Abstract:
A perforating system having a perforating gun with a tubular gun housing defining an inner volume and extending in an axial direction. A shaped charge is held in a loading tube. The loading tube is located in the gun housing. The loading tube extends along the axial direction. The shaped charge faces in a firing direction substantially perpendicular to the axial direction. A portion of the gun housing adjacent to the shaped charge in the firing direction is a perforating portion for removal upon firing of the shaped charge. An eccentralizer member extends from the perforating gun in a second direction that is substantially opposite and parallel with the firing direction. A first retainer part extends from an outer surface of the gun housing adjacent to the perforating portion. A second retainer part extends from the outside of the gun housing adjacent to the perforating portion.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims priority and benefit to U.S. Provisional Application No. 61/140,937 that was filed on Dec. 27, 2008, which is incorporated by reference herein in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present application generally relates to perforating activities, and more specifically to reduction of debris in a wellbore. 
       BACKGROUND 
       [0003]    Productivity or injectivity of a well relates to the wellbore radius. The larger the wellbore radius, the better the productivity or infectivity. However, drilling a larger borehole could be prohibitive because of substantial increase of drilling and completion cost for a larger borehole. For a weak or unconsolidated formation, it would be beneficial to enlarge the wellbore by producing sand to some extent before fracture packing and other gravel packing operations. Perforating in such weak or unconsolidated sand formations often induces collapse of the perforation tunnels and even the near wellbore formation. Hence, the perforation naturally allows sand production from the formation for enhancement of the productivity or injectivity. However, conventional perforation in weak or unconsolidated sand also results in sand accumulation in the wellbore. The produced sand in the wellbore can clog the gun and complicate the completion operations. For example, sand control and other completion devices may not be able to be positioned at the right place before the sand in the wellbore is completely cleaned out. Therefore, although producing some sand from formation through perforations may increase the well productivity and infectivity, it is beneficial not to produce any sand into the wellbore after perforation. 
         [0004]    Except for sand production from the perforation in weak or unconsolidated formation, debris in the perforation tunnels for consolidated formation is also detrimental for well productivity and injectivity. Dynamic underbalanced perforating techniques, disclosed in U.S. Pat. No. 6,554,081, U.S. Pat. No. 6,598,682, U.S. Pat. No. 7,121,340 and U.S. Pat. No. 7,182,138, can be very efficient to remove the crushed zone near the wall of the perforation tunnels and clean the debris in the perforation tunnels out of formation. However, for weak or unconsolidated sand formation, dynamic underbalance perforating can actually sometimes make the sanding worse. Without proper control, the produced sand could lead to the failure of the completion operations. 
         [0005]    Hence, it is desirable to have a better perforating technique in weak or unconsolidated formation. 
       SUMMARY 
       [0006]    The following summary highlights features of preferred embodiments and is in no way meant to unduly limit the scope of any present or future related claims. 
         [0007]    According to various features and embodiments of the present application, a perforating method includes lowering the perforating system into a well to the targeted formation interval, orienting the gun and all charges at a pre-selected direction or within a confined angle around the azimuth of the wellbore, using mechanical means to allow the perforation gun sufficiently contacting/closing the casing in the targeted direction, and detonating the charges and establishing communication between the inner volume of the gun carrier and the formation, and allowing formation fluids, loosening sand and other debris to flow into the gun carrier without discharging into the annulus between the gun carrier and casing. In one embodiment, the perforating system includes sealing rings that restricts the flow communication between wellbore space and the inner gun carrier. In another embodiment, flow restrictors are installed on the perimeter of the gun carrier and surround the shaped charges. In another embodiment, the perforating system includes a sliding sleeve that closes the perforated holes in the gun carrier after some times of the charges being detonated. 
         [0008]    An embodiment includes a perforating system having a perforating gun with a tubular gun housing defining an inner volume and extending in an axial direction. A shaped charge is held in a loading tube. The loading tube is located in the gun housing. The loading tube extends along the axial direction. The shaped charge faces in a firing direction substantially perpendicular to the axial direction. A portion of the gun housing adjacent to the shaped charge in the firing direction is a perforating portion for removal upon firing of the shaped charge. An eccentralizer member extends from the perforating gun in a second direction that is substantially opposite and parallel with the firing direction. A first retainer part extends from an outer surface of the gun housing adjacent to the perforating portion. A second retainer part extends from the outside of the gun housing adjacent to the perforating portion. The inner volume of the gun housing is insulated from pressure outside of the gun housing until firing of the shaped charge perforates the perforating area. 
