsurface formation 16 up through the coiled tubing string 38. The tester valve 48 can be closed to shut in the subsurface formation 16. This can be repeated to perform multiple draw-down and build-up tests. Throughout this repeated draw-down and build-up testing, various parameters of the well such as the pressure of the fluids produced from the well may be measured by various instrumentation carried by gauge carrier 52. For example, the gauge carrier 52 may include a pressure sensor 64 for measuring pressure, and a recorder 66 for recording those pressure measurements for later analysis. Also, at a desired time during the draw-down and build-up testing, one or more samples of well fluid may be trapped in sampler 50, and the sampler 50 with its trapped sample will subsequently be retrieved from the well 10 when the coiled tubing test string 36 is retrieved from the well 10. After the draw-down and build-up testing is completed, it may be desired to eliminate all well fluids from the coiled tubing string 38, and this can be done by opening the reverse circulating valve 46 and then pumping a flushing fluid downward through the coiled tubing string 38 and pushing well fluid therefrom back into an annulus 68 between the coiled tubing test string 36 and the casing bore 22. After the draw-down and build-up testing operations are completed, the coiled tubing test string 36 may be retrieved from the production tubing 26, and then production of the well 10 may be resumed by opening the appropriate valves on wellhead 34 and again permitting well fluids to flow through the perforations 24 and up through the production tubing bore 32 to the surface. Thus, a method is provided for economically and easily conducting comprehensive draw-down and build-up testing on a production well without removing the production tubing string 26 from the well. Various forms of each of the tools carried by the coiled tubing string 38 may be utilized. The following are some examples of the tools. The straddle packer 54 may be constructed in accordance with the teachings of U. S. Patent No. 4,962,815 to Schultz et al., and assigned to the assignee of the present invention. The straddle packer of U. S. Patent 4,962,815 is set by inflation fluid pumped down through the coiled tubing string. The straddle packer of U. S. Patent No. 4,962,815 is disclosed for use in well treating operations where fluid is pumped down through the coiled tubing string. It may, however, be utilized for draw-down and build-up testing when assembled in combination with the other tools such as tester valve 48 disclosed herein. Longitudinal reciprocation of the upper end of the tool by picking up and setting down weight with the coiled tubing string allows the inflatable straddle packer 54 to move between an endlessly repeating sequence of an inflating position, a treating or in this instance production testing position, an equalizing position wherein fluid pressure above and below the packer elements is equalized, and a ready position wherein the tool is ready to return to the original inflating position. When the tool is returned to the original inflating position, the upper and lower packer elements 56 and 58 may be deflated to allow the straddle packer to be removed from the well. The gauge carrier 52 and pressure sensor 64 and recording apparatus 66 may for example be an instream gauge carrier and electronic memory gauge available from Halliburton Services, such as shown in U. S. Patent No. 4,866,607 to Anderson et al. The sampler apparatus 50 may for example be constructed in accordance with U. S. Patent No. 5,058,674 to Schultz et al. The tester valve 48 preferably is constructed to open and close by picking up and setting down weight with the coiled tubing string 38. Alternatively, the tester valve 48 may be controlled by an electric wireline. The tester valve 48 may for example be a Hydrospring® tester available from Halliburton Services of Duncan, Oklahoma. The circulating valve 46 may for example be a Hydraulic Circulating Valve available from Halliburton Services of Duncan, Oklahoma. Other forms of the various tools described above may be utilized. Also, other means of operating the various tools can be utilized. The Embodiment Of FIG. 2 In FIG. 2, a modified coiled tubing test string is generally designated by the numeral 200. Most of its components are identical to the coiled tubing test string 38 and such identical components are indicated by the identical identifying numerals utilized with regard to FIGS. 1A-1B. In the coiled tubing test string 200, the straddle packer 54 has been eliminated and has been replaced by a test packer 202 having an annular sealing element 204 which is sealingly received within the production tubing bore 32. The annular sealing element 204 of test packer 202 may either be an inflatable sealing element 204 or a compression set sealing element 204. For example, the test packer 202 may be a Champ® packer or RTTS packer available from Halliburton Services of Duncan, Oklahoma. With the arrangement of FIG. 2, the test packer 202 is set within the production tubing bore 32, instead of the casing bore 22, but it still is set above the perforations 24 of casing 18 and will control the flow of well fluid from the formation 16 up through the coiled tubing string 38. For all of the various forms of test packers disclosed with the several embodiments described herein, the test packer is set within one of the casing bore 22 and the production tubing bore 32. The Embodiment Of FIG. 3 In FIG. 3, another alternative version of the coiled tubing test string is shown and generally designated by the numeral 300. Again, the difference as compared to the coiled tubing test string 36 of FIGS. 1A-1B lies in the type of test packer utilized. In this instance, the straddle packer 54 has been replaced with an inflatable test packer 302, and an inflatable bridge plug 304. When the coiled tubing test string 300 is initially run into place