EP0647767A2

EP0647767A2 - Methods for conducting tubing-conveyed perforating operations in well bores

Info

Publication number: EP0647767A2
Application number: EP94306792A
Authority: EP
Inventors: David P. Decker
Original assignee: Services Petroliers Schlumberger SA; Anadrill International SA
Current assignee: Services Petroliers Schlumberger SA; Anadrill International SA
Priority date: 1993-10-12
Filing date: 1994-09-16
Publication date: 1995-04-12
Also published as: NO943310D0; EP0647767A3; CA2131595A1

Abstract

In the representative mode for practicing the invention disclosed herein for accurately positioning tubing-conveyed well bore apparatus in a well bore a retrievable MWD tool (32) having a radiation detector is positioned in the lower portion of a tubing string (12) carrying a tubing-conveyed perforator (17) carrying shaped explosive charges. Once the tubing string has been lowered into a well bore, the MWD tool is operated for transmitting signals which are representative of the radioactive characteristics of either a radioactive marker at a known depth or the formations adjacent to the MWD tool. The signals are correlated for determining the location of the tubing-conveyed perforator within the well bore. The correlated data is used for adjusting the tubing string so as to accurately position the tubing-conveyed perforator at a desired depth location.

Description

BACKGROUND OF THE INVENTION

Field of The Invention

The present invention relates to perforation of well bores and, more specifically, to the positioning of perforating guns in the well bore adjacent to the formations to be perforated.

