Patent Publication Number: US-6336506-B2

Title: Apparatus and method for perforating and stimulating a subterranean formation

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application, Ser. No. 09/110,728, filed Jul. 6, 1998 and now U.S. Pat. No. 6,158,511, which is a continuation-in-part of U.S. patent application, Ser. No. 08/711,188, filed Sep. 9, 1996 and now U.S. Pat. No. 5,775,426. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to an apparatus and method for perforating well casing and/or a subterranean formation(s), and more particularly, to such an apparatus and process wherein a propellant is employed to substantially simultaneously enhance the effectiveness of such perforations and to stimulate the subterranean formation(s). 
     2. Description of Related Art 
     Individual lengths of relatively large diameter metal tubulars are secured together to form a casing string which is positioned within a subterranean well bore to increase the integrity of the well bore and provide a path for producing fluids to the surface. Conventionally, the casing is cemented to the well bore face and subsequently perforated by detonating shaped explosive charges. These perforations extend through the casing and cement a short distance into the formation. In certain instances, It is desirable to conduct such perforating operations with the pressure in the well being overbalanced with respect to the formation pressure. Under overbalanced conditions, the well pressure exceeds the pressure at which the formation will fracture, and therefor, hydraulic fracturing occurs in the vicinity of the perforations. As an example, the perforations may penetrate several inches into the formation, and the fracture network may extend several feet into the formation. Thus, an enlarged conduit can be created for fluid flow between the formation and the well, and well productivity may be significantly Increased by deliberately inducing fractures at the perforations. 
     When the perforating process is complete, the pressure within the well is allowed to decrease to the desired operating pressure for fluid production or injection. As the pressure decreases, the newly created fractures tend to close under the overburden pressure. To ensure that fractures and perforations remain open conduits for fluids flowing from the formation into to the well or from the well into the formation, particulate material or proppants are conventionally injected into the perforations so as to prop the fractures open. In addition, the particulate material or proppant may scour the surface of the perforations and/or the fractures, thereby enlarging the conduits created for enhanced fluid flow. The proppant can be emplaced either simultaneously with formation of the perforations or at a later time by any of a variety of methods. For example, the lower portion of the wellbore can be filled with a sand slurry prior to perforation. The sand is subsequently driven into the perforations and fractures by the pressured fluid in the wellbore during conventional overbalanced perforating operations. 
     As the high pressure pumps necessary to achieve an overbalanced condition in a well bore are relatively expensive and time consuming to operate, gas propellants have been utilized in conjunction with perforating techniques as a less expensive alterative to hydraulic fracturing. Shaped explosive charges are detonated to form perforations which extend through the casing and into the subterranean formation and a propellant is ignited to pressurize the perforated subterranean interval and propagate fractures therein. U.S. Pat. Nos. 4,633,951, 4,683,943 and 4,823,875 to Hill et al. describe a method of fracturing subterranean oil and gas producing formations wherein one or more gas generating and perforating devices are positioned at a selected depth in a wellbore by means of by a section of wireline which may also be a consumable electrical signal transmitting cable or an ignition cord type fuse. The gas generating and perforating device is comprised of a plurality of generator sections. The center section includes a plurality of axially spaced and radially directed perforating shaped charges which are interconnected by a fast burning fuse. Each gas generator section includes a cylindrical thin walled outer canister member. Each gas generator section is provided with a substantially solid mass of gas generating propellant which may include, if necessary, a fast burn ring disposed adjacent to the canister member and a relatively slow bum core portion within the confines of ring. An elongated bore is also provided through which the wireline, electrical conductor wire or fuse which leads to the center or perforating charge section may be extended. Primacord fuses or similar igniters are disposed near the circumference of the canister members. Each gas generator section is simultaneously ignited to generate combustion gasses and perforate the well casing. The casing is perforated to form apertures while generation of gas commences virtually simultaneously. Detonation of the perforating shaped charges occurs at approximately 110 milliseconds after ignition of gas generating unit and that from a period of about 110 milliseconds to 200 milliseconds a substantial portion of the total flow through the perforations is gas generated by gas generating unit. 
     U.S. Pat. No. 4,391,337 to Ford et al. discloses an integrated jet perforation and controlled propellant fracture device and method for enhancing production in oil or gas wells. A canister contains a plurality of shaped charge grenades around which is packed a gas propellant material so as to form a solid fuel pack. 