within the well 10, the test packer 302 and bridge plug 304 are both in an uninflated position, and an upper end 306 of bridge plug 304 is connected to a lower end 308 of test packer 302. The coiled tubing test string 300 is lowered into the well 10 until the bridge plug 304 is at a depth below the perforations 24. Then the bridge plug 304 is inflated as shown in FIG. 3 to block the casing bore 22 below the perforations 24. Then the upper end 306 of bridge plug 304 is released from the lower end 308 of test packer 302, and the coiled tubing test string 300 is raised until the test packer 302 is located above the perforations 24. Then the test packer 302 is inflated to seal against the casing bore 22 above the perforations 24 as illustrated in FIG. 3. Then flow of formation fluid from the subsurface formation 16 passes through the perforations 24 and up through the open lower end 308 of test packer 302 and flows up through the coiled tubing string 38 under the control of tester valve 48. After the testing is completed, the test packer 302 is deflated, and then the coiled tubing test string 300 is lowered to again engage the lower end 308 of test packer 302 with the upper end 306 of bridge plug 304. The bridge plug 304 is then deflated, and the entire coiled tubing test string 300 is retrieved from the well. Alternatively, if desired, the bridge plug 304 may be left in place in the well. The Embodiment Of FIG. 4 In FIG. 4, a modified coiled tubing string is generally designated by the numeral 400. The coiled tubing string 400 is for use in the method according to the invention. The coiled tubing test string 400 is similar to the coiled tubing test string 36 of FIG. 1B, except that a perforating gun 402 has been added between the upper and lower packer elements 56 and 58 of the straddle packer 54. The previously existing perforations 24 described with regard to FIG. 1B are shown in FIG. 4 and may be described as identifying a first subsurface zone 404 of the subsurface formation 16. The first subsurface zone 404 may also be referred to as a pre-existing subsurface zone 404. FIG. 4 illustrates how the modified coiled tubing test string 400 including the perforating gun 402 may be utilized to perforate and test a new subsurface zone 406. This is accomplished by setting the straddle packer 54 with the upper packer element 56 above the new zone 406 and with the lower packer element 58 below the new zone 406 and above the pre-existing zone 404. The straddle packer 54 is inflated and this isolates the second zone 406 from the hydrostatic pressure of the column of well fluid standing in the production tubing bore 32 and also isolates the second zone 406 from the pre-existing zone 404. After the upper and lower packer elements 56 and 58 have been inflated to isolate the new zone 406, the perforating gun 402 is fired to form a plurality of perforations 408 through the casing 18 thus defining the new zone 406. The perforations 408 of the new subsurface zone 406 may communicate with the same geological subsurface formation 16 or with another geological formation. Once the new zone 406 has been perforated, it may be immediately flow tested by flowing fluid therefrom through the screen 60 and up through the coiled tubing string 38 under control of the tester valve 48 as previously described. After the testing operation is completed, the upper and lower packer elements 56 and 58 are deflated and the coiled tubing test string 400 is withdrawn from the well 10. Production can then be resumed from the well 10 from both the pre-existing zone 404 and the new zone 406. Also, if it is desired to resume production of the well solely from the new zone 406, this can be accomplished by placing a bridge plug (not shown) similar to bridge plug 304 of FIG. 3 within the casing bore 22 between the pre-existing zone 404 and the new zone 406. The Embodiment Of FIG. 5 FIG. 5 illustrates another alternative version of the coiled tubing test string which is generally designated by the numeral 500. The coiled tubing string 500 is for use in the method according to the invention. The coiled tubing test string 500 is similar to the test string 200 of FIG. 2, except that a production screen or perforated sub 502 and a perforating gun 504 have been added to the coiled tubing test string 500 below the test packer 202. Again, the previously existing perforations 24 may be described as a first or pre-existing zone 506 of the subsurface formation 16. The perforating gun 504 is utilized to create a second set of perforations 508 defining a new zone 510 of the well. If it is desired to isolate the new zone 510 from the pre-existing zone 506 prior to creation of the perforations 508, this can be accomplished by carrying an optional bridge plug 512 which is originally connected to the lower end 514 of perforating gun 504. Prior to setting the packer element 204 within the production tubing bore 32, the coiled tubing test string 500 is lowered until the bridge plug 512 is at the location illustrated in FIG. 5, and then the bridge plug 512 is inflated to seal the casing bore 22 between the pre-existing zone 506 and the new zone 510. The coiled tubing test string 500 is then raised to the location shown in FIG. 5 and the packing element 204 of test packer 202 is set within production tubing bore 32, with the perforating gun 504 being located adjacent the new zone 510 which is to be perforated. After new zone 510 is perforated, it can be flow tested under control of tester valve 48. Then coiled tubing test string 500 is withdrawn and the well is placed back on production. Bridge plug 512 is withdrawn if it is desired to produce from both zones 506 and 510. Bridge plug 512 is left in place if it is desired to produce only new zone 510. The Embodiment of FIG. 6 FIG. 6 illustrates another alternative embodiment of the coiled tubing test string which is shown and generally designated by the numeral 600. The coiled tubing string 600 is for use in the