Abstract:
A method of perforating a wellbore by forming a perforation that is aligned with a reservoir characteristic, such as direction of maximum stress, lines of constant formation properties, and the formation dip. The wellbore can be perforated using a perforating system employing a shaped charge, a mechanical device, or a high pressure fluid. The perforating system can be aligned by asymmetric weights, a motor, or manipulation from the wellbore surface.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to and the benefit of co-pending U.S. Provisional Application Ser. No. 61/039,595, filed Mar. 26, 2008, the full disclosure of which is hereby incorporated by reference herein. 
     
    
     BACKGROUND 
       [0002]    1. Field of Invention 
         [0003]    The invention relates generally to the field of oil and gas production. More specifically, the present invention relates to a perforating system. Yet more specifically, the invention concerns aligning perforations based on one or more reservoir characteristics. 
         [0004]    2. Description of Prior Art 
         [0005]    Perforating systems are used for the purpose, among others, of making hydraulic communication passages, called perforations, in wellbores drilled through earth formations so that predetermined zones of the earth formations can be hydraulically connected to the wellbore. Perforations are needed because wellbores are typically completed by coaxially inserting a pipe or casing into the wellbore. The casing is retained in the wellbore by pumping cement into the annular space between the wellbore and the casing. The cemented casing is provided in the wellbore for the specific purpose of hydraulically isolating from each other the various earth formations penetrated by the wellbore. 
         [0006]    Perforating systems typically comprise one or more perforating guns strung together, these strings of guns can sometimes surpass a thousand feet of perforating length. In  FIG. 1  an example of a perforating system  4  is shown. For the sake of clarity, the system  4  depicted comprises a single perforating gun  6  instead of a multitude of guns. The gun  6  is shown disposed within a wellbore  1  on a wire line  5 . The perforating system  4  as shown also includes a service truck  7  on the surface  9 , where in addition to providing a raising and lowering means, the wire line  5  also provides communication and control connectivity between the truck  7  and the perforating gun  6 . The wire line  5  is threaded through pulleys  3  supported above the wellbore  1 . As is known, perforating systems may also be disposed into a wellbore via tubing, drill pipe, slick line, coiled tubing, to mention a few. 
         [0007]    Included with the perforating gun  6  are shaped charges  8  that typically include a housing, a liner, and a quantity of high explosive inserted between the liner and the housing. When the high explosive is detonated, the force of the detonation collapses the liner and ejects it from one end of the charge  8  at very high velocity in a pattern called a “jet”  12 . The jet  12  perforates the casing and the cement and creates a perforation  10  that extends into the surrounding formation  2 . Generally the wellbore pressure is different from the pressure within the formation  2 , thus upon perforation pressure equalization occurs between the formation and the wellbore which in turn produces either flow into the wellbore from the formation, or into the formation from the wellbore. 
       SUMMARY OF INVENTION 
       [0008]    Disclosed herein is a method of perforating wherein the perforations are aligned with a characteristic of the reservoir. In one embodiment, the perforations are aligned with a reservoir characteristic such as the direction of maximum stress or the formation dip. Disclosed herein is also method of perforating a wellbore that intersects a formation, the method involving forming a perforation in the wellbore, where the perforation is aligned with the direction of maximum stress or the formation dip. The method may further comprise disposing a perforating system in the wellbore, the direction of maximum stress or the perforating system comprising a shaped charge, aiming the shaped charge for alignment with the direction of maximum stress or the formation dip, and detonating the shaped charge. The perforating system may further comprise a body housing the shaped charge with the method further comprising orienting the body to aim the shaped charge for alignment with the direction of maximum stress or the formation dip. The step of orienting may include asymmetrically weighting the body, rotating the body with a motor, or rotating the body from the wellbore surface. Perforating can be performed with shaped charges, mechanical drilling devices or systems, or high pressure fluid. Optionally, the charges may be rotated about a pivot point for orientation purposes. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0009]    Some of the features and benefits of the present invention having been stated, others will become apparent as the description proceeds when taken in conjunction with the accompanying drawings, in which: 
           [0010]      FIG. 1  is partial cutaway side view of a perforating system in a wellbore not aligned with a formation dip angle. 
           [0011]      FIG. 2  is side cutaway views of a perforating system aligned with a formation dip angle. 
           [0012]      FIG. 3  is a partial cutaway view of a gun tube having shaped charges. 
           [0013]      FIG. 4  is a partial cutaway view of a wellbore and a surrounding formation with a zone of maximum stress. 