Description of The Related Art

Those skilled in the art will appreciate that so-called "tubing-conveyed perforators" are frequently employed to conduct perforating operations in those deviated well bores where typical cable-suspended or so-called "wireline" perforating guns cannot be effectively utilized. Moreover, as described in U.S. Patent No. 4,509,604, a technique that is widely used for completing deviated well bores as well as those well bores which traverse multiple formations is to dependently couple a tubing-conveyed perforating-and-testing tool to a tubing joint and progressively lower the tool assembly into a cased well bore by successively assembling a tubing string of sufficient length for dependently positioning the tool assembly at a selected depth location in the well bore. Once the tool assembly has been positioned, a packer included with the assembly is expanded into sealing engagement with the casing for isolating that portion of the well bore lying below the expanded packer. To establish fluid communication with the earth formations adjacent to the isolated well bore portion, shaped explosive charges mounted in one or more enclosed-carrier perforators on the lower end of the tool assembly are actuated for perforating the steel casing and cement annulus between the casing and the adjacent borehole wall. Once the perforator has been fired, a test valve in the well tool is then selectively operated from the surface for controlling fluid communication between the perforated formation interval and the tubing string for conducting various flow and pressure tests of the connate fluids in the isolated earth formations.
It is, of course, essential that these tubing-conveyed tools are accurately positioned in the well bore before the perforators are actuated. It will be particularly appreciated that the accurate positioning of those perforators is even more critical where the formation intervals to be perforated are relatively thin. Typically, a perforating operation is carried out by referring to logs previously made in that well bore which show parameters of the earth formations traversed by the borehole as well as the precise upper and lower depth boundaries of those formations. By consulting such prior logs, these perforators are assembled in advance with their respective shaped charges being arranged within each of the carriers for disposing the charges in predetermined depth and orientational relationships with respect to each of the formation intervals that are to be perforated once the tool assembly is positioned at a selected depth location in that well bore. In addition, the tubing string is arranged in accordance with those prior logs to be of sufficient length for accurately positioning the assembled perforating-and-testing tool at that selected depth location. As a matter of precaution, these prior logs are often typically correlated with additional measurements such as may be obtained by moving a typical wireline logging tool through the assembled tubing string to verify that the perforators carried by the tubing-conveyed tool assembly have been correctly positioned in relation to the earth formations which are to be perforated.
Various techniques have been employed heretofore for reliably identifying the earth formations to be perforated as well as for accurately positioning the tubing-conveyed assembly that is to be employed. Typically, a prior so-called "collar log" of the existing well bore casing is employed for determining the overall length of the tubing string required to situate the perforating-and-testing tool assembly at a predetermined depth once the tubing string has been assembled. The positioning of the tubing-conveyed perforating-and-testing assembly in relation to the formations to be subsequently perforated has been carried out heretofore by employing a wireline logging tool equipped with a typical radiation detector which is responsive to one or more radioactive characteristics of the earth formations penetrated by the well bore. This logging tool is moved through the tubing string supporting the tool assembly and temporarily positioned just above the tubing-conveyed tool assembly for determining whether or not the perforating guns are adjacent to those earth formations which are to be perforated.
If desired, the tubing string may also be assembled with one or more so-called "pup joints" or shortened joints of tubing installed at selected locations in the tubing string to serve as distinctive markers that will be readily detected if the wireline logging tool is also equipped with a collar locator for providing additional signals which will verify the position of the logging tool as it is moved through the tubing string supporting the tubing-conveyed tool assembly.
Another common technique is to place detectable devices such as radioactive markers or tags at selected depth locations which having a known relationship with respect to the formations which are to be perforated. Such radioactive tags or markers may take the form of radioactive markers or so-called "pip tags" which are normally taped at known locations on selected casing joints of casing before the casing string is assembled. In this manner, after the casing string has been progressively assembled and lowered into the borehole, the radioactive pip tags will be positioned at predetermined depth locations in the well bore and will thereby provide distinctive reference points in the well bore that can be readily detected by typical radiation detectors. Regardless of which of the various techniques are employed for providing distinctive depth indicators or markers in a well bore, positioning of tubing-conveyed perforating-and-testing assemblies has been carried out heretofore by moving a wireline logging tool through the tubing string supporting the assembly of tools. Such wireline logging tools are equipped with a typical radiation detector that responds to one or more radioactive characteristics of the earth formations penetrated by the well bore as well as showing the depth location of the radioactive markers which have been previously positioned in the well bore.
In any event, the correlation measurements provided by any of these wireline logging tools will, of course, necessitate the services of a specialized logging truck and a crew of technicians before another crew of specialists can conduct the perforating operation. It will be realized that if the initial correlation measurements indicate that the perforating guns on the tubing-conveyed tool have been correctly positioned, the wireline logging tool can be returned to the surface without undue delay and the perforating operation commenced without further ado. Even should these initial measurements show that the perforators are positioned only a few feet away from their intended depths, the assembled tubing string can be readily raised or lowered at the surface as deemed necessary to shift the perforators to their correct locations in the well bore without having to first return the logging tool to the surface. So long as the wireline logging tool is still disposed in the tubing string, there is, of course, no problem in obtaining corroborating verification measurements to confirm the positioning of the perforators before the wireline logging tool is finally returned to the surface.
On the other hand, it will be appreciated that, at times, the initial correlation measurements provided by the wireline logging tool will instead indicate that the perforators cannot be properly positioned in the well bore without first changing the overall length of the supporting tubing string. This latter situation will frequently occur in deviated well bores having substantially horizontal intervals since significant changes in the overall length of the tubing string are often required to make even minor adjustments in the positions of the perforators in relation to the formation intervals to be perforated. Should it be determined that such adjustments must be made, the wireline logging tool must, of course, be temporarily removed from the well bore before tubing joints can be added to or removed from the tubing string to adjust the overall length of the tubing string. This will, therefore, necessitate the subsequent return of the logging tool back through the tubing string for obtaining additional correlation measurements before the perforating-and-testing operations can be safely conducted. It will be realized that even if the logging tool can be readily returned through the tubing string, these further correlation measurements will entail unplanned expenses such as additional stand-by charges since the logging crew must remain idle at the well site while the overall length of the tubing string is being modified. Those skilled in the art will also appreciate that there will be increased time delays every time that the wireline logging tool must be moved back through a tubing string which has one or more portions that are disposed in one or more significantly-inclined intervals of a particular well bore which is to be perforated with a tubing-conveyed perforator.
Accordingly, it is an object of the present invention to teach new and improved methods for employing tubing-conveyed well perforators for accurately perforating cased well bore intervals at a minimum cost.
It is a further object of the present invention to provide new and improved methods for reliably positioning typical tubing-conveyed well tools in well bores for subsequently conducting one or more completion operations in relation to selected formations traversed by the well bore.
It is an additional object of the present invention to disclose new and improved methods for accurately positioning tubing-conveyed well bore perforating apparatus at selected depth locations in deviated well bores without experiencing needless delays whenever adjustments must be made in the position of the apparatus and thereafter actuating the perforating apparatus with the full assurance that the resulting perforations will be correctly placed at those selected depth locations.

