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CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    NA 
       BACKGROUND OF THE INVENTION 
     Field of the Invention 
       [0002]    The traditional prior art procedure for completing some gas wells after a well casing is set and cemented in place, is to run into the wellbore with a “bit and scraper” attached to the bottom of a tubing or drill string and “clean out” the well. First, a bore wall scraping or reaming tool is attached to the end of a pipe string. The pipe string is lowered into the well while the scraping tool is rotating. At or near the bottom of the well, the bit may encounter a plug of cement within the casing bore which is the residual of the cementing operation that secures the well casing to raw borewall. Following the scraping and boring process, clean fluid is circulated down the tubing bore and up through the tubing/casing annulus for flushing the well of debris created by the bit and scraper. After the well is circulated clean, this pipe string is pulled from the wellbore. 
         [0003]    Next, a perforating gun assembly is attached to the end of a pipe string and run into the wellbore. The perforating gun or guns are positioned across from the geologic formation zones of interest for fluid production and discharged. There are several types of perforation methods including shaped charges, ballistic (projectiles) and chemicals. All types, however, have the objective of perforating the well casing, the surrounding cement collar and a short distance into the geologic formation. The purpose of such perforations is to facilitate an extractive flow of in situ formation fluid into the bore of the well casing and ultimately to the wellhead at the surface. 
         [0004]    In many cases, after the perforating guns are detonated and holes are made through the casing and out into the formation, a “frac-treatment” on the formation is performed. The “frac-treatment” may consist of pumping some type of acid down the wellbore and out through the casing perforations under pressure into the formation to dissolve fines and other debris for enhancing in situ formation fluid production. Also characterized as frac-treatment are “proppants” which are liquid/particulate mixtures that are pumped down the well under high pressure and driven into the fracture channels to prevent subsequent closure. Any of these processes normally take a minimum of two complete “trips” into the wellbore to bottom. 
         [0005]    Traditionally, a “trip” is defined as that process of assembling a tubing or drill string into a borehole or wellbore, incrementally, in approximately 90 ft. “stand” sections of pipe comprising three “joints” of about 30 ft. each. In this specification, the terms “pipe” and “tubing” will be used interchangeably. This incremental assembly process is performed manually on the derrick or rig floor as the accumulated length of assembled pipe is lowered into the wellbore. Assembly continues until the bottom end of the pipe or tubing string reaches the bottom of the wellbore. For a typical, 3,000 ft. well, this requires about 33 stands of pipe or tubing and 32 stand connections. Many land wells are 7,000 ft. deep and a few exceed 20,000 ft. Off-shore wells frequently exceed 20,000 ft. of deviated direction penetration length. A skilled rig crew can assemble a 3,000 ft. tubing string in about two to two and one half hours. Extraction of the tubing string requires about the same amount of time. Accordingly, a “round trip” into and out of a wellbore by a minimum rig crew of four requires about five to five and one half hours of strenuous manual labor; assuming no difficulties are encountered. Ergo, any procedure, process or equipment that promises to save the time of even one “trip” in the well completion process is highly valued. 
       SUMMARY OF THE INVENTION 
       [0006]    The pipe string assembly of the invention includes a series of end-to-end connected joints of conventional drill pipe or production tubing having a reaming or scraper bit secured onto the lower distal end of the string. Above the bit at selected locations among the serial string of conventional pipe joints are perforation assemblies according to the invention. 
         [0007]    Each perforation assembly comprises a first Y-adapter at the upper distal end for transition of an internal fluid flow channel from a conventional pipe bore into a circulation mandrel of the perforation assembly. At the lower distal end of the perforation assembly is a second Y-adapter for transition of the fluid flow channel from the circulation mandrel into another pipe bore or a successive perforation assembly connected by a nipple sub. Extending between the opposite end Y-adapters in adjacent parallelism with the assembly circulation mandrel is an angularly oriented, well pressure actuated, casing perforation gun. 
         [0008]    The perforating gun comprises a gun body tube that houses a shaped charge loading tube within an internal bore of the body tube. The shaped charge loading tube confines a plurality of shaped charge explosive cells connected to a detonator cord that extends the length of the gun body tube. At one end of the gun body tube bore is a pressure firing head assembly. One end of the detonating cord is secured to the pressure firing head assembly. 
         [0009]    Each Y-adapter also includes a receptacle collar for radially confining respective ends of the perforation gun. Locking collars threaded along end elements of the perforation gun are turned tightly against opposite faces of the Y-adapter receptacle collar to clamp the gun from movement in opposite axial directions. The angular orientation of the gun about the gun axis is secured by one or more cap screw heads. The cap screw shafts are turned into the perforating gun whereas the cap screw heads project into apertures in the respective receptacle collar. 