           [0014]      FIG. 5  is a partial cutaway view of a perforating gun in a deviated wellbore. 
           [0015]    While the invention will be described in connection with the preferred embodiments, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the invention as defined by the appended claims. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0016]    The present invention will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. For the convenience in referring to the accompanying figures, directional terms are used for reference and illustration only. For example, the directional terms such as “upper”, “lower”, “above”, “below”, and the like are being used to illustrate a relational location. 
         [0017]    It is to be understood that the invention is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation. Accordingly, the invention is therefore to be limited only by the scope of the appended claims. 
         [0018]    With reference again to  FIG. 1  the subterranean formations  2  intersected by the wellbore  1  comprise a series of individual and distinct layers or formations  14 . Boundary lines  16  are provided between adjacent formations  14  illustrating a border thereby defining the contour of the formations  14 . Each individual formation  14  is defined as a body of subterranean strata, such as rock, comprising predominantly a single type or types of composition. For example, the formation  14  could comprise a type or types of rock having relatively consistent properties throughout that formation  14 . Examples of characteristics include permeability, density, porosity, resistivity, saturation, dip angle, stress, and combinations thereof. Optionally, a formation  14  may be comprised of low density material other than rock, such as sand, sediment, sedimentary rock, stratum, or sandstone. For the purposes of discussion herein, the formation  14  can be any stratigraphic unit, including a bed, wherein the beds are distinguishable from one another. Thus the formation  14  includes subterranean layers that are distinguishable from adjacent layers and can have thicknesses measurable in tenths of inches and up to hundreds of feet. 
         [0019]    The formations  14  and boundaries  16  as illustrated are oriented generally oblique to the axis A x  of the wellbore  1 ; perforations  10  are shown formed through the wellbore  1  and into the formation may cross one or more boundary lines  16 . These perforations  10  that intersect one or more boundary lines  16  may pass through adjacent strata with different and distinctive properties, thereby affecting the permeability from the strata into the perforation  10 . 
         [0020]    The method and apparatus disclosed herein includes a manner of perforating with respect to a subterranean formation characteristic. The formation characteristics include formation bedding, formation dip angles, directions of constant stress, including a direction of maximum stress, and isotropic zones such as zones of constant density, porosity, permeability, saturation, and the like. The step of perforating thus includes aiming shaped charges with respect to a line(s) or plane(s) defining the formation characteristic. Aiming may include aligning shaped charges with a formation characteristic, or at a desired angle from a formation characteristic. A plane of maximum stress is defined herein as a plane in which the formation stress exceeds that in an adjacent formation(s). The direction of maximum stress denotes the plane&#39;s general trajectory along a line within the formation. 
         [0021]      FIG. 2  provides a side partial cross-sectional view of a perforating system  4   a  disposed in a wellbore  1 . The perforating system  4   a  includes a perforating gun  6   a  having shaped charges  8  aimed with the intent of forming a jet  12   a  that dodges boundary lines  16 . Forming a perforating jet  12   a  that avoids the boundary lines  16  creates perforations  10   a  lying within a single identifiable formation  14  and thus can also be within a single formation characteristic. Moreover, the shaped charge  8  can be aimed so its jet  12   a  is aligned with the formation  14 . One example of alignment comprises a perforation  10   a  parallel with one or both of the boundary lines  16  lying adjacent to the particular formation  14 . 
         [0022]    In one method of forming the perforation  10   a  of  FIG. 2 , the shaped charge  8  is aimed to form a jet  12   a  largely parallel with the formation  14  dip angle. The dip angle may be defined as the angle at which the formation  14  and/or boundary line  16  lies relative to the axis A x  of the wellbore  1 . This is sometimes also referred to as the dip of the formation. Perforating into the formation  14  at its dip angle aligns the perforation  10   a  to the optimal permeability of the reservoir from which hydrocarbons are to be produced. This results in an enhanced and increased flow of hydrocarbons through the perforations  10   a  and into the wellbore  10   a  for production of the hydrocarbons. 
         [0023]    Aligning the shaped charges  8  with the dip angle of the formation  14  can be accomplished in any number of ways. In one example, the individual shaped charges  8  are gimbaled within the body of the perforating gun  6   a  and allowed to pivot or gimbal within the gun  6   a.  The gimballing may be further coupled with a perforating gun that rotates azimuthally within the wellbore  1 . The azimuthal rotation can be produced by asymmetrically weighting components within the perforating system, such as the gun body  6   a,  a gun tube, shaped charges. Additionally, a motor (not shown) may be included with the system for rotating the gun body  6   a.    