SUMMARY OF THE INVENTION

These and other objects of the invention are attained by providing new and improved methods for accurately positioning tubing-conveyed well bore apparatus in a well bore without having to employ wireline logging tools. In practicing the invention, a shoulder is arranged to support a retrievable measurement-while-drilling (MWD) tool having a radiation detector at a selected location in a tubing string carrying a tubing-conveyed tool such as a perforator with shaped explosive charges. Once a tubing string has been lowered into a well bore and the MWD tool positioned on its supportive shoulder, the MWD tool is operated to transmit acoustic signals through the tubing string representative of the radioactive characteristics of either a radioactive marker at a known depth or the formations adjacent to the MWD tool. The acoustic signals are correlated to determine the location of the tubing-conveyed tool within the well bore. The correlated data is then used for determining how to adjust the tubing string to accurately position the tubing-conveyed tool at a proposed depth location in the well bore.

BRIEF DESCRIPTION OF THE DRAWINGS

The particular features of the invention are set forth in the appended claims. The practice of the new and improved methods of the invention, together with further objects and various advantages thereof, may best be understood by way of the following description of typical apparatus as it may be employed for carrying out the methods of the invention as depicted in the accompanying drawings, in which:

FIGURE 1 illustrates a preferred embodiment of typical well bore apparatus which may be successfully employed to carry out the new and improved methods of the present invention; and
FIGURES 2-5 schematically depict the sequential positions of the well bore apparatus shown in FIGURE 1 showing the successive steps of the preferred manner of employing that apparatus to practice the methods of the present invention for conducting a perforating and testing operation in a cased well bore.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Turning now to FIGURE 1, as indicated generally at 10, a typical tubing-conveyed perforating-and-testing tool (such as the tool assembly fully described in U.S. Patent No. 4,509,604 which is hereby incorporated herein by reference) is depicted as that tool assembly will appear while suspended in a cased well bore 11. As is typical, the tool assembly 10 was previously coupled to the lower end of a joint or stand of well tubing and the tool assembly was then progressively lowered into the cased well bore 11 as an elongated tubing string 12 was successively assembled from tandemly-coupled joints with a combined overall length sufficient for positioning the tool adjacent to a selected earth formation, as at 13, containing producible connate fluids. The tubing-conveyed perforating-and-testing tool 10 preferably includes a full-bore reversing valve 14 tandemly coupled between the lower end of the tubing string 12 and the upper end of a full-bore test valve 15. The test valve 15 is, in turn, coupled to the upper end of a tubular mandrel of a full-bore packer 16 which is arranged for dependently supporting a tubing-conveyed perforator such as shown generally at 17. As is typical, the perforator 17 is preferably dependently coupled to the lower end of the packer 16 by a so-called "safety joint" 18 placed so that the perforator 17 is below the rig floor when the perforating guns are armed. A slotted section of pipe 19 is also typically coupled between the perforator 17 and the safety joint 18 to facilitate the entry of connate fluids into the tubing string 12 once the perforator has been actuated.
Accordingly, in practicing the invention, the packer 16 may be a typical full-bore packer including normally-retracted slips and expandable elastomeric packing elements which are each operable to be shifted outwardly against the internal wall of the casing 111 at a selected depth location just above the formation 13. In a similar fashion, as an example of exemplary apparatus for practicing the new and improved methods of the invention, the reversing valve 14 represented in FIGURE 1 is preferably a selectively-operable full-bore, pressure-controlled reversing valve. As is typical, the reversing valve 14 is fully operable for selectively controlling communication between the internal bore of the tubing string, as at 12, and the annulus of the well bore, as at 11, by means of controlled pressure changes in the fluids in the annulus and the tubing string. Those skilled in the art will recognize, of course, that various types of typical full-bore reversing valves can also be readily employed as well without departing beyond the scope of the present invention disclosed and claimed herein.