     U.S. Pat. No. 5,355,802 to Petijean describes a method and apparatus for perforating a formation surrounding a wellbore and Initiating and propagating a fracture In the formation to stimulate hydrocarbon production from the wellbore. A tool includes at least one oriented shaped charge which is connected to detonator via a firing cord. At least one propellant generating cartridge is also positioned within tool and is connected to wireline cable through delay box via wires and cord. 
     U.S. Pat. No. 4,253,523 to Ibsen discloses a method and apparatus for well perforations and fracturing operations. A perforating gun assembly is comprised of a plurality of shaped charges positioned in spaced-apart relationship to each other in an elongated cylindrical carrier. The spaces in the carrier between the shaped charges are filled with a secondary explosive, such as an activated ammonium nitrate. 
     U.S. Pat. No. 5,005,641 to Mohaupt discloses a gas generating tool for generate a large quantity of high pressure gases to stimulate a subterranean formation. The tool comprises a carrier or frame having a series of staggered openings spaced longitudinally along the tubular member. Carrier receives a charge of propellant material which has a passage through which an ignition tube is inserted. 
     However, none of these prior art devices which utilized propellants in conjunction with perforating devices have proved to provide completely satisfactory results. Thus, a need exists for an apparatus and method for perforating and stimulating a subterranean formation which provides for improved communication between the wellbore and the subterranean formation penetrated thereby. 
     Thus, it is an object of the present Invention to provide an apparatus and method for perforating and stimulating a subterranean formation which provides for improved communication between the wellbore and the subterranean formation penetrated thereby. 
     It is also object of the present invention to provide an apparatus for perforating and stimulating a subterranean formation which is relatively simple in design and can be readily employed with a variety of perforating gun designs. 
     It is a further object of the present invention to provide an apparatus for perforating and stimulating a subterranean formation which provides repeatable burns of the propellant component of the apparatus. 
     It is still a further object of the present Invention to provide an apparatus for perforating and stimulating a subterranean formation which uses perforating charges of lesser energy than previously employed. 
     It is a still further object of the present invention to provide an apparatus and method for perforating and stimulating a subterranean formation wherein propellant is positioned between a perforating charge and the casing of a well bore. 
     SUMMARY OF THE INVENTION 
     To achieve the foregoing and other objects, and in accordance with the purposes of the present invention, as embodied and broadly described herein, one characterization of the present invention comprises an apparatus for perforating and stimulating a subterranean formation which is penetrated by a well bore having casing positioned therein so as to establish fluid communication between the formation and the well bore. The apparatus comprises one or more explosive charges, propellant interposed between the casing and at least one of the one or more explosive charges, and a detonator ballistically connected to the one or more charges. 
     Another characterization of the present invention comprises an apparatus for perforating a subterranean formation comprising an apparatus for perforating and stimulating a subterranean formation which is penetrated by a well bore having casing positioned therein so as to establish fluid communication between the formation and the well bore. The apparatus comprises a tube having one or more apertures therethrough, one or more shaped charges positioned within the tube, and propellant interposed between the casing and at least one of the one or more shaped charges. Each of the one or more shaped charges is aligned with one of the one or more apertures. 
     Yet another characterization of the present invention comprises a method of a method of perforating and stimulating a subterranean formation which is penetrated by a well bore having casing positioned therein so as to establish fluid communication between the formation and the well bore. In accordance with the method, a liquid propellant is positioned between at least one perforating charge in the well bore and the casing. The at least one perforating charge is detonated so as to form perforations through the casing and into the formation. Detonation of the perforating charge ignites the liquid propellant thereby forming gases which clean the perforations and extend fluid communication between the formation and the well bore. 
     A further characterization of the present invention is a kit for an apparatus for perforating and stimulating a subterranean formation which is penetrated by a well bore having casing positioned therein so as to establish fluid communication between the formation and the well bore. The kit comprises an apparatus for perforating a subterranean formation which has one or more shaped charges and a propellant adapted to interposed at least one of the shaped charges and the casing when the apparatus is positioned within the well bore. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and form a part of the specification, illustrate the embodiments of the present invention and, together with the description, serve to explain the principles of the invention. 