         [0009]    This and other features and embodiments are discussed herein. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The following is a brief description of the figures herein which illustrate various features of embodiments. 
           [0011]      FIG. 1  is a schematic of features of a perforating system according to an embodiment. 
           [0012]      FIG. 2  shows a top sectioned view of features of the system of  FIG. 1  according to an embodiment. 
           [0013]      FIG. 3  shows a top sectioned view of features of the system of  FIG. 1  after Firing according to an embodiment. 
           [0014]      FIG. 4A  shows a front view of features including a sealing ring according to an embodiment. 
           [0015]      FIG. 4B  shows a top section view of features including the sealing ring and a portion of a perforating system according to an embodiment. 
           [0016]      FIG. 4C  shows a sealing ring according to an embodiment. 
           [0017]      FIG. 4D  shows a top view of a sealing ring and portions of the perforating system according to an embodiment. 
           [0018]      FIG. 5  shows a top cut away view of a perforating system with a sleeve according to an embodiment. 
           [0019]      FIG. 6  shows a top cut away view of a perforating system with vertical flow restrictors. 
           [0020]      FIG. 7  shows a front view of a perforating system with horizontal flow restrictors. 
           [0021]      FIG. 8  shows a front view of a perforating system with vertical flow restrictors and horizontal flow restrictors. 
       
    
    
       [0022]    The preceding brief description of figures is meant to help understand the features of embodiments discussed in the present application and is in no way meant to be used to limit any claims in this application or any subsequent related claims. 
       DETAILED DESCRIPTION 
       [0023]    In the following description, numerous details are set forth to provide an understanding of features and embodiments of the present application. However, it will be understood by those skilled in the art that features and embodiments within the present application may be practiced without many of these details and that numerous variations or modifications from the described embodiments are possible. These details are not meant in any way to be used to unduly limit claims in this application or any future related claims. 
         [0024]    As used here, the terms “above” and “below”; “up” and “down”; “tipper” and “lower”; “upwardly” and “downwardly”; and other like terms indicating relative positions above or below a given point or element are used in this description to more clearly describe some embodiments. However, when applied to equipment and methods for use in wells that are deviated or horizontal, such terms may refer to a left to right, right to left, or diagonal relationship as appropriate. 
         [0025]      FIG. 1  shows an embodiment of a perforating gun system  10 . The perforating gun system  10  includes a wireline cable  11  connected to a cable head  13 . It should be noted that other conveyance devices can be used in place of wireline, e.g., coiled tubing, piping, slickline, etc. The gun system  10  also includes a casing collar locator (CCL)  15  and a gyroscope module  17 . Both such devices are available commercially, e.g. from Schlumberger (CCL tool and/or Wireline Oriented Perforating Tool). The CCL  15  measures the location of the perforating system  10  along a borehole while the gyroscope  17  provides the azimuthal measurement of the system  10 , e.g., with respect to the magnetic north. An upper eccentralizer  19  can include bowed springs and can be connected beneath the gyroscope  17 . A firing head  21  is located below the eccentralizer  19 . A gun carrier  44  is connected to the firing head  21 . The lower eccentralizer  27  is below the gun carrier  44 . The upper and lower eccentralizer  19  and  27  have the same setting direction. Charges  47  in the gun carrier  44  are preferably loaded in a 180° phasing angle opposite to the setting direction of the eccentralizers  19  and  27 , but given various circumstances, can be slightly deviated from a 180° phase. Device  26  is an empty volume adapted to hold produced sand and debris. The device  26  can be the bottom part of the gun carrier  44  if all charges are loaded at the upper portion of the gun carrier  44 . Alternatively, a properly sized chamber can be used for the chamber  26 . The chamber  26  is attached beneath the gun carrier  44  to hold the produced sand and debris and is internally communicated to the gun carrier  44 . Although this embodiment is valid for the device  26  being either the bottom portion of the gun carrier  44  or an individual chamber, a chamber  26  is assumed to hold the sand and debris in the following description. 
         [0026]    A first step of a perforating method according to embodiments in the present application includes running the perforating system  10  into the wellbore. Based on the CCL measurements, the perforating system  10  is set at the formation interval to be perforated. 