Similarly, in carrying out the methods of the present invention, it is preferred to utilize the repetitively-operable full-bore test valve 15 fully disclosed in U.S. Reissue Patent No. 29,638 which is also incorporated herein by reference. As described in that reissue patent, the test valve has a rotatable ball valve member (not illustrated in the present drawings) which is selectively rotated between its opened and closed positions in response to controlled pressure changes of the fluids in the annulus of the well bore 11 and the fluids in the tubing string 12 for controlling communication through the tubing-conveyed perforating-and-testing assembly 10 and its supporting tubing string 12. Here again, it must be understood that in lieu of using the full-bore test valve 15 described in the aforementioned reissue patent, other types of test valves can be employed for practicing the methods of the present invention. For example, the new and improved methods of the invention may also be successfully practiced by employing a simpler test tool (not illustrated in the present drawings) such as those having a glass disc or other frangible barrier initially blocking the axial bore of these simpler tools until the barrier is broken by dropping a so-called "drop bar" through the tubing string 12 whenever communication is to be permanently established through the tubing string.
The particular perforator 17 which is to be utilized in successfully practicing the methods of the invention can be any one of the typical tubing-conveyed perforators currently in use in the industry. For example, the perforator 17 can be arranged in accordance with the new and improved perforator disclosed in U.S. Patent No. 4,509,604. As schematically depicted in FIGURE 1, the perforator 17 typically has a so-called "firing head" 20 coupled to the upper end of an assembly of one or more enclosed tubular carriers, as indicated generally at 21 and 22, which are respectively arranged for supporting therein a plurality of shaped explosive charges as shown at 23 and 24 in FIGURE 2. As fully described in the last-cited patent, the firing head 20 is operatively arranged as seen in FIGURE 2 for detonating a typical blasting cap 25 coupled to a length of flexible detonating cord, such as at 26, which is disposed through the enclosed carriers 21 and 22 and cooperatively arranged within detonating proximity of each of the several shaped charges as at 23 and 24. In the preferred manner of practicing the methods of the present invention, as described in the last-cited patent, the firing head 20 is arranged so that it can be selectively operated from the surface by controlled pressure variations in the fluids in the well bore 11 and the tubing string 12. If the configuration of the tubing string 12 will permit, the firing head 20 is also arranged to be fired by dropping a weighted so-called "drop bar" (not illustrated) into the tubing string when it is reasonably assured that this drop bar will be able to strike the firing head with sufficient impact to detonate the blasting cap 25.
Since the present invention relates to new and improved methods for accurately positioning tubing-conveyed well bore tools such as the depicted perforating-and-testing tool assembly 10, it must be understood that the successful practice of the invention is wholly independent of the particular well bore devices, as at 14-26, which may be collectively employed for assembling the combined perforating-and-testing tool 10 depicted in FIGURE 1. Those skilled in the art will appreciate that there is a wide variety of typical well bore devices, such as at 14-26, which are readily available. Accordingly, as will subsequently become apparent, it will be appreciated that a full and complete understanding of the practice of the present invention does not require a detailed description or drawings of any of the well bore devices 14-26 which may be selected and readily incorporated into the tool assembly 10 by anyone skilled in the art for successfully practicing the methods of the present invention.
Nevertheless, irrespective of the particular well bore devices 14-26 which have been selected for inclusion in the tool assembly 10, to practice the methods of the present invention it is essential that a tool-positioning device, such as a tubular sub or landing nipple 30, be located in the tubing string 12 at a known spatial relationship in relation to the perforator 17 that is included in the tool assembly. As is typical, the tubular landing nipple 30 includes means, as generally indicated at 31 in FIGURE 2, such as a reduced-diameter intermediate portion in the axial bore of the tubular sub for defining an upwardly-facing internal shoulder or inwardly-projecting abutment cooperatively configured for receiving a matching shoulder on a MWD tool such as the MWD tool shown at 32.
To practice the methods of the present invention, it will, of course, be recognized that in order for the MWD tool 32 to be capable of being safely moved through the tubing string 12, the external diameter of the tool must be somewhat less than the internal diameter of the tubing string. Accordingly, to practice the methods of the present invention, it is preferred that the MWD tool 32 is the new and improved reduced-diameter MWD tool that is fully described in U.S. Patent No. 4,914,637 which is hereby incorporated herein by reference. As pointed out in that patent, that particular MWD tool, as at 32, is not nearly as complicated as conventional MWD tools which are typically coupled into a string of drill pipe and drilling collars and arranged for providing selected measurements during the course of drilling a borehole with a rotary bit. Accordingly, it has been found that the reduced-diameter MWD tool 32 depicted in FIGURE 1 uniquely lends itself to being readily arranged for safe passage through a tubing string such as at 12. It will, of course, be recognized that the MWD tool 32 can be readily arranged by those with only routine skill in the art to carry a sensor package, as indicated generally at 33 in FIGURE 2, which includes a variety of typical sensor devices such as gamma-energy radioactivity detectors as well as their associated electronic circuitry, with this combined sensor package being located in an enclosed pressure-balanced housing 34 which, as depicted in FIGURE 1, is preferably arranged on the lower end of the MWD tool.