     In the drawings: 
     FIG. 1 is a cross sectional view of the apparatus of the present invention as positioned within a well penetrating a subterranean formation; 
     FIG. 2 is a cross sectional view of the apparatus of one embodiment of the present invention; 
     FIG. 3 is a cross sectional view illustrating the spatial relationships between the certain component parts of the apparatus of the present invention taken along line  3 — 3  of FIG. 2; 
     FIG. 4 is a partial cross sectional view of a perforating charge as connected to a detonating cord; 
     FIG. 5 is a perspective view of one embodiment of the propellant sleeve of the apparatus of the present invention which is illustrated in FIG. 2; 
     FIG. 6 is a cross section of a portion of a detonating system suitable for use in the present invention; 
     FIG. 7 is a perspective view of another embodiment of the propellant sleeve of the apparatus of the present invention which is illustrated in FIG. 2; 
     FIG. 8 is a cross sectional view of the propellant sleeve taken along line  8 — 8  of FIG. 7; 
     FIG. 9 is a cross sectional view of another embodiment of a propellant sleeve utilized in the apparatus of the present invention which is illustrated in FIG. 2; 
     FIG. 10 is a cutaway view of the propellant sleeve embodiment depicted in FIG. 9 which illustrates the interior wall of the sleeve; 
     FIG. 11 is a cross sectional view of another embodiment of the apparatus of the present invention; 
     FIG. 12 is a cross sectional view of the another embodiment of the propellant as utilized in conjunction with the apparatus of the present invention; 
     FIG. 13 is a perspective view of the embodiment of propellant utilized in conjunction with the apparatus of the present invention which is also illustrated in FIG. 12; 
     FIG. 14 is a schematic view of another embodiment of the present invention in which liquid propellant is introduced Into a subterranean well bore; and 
     FIG. 15 is a schematic view of the embodiment illustrated in FIG. 15 further illustrating a perforating gun being positioned within the liquid propellant in a subterranean well bore. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As illustrated in FIG. 1, a well  10  having a casing  12  which is secured therein by means of cement  13  extends from the surface of the earth  14  at least into a subterranean formation  16 . One or more perforating and propellant apparatus  20  of the present invention are secured to the lower end of tubing string  18  and lowered into well  10 . The upper most apparatus  20  as positioned within well  10  may be secured directly to the end of tubing string  18 . A tandem sub  60  may be utilized to secure apparatus  20  together while a bull plug  66  may be secured to the terminal end of the lowermost apparatus  20 . Any suitable means, such as a packer  21 , may be employed to isolate the portion of well  10  adjacent interval  16 , if desired. A tubing string may be utilized to position and support the apparatus of the present invention within a well bore. Tubing will preferably be employed to convey several apparatus  20  into the same well bore. Alternatively, a wireline, slick line, coil tubing or any other suitable means as will be evident to a skilled artisan may be used to position and support one or more apparatus  20  within a well bore. 
     Referring now to FIG. 2, the perforating and propellant apparatus of the present invention is illustrated generally as  20  and has one end thereof secured to a tandem sub  60  while the other end thereof is secured to a bull plug  66 . A perforating charge carrier  22  is positioned between tandem sub  60  and bull plug  66  and is secured thereto by any suitable means, such as by mating screw threads  23  and  24  which are provided In the internal surface of carrier  22  adjacent each end thereof with corresponding threads  61  and  67  of tandem sub  60  and bull plug  66 , respectively. O-rings  70  provide a fluid tight seal between carrier  22  and tandem sub  60  while O-rings  74  provide a fluid tight seal between carrier  22  and bull plug  66 . Carrier  22  may be a commercially available carrier for perforating charges and contains at least one conventional perforating charge  40  capable of creating an aperture in the carrier wall  30 , well casing  12 , and a portion of the adjacent subterranean formation  16 . A perforating charge tube  34  is positioned within carrier  22  and has at least one relatively large aperture or opening  35  and a plurality of smaller apertures or openings  36  therein. Openings  35  in the wall of charge tube  34  may be spaced both vertically along and angularly about the axis of the tube. Charge carrier  22  and perforating charge tube  34  have generally elongated tubular configurations. A lined perforating charge  40  has a small end  46  secured in an aperture or opening  36  in perforating charge tube  34 , as described below, and a large end  48  aligned with and protruding through opening or aperture  35  in tube  34 . At least one lined perforating charge  40  is mounted In perforating charge tube  34 . A detonating cord  86  is connected to a detonator above tandem sub  60 , to the small end  46  of each perforating charge  40 , and to end cap  68  in bull plug  66 . One or more additional combinations of a perforating charge carrier, booster transfer and a tandem sub could be mounted above carrier  22 . Tube alignment end plates  50  function to align charge tube  34  within carrier  22  so that the front of each charge is adjacent a scallop  27  in the wall of carrier  22 . 