         [0010]    The invention string assembly as described above is lowered into the well while rotating to facilitate the bit and scraper operation on any residual cement or cutting debris. As the bit attains bottom hole, clean well fluid is pumped down the pipe string and circulation mandrels, through the drill bit orifices and up the wellbore annulus between the string assembly and the inside casing wall. This circulation continues until the operator feels the well has been sufficiently flushed of debris. 
         [0011]    Once the wellbore is circulated over to clean fluid, a predetermined pressure is applied to the wellbore to shear the pins that restrain the firing pin in the pressure firing heads. This begins a chain of events resulting in the detonation of the detonating cord. Progressive ignition of the detonating cord sequentially ignites the shaped charges to penetrate the casing at points contiguous with the well fluid production zone(s). 
         [0012]    Following the casing perforation, the well may be immediately frac-treated by pumping down the completion pipe string and into the well annulus the essential fracturing chemical or sand mixture. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The advantages and further features of the invention will be readily appreciated by those of ordinary skill in the art as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference characters designate like or similar elements throughout. 
           [0014]      FIG. 1  is a schematic of a cased borehole having the present invention pipe string in place. 
           [0015]      FIG. 2  is a side profile view of the present perforation assembly. 
           [0016]      FIG. 3  is a partially sectioned view of the upper end of the perforation assembly. 
           [0017]      FIG. 4  is a partially sectioned view of the firing body portion of the perforation gun 
           [0018]      FIG. 5  is a partially sectioned view of the perforation gun. 
           [0019]      FIG. 6  is a partially sectioned view of the bottom end of the perforation gun. 
           [0020]      FIG. 7  is a detailed and partially sectioned view of the bottom Y-adapter and perforating gun. 
           [0021]      FIG. 8  is a pictorial view of the gun bottom bull plug. 
           [0022]      FIG. 9  is a partially sectioned plan view of the perforation assembly. 
           [0023]      FIG. 10  is a side view of the perforation assembly in full cross-section. 
           [0024]      FIG. 11  is a side view of the perforation assembly showing the perforating gun in cross-section. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Apparatus Construction and Assembly 
       [0025]    The configuration of the present well completion apparatus is represented by the pipe string  10  of  FIG. 1 . The bottom end of the pipe string is terminated by a scraper and reaming bit  16  having a functional capacity for scraping or cutting debris and other foreign irregularities from the interior bore wall and bottom end of a wellbore casing  18 . Traditionally, a scraper bit  16  comprises an interior fluid flow path that channels drilling fluid from the internal bore of a drive pipe or tube  12  for high velocity discharge against the bit end-cutting elements. This high velocity discharge impacts the teeth or other cutting elements of the bit to flush them free of cutting debris and flow the loose debris up the wellbore annulus  20  between the exterior surfaces of the drive tube  12  and the interior surface of the casing  18 . 
         [0026]    Hereafter, the term “drilling” fluid is used to characterize any fluid originating from a pump or compressor at or near the earth&#39;s surface. It may be “clean” water or a more complex liquid such as mixtures of water and clay (common drilling fluid) or emulsions of refined petroleum. In certain cases, the fluid may be a gaseous vapor such as steam, a true gas such as nitrogen or a molecular mixture of gases such as “natural gas”. The term “tube” is used to designate a tubular structural component that links the bit  16  to the surface for fluid and power transmission whether characterized as a production tube or drill pipe. 
         [0027]    The assembled continuity of the drive tube  12  from the rig floor (not shown) down to the bit  16  is interrupted at selected locations by insertion of perforation assemblies  14 . These perforation assemblies  14  are operative to accomplish two basic functions: a) to perforate the casing  18  and surrounding cement sleeve and b) to provide a drilling fluid flow path around a perforation gun assembly  34 . The perforation assemblies  14  are positioned along the length of the pipe string for adjacent alignment with the location of a geologic strata deemed suitable for extracting the in situ well fluids. Such geologic strata are characterized herein as “production zones”. There may be a plurality of such strata traversed by the wellbore. Hence, there may be a corresponding plurality of perforation assemblies  14 . Moreover, there may be a plurality of closely coupled perforation assemblies  14  positioned in the pipe string  10  for perforating a single production zone. Frequently, The perforation assemblies are positioned in the pipe string  10  relative to the bit  16 . The location of the production zones along the wellbore length from the wellbore bottom is known to the driller. Hence, when the bit is at or near the wellbore bottom, the perforation assemblies will align adjacently with the desired perforation zones. There are other methods, however, for locating a specific perforation assembly  14  adjacent a specific well fluid production zone. The exact method of locating perforation assemblies  14  along the length of the pipe string  10  will depend on the method desired by the driller for locating the pipe string along the length of the wellbore. 