As fully described in U.S. Patent No. 4,914,637, it will be appreciated that as illustrated in FIGURE 2B in that patent, the landing nipple 30 and the complementary shoulders indicated generally at 31 can be arranged for orienting the MWD tool 32 in a known angular relationship with respect to the perforator 17 should it be desired that the sensor package 33 further include sensors capable of monitoring the angular orientation of the MWD tool 32 in relation to the orientation of the firing axes of the shaped charges 23 and 24. It must be recognized, however, that the successful practice of the method of the present invention does not require that the MWD tool 32 must always be oriented in a known angular relationship unless a particular perforating-and-testing operation which is to be performed necessitates that the shaped charges 23 and 24 are aligned in a particular orientation.
Turning now to FIGURES 2-5, schematic representations of the perforating-and-testing tool 10 are respectively depicted in those drawings as the assembled tool is successively employed to practice the preferred steps of methods of the present invention to perforate a selected earth formation as at 13. As represented in FIGURE 2, individual joints or stands of well tubing have been successively coupled to the upper end of the tubing string 12 and progressively lowered from the surface into the cased well bore 11 until the combined length of the tubing string was sufficient for positioning the perforator 17 depending from the lower end of the tool assembly 10 adjacent to the earth formation 13. It will be noted that as depicted in FIGURES 1-5, the landing nipple 30 is preferably coupled to the lower end of the tubing string 12 so that the MWD tool 32 will be offset only a minimal distance above the perforating-and-testing tool assembly 10. With such minimal spacing, it will be appreciated that the sensor package 33 will be better able to provide real-time measurements representative of the characteristics of the particular earth formation, as at 13, that the perforator 17 is then facing. It will, however, be recognized that the particular spatial relationship of the sensor package 33 and the perforating-and-testing tool 10 is not of a critical importance to the successful practice of the new and improved methods of the present invention since the tubing string 12 can be moved upwardly and downwardly from the surface whenever it is necessary to determine various formation characteristics as well as to accurately locate the upper and lower boundaries of any given earth formation. Accordingly, those skilled in the art will appreciate that the successful practice of the present invention requires only knowing the precise spatial relationship between the sensor package 33 and the perforators 17 whenever the MWD tool 32 is seated in the landing nipple 30.
In FIGURE 2 the perforating-and-testing tool assembly 10 is depicted as the tool assembly is being lowered into the well bore 11. At this point in the operation, the reverse circulating valve 14 is in its open position to allow the tubing string 12 to be progressively filled with the fluids (typically a salt water brine solution) in the well bore 11 as the tool assembly 10 is being lowered to its selected depth location. At this time, the test valve 15 is in its closed position. Although the MWD tool 32 is seen in FIGURE 2 it should be recognized that, as a matter of choice, it may be desired to position the MWD tool on the landing nipple 30 after the entire tubing string 12 has been assembled. In that situation, the MWD tool 32 will be spared from any rough handling that it might otherwise encounter as the tubing string 12 is assembled. The MWD tool 32 can, of course, be subsequently transported to its selected depth location by releasably coupling a typical wireline overshot (not illustrated in FIGURE 2) to a matching upstanding fishing neck 35 on the upper end of the MWD tool and lowering the MWD tool through the tubing string 12 until it has reached its operating position defined by the engagement of the opposing shoulders 31 on the landing nipple 30 and body of the MWD tool. Nevertheless, it will be recognized that it is a only a matter of choice whether the MWD tool 32 is alternatively initially positioned on the landing nipple 30 with the mating shoulders 31 cooperatively engaged and the tool transported into the well bore 11 as the tubing string 12 is being progressively assembled.