     If multiple charges are present, they may be spaced vertically along and angularly about the axis of the carrier. The charge density is an appropriate density determined by methods known to those skilled in the art. Common charge densities range between two and twenty four per foot. Detonating cord  86  connects a booster transfer (not illustrated) in tandem sub  60  above carrier  22 , all charges  40 , and end cap  68  in bull plug  66 . 
     As illustrated in FIG. 3, brackets  80  on the small end  46  of lined perforating charge  40  extend through opening  36  in charge tube  34 . A clip  82  secures punch charge  40  to charge tube  34 . Detonating cord  86  is threaded through a space  84  between brackets  80  and clip  82 . Charge tube  34  is mounted in carrier  22  so that the small end  46  of charge  40  is adjacent scallop  27  in carrier  22 . 
     Referring to FIG. 4, a typical perforating charge is illustrated generally as  40 . A highly compressed explosive  41  partially fills perforating charge case  42 . Liner  43  covers the exposed surface of the explosive. The liner  43  is commonly metallic and serves to focus the energy of the charge and enable the charge to perforate a well casing. 
     In accordance with the present invention, a sleeve  90  which has a generally tubular configuration (FIG. 5) is positioned around perforating charge carrier  22  during manufacture of the perforating and propellant apparatus  20  of the present invention or during final assembly thereof which may take place at the well site. As assembled (FIG.  2 ), sleeve  90  is secured in positioned around perforating charge carrier  22  at one end by tandem sub  60  and by bull plug  66  at the other end. Tandem sub  60  and bull plug  66  may be sized to have an external diameter greater than sleeve  90  so as to inhibit damage to sleeve  90  during positioning within a well bore. Alternatively, protective rings or the like (not illustrated) which have a larger external diameter than sleeve  90  may be inserted between tandem sub  60 , bull plug  66  and sleeve  90  during manufacture or final assembly of the apparatus of the present invention so as to inhibit damage to sleeve  90 . Sleeve  90  may extend the entire distance between tandem sub  60  and bull plug  66  or a portion thereof. Sleeve  90  is constructed of a water repellant or water proof propellant material which is not physically effected by hydrostatic pressures commonly observed during perforation of a subterranean formation(s) and is unreactive or inert to almost all fluids, in particular those fluids encountered in a subterranean well bore. Preferably, the propellant is a cured epoxy or plastic having an oxidizer incorporated therein such as that commercially available from HTH Technical Services, Inc. of Coeur d&#39;Alene, Id. 
     Any suitable detonating system may be used in conjunction with the perforating and propellant apparatus  20  of the present invention as will be evident to a skilled artisan. An example of such a suitable detonating system suitable is illustrated in FIG.  6 . Vent housing  210  is capable of attachment to the end of a tubing string  211  or wireline (not shown). A vent  212  is attached to connecting rod  214  inside vent housing  210  and seals fluid passage  216 . Rod  214  is in contact with a piston  218 . An annular chamber  220  between piston  218  and the interior wall of housing  210  is filled with air at atmospheric pressure. Adjacent the bottom of piston  218 , shear pins  222  are mounted in shear set  224 , and a firing pin  226  extends downward from the bottom of piston  218 . Retainer  228  joins vent housing  200  and tandem sub  60 . Percussion detonator  230  is mounted in retainer  228  in firing head  236  which is attached to vent housing  210  and capable of attachment to tandem sub  60 . Sub  60  is attached to perforating charge carrier  22 . An ignition transfer  232  at the top of sub  60  is in contact with detonating cord  86  passing through central channel  234  and charge carrier  22 , as described above. A booster transfer is located in each tandem sub  60 , linking the detonating cords in the charge carriers above and below the tandem sub. 