         [0027]    A second step is to orient the perforating system  10  at the pre-defined azimuthal direction based on the measurements from the gyroscope  17 . Once the pre-defined azimuthal direction is achieved, the eccentralizers  19  and  27  are set to push the charge shooting portion of the gun carrier  44  against the casing wall. The cross-section view of the perforating system  10  is shown in  FIG. 2 . The perforating system  10  is positioned inside the casing  42  with the shooting side (perforating portion) of the gun carrier  44  adjacent to, and preferably, contacting the casing wall  42  after the bowed springs of the eccentralizers  19  and  27  are properly set in 180° phasing from the charge firing direction. 
         [0028]    A third step is to control the pressure differentials among the major regions before the charge detonation. Referring to  FIG. 2 , the entire working space can be distinguished into three major regions. The first region is the formation sand  40 , which is isolated from the wellbore space  43 , which is the second region, by the cement sheath  41  and the casing  42 . The formation sand region  40  contains formation fluid. The fluid pressure in the formation sand region  40  is denoted by P pore . The wellbore space  43  can contain completion fluid. The wellbore fluid pressure at the location of the gun carrier  44  is P well . The third region is the inner gun space  46 , which is isolated from the wellbore  43  by the gun carrier  44 . The inner gun space  46  is filled with air or other low pressure gases. Shaped charges  47  and loading tube  45  are inside the gun carrier  44 , so they are preferably completely isolated from the wellbore space  43  and formation sand region  40  before the cement sheath  41 , casing  42  and the gun carrier shell  44  are perforated by the shaped charges  47 . The loading tube  45  could be other designs other than a tube so long as the charges  47  are held properly. The loading tube  45  preferably is not completely pressure insulated so that the fluid pressure inside the gun carrier  44  and inside the loading tube  45  has the same pressure P gun  before the perforation. The current embodiment adjusts P well  and P gun  to setup the suitable pressure differentials among the three regions. Through properly designing the gun carrier  44 , loading tubing  45 , charges  47 , e.g. number of charges per foot of perforation, the P gun  is maintained below the P pore  and P well , i.e., achieving dynamic underbalance after a short time after the charge detonation. These ideas are discussed in U.S. Pat. No. 6,554,081, U.S. Pat. No. 6,598,682, U.S. Pat. No. 7,121,340 and U.S. Pat. No. 7,182,138, which are incorporated herein by reference in their entirety. Although not absolutely necessary, it is preferable that P well  be close to or somewhat less than P pore  before the first perforating run. An appropriate P well  value can be set by using a particular density and height of the completion fluid in the wellbore  43 . If the communication between the wellbore space  43  and the formation  40  is established after the first run and the formation  40  has a single hydrostatic pressure gradient system, the P well  can be equal or very close to P pore  in the subsequent runs. 
         [0029]    A fourth step is to detonate the charges in the perforating system  10 . The perforated cement sheath  41 , casing  42  and gun carrier shell  44  establish communications between the formation fluid  40  and the inner gun volume  46 . P gun  is substantially lower than P pore  and P well  after a very short period of time after the charge detonation (e.g., about several to tens of milliseconds). This results in the dynamic underbalance phenomenon which can lead to collapse of some perforation tunnels for weak or unconsolidated formation and the formation fluid  40  and wellbore fluid  43  filling in the inner gun volume  46 . Because the shooting portion of the gun carrier  44  is set against the casing wall  42  at the perforated holes  48  and  49  as shown in  FIG. 3 , the communication between formation  40  and the inner gun volume  46  is maximized while the communication between the wellbore space  43  and the inner gun volume  46  is substantially restricted. This directs surge fluid flow from the formation  40  to the inner gun volume  46 . The directed surge flow enables the loose sand and debris in the perforation tunnel  49  to move into the inner gun volume  46  while reducing/minimizing sand and debris production in the wellbore space  43 . 
         [0030]    After sufficient time, the produced sand and debris settle down to the sand and debris holder  26 . The eccentralizers  19  and  27  are unset and the perforating system  10  is retrieved from the wellbore. Enlarging wellbore radius behind casing by producing some formation sand without the sand accumulation in wellbore is achieved at the same time using the present embodiment. 