As shown in FIGURE 3, the perforating-and-testing tool assembly 10 has been positioned at a selected depth location in the well bore 11 as is determined by the combined length of the tubing string 12 which has been assembled at that time. The test valve 15 is still closed and, as depicted, the packer 16 has not been set. It should be noted that if desired to protect various earth formations from damage, the full-bore packer 16 could be set if deemed best for isolating that portion of the well bore below the present depth location of the tool assembly 10. As indicated by the flow arrows 40 in FIGURE 3, a fluid, such as a typical brine solution, is then pumped into the tubing string 12 by operating suitable surface equipment (not illustrated) to carry the fluid downwardly through the tubing string and out of the still-open ports of the circulating valve 14 into the annulus of the well bore 11 from where the fluid is then returned to the surface. In this manner, as fully described in the above-cited U.S. Patent No. 4,914,637, the downward flow of the fluid through the tubing string 12 will be effective for initiating the operation of the MWD tool 32 for producing one or more detectable acoustic signals which will be transmitted through the downwardly-moving fluid to typical signal-detecting equipment (not illustrated) that is coupled to the upper end of the tubing string for decoding the acoustic signals which are representative of the real-time measurements produced by the sensor package 33.
It will, of course, be appreciated that the successful practice of the present invention is not limited to positioning the tool assembly 10 either at its final depth location or at one or more intermediate depth locations before the MWD tool 32 is operated. The MWD tool 32 may be operated any number of times at one or more intermediate depth locations while the tubing string 12 which has been assembled to that point is moving or stationary so that the sensor package 33 can provide one or more sets of measurements that may be utilized for verifying the current depth location of the tool assembly 10 and the nature of the earth formations which are then immediately adjacent to the sensor package.
Nevertheless, as shown in FIGURE 4, once the tubing string 12 is believed to have been fully assembled so as to accurately position the perforator 17 adjacent to the selected formation 13 to be perforated, the downward flow of fluids, as indicated at 45, through the assembled tubing string is employed for operating the MWD tool 32 to determine the nature of the formation interval that is penetrated at that particular depth location in the cased well bore 11. By including a typical radiation detector in the sensor package 33, the output signals provided by the MWD tool 32 can be effectively utilized for providing surface indications that are representative of the radioactivity characteristics of the formation 13. It will also be recognized that, if desired, this typical radiation detector in the sensor package 33 can also be used to sense the proximity of the detector to one or more radioactive tags, as at 50, which have been previously placed at one or more selected depth locations in the well bore 11. In any case, by simply correlating those surface indications with previous logs which have been obtained of the various formations at different depth locations in the well bore 11, as well as of radioactive tags, as at 50, a determination can be readily made whether or not the perforator 17 has been accurately located with respect to the selected formation 13.
Should these initial measurements show that the perforator 17 is not precisely located at its intended depth, it is quite convenient, of course, to simply raise or lower the upper end of the tubing string 12 at the surface for whatever distance that may be required to bring the perforator to that depth. It will be fully appreciated by those skilled in the art that since the MWD tool 32 will remain in its depicted operating position, the tubing string 12 can be carefully shifted from the surface while a series of real-time measurements are transmitted to the signal-detecting equipment (not illustrated in the drawings) located at the surface. Moreover, in sharp contrast with the time-consuming (and sometimes imprecise) prior-art depth-correlation techniques with typical wireline logging tools which require the removal of the logging tools from the well bore 11 before any changes can be made in the overall length of the tubing string, in practicing the present invention, the overall length of the tubing string 12 can be readily increased or decreased without ever having to remove the MWD tool 32. It will, of course, be recognized by those with skill in the art that by simply observing the various real-time measurements provided by the MWD tool as the tubing string 12 is being shifted, the overall length of the tubing string can be quickly modified as deemed necessary; and then the tubing string can thereafter be incrementally positioned both upwardly and downwardly as may be necessary for locating the perforator 17 at the precise depth for efficiently perforating the formation 13. It should also be recognized that so long as the MWD tool 32 is at its location depicted in FIGURE 4, these critical measurements can be readily obtained until the tool assembly 10 is correctly positioned and the perforator 17 is in readiness to be actuated.