     Upon application of sufficient hydraulic pressure to the top of piston  218 , vent  212  and piston  218  simultaneously move downward, opening fluid passage  214  and causing firing pin  226  to contact percussion detonator  230 . The ignition of percussion detonator  230  causes a secondary detonation in ignition transfer  232 , which in turn ignites detonating cord  86 . Detonating cord  86  comprises an explosive and runs between the ends of each charge carrier, passing between the backs of the charges and the charge clips holding the charges in the carrier. Cord  86  ignites the shaped charges  40  in charge carrier  22  and booster transfer, which contains a higher grade explosive than detonating cord  86 . 
     As described above and shown in FIG. 6, an impact detonator provides a primary detonation. If the perforating apparatus is run on a wireline, the primary detonator could, alternatively, be an electrical detonator. The primary detonator ignites a pressure-sensitive chemical in ignition transfer  232 , which in turn ignites detonating cord. The detonating cord then ignites the one or more charges  40  in the carrier  22  simultaneously. Each transfer booster also contains an explosive for detonating the cord  86  in the adjacent carrier. The system may be detonated from the top, the bottom, or both. 
     In operation, the desired number of perforating charge carriers  22  are loaded with charges  40  and are connected with a detonating means, such as detonating cord  86 . A string of apparatus  20  separated by tandem subs  60  is assembled at the well site as the units are lowered into well  10  at the end of a tubing string, wireline, slick line, coil tubing or any other suitable means as will be evident to a skilled artisan. Propellant sleeve  90  may be cut from a length of propellant tubular and positioned around perforating charge carrier  22  at the well site. The apparatus  20  is then located in the well with the perforating charges adjacent the formation interval  16  to be perforated. The perforating charges  40  are then detonated. Upon detonation, each perforating charge  40  blasts through a scallop  27  in carrier  32 , penetrates propellant sleeve  90 , creates an opening in casing  12  and penetrates formation  16  forming perforations therein. Propellant sleeve  90  breaks apart and ignites due to the shock, heat, and pressure of the detonated shaped charge  40 . When one or more perforating charges penetrate the formation, pressurized gas generated from the burning of propellant sleeve  90  enters formation  16  through the recently formed perforations thereby cleaning such perforations of debris. These propellant gases also stimulate formation  16  by extending the connectivity of formation  16  with well  10  by means of the pressure of the propellant gases fracturing the formation. 
     A proppant, such as sand, may be introduced into well  10  almost simultaneously with the ignition of the perforation and propellant apparatus  20  of the present invention by any of a variety of suitable means, such as a conventional perforating charge carrier which is equipped with punch charges, filled with sand and connected in series to detonating cord  86 , as is commercially available under the trademark POWR*PERF from Halliburton Energy Services or Advance Completion Technologies Inc. As such gases generated by burning propellant sleeve  90  escape from the well and enter the perforations formed in formation  16 , the sand which is carried into the fractures by the propellant gases abrades or scours the walls of the perforations and fractures, thereby enlarging the conduits for fluid flow between the formation and the well  10 . Some of the sand may remain in the fractures as a proppant, thereby preventing the fractures from closing when the fluid pressure is relieved. 
     To assist in Ignition, sleeve  90  may be provided with one or more grooves or slits  92  which may extend through the entire thickness of sleeve  90  (FIG. 7) and which may extend substantially the entire length thereof. The slit(s) is positioned adjacent a shaped charge  40  such that upon ignition shaped charge  40  impacts slit  92  which provides a greater surface area for sleeve  90  to ignite and bum. Preferably, slit(s)  92  is tapered (FIG. 8) such that the slit is wider at the internal surface of sleeve  90  than the external surface thereof. To achieve a uniform and repeatable burn, the internal surface of sleeve  90  may be provided with grooves or channels  94  (FIGS. 9 and 10) to assist in propellant sleeve  90  uniformly breaking upon being impacted by shaped charge  40 . Grooves or channels  94  may have a varied or a uniform thickness or depth and may be formed in a uniform or random patten. 
