Methods and apparatus for completing production wells

[57] ABSTRACT

This application discloses new and improved methods and apparatus for completing production wells having perforations which either are to be cleaned or penetrate earth formations which are to be fractured, acidized, or treated such as, for example, to inhibit the subsequent production of unconsolidated formation materials. To practice the present invention, a new and improved production tool is arranged for coupling into a string of production tubing and includes a typical well packer having an elongated tubular member dependently coupled therebelow and capped at its lower end for defining an enclosed chamber of a substantial volume and which is initially maintained at a reduced pressure by new and improved normally-closed pressure-actuated valves serially arranged at the upper end of the tubular member and adapted to be selectively opened in succession. The production string and the tool are installed in a cased well bore with the packer being set above a previously-perforated interval traversing an earth formation which is to be subsequently produced. Once the customary wellhead equipment is installed to provide selective communication from the surface with the tubing and casing, the first of the two normally-closed valves is selectively opened by increasing the pressure of the well bore fluids in the production string above the packer. Upon opening of this first valve, formation fluids will be suddenly exhausted into the reduced-pressure chamber for removing contaminants that may have previously entered the formation following the perforation of the casing so as to leave only uncontaminated formation materials immediately surrounding the perforations. Thereafter, the second normally-closed valve is selectively opened by injecting selected fluids by way of the production string through the perforations and into the adjacent earth formations.

Claims, 7 Drawing Figures

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PATENTED JUL 4 are.

3,674,091

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ATTORNEY

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ATTORNEY

PATENTEOJUL 41972

3,674,091

SHEET 3 OF 3

FIG. 7

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James W. Kisling, HI INVENTOR

3,674,091

2

METHODS AND APPARATUS FOR COMPLETING PRODUCTION WELLS

It is, of course, customary for a cased well bore to be perforated at one or more points to provide fluid communication with selected earth formations therearound. Once the well is perforated, various treating operations — such as acidizing, fracturing, or sand-consolidating operations — are typically conducted to prepare the well for efficient production. Those skilled in the art will appreciate, however, that it is not at all uncommon for one or more of the perforations along a given perforated interval to be at least partially blocked by loose formation materials, debris, or foreign matter which is usually deposited in a perforation by typical shaped charges. A partial or total blockage of one or more of the perforations will, of course, impede or prohibit the introduction of treating fluids into those perforations and result in the inadequate treatment of at least those portions of the earth formation immediately adjacent thereto. As a result, further and otherwise needless treating operations will ultimately be required. Accordingly, unless all of the perforations along a perforated interval are capable of readily conducting fluids, subsequent treating operations as well as the production rate of the well will be significantly impaired.

Heretofore, such treating operations have had to be conducted before the drilling rig is removed from the well site so that its associated equipment and drill string could be employed. This, of course, results in needless expenses as well as additional delays before the production string and the related surface equipment can be installed to prepare the well for production.

Accordingly, it is an object of the present invention to provide new and improved methods and apparatus for completing wells to obtain improved fluid communication between the well bore and selected earth formations traversed thereby without delaying the installation of the production string and the associated wellhead and surface equipment once the drilling operation is concluded.

This and other objects of the present invention are attained by tandemly arranging pressure-actuated valve means in a production string and below a production packer included therewith. The valve means are initially closed to define an enclosed chamber of selected volume in a section of tubing arranged therebelow and capped at its lower end to maintain the chamber at a reduced pressure until after the packer is set and the production string is installed and connected to the usual wellhead and surface equipment. When the well is to be prepared for production, the valve means are selectively operated from the surface to draw formation fluids into the enclosed chamber for clearing the perforations below the production packer of debris or contaminants that would otherwise impair fluid communication between the production string and the perforated earth formations. Thereafter, the valve means are again selectively operated for injecting fluids from the surface into the well bore below the packer as may be necessary to prepare the well for production.

In the preferred embodiment of the apparatus of the present invention, the new and improved valve means are operatively arranged to be selectively opened in response to first and second predetermined changes in the pressure in the production string above the production packer. In this manner, communication can be first established between the perforated interval and the enclosed chamber below the upper valve means thereabove and thereafter between the production string and the perforated interval of the well bore below the packer.

