Abstract:
One embodiment of the present invention discloses a system and method for orienting perforating guns inside of slanted or deviated wellbores. The invention involves adding a weight inside of the guns to gravitate the gun to a specified orientation. The weight is situated on the outer circumference of the gun tube and within the inner diameter of the gun body. The invention is capable of orienting the gun in any radial position without affecting the shot performance of any of the shaped charges.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates generally to the field of oil and gas well services. More specifically, the present invention relates to an apparatus that orients a tool into a desired position while the tool is in a deviated wellbore. 
     2. Description of Related Art 
     When downhole tools, including perforating guns, are used in slanted or deviated wellbores it is often important that the tool be in a specific radial orientation. For example, orienting perforating guns in deviated wells enables the well operator to aim the shaped charges of the perforating gun at specific radial locations along the circumference of the wellbore. This is desired because the potential oil and gas producing zones of each specific well could exist at any radial position or region along the wellbore circumference. Based on the presence and location of these potential producing zones adjacent a deviated well, a well operator can discern a perforating gun orientation whose resulting perforations result in maximum hydrocarbon production. 
     Information relevant to attempts to orient downhole tools, including perforating guns, can be found in U.S. Pat. Nos. 4,410,051, 4,438,810, 5,040,619, 5,211,714, 4,637,478, 5,603,379, 5,964,294. However, each of these references suffers from one or more of the following disadvantages. Some of the devices described in these references position a perforating gun such that only downward perforations are possible, others obstruct the path of the some of the shaped charges located on the perforating gun, while others are attached to the exterior of the perforating gun which can make handling of the tool inside of a wellbore more cumbersome. 
     Daniel et al, U.S. Pat. No. 4,410,051 discloses a system for orienting a perforating gun to be used in wells having multiple tubing strings. The apparatus of Daniel et al. &#39;051 consists of a plurality of subassemblies connected end to end. Situated in one of the subassemblies is an eccentric weight sub that contains a weight positioned asymmetric to the longitudinal axis of the housing. Connected to the bottom of the eccentric weight sub is the alignment joint sub which is used to align the bottom portion of the housing with outlets of the perforating gun. In Daniel et al. &#39;051 the perforating gun section of the apparatus is disclosed as being below the eccentric weight sub. Wilkinson, U.S. Pat. No. 4,438,810 and Jordan et al., U.S. Pat. Nos. 5,040,619 and 5,211,714 also disclose the use of an eccentrically weighted sub attached to a perforating gun to rotate the perforating gun inside of a deviates wellbore. 
     George, U.S. Pat. No. 4,637,478 involves a gravity oriented perforating gun for use in slanted wells comprised of one or more segments or subs, where each sub contains a center of gravity movement means which is a window that is cut out of the sub wall to alter the sub symmetry. Because it is asymmetric, the sub will rotate until the heavier portion of the sub circumference is below the lighter portion of the sub circumference. 
     Henke et al., U.S. Pat. No. 5,603,379, involves an apparatus for connecting and orienting perforating guns in a deviated well bore. The orientation aspect of the device consists of a fin longitudinally connected to the body of the perforating gun that positions the gun off center in the casing so that gravity will position the gun body at the bottom of the casing. Because of the positioning aspect of Henke &#39;379, the perforations are generally directed into a downward trajectory. Vann, U.S. Pat. Nos. 4,194,577 and 4,269,278 also disclose a perforating gun including longitudinal disposed fins on the gun outer circumference which act to direct the perforating charges in a downward pattern. 
     Edwards et al., U.S. Pat. No. 5,964,294, discloses a downhole tool for use in a deviated well constructed to rotate in response to a moment applied at its axis. The tool includes ballast chambers filled with a flowable ballast material to produce a gravitational force for rotating the tool. The ballast chambers are formed on the inner diameter of the loading tube assembly. The flowable ballast material consists of a high density metal such as tungsten or depleted uranium. Alternative embodiments include a multiple segmented tool where each tool has offset centers to produce rotation of the tool. 
     Therefore, there exists a need for a system that orients perforating guns in deviated wellbores where the shaped charges of the perforation gun can be directed in any radial orientation, a system that cooperates with a perforating gun having any shot pattern without affecting the shot pattern, and a system that is integral within the perforating gun. 