     Referring now to FIG. 11, another embodiment of the perforating and propellant apparatus of the present invention is illustrated generally as  120  and has a perforating charge carrier  122  is located between two tandem subs  160  or between a tandem sub  160  and bull plug  166 . In this embodiment, carrier  122  is constructed of a water repellant or proof propellant material which is not physically effected by hydrostatic pressures commonly observed during perforation or subterranean formations and is unreactive or inert to almost all fluids, in particular those fluids encountered in a subterranean well bore. Preferably, the propellant is a cured epoxy, carbon fiber composite having an oxidizer incorporated therein such as that commercially available from HTH Technical Services, Inc. of Coeur d&#39;Alene, Idaho. Carrier  122  contains at least one conventional perforating charge  140  capable of creating an aperture in the carrier wall  130 , well casing  12 , and a portion of the interval  16  in the adjacent subterranean formation. Each perforating charge  140  is secured in an opening  136  in perforating charge tube  134  with a clip. Preferably, tandem sub  160 , bull plug  166  and charge tube  134  are constructed of a material which substantially entirely breaks up or decomposes, for example thin walled steel, a material which substantially disintegrates, for example a carbon fiber, epoxy composite, upon detonation of charges  140 , or a material which is completely burnable, such as a epoxy, oxidizer propellant similar to that used for sleeve  90 . If more than one shaped charges is utilized, they may be spaced vertically along and angularly about the axis of the carrier. The charge density is an appropriate density determined by methods known to those skilled in the art. Common charge densities range between six and twelve per foot. Detonating cord  186  connects a booster transfer in tandem sub  160  above carrier  122 , all charges  40 , and end cap  168  in bull plug  166 . As previously discussed with respect to the embodiment illustrated in FIG. 2, one or more combinations of an additional tandem sub and an additional perforating charge carrier could be mounted below carrier  122 . The detonating cord  186  would then be connected to a booster transfer in the tandem sub  160  below each additional perforating charge carrier. In this embodiment, removal of any portion of the gun from well  10  after detonation is obviated since the carrier is Ignited and the charge tube decomposed and/or disintegrated upon detonation of charge(s)  140 . This advantage is especially pronounced in instances where a very small amount of space, if any, exists below the interval of formation  16  which is perforated. 
     Although the propellant as utilized in the present invention is described above as being a sleeve, shell or sheath which is generally rigid, the propellant may utilized in different shapes, configurations and/or forms so long as propellant is interposed casing which is positioned within a subterranean well bore and at least one perforating charge which is positioned within the casing. For example, propellant  190  as illustrated in FIG. 13 may be substantially helical or spiral in form and is positioned around perforating charge carrier  22  during manufacture of the perforating and propellant apparatus  20  of the present invention or during final assembly thereof which may take place at the well site. As assembled (FIG.  12 ), propellant  190  is secured in positioned around perforating charge carrier  22  at one end by tandem sub  60  and by bull plug  66  at the other end. Tandem sub  60  and bull plug  66  may be sized to have an external diameter greater than sleeve  90  so as to inhibit damage to propellant  190  during positioning within a well bore. Alternatively, protective rings or the like (not illustrated) which have a larger external diameter than propellant  190  may be inserted between tandem sub  60 , bull plug  66  and propellant  190  during manufacture or final assembly of the apparatus of the present invention so as to inhibit damage to propellant  190 . Propellant  190  may extend the entire distance between tandem sub  60  and bull plug  66  or a portion thereof. As with sleeve  90 , propellant  190  is constructed of a water repellant or water proof propellant material which is not physically effected by hydrostatic pressures commonly observed during perforation of a subterranean formation(s) and is unreactive or inert to almost all fluids, in particular those fluids encountered in a subterranean well bore. Preferably, the propellant is a cured epoxy or plastic having an oxidizer incorporated therein such as that commercially available from HTH Technical Services, Inc. of Coeur d&#39;Alene, Idaho. Alternatively, propellant  190  may be in the form of one or more bands or in the form of one or more generally linear or generally arcuate strips which are positioned about charge carrier  22  so as to be interposed at least one perforating charge  40  and casing  12 . The bands of propellant  190  may be generally annular and may have gap therein so as to be U-shaped or C-shaped in cross section. As another example, propellant  190  may be flexible and wrapped about all or a portion of charge carrier  22  in any shape or pattern so as to be interposed at least one perforating charge  40  and casing  12 . In both of these embodiments, propellant  190  may be secured to charge carrier by any suitable means as will be evident to a skilled artisan, such as a commercially available adhesive. Pursuant to a further alterative, propellant  190  is a relatively thin, discrete shape having any suitable peripheral configuration, for example polygonal or a closed plane curve such as a circle, and is secured to the outer surface of charge carrier  22  by any suitable means, for example adhesive or screw threads, so as to be interposed at least one perforating charge  40  and casing  12 . 