The novel features of the present invention are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may be best understood by way of the following description of new and improved apparatus and exemplary methods employing the principles of the invention as illustrated in the accompanying drawings, in which:

FIGS. 1,3 and 5 schematically depict the successive steps of the methods of the present invention;

FIGS. 2,4 and 6 respectively show a typical perforation as it may appear during the course of a completion operation being conducted in accordance with the methods of the present invention;and

FIG. 7 depicts a preferred embodiment of the new and improved apparatus of the present invention.

Turning now to FIG. 1, a new and improved production tool 10 arranged in accordance with the principles of the present invention is schematically illustrated as being dependently coupled from the lower end of a String of production tubing 11 and positioned in a well bore 12 having a casing 13 secured in place by an external sheath of cement 14. To gain communication with an earth formation 15 traversed by the well bore 12, one or more perforations, as at 16, have been previously produced through the casing 13 and cement 14 in the usual manner. As is customary, the production tubing is dependently supported in the well bore 12 by a typical wellhead assembly 17 including at least a pair of valves, as at 18 and 19, for selectively controlling communication with the tubing string 11 and casing 13.

As illustrated in FIG. 1, the tool 10 is comprised of a selectively-settable production packer 20 from which an elongated tubular body 21 having its lower end capped, as at 22, is dependently coupled. To provide an enclosed chamber 23 that is initially maintained at a low or atmospheric pressure, selectively-operable normally-closed valve means 24 are arranged at the upper end of the body. As a matter of convenience, it is, of course, preferred to employ one or more joints of conventional production tubing for the elongated body 21. The chamber 23 can, if desired, be filled with an inert gas that is at a selected pressure which is less than the anticipated formation pressure. Although other well packers may, of course, be employed, it is preferred that the packer 20 be one of the production packers shown in either U.S. Pat. No. 3,074,484 or U.S. Pat. No. 3,352,362.

As will be subsequently discussed, the methods of the present invention are uniquely applicable for performing acidizing and fracturing operations as well as sand-consolidation operations after the production string 11 and the wellhead 17 are in position. However, for purposes of illustration, FIGS. 2-6 depict the practice of the methods of the present invention as it might be conducted for a sand-consolidation operation. Accordingly, as depicted in FIG. 2, an enlarged view is shown of one of the perforations 16 as it may well appear where the adjacent formation 15 is substantially unconsolidated or incompetent.

It will, of course, be appreciated that when a perforating tool (not shown) which typically includes one or more shaped charges is positioned in the well bore 12 and actuated for producing the perforations 16, the perforations will initially extend into the incompetent formation 15 as generally represented in FIG. 2. It is believed, however, by those skilled in the art that the perforation 16 will quickly fill up with loose materials from the incompetent formation 15 leaving open only a passage or so-called “tunnel” 25 extending through the casing 13 and the adjacent cement sheath 14.

In any event, irrespective of the nature of the formation, debris (such as at 26) will be left in the formation 15 as a result of the disintegration of a typical shaped charge liner. Moreover, by observing test shots fired into laboratory targets, it is known that a typical shaped charge perforating jet will leave a somewhat-impermeable layer of debris (as indicated at 27) around the walls of the forward portion of the perforation 16. This relatively-impermeable sheath of debris will either remain substantially in the position illustrated at 27; or, if the formation (as at 15) is incompetent, this impermeable layer will most likely be collapsed inwardly as the forward portion of the perforation 16 is filled with loose formation materials. In any event, flow communication between the entrance tunnel 25 and the formation 15 will be at least retarded, if not substantially impaired, by the debris 26 and 27 deposited in the formation just outside of the tunnel. It is, therefore, this debris 26 and 27 which, irrespective of the competency of the

3,674,091

4 formation 15, must be removed before the well bore 12 can be successfully completed and production commenced.