Turning now to FIGURE 5, the perforating-and-testing tool 10 is depicted after it has been positioned so as to accurately locate the perforator 17 in its intended position before being actuated. At this time, the downward circulation of brine, as previously shown at 45 in FIGURE 4, has been discontinued. As schematically depicted in FIGURE 5, a typical overshot or grapple 55 which is dependently supported on a suspension line or so-called "slick line" 56 spooled on a winch (not illustrated) at the surface is then lowered into the tubing string 12 and maneuvered as needed for securing the grapple to the upstanding fishing neck 35 on top of the MWD tool 32. As is typical, once the fishing neck 35 has been engaged, the winch carrying the suspension line 56 is then operated for returning the MWD tool 32 to the surface. If it has not been previously set, the full-bore packer 16 is then operated for expanding the elastomeric elements on the packer into sealing engagement with the adjacent wall of the casing 111.
Once the MWD tool 32 has been returned to the surface, it is typically preferred to replace the fluid, such as brine, that has been pumped through the tubing string 12 to operate the MWD tool. As represented by the flow arrows 57, replacement of the brine in the tubing string 12 is conveniently accomplished by pumping a suitable pressure-control fluid such as diesel oil into the tubing string while the circulating valve 14 is still open. This circulation will, of course, serve to displace at least some of the brine through the still-open ports of the circulating valve 14 and out into the annulus of the well bore 11. Once it is believed that the diesel oil has displaced a sufficient amount of the brine from the tubing string 11 to reduce the hydrostatic head of the fluids in the tubing string below the anticipated formation pressure of the connate fluids in the formation 13, the circulating valve 14 is then operated for closing its outer ports; and the tool assembly 10 will then be in readiness for commencing the perforating operation.
At this point, the test valve 15 is operated as previously described as required for opening fluid communication through the tubing string 12 to the isolated well bore interval lying below the expanded full-bore packer 16. Opening of the test valve 15 will also be effective for making the upper end of the firing head 20 accessible from the surface by way of the axial bore through the tubing string 12. Thus, as previously discussed, the perforator 17 is then fired either by controlling the pressure differential between the axial bore of the tubing string 12 and the annulus of the well bore 11 or by dropping a weighted drop bar (not seen in the drawings) through the tubing string for striking the impact-responsive actuator on the firing head 20.
Once the perforating operation has been completed, the testing valve 15 is then operated in the typical fashion for conducting one or more pressure-testing operations of the connate fluids that are produced upon opening of the test valve. When it is desired to recover a sample of these fluids, the testing valve 15 can, of course, be left open as necessary for bringing any connate fluids which may have entered the tubing string 12 to the surface. Those skilled in the art will obviously appreciate that one or more various pressure and flow tests may be performed while the tool assembly 10 remains in the operating position depicted in FIGURE 5. The nature and number of such tests are, of course, well beyond the scope of the new and improved methods of the present invention. In any event, once these tests have been conducted, the tool assembly 10 is operated for releasing the packer 16 and then progressively raising the tubing string 12 and successively removing one or more joints or stands of the tubing until the tool assembly 10 has been returned to the surface.
Accordingly, it will be appreciated from the preceding description that the new and improved methods of the present invention provide techniques for accurately locating tubing-conveyed well bore apparatus such as the combined perforating-and-testing tool 10 in a well bore as at 11. As described, the methods of the invention are successfully carried out by first positioning a reduced-diameter MWD tool 32 at a selected location in the tubing string 12 which is arranged to be assembled for positioning the perforating-and-testing tool 10 at a selected depth location in a well bore. The MWD tool 32 is then operated for obtaining signals representative of the measurements provided by radiation-detecting sensing means on the MWD tool 32 which are representative of the radioactivity characteristics of either one or more radioactive markers that were previously placed at known depth locations in the well bore or the earth formations adjacent to the MWD tool. Those representative measurements are then used to accurately determine the depth location of the perforating-and-testing tool 10 so that the perforator 17 carried thereby can be positioned correctly to assure the perforation of a chosen earth formation as at 13.
While only a particular mode of practicing the present invention has been shown and described herein, it is apparent that various changes and modifications may be made without departing from the broader aspects of this invention; and, therefore, the aim in the appended claims is to cover all changes and modifications that fall within the true spirit and scope of this invention.