         [0031]    The perforating system  10  can be reloaded and rerun numerous times as needed to perforate the well in the same or other azimuthal directions. In each of these runs, sand and debris accumulation in the wellbore will be reduced/minimized. Therefore, the goal of reduced, preferably no, debris perforating can be better realized while productivity of the well is enhanced by removing some sands near the perforating tunnels. 
         [0032]    The eccentralizers  19  and  27  with bowed springs used in the perforating system  10  are only one example of various devices applicable in this application. Other devices may be installed in the perforating system  10  with similar functionality, e.g., springs, magnets, telescoping devices or arms. Also, more than one eccentralizer spaced radially can be used so long as they are evenly spaced from 180° of the firing direction of the shaped charge  47 , e.g. one on each side. 
         [0033]    To further restrict the flow communication between the wellbore space  43  and the inner gun volume  46 , retainer parts can be applied to an outside surface of the gun carrier  44  in proximity to the perforating portion of the gun carrier  44 . For example, sealing rings  102  can be used on scallops  100  on the gun carrier  44 .  FIG. 4B  shows the sealing ring  102  and its application in reducing the fluid flow from the wellbore space  43  to the inner gun volume  46 .  FIG. 4A  shows the sealing ring  102  installed on a scallop  100  of the gun carrier  44 .  FIG. 4B  is the side view of the sealing ring  102  installed on a scallop  100  in the gun shell  44 .  FIG. 4C  shows the front view of the sealing ring  102  while  FIG. 4D  is its side view. The curvature of the sealing ring  102  used in the perforating system  10  is determined by the curvature of the casing inside diameter  42  for the job. The outer edge  105  of the sealing ring  102  has a curvature substantially close to that of the casing inside diameter  42 . This minimizes flow communication between the wellbore space  43  and the inner gun space  46  while maximizing the flow communication between the formation  40  and the inner gun volume  46 . Preferably, the sealing rings  102  are made with conventional elastomer in this application but other materials can also be used. For example, the sealing rings could be made from high temperature polymers. Also, the sealing rings  102  can be made from metal, e.g. steel. The sealing rings  102  can be installed on the gun carrier  44  through the spiral grooves on the sealing rings  102  and the scallops  100 . The sealing rings  102  can also be attached with adhesives, by fasteners, by clamps, or by welding. Alternatively, the sealing rings  102  can be an extension of the material making up the gun carrier  44 . Note that the inner diameter of the sealing rings  102  should be larger than that of the perforating portion of the gun carrier  44 , i.e., perforated holes on the gun carrier  44 , in that the sealing rings  100  would not be damaged by the perforators during perforation. 
         [0034]    Another method to reduce the debris and sand production in the wellbore is to close the perforated holes on the gun carrier  44  after the gun volume  46  contains debris, e.g. is filled up.  FIG. 5  shows a sliding sleeve  60  for this purpose. The sliding sleeve  60  has a pre-manufactured hole  62  coaxially aligned with the shaped charge. The diameter of the hole  62  is larger than that of the perforated hole on the gun carrier  44  so that the jet of a detonated charge  47  would not be spent in penetrating the sleeve  60 . Therefore, the penetration of the shaped charge  47  would not be reduced by the existence of the sleeve  60 . Note that the sleeve  60  can close either all perforated holes or a portion of the holes in gun carrier  44 . For closing a portion of the holes, it is preferable to close those at the lower part of the gun carrier  44 . Also note that the sleeve  60  can close the perforated holes through longitudinal movement along the axis of the gun carrier  44 . Alternatively, it can close them through rotating along the azimuth of the gun carrier  44 , or the combination of the longitudinal and azimuthal movements. Closing the perforated holes in the gun carrier  44  is particularly beneficial for perforating a horizontal or large deviated well. The holes on the gun carrier  44  can be closed either just after the charges are detonated or at the termination of the dynamic under-balance response or after the complete settlement of the produced sands inside the gun carrier  44 . The exact timing of perforated-hole closure by the sleeve  60  depends on operational considerations in each individual dynamic under-balance operation. The closure can be performed automatically by setting time delay after the detonation of the charges or controlled by operators on the surface. 