     BRIEF SUMMARY OF THE INVENTION 
     One embodiment of the present invention discloses a system and method for orienting downhole tools, including perforating guns, into a specified orientation, while the tool is inside of a deviated or slanted wellbore. The tool comprises a perforating gun having a substantially cylindrical gun body with an inner and an outer diameter. Disposed within the gun body is a gun tube also with an inner and an outer diameter. The gun tube contains at least one shaped charge. Attached to the outer surface of the gun tube is a weight. Each weight has apertures formed therethrough that are aligned with each shaped charge so that the shot performance of each shaped charge is not affected by the attached weight during detonation. The attached weight can be equal to or less than the length of the gun tube. 
     A method of aligning a perforating gun in a deviated wellbore comprises adapting a weight for attachment to the outer surface of a gun tube having one or more shaped charges. Radial locations along the weight are identified that coincide with the location of each shaped charge. Apertures through the weight are formed at each radial location. The weight is attached to the outer surface of gun tube such that the apertures are coaxially aligned with each shaped charge. The gun tube is placed into the gun body of a perforating gun, and the perforating gun containing the gun tube is inserted into the deviated section of a wellbore. When the rotation of the gun body caused by the Earth&#39;s gravitational force upon the eccentric weight has ceased, the shaped charges are ready to be detonated. 
     The method also envisions receiving coordinates where perforations are desired within the wellbore. The weight is then strategically situated on the gun body such that rotation of the gun body caused by the Earth&#39;s gravitational force upon the weight orients the gun body so the shaped charges are aimed at the coordinates. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     FIG. 1 illustrates a perspective view of a gun tube and eccentrically loaded weight of the Internal Oriented Perforating System. 
     FIG. 2 depicts a cross-sectional view of the Internal Oriented Perforating System. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to the drawing herein, an internal oriented perforating system according to one embodiment of the present invention is shown in FIG.  1 . The perspective view of FIG. 1 illustrates a gun tube  20  for use in a perforating system that incorporates one or more shaped charges  30  situated within the gun tube  20 . The gun tube  20  is suitable for use in perforating subterranean wells, it is appreciated that one reasonably skilled in the art can produce a gun tube having shaped charges with ordinary effort and without undue experimentation. As is well known in the art, the gun tube  20  is a generally cylindrical elongated body with a range of lengths and diameters. While the length of the gun tube  20  of the present invention ranges from 4 feet to 28 feet, the advantages of the present invention can be enjoyed with a gun tube  20  of any length. The preferred diameters of the gun tube  20  are 2¾″ and 2″, however gun tubes of any diameter can be practiced as a part of this invention. 
     The perforating system of the present invention involves the gun tube  20  disposed within a gun body  21 , the gun body  21  having a slightly longer length than the gun tube  20  located therein. Often times individual perforating guns are connected end to end to create a perforating gun assembly. Because perforation operations can involve perforating a section of wellbore of less than 10 feet to over 10,000 feet, the length of the perforating gun assembly will vary accordingly. To accommodate these situations, and as is well known, the perforating gun of the present invention can comprise a single gun tube  20  with a gun body  21 , or multiple sections of the gun tube  20  and gun body  21 . A swiveling connection (not shown) is used to connect multiple perforating guns into the perforating gun assembly. It is important that the connections allow the gun body  21  to rotate freely with respect to the connection and other gun bodies included in the perforating assembly. 
     Attached to the outer circumference of the gun tube  20  is a weight  40  that produces an eccentric loading about the axis of the gun tube  20 . While it is preferred that the weight  40  be secured to the gun tube  20  by fasteners  42 , such as rivets, bolts, pins, tabs, or screws, other attachments could also include welding. The weight  40 , as can be seen in FIG. 2, is generally semi-circular in cross section and includes apertures  41  formed at various locations along its body. The apertures  41  should be formed to be aligned with openings on the gun tube  20  where the shaped charge openings  31  and the shaped charge back  32  are located. While the weight  40  can be formed from any material, the material should have a high density and be machinable. As such, the preferred materials include carbon steel, depleted uranium, tungsten, steel alloys, copper alloys, stainless steel, and lead. 
     As can be seen from the figures, the shaped charge back  32  and the detonation cord  33  can extend past the outer circumference of the gun tube  20 . To accommodate for these protrusions, the apertures  41  proximate to the shaped charge back  32  are created to tailor the weight  40  for a better fit onto the gun tube  20 , while the apertures  41  proximate to the shaped charge openings  31  act to prevent the weight  40  from obstructing the discharge perforating jet produced by detonation of the shaped charges  30 . 