         [0024]    Optionally, a gyroscope (not shown) can be included with the perforating system  4   a  to provide orientation control within the wellbore  1 . It should be pointed out that the perforating system  4   a  of  FIG. 2  is not limited to a single gun body, but can include multiple gun bodies strung together adjacently as part of a larger string. Other downhole tools may also be provided in the tool string. Additionally, the perforating method described herein is not limited to a vertical wellbore, but can be in deviated as well as horizontal wellbores. As such, the perforating system  4   a  may be disposed on wire line as well as any type of tubing, including coiled tubing and a tractor device. 
         [0025]    Another embodiment is provided in side view in  FIG. 3  illustrating shaped charges  8   a  statically affixed within a gun body  6   b  at an angle oblique to the gun body axis A x1 . The shaped charges  8   a  may be disposed in a charge tube that is cylindrical and machined to hold the charges  8  pointing at a desired attitude relative to the gun body axis A x1 . This orientation angle can form perforations  10   a  aligned with the dip angle of the formation  14 . The charge tube  18  in this embodiment may be longitudinally split into two or more parts ( 20 ,  22 ) having end fittings  32  at each end to allow the two pieces ( 20 ,  22 ) to be secured at different longitudinal positions with respect to one another. The shaped charge  8   a  ends are shown engaged with holes ( 24 ,  25 ,  26 ,  27 ) formed through the charge tube  18  body. When the shaped charge  8   a  ends are engaged in the holes ( 24 ,  25 ,  26 ,  27 ) selective longitudinal placement of the charge tube  18  parts ( 20 ,  22 ) in turn angles the shape charges  8   a  oblique to the axis A x   1 . This shifting angularly cants the charges  8   a  for a desired alignment to be shot by the charges  8   a.  The angle of the shaped charge  8   a  can be controlled and selected by adding drilled and tap holes  30  formed to receive screws or bolts  31  in the end fittings  32 . 
         [0026]    In another embodiment, the holes ( 24 ,  25 ,  26 ,  27 ) in which the shaped charges  8   a  are placed can be enlarged or can be elliptically shaped. Special bushings can be including within the holes ( 24 ,  25 ,  26 ,  27 ) to anchor the shaped charges  8   a  in these different holes and align them as desired. 
         [0027]      FIG. 4  provides a partial cross sectional view of an example of perforating with respect to a formation characteristic. Here a perforating system  4   b  is disposed in a wellbore  1 . Illustrated are jets  12   b  forming perforations  10   b  in a reservoir  36  surrounding the wellbore  1 . The jets  12   b  emanate from shaped charges  8   b  in a perforating gun  6   b.  A direction of maximum stress  34  in the reservoir  36  is shown intersecting the wellbore  1 . In the example, the direction of maximum stress  34  is generally oblique to the wellbore axis A x . The shaped charges  8   b  have been oriented and/or aligned within the perforating gun  6   b  so the jets  12   b  are either substantially aligned with the direction of maximum stress  34  or extend generally parallel to the direction  34 . Optionally the shot phasing on the gun  6   b  may be at 0° and 180°. For example, the shaped charges  8   b  at either 0° or 180° may be aligned with the plane and oriented to form a perforation  10   b  in the plane  34  coincident with the azimuth radial position where the angle between the direction  34  and the wellbore axis A x  is at a minimum. Using the embodiment of  FIG. 4  as an example, if the 0° phased shot is directed azimuthally as described above and angled upward, the shot at 180° phasing would also be aligned in the plane and directed downward. 
         [0028]      FIG. 5  is a cross sectional view of an embodiment of a perforating system  4   a  in accordance with the present disclosure disposed in a deviated wellbore  1   a.  The perforating gun  6   a  is disposed on wireline  5  in the deviated portion of the wellbore  1   a.  A coordinate axis V A  and H A  are provided that represent potential shot direction. V A  is largely parallel with vertical axis at surface  42  and H A  is largely parallel with horizontal axis at surface  42 . Also provided is a dashed axis V A ′ and H A ′, these lines graphically illustrate ranges of shot angles (A 1 , A 2 ) possible with a perforating device, such as an angled perforating system as described herein. A 1  and A 2  are greater than 90°, and may be equal in some instances. Thus implementation of the angled shaped charges provides for shot angles that exceed vertical and horizontal alignments. 
         [0029]    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 exist in the details of procedures for accomplishing the desired results. 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.