Accordingly, as illustrated in FIG. 3, after the packer 20 has been set for isolating the interval of the well bore 12 immediately adjacent to the perforations 16 from the remainder of the well bore thereabove and the wellhead 17 is in position, the valve 24 is first actuated to establish communication between the isolated interval of the well bore and the enclosed chamber 23. It will be appreciated, therefore, that upon opening of the valve 24, a sudden high-pressure differential is developed between the connate fluids in the formation 15 and the enclosed chamber 23 which, preferably, is initially at atmospheric pressure. This sudden pressure differential across the perforated well bore interval will induce a rapid, highvelocity flow of connate fluids, from the formation 15 through the various entrance tunnels 25 and into the empty chamber 23. These rushing fluids will, therefore, effectively wash out the debris, as at 26 and 27 (FIG. 2), along with a limited quantity of loose formation materials through the several tunnels 25. As a result, as shown in FIG. 4, once this sudden flow ceases upon the filling of the chamber 23, the formation 15 surrounding the perforations 16 will be effectively cleaned leaving only clean formation particles, as at 29, partially or totally filling the tunnels 25 through the casing 13 and the cement 14.

It will be recognized, of course, that with even these clean formation particles, as at 29, in the entrance passages 25, the subsequent injection of consolidating agents or the production of connate fluids from the formation 15 will be materially limited. It is, therefore, one of the paramount objects of the present invention to remove these loosened particles 29 from the tunnels 25 before further completion operations are conducted.

Accordingly, to accomplish this, a clean fluid, as at 30 in FIG. 5, is admitted to the production string 11 by way of the wellhead valve 18; and, by actuating the new and improved valve 24 to now open communication between the production string and the chamber 23, the fluid will be suddenly introduced into the previously-closed chamber to produce a sudden shock or transitory pressure surge in the isolated interval of the well bore 12 below the packer 20 for driving the clean sand particles 29 back into the formation 15 and clearing the tunnels 25 as illustrated in FIG. 6.

It will, of course, be appreciated that although the chamber 23 is completely filled with the connate fluids upon the second actuation of the valve 24, these fluids as well as those in the isolated portion of the well bore 12 below the packer 20 will be at a pressure no greater than the natural formation pressure of the earth formation 15. Accordingly, by rapidly discharging the fluid 30 into the chamber 23 as well as the well bore, significant dynamic shock pressures will be developed which are substantially greater than the formation pressure of the well fluids within the isolated portion of the well bore 12 below the packer 20. Thus, as previously noted, the sudden release of the fluid 30 into the chamber 23 will be effective for forcibly driving the sand particles 29 out of the several tunnels 25 and back into the surrounding formation 15. It will, of course, be appreciated that once these transitory shock pressures have subsided, the injection fluid 30 is maintained at an elevated pressure which will be sufficient for preventing the production of further connate fluids through the several perforations 16 so that additional sand particles will not re-enter the several tunnels 25.

Where the formation 15 does not require a consolidation operation, the fluid 30 needs only to be a suitable fluid such as a clean saline solution. By properly selecting a saline solution of sufficient density, the resulting hydrostatic pressure of the fluid 30 will along be effective for retaining control of the well until production is commenced.

On the other hand, where the earth formation 15 is to be consolidated by typical sand-consolidating agents, it is generally preferred that the fluid 30 be a so-called “pre-flush fluid” such as kerosene, diesel oil, or a clean saline solution.

This injection fluid 30 is maintained at an elevated pressure before the valve 24 is first opened; and once the pressured pre-flush fluid is pumped into the formation 15, one or more consolidating agents (not shown) are successively pumped 5 through the tubing string 11 and into the formation to accomplish the desired consolidation. As is typical, if production is not to be commenced immediately, the consolidating fluids may then be followed by a suitable after-flush agent, such as kerosene, as well as in some instances, temporary plugging agents such as “Black Magic” an oil-base mud as supplied by Oil Base, Inc., of Houston, Texas. It will be recognized that the hydrostatic pressure and the pumping pressure of these successively-injected treating fluids will be greater than the formation pressure of the formation 15 so that the tunnels 25 will ¹⁵ remain open throughout the consolidation operation. The particular nature or type of the sand-consolidation agents employed are, of course, of no significance to the present invention and the consolidating agents may be either porous-setting or solid-setting plastics.