     As seen in FIG. 2, the weight  40  attaches along a portion of the circumference of the gun tube  20  which produces an asymmetric structure. As is well known, when the perforating gun is in a generally horizontal position and the center of gravity of the weight  40  is directly below the gun tube center  22 , the gravitational forces acting on the weight  40  on both sides of the gun tube centerline  23  are equal. When the gravitational forces about the gun tube centerline  23  are equal, gravity cannot cause rotation of the gun tube  20 . However, when the center of gravity of the weight  40  is not directly below the gun tube center  22 , the gravitational forces about the gun tube centerline  23  are not equal. The resulting imbalance will urge the weight  40  downward until the center of gravity of the weight  40  is directly below the gun tube center  22 , i.e. or until the gravitational forces applied to the weight  40  on either side of the gun tube center  22  are equal. When this occurs the weight  40  is at its “low point.” 
     Attaching the weight  40  to the gun tube  20  outer circumference, instead of some other location along the gun tube  20  radius, maximizes the gravitational moment arm experienced by the eccentrically weighted gun tube  20 . Maximizing the moment arm produces a gun tube  20  more responsive to eccentrically applied gravitational forces. A gun tube  20  being more responsive to eccentrically applied gravitational forces will rotate quicker when these forces are applied. Additionally, a more responsive gun tube  20  is more likely to rotate until the weight  40  is in the low point without prematurely stopping and leaving the center of gravity of the weight  40  at a point higher than the low point. For reasons to be discussed below, it is important that the weight  40  be in the low point before the shaped charges  30  of the perforating gun are detonated. 
     In operation, one or more perforating guns of the present invention are assembled and inserted into a well that is to be perforated. Inserting the present invention into a wellbore can be done with a conventional wireline, in conjunction with a tractor sub, or can be tubing conveyed. When the perforating gun reaches a deviated or slanted portion of the well, the gravitational forces will act upon the eccentric weight  40  until the weight  40  is in the low position. Prior to assembly the wellbore technical personnel evaluate how the shaped charges  30  should be aimed based on potential producing zones adjacent the wellbore. The gun tube  20  orientation during detonation is dependent upon how the shaped charges should be aimed during the perforation sequence. Once the desired orientation of the gun tube  20  during detonation is finalized, it can then be determined where the weight  40  should be attached such that its eccentrically loaded mass can rotate the gun tube  20  into the desired orientation. Before the weight  40  is attached to the gun tube  20  apertures  41  are formed through the weight  40  so that the weight  40  will not cover the shaped charge opening  31  or the shaped charge back  32 . 
     As the perforating gun is put into position for detonating the shaped charges, it will be cycled up and down inside of the wellbore to provide some mechanical force impulses to the gun tube  20 . These impulses can shake the gun tube  20  and further ensure that the weight  40  has rotated into a low position. Cycling the perforation gun may be more important in instances where the deviated section of the wellbore exceeds 15° to 20° from horizontal, or if some foreign matter has become stuck between the gun tube  20  and the gun body  21 , thereby retarding rotation of the gun tube  20  inside of the gun body  21 . After completing the cycling process, the well operator positions the perforation gun to the depth inside of the wellbore where perforations are to be made. When the perforation gun is at the proper depth, the shaped charges  30  will be detonated thereby perforating the wellbore. 
     Alternative embodiments of eccentrically loading a perforating gun include introducing a semi-cylindrical gun tube that is asymmetric about its longitudinal axis. The asymmetry of the gun tube in and of itself eccentrically weights the perforating gun so that when non-vertical the perforating gun will rotate in response to gravitational pulls on the eccentric loading. Another alternative embodiment involves creating longitudinal recesses along sections of the gun tube  21  and adding metal rods or bars into those recesses. The presence of the metal rods or bars will produce an asymmetry that also can rotate the perforating gun. However, the recesses should be located in the same hemispherical section of the gun tube  21  to produce an eccentrically loaded situation. A yet additional alternative embodiment exists where asymmetry of the gun body  20  is developed by securing the gun tube  21  inside of the gun body  20  at or proximate to the inner circumference gun body  20  and not coaxial within the gun body  20 . 
     The present invention described herein, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While a presently preferred embodiment of the invention has been given for purposes of disclosure, numerous changes in the details of procedures for accomplishing the desired results. Such as the utilization of non-metallic materials in the construction of the weight  40 . Additionally, the device and method described herein is suitable for use in any type of well, such as a water well, and is not restricted to use in hydrocarbon producing wells. These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the present invention disclosed herein and the scope of the appended claims.