Claims

A method for accurately positioning tubing-conveyed well bore apparatus in a well bore traversing a selected earth formation having a known detectable radioactive characteristic and comprising the steps of:
positioning a MWD tool having a radiation detector in a tubing string carrying said tubing-conveyed apparatus;
lowering said tubing string into a well bore;
operating said MWD tool for transmitting to the surface a series of signals representative of the radioactive characteristics of the earth formations which are then adjacent to said MWD tool;
correlating said radioactive characteristics of the formations provided by said signals with said known radioactive characteristic of said selected earth formation for determining whether said MWD tool is then positioned adjacent to said selected earth formation; and
adjusting the position of said tubing string within said well bore in accordance with the correlation of said radioactive characteristics for accurately positioning said tubing-conveyed apparatus adjacent to said selected earth formation.
The method of Claim 1 further including the additional step of operating said tubing-conveyed apparatus once it has been accurately positioned adjacent to said selected earth formation.
The method of Claim 1 further including the additional steps of:
operating said MWD tool for transmitting a second series of signals to the surface that are representative of the radioactive characteristics of the earth formations which are then adjacent to said MWD tool;
correlating said second series of signals with said known radioactive characteristic of said selected earth formation for verifying that said MWD tool is then positioned adjacent to said selected earth formation; and
operating said tubing-conveyed apparatus once it has been verified that said tubing-conveyed apparatus has been accurately positioned adjacent to said selected earth formation.
The method of Claim 3 wherein said tubing-conveyed apparatus includes a perforator and including the further step of operating said perforator for establishing fluid communication between said selected earth formation and said tubing string.
The method of Claim 4 wherein said tubing-conveyed apparatus further includes a selectively-operated test valve and including the further step of opening said test valve after said perforator has been operated for admitting connate fluids from said selected earth formation into said tubing string.
The method of Claim 4 wherein said tubing-conveyed apparatus further includes a selectively-operated test valve and including the further step of opening said test valve after said perforator has been operated for admitting connate fluids from said selected earth formation into said tubing string for determining pressure characteristics of said selected earth formation while connate fluids are being produced therefrom.
The method of Claim 4 wherein said tubing-conveyed apparatus further includes a selectively-operated test valve and including the further step of opening said test valve after said perforator has been operated for admitting connate fluids from said selected earth formation into said tubing string for obtaining a sample of said connate fluids produced from said selected earth formation while said test valve is open.
The method of Claim 3 wherein said tubing-conveyed apparatus includes a perforator and including the further steps of:
removing said MWD tool from said tubing string; and
thereafter operating said perforator for establishing fluid communication between said selected earth formation and said tubing string.
The method of Claim 8 wherein said tubing-conveyed apparatus further includes a selectively-operated test valve and including the further step of opening said test valve after said perforator has been operated for admitting connate fluids from said selected earth formation into said tubing string for obtaining a sample of said connate fluids produced from said selected earth formation while said test valve is open and for determining the pressure characteristics of said selected earth formation while connate fluids produced therefrom are entering said tubing string.
A method for accurately positioning a tubing-conveyed perforator in a well bore traversing a selected earth formation having a predetermined detectable radioactive characteristic and comprising the steps of:
positioning a retrievable MWD tool having a radiation detector at a selected location in a tubing string carrying a tubing-conveyed perforator;
lowering said tubing string into a well bore;
operating said MWD tool for transmitting signals to the surface that are representative of the radioactive characteristics of the earth formations which are then adjacent to said MWD tool;
correlating said signals for determining whether said tubing-conveyed perforator is then adjacent to said selected earth formation;
adjusting the position of said tubing string within said well bore as determined from said correlated data for accurately positioning said tubing-conveyed perforator adjacent to said selected earth formation;
operating said MWD tool for transmitting additional signals to the surface that are representative of the radioactive characteristics of the earth formations which are then adjacent to said tubing-conveyed perforator;
correlating said additional signals with said known radioactive characteristic of said selected earth formation for verifying that said tubing-conveyed perforator is positioned adjacent to said selected earth formation; and
once it is verified that said tubing-conveyed perforator has been accurately positioned adjacent to said selected earth formation, then actuating said tubing-conveyed perforator for perforating said selected earth formation.
The method of Claim 10 wherein said MWD tool is movably positioned within said tubing string and including the further step of returning said MWD tool to the surface before actuating said perforator.
The method of Claim 10 including the further steps of:
movably positioning said MWD tool within said tubing string; and
returning said MWD tool to the surface before actuating said perforator.
The method of Claim 10 including the further steps of:
positioning a radioactive tag at a known depth location in said well bore before said tubing string is lowered into said well bore;
operating said MWD tool for transmitting signals to the surface representative of the radioactive characteristics of said radioactive tag; and
correlating said signals that are representative of the radioactive characteristics of said radioactive tag with said signals which are representative of the radioactive characteristics of said selected earth formation for obtaining yet another verification that said tubing-conveyed perforator has been positioned adjacent to said selected earth formation before said perforator is actuated.
A method for accurately positioning a tubing-conveyed perforator and test valve in a well bore traversing a selected earth formation having a known radioactive characteristic and comprising the steps of:
positioning a retrievable MWD tool having a radiation detector at a selected location in a tubing string carrying a tubing-conveyed perforator and test valve;
lowering said tubing string into a well bore;
operating said MWD tool for transmitting signals to the surface which are representative of the radioactive characteristics of the earth formations which are then adjacent to said MWD tool;
correlating said signals for determining whether said tubing-conveyed perforator and test valve are adjacent to said selected earth formation;
adjusting the position of said tubing string within said well bore in accordance with said correlated data for positioning said tubing-conveyed perforator and test valve adjacent to said selected earth formation;
actuating said perforator for perforating said selected earth formation; and
opening said test valve for establishing communication between said selected earth formation and said tubing string.
The method of Claim 14 including the further step of retrieving said MWD tool before actuating said perforator.
The method of Claim 14 including the further steps of:
positioning a radioactive tag at a known depth location in said well bore before said tubing string is lowered into said well bore;
operating said MWD tool for transmitting signals to the surface representative of the radioactive characteristics of said radioactive tag; and
correlating said signals that are representative of the radioactive characteristics of said radioactive tag with said signals which are representative of the radioactive characteristics of said selected earth formation for obtaining yet another verification that said tubing-conveyed perforator has been positioned adjacent to said selected earth formation before said perforator is actuated.