As previously mentioned, the methods of the present invention are also equally applicable for acidizing or hydraulic fracturing operations after the wellhead 17 and the production string 11 are in position. Accordingly, where the formation 15 25 is to be either acidized or fractured, the treating fluid 30 will, of course, be the fluid or fluids which are typically employed for such operations. Otherwise, the sequence of events will be substantially as depicted in FIGS. 1-6 with the possible exception that the formation 15 may be sufficiently competent that 30 there will be little or no loose formation materials, as at 29, drawn into the tunnels 25 as the debris 26 and 27 is cleared from the perforations 16. In either situation, however, those skilled in the art will appreciate that the new and improved methods of the present invention will be of significant benefit 35 for economically conducting either an acidizing operation or a hydraulic fracturing operation.

Of particular significance, it should be recognized that by employing the methods of the present invention to commence either an acidizing operation or a fracturing operation, the 40 dynamic shock or surge pressures that are developed when the treating fluid 30 is suddenly released upon the second actuation of the valve 24 will be of material benefit in commencing the operation. This sudden surge or pressure shock will, therefore, be particularly useful in “breaking down” the formation 4³ 15 to assure that the treating fluid 30 is entering all of the perforations 16. As a further benefit, it has been found that the pumping pressures required to continue movement of the treating fluid 30 into the formation 15 will be significantly reduced in comparison to the pumping pressures normally ⁵⁰ required for conducting acidizing or fracturing operations as heretofore conducted before the present invention.

Turning now to FIG. 7, a preferred embodiment is shown of the new and improved valve 24 which is particularly adapted -- for use with the production tool 10 of the present invention.

As best seen in FIG. 7, the valve 24 includes a tubular body 31 suitably adapted for tandemly coupling the valve between the packer 20 and the depending tubing 21. In the preferred embodiment of the valve 24, the axial bore of the tubular body 31 ¢0 is divided into three longitudinally-spaced progressively-larger portions 32-34 with the internal diameter of the upper and smallest bore portion being substantially equal to the internal diameter of the production string 11. Similarly, the depending length of tubing 21 is selected from a larger size of tubing than 65 that used to assemble the production string 11 so that its internal diameter will at least be no smaller — if not slightly larger — than the internal diameter of the lowest and largest bore 34 in the valve body 31.

An actuating piston 35 and a pair of valve members 36 and 70 37 are respectively arranged at spaced intervals in the progressively-larger bores 32-34 and fluidly sealed therein as by external sealing members 38-40. The upper valve member 36 is annularly formed and carries a coaxially-mounted internal sealing member 41 adapted for sealingly receiving an elon75 gated actuating member such as a cylindrical rod 42 that is de3,674,091 pendently secured to the actuating piston 35 and passed through the upper valve member so as to normally position its lower end adjacent to or in engagement with the lower valve member 37.

To provide selective fluid communication between the chamber 23 and the well bore 12 below the packer 20, one or more lateral ports 43 are arranged in the valve body 31 to admit well fluids into the intermediate bore 33 and the lower valve member 37 is releasably secured to the valve body by means, such as a shear pin 44, for normally retaining the valve member in a position blocking fluid communication with the enclosed chamber. The shear pin 44 must, of course, be of sufficient strength to withstand the unbalanced pressure forces acting downwardly on the lower valve member 37 as the new and improved production tool 10 is lowered into the well bore 12 to the position shown in FIG. 1.

Accordingly, it will be appreciated that so long as the shear pin 44 is not disrupted, the valve member 37 will be retained in its depicted initial position to close the chamber 23. Thus, to control communication between the enclosed chamber 23 and the ports 43, the actuating piston 35 is cooperatively arranged to urge the rod 42 downwardly against the valve member 37 whenever the fluid pressure in the tubing string 11 is selectively increased for imposing a downwardly-acting force on the lower valve member that is sufficient to fail the shear pin 44. Once the shear pin 44 is disrupted, the lower valve member 37 will be forcibly driven to the bottom of the depending length of tubing 21 for admitting well bore fluids and connate fluids as at 28 into the enclosed chamber 23.

It should be noted that the downwardly-facing shoulder 45 defined by the junction of the bores 32 and 33 will prevent the upper valve member 36 from being forced upwardly in the valve body 31 by the pressure surges developed as the lower valve member 37 is forcibly driven into the depending tubing 21 by the inrushing connate fluids. Moreover, since the piston 35 will be driven downwardly against the upper valve member 36 once the lower valve member 37 is released, the upper valve member is releasably secured to the valve body as by a shear pin 46 of sufficient strength to withstand the downwardly-acting pressure and impact forces imposed on the upper valve member when the actuating piston releases the lower valve member.