     In yet another embodiment of the present invention, a liquid propellant  290 , such as that manufactured under the trade name designation Re-flo  403  by Hercules, Inc. of Wilmington, Delaware, is injected into well  10  via casing  12  and forms a first upper liquid surface  291  within well  10 . One or more conventional perforating guns  320  are then lowered into well  10  at the end of a tubing string, wireline, slick line, coil tubing or any other suitable means as will be evident to a skilled artisan. The perforating guns are positioned adjacent the subterranean formation of interest which is formation  16  as illustrated in FIG.  14 . As thus positioned, the liquid propellant previously injected into well  10  is displaced by the perforating gun(s)  320  such that the liquid propellant is interposed at least the lowermost perforating charge  322  present in the lowermost perforating gun  320 . Preferably, the volume of liquid propellant  290  previously injected into well  10  is sufficient to cover all of the perforating charges in every perforating gun  320  lowered into well  10 . As displaced about the perforating gun(s)  320 , the liquid propellant forms a second upper liquid surface charges  322  are then detonated by means of a suitable detonating system as previously described. Upon detonation, each perforating charge  322  penetrates liquid propellant  290 , creates an opening in casing  12  and penetrates formation  16  forming perforations therein. The liquid propellant  290  ignites due to the shock, heat, and pressure of the detonated shaped charge(s)  322 . When one or more perforating charges penetrate the formation, pressurized gas generated from the burning of liquid propellant  290  enters formation  16  through the recently formed perforations thereby cleaning such perforations of debris. These gases also stimulate formation  16  by extending the connectivity of formation  16  with well  10  by means of the pressure of the gases fracturing the formation. Alternatively, the liquid propellant may be injected into well  10  simultaneously with lowering of perforating gun  320  into the well or after perforating gun  320  is positioned within well  10 . 
     The perforating and propellant apparatus of the present invention can be utilized with tubing or wireline. The increased strength of the tubing over wireline allows the use of a longer perforating and propellant apparatus, thereby allowing a longer interval to be perforated and stimulated in a single trip into a well. A tubing conveyed apparatus is also compatible with the use of packers to isolate one or more portions of the well adjacent one or more intervals of the formation. Thus, the method may be used where it is desired for some other reason to limit the pressure to which another portion of the well is subjected, for example, in a well where one or more other zones have already been completed. Further, if the well has a high deviation angle from vertical or is horizontal, the tubing may be used to push the perforating and propellant apparatus into the well. 
     Multiple intervals of a subterranean formation can be perforated and fractured in a single operation by combining two or more perforating and propellant apparatus  20  and/or  120  of the present invention with a single tubing string in a spaced apart manner as will be evident to a skilled artisan. In using the perforating and propellant apparatus of the present invention, shaped charges containing a smaller amount of highly compressed explosive than conventional charges may be employed since the shaped charge need only perforate casing  12  as gases which are generated by burning propellant extend the perforation and fractures into the subterranean formation. Accordingly, a greater number of shaped charges may be employed in the apparatus of the present invention than in a conventional perforating apparatus and/or shaped charges which produce larger diameter perforations than those produced by conventional shaped charges may be employed in the apparatus of the present invention. Further, propellant sleeve  90  or carrier  122  may have proppant dispersed throughout or embedded upon the outer surface thereof. This proppant may also contain a radioactive tag to assist in determining the dispersion of the proppant into the perforations in the subterranean formation(s). 
     Although the various embodiments of the apparatus of the present invention have been described and illustrated as being comprised of several component parts which are secured together in a fluid tight relationship, it is within the scope of the present invention to construct the apparatus  20  or  120  of an integral piece of propellant material which is open to flow of fluids from the well bore and in which shaped charges are secured. 
     As discussed above, the ignition means may be a detonating material, such as detonating cord  28 . Altematively, the ignition means may be a deflagrating material or cord. For example, a tube containing black powder may be utilized as the ignition system to ignite the propellant in the apparatus and method of the present invention. 
     While the foregoing preferred embodiments of the invention have been described and shown, it is understood that the alternatives and modifications, such as those suggested and others, may be made thereto and fall within the scope of the invention.