method according to the invention.The coiled tubing test string 600 is similar to the coiled tubing test string 300 of FIG. 3, except that a production screen or perforated sub 602 and perforating gun 604 have been added below the inflatable packer 302. The bridge plug 304 is originally carried on the lower end 612 of perforating gun 604. The previously existing perforations 24 may again be described as defining a first zone 606 of the subsurface formation 16. The perforating gun 604 is utilized to create a new set of perforations 608 defining a new subsurface zone 610 of the subsurface formation 16. The new zone 610 is then flow tested. Then coiled tubing test string 600 is withdrawn and the well is placed back on production. Bridge plug 304 is withdrawn if it is desired to produce both zones 606 and 610. It is left if only the new zone 610 is to be produced. Perforating Without Testing The embodiments of FIGS. 4, 5 and 6 including perforating guns in their coiled tubing test strings, illustrate several methods according to the invention for perforating a new zone of the existing production well and then flow testing that new zone with the coiled tubing test string. It will be appreciated that it is also possible utilizing these strings to simply perforate a new subsurface zone of the production well and then remove the coiled tubing string and allow the well to be placed back on production without having conducted draw-down and build-up tests on the new subsurface zone. Advantages Of The Described Methods There are several advantages provided by the methods described above. First, extensive testing may be performed on production wells without removing production tubing or mobilizing the extensive equipment necessary for pulling production tubing. The testing may be performed relatively quickly. Coiled tubing has no connections to leak and it is faster to run than is threaded jointed tubing. Also, long intervals of the wellbore may be isolated and tested using these methods, and particularly using the methods of FIGS. 3 or 6. Thus it is seen that the methods of the present invention readily achieve the ends and advantages mentioned as well as those inherent therein. While certain preferred embodiments of the invention have been illustrated and described for the purposes of the present disclosure, numerous changes may be made by those skilled in the art within the scope of the invention as defined by the appended claims.

Claims: A method of perforating a new subsurface zone of a production well (10), said well having a casing (18) set in a borehole (12) intersecting said new subsurface zone (406) and a pre-existing subsurface zone (404) said casing having a casing bore (22) and having pre-existing perforations (24) communicating said casing bore with said pre-existing subsurface zone, said well further having a production tubing string (26) received within said casing (18) and having a production tubing bore (32), and a production packer sealing between said casing bore (22) and said production tubing string (26) above said pre-existing perforations (24), said well having previously been on production by flowing well fluid from said pre-existing subsurface zone (16) through said pre-existing perforations (24) and through said production tubing bore (32), said method comprising: (a) shutting down production of said well through said production tubing bore (32); (b) leaving said production tubing string (26) in place in said well and running a coiled tubing test string (400) downward into said production tubing string, said coiled tubing test string including a coiled tubing string and a perforating gun (402) carried by said coiled tubing string; (c) placing said perforating gun (402) adjacent said new subsurface zone (406); (d) firing said perforating gun (402) and thereby forming new perforations (408) communicating said casing bore (22) with said new subsurface zone (406); (e) after step (d), removing said coiled tubing test string (400) from said production tubing (26); and (f) resuming production of said well up through said production tubing bore (32). A method according to claim 1, wherein in step (b), said coiled tubing test string (400) further includes a test packer (54) carried by said coiled tubing string; and step (c) includes setting said test packer (54) within one of said casing bore (22) and said production tubing bore (32) above said subsurface zone, with said perforating gun (402) located below said test packer (54) adjacent said new subsurface zone (406). A method according to claim 2, wherein the test packer (54) is a straddle packer having upper (56) and lower (58) packer elements, and said perforating gun (402) is located between said upper and lower packer elements; and step (c) includes setting said straddle packer (54) in said casing bore (22) with said upper (56) and lower (58) packer elements above and below said new subsurface zone (406), respectively, thereby isolating said new subsurface zone from said pre-existing subsurface zone (404). A method according to claim 2, wherein step (c) includes setting said test packer (54) in said production tubing bore (32) with said perforating gun (402) located below said production tubing (26) within said casing bore (22) adjacent said new subsurface zone (406). A method according to claim 4, wherein in step (b), said test packer is a compression set test packer. A method according to claim 2, wherein in step (b), said coiled tubing test string (400) includes a bridge plug carried by said coiled tubing test string below said perforating gun (402); and between steps (b) and (c), said bridge plug is set to block said casing bore (22) below said new subsurface zone (406) and then released from said coiled tubing test string (400).

Inventors: HARKINS GARY O, SCHULTZ ROGER L, HARKINS, GARY O., SCHULTZ, ROGER L.
Applicants: HALLIBURTON CO, HALLIBURTON COMPANY
Application year: 1993
Main classification: E21B49
IPC codes: E21B43, E21B49