Referring again to FIG. 1, it will be appreciated that when the new and improved tool 10 of the present invention is positioned in the well bore 12, the upper and lower valve members 36 and 37 will respectively be in their normally-closed positions as depicted in FIG. 7. The enclosed chamber 23 will remain closed so long as the lower valve member 37 remains in its initial position; and fluid communication will be blocked between the production string 11 and the ports 43 so long as the upper valve member 36 remains in its elevated position in relation to the valve body 31.

As previously described in relation to FIG. 3, the lower valve member 37 is selectively displaced to induce a rapid flow of connate fluids into the enclosed chamber 23 for flushing the debris 26 and 27 from the perforations 16. To accomplish this, the wellhead valve 18 is opened and sufficient pumping pressure is applied from the surface to the production string 11 above the packer 20 to shift the actuating piston 35 downwardly to fail the shear pin 44. As previously described, once the shear pin 44 is disrupted, the lower valve member 37 will be driven into the depending tubing member 21 to establish fluid communication (by way of the ports 43) between the enclosed chamber 23 and the well bore 12 below the packer 20.

It will, of course, be appreciated that the upper valve member 36 will still be retained in its depicted initial position by the shear pin 46. Thus, the upper valve member 36 may be left closed as long as is desired after communication has been established between the ports 43 and the enclosed chamber 23.

Accordingly, when it is desired to open the upper valve member 36 for introducing a treating fluid into the well bore below the packer 20 as previously described in relation to FIG. 5, the wellhead valve 18 is reopened and an increased pressure is applied to the fluid 30 in the production string 11 for urging the actuating piston 35 downwardly with sufficient 5 force to fail the shear pin 46. The upper valve member 36 will, of course, be released once the shear pin 46 is disrupted. It will be noted that once the upper valve member is released and passes below the intermediate bore 33, the valve member 36 and the actuating piston 35 will be free to move easily through ¹⁰ the larger depending tubing 21 and come to rest on top of the lower valve member 37.

In the preferred embodiment of the tool 10 of the present invention, it is preferred to fabricate the cap 22 as well as the j pistons 34-36 and the rod 42 of materials such as aluminum which will be ultimately disintegrated in time by the corrosive action of the well bore fluids so as to minimize the debris left in the well bore 12 and ultimately open the lower end of the depending tubing 21. It will, of course, be appreciated that the 2q cap 22 could also be releasably secured to the depending tubing 21 so that the cap can be released therefrom by subsequently dropping a so-called “sinker bar” (not shown) from the surface through the production string 11 to allow the pistons 34-36 and the rod 42 to fall into the well bore 12 25 therebelow. In this manner, a continuous and substantiallyuninterrupted passage will be provided through the tubing string 11 and the production tool 10 between the wellhead 17 and the well bore 12 below the packer 20. Thus, any so-called “through tubing” completion or treating operation that is typi30 cally conducted in a production well can be readily conducted in the well bore 12 without having to remove either wellhead 17 or the production tool 10 and its supporting string of production tubing 11.

Accordingly, it will be appreciated that the present inven35 tion has provided new and improved methods and apparatus for completing wells to obtain improved fluid communication between the well bore and selected earth formations traversed thereby without delaying the installation of the production string and the associated wellhead and surface equipment 40 _once the drilling operation is concluded. By arranging the new and improved production tool of the present invention into an otherwise-typical production string once the formation interval below the intended position of the production packer has been perforated, the wellhead and other associated surface ⁴⁵ equipment can be installed in the usual manner without further delay. Then, when the well is to be prepared for production, the lower valve member in the new and improved production tool of the present invention is opened to clear the perforations of debris and the like. Thereafter, a fluid is discharged into the production string and the upper valve member in the production tool is opened to establish communication from the surface with the formations below the packer. Where the formations require acidizing, fracturing or 55 consolidation treatments to prepare the well for production, one or more treating fluids can be readily dispatched through the now-opened production string and into the well bore below the packer.

While particular illustrations and embodiments of the gQ present invention have been shown and described, it is apparent that changes and modifications may be made without departing from this invention in its broader aspects; and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and 65 scope of this invention.