         [0035]    In another embodiment, flow restrictors are used to reduce the flow communication between the inner gun volume  46  and the wellbore  43 .  FIG. 6  shows an application of the flow restrictors  150  and  151  on the gun  23 . The flow restrictors  150  and  151  can be made by various materials with a variety of geometries. The flow restrictors  150  and  151  can be installed in any locations that straddle (preferably symmetrically) the zero phasing line  153  of the perforating. The two flow restrictors  150  and  151  should contact the casing  42  and allow a small gap  155  between the gun shell  44  and the inside diameter (ID) of casing  42 . This gap enables the flow communication between the formation  40  and the gun inner space  46  when the perforated tunnels on the casing and holes on gun carrier  44  do not line up if there is a gun movement after perforating. The devices  150  and  151  substantially reduce the fluid flow moving from outside of the two restrictors into the gap  155  within the two restrictors. This maximizes the fluid flow from the formation  40  to the inner gun space  46  so that the produced solid debris and sands are drawn into the inner gun volume  46 . Another benefit of using the flow restrictors  150  and  151  is that the perforating does not have to be zero phasing. A range of azimuthal angles of perforating phasing is possible depending on the position and height of the flow restrictors  150  and  151  installed on the gun carrier  44 . 
         [0036]      FIG. 7  is the front view of the flow restrictors  150  and  151  that are assembled on the perimeter of the gun carrier  44 . The two clamps  160  and  161  are connected to the two ends of the gun  23 . A number of holes  170  and  171  with spiral grooves are distributed in the clamps  160  and  161 . The flow restrictor  150  is attached to the gun carrier  44  by the two screws  164  and  165  into the threaded holes  170  and  171  on the clamps  160  and  161 , respectively. The flow restrictor  151  is attached to the gun carrier  44  through the two screws  166  and  167  on the clamps  160  and  161 , respectively. In another embodiment, the holes  170  and  171  with the spiral grooves are manufactured near the end of the gun carrier  44  rather than on the clamps  160  and  161 . To secure the flow restrictors  150  and  151  on the gun carrier  44 , there may be one or more groups of the threaded holes  173  in the middle of the gun carrier  44 . The screws  174  and  175  further secure the flow restrictors  150  and  151 , respectively, on the gun carrier  44 . Other types of assembly are also possible to install the flow restrictors  150  and  151  on the gun carrier  44 . For example, the flow restrictors  150  and  151  can be welded on the gun carrier  44 . 
         [0037]    In addition to the flow restrictors  150  and  151  that reduce the lateral fluid flow from the wellbore  43  into the gap  155  between the two restrictors, the vertical fluid flow from the wellbore  43  above and below the gun carrier  44  into the gap region  155  should also be confined.  FIG. 8  shows the vertical flow restrictors  190  installed between the two horizontal flow restrictors  150  and  151  on the upper end of the gun carrier  44 . The outer curvature of the restrictor  190  has substantially similar to that of the casing ID  42 , while its inner curvature is substantially similar to that of the gun OD. Screws  191  can be used to connected the vertical flow restrictor  190  to the gun carrier  44 . The same installation of the vertical flow restrictor can be applied on the bottom end of the gun. The vertical flow restrictor  190  can also be installed at the bottom of the gun carrier  44 . 
         [0038]    In another embodiment, multiple flow restrictors can be used to replace the single vertical flow restrictor  190 . As shown in  FIG. 8 , the multiple vertical flow restrictors  195  are installed on the bottom end of the gun carrier  44 . Each piece of the multiple vertical flow restrictors  195  is connected to the gun carrier  44  through a screw  196  and the holes with spiral groove on the gun. The inner and outer curvatures of the multiple vertical flow restrictors  1 . 95  are substantially similar to those of the gun carrier  44  and the casing ID  42 , respectively. The multiple vertical flow restrictors  195  can also be installed on the top of the gun carrier  44 . 
         [0039]    The vertical flow restrictors  190  and  195  may be installed without the horizontal flow restrictors  150  and  151 , and vice versa. There is also no restriction that the vertical flow restrictors are installed within the horizontal flow restrictors  150  and  151 . The vertical flow restrictor  190  or  195  can be installed on the entire periphery of the gun carrier  44 , or just a portion thereof. 
         [0040]    In addition to the wireline, the perforating system  10  can also be conveyed to the targeted location in a well by other methods. For example, the perforating system  10  can be installed in drill pipes, tubing pipes, coiled tubing or other convey means to realize the same perforating results with low debris in the wellbore. All the embodiments herein are applicable regardless of the conveyance differences. 
         [0041]    The preceding description is mean to illustrate various features described in the present application and is not meant to limit the present or future related claim scope in any way.