         [0028]    The construction and assembly elements of a perforation assembly  14  shall be described in greater detail with respect to  FIG. 2-11 . The general organization of the perforation assembly  14  is shown by  FIG. 2  to include identical upper and lower Y-adapters  30  and  31 , respectively. Each of these Y-adapters receive the pin end of a production tube  12  or connector sub  13 . Both Y-adapters are linked together by a circulation mandrel  32 . Relative to  FIG. 10 , the Y-adapter box bores  50  are open to fluid flow with the adapter lateral bores  52 . Opposite pin ends of the mandrel  32  are turned into the box threads of the lateral bore  52  for fluid flow continuity from the lateral bores  52  along the mandrel bore  54 . 
         [0029]    Each Y-adapter also includes a structurally integral receptacle collar  36 . Each receptacle collar is bored along an axis parallel with the axis of mandrel  32  to provide a gun confinement aperture. The perforation gun assembly  34  is secured within and between these receptacle collars  36 . Both of the collars  36  have one or more, three in this example, apertures  38  bored radially relative to the collar bore  36  axis. These apertures  38  serve as confinement sockets for socket screw heads, the threaded shafts of which are turned into the perforating gun structure to secure the angular orientation of the gun assembly  34  about the gun assembly axis. 
         [0030]    With particular reference to  FIG. 3 , the perforation gun assembly may include a firing head assembly  60  comprising an adapter sleeve  62  having an internal bore opening  63  and a threaded external shaft that receives the internally threaded locking rings  44  and  45 . With the sleeve  62  penetrating the confinement bore of the collar  36 , the two locking rings  44  and  46  are turned tightly against the opposite abutment faces of the collar  36  to secure the desired longitudinal position of the gun assembly relative to the Y-adapter  30 . 
         [0031]    The lower end of the adapter sleeve  62  is provided with a stepped boring. The deeper, smaller I.D. bore receives a shear pin set sleeve  64 . The axial position of the set sleeve  64  is confined by the distal end of the firing pin cylinder  66 . The firing pin cylinder  66  is threaded at  67  to the adapter sleeve  62 . O-ring seals  68  environmentally protect the assembly interior at this point. A firing pin piston  70 , slideably disposed within the internal bore  72  of the firing pin cylinder  66 , carries a firing pin  74  at its lower distal end and the shear pin skirt  78  at its upper end. The shear pin skirt is dimensioned to a close sliding fit within the internal bore of set sleeve  64 . Shear pins  80  bridge the cylindrical interface between the skirt  78  and the set sleeve  64  to restrain the arm position of the firing pin piston until sheared by sufficient fluid pressure against the upper sectional area of the piston  70 . 
         [0032]    The lower end of the firing pin cylinder  66  is shown by  FIG. 4  to have a threaded engagement  82  with a firing body  84 . The lower distal end of the firing pin cylinder confines a percussion initiator  86  within a firing body bore against an internal bore shoulder. The firing body  84  is attached by threads  88  to a bi-directional booster assembly  90  which confines the assembly interface between a detonation booster cartridge  92  and a detonation cord  94 . The lower end of the booster assembly is attached by threads  96  to a perforating gun housing  98 . 
         [0033]      FIG. 5  shows the gun housing  98  as protectively confining a charge holder tube  100 . Distributed along the length of the charge holder tube is a plurality of shaped explosive charges  102  set in holder tube sockets. The discharge axes of the charges are set at various radial angles from the holder tube axis within a limited arc that prevents the shaped charge discharge jets from damaging the circulation mandrel  32 . The detonation cord  94  is threaded along the charge holder tube length to serially engage each of the shaped charge bases. Traditionally, the gun housing  98  wall is weakened with scallops  104 , for example, at selected locations in radial opposition from the shaped charges  102 . 
         [0034]    The bottom end of the gun housing  98  is closed with a solid material bull plug  106  attached to the gun housing internal bore by threads  108 . O-rings seal the bore and shaft assembly interface. Referring to  FIGS. 7 and 8 , the external shaft of the bull plug is threaded to receive locking rings  44  and  45 . Additionally, the external shaft is counter-bored  114  at selected radial angles around the circumference for socket-head set screws  112 . The inner bore  116  is threaded to receive the socket screw shaft whereas the outer bore is smooth to receive a portion of the socket screw head. A half portion of the socket screw head height projects into the sockets  38  in the receptacle collar  36  to prevent rotation of the gun assembly  34  relative to the receptacle collar  36 . 
       Operation 
       [0035]    The pipe string  10  is assembled substantially according to the schematic of  FIG. 1  with the bit and scraper  16  on the wellbore bottom and a sufficient length of spacer tube  12  above the bit  16  to the first production zone. One or more joints of perforation assembly  14  continue the string  10  along the first production zone. If additional production zones are traversed by the wellbore, additional spacer tube  12  is provided to the next production zone. More perforation assemblies are added to the string in sufficient number to traverse the next production zone. The number of perforation assembly groups will depend on the number zones to be produced. 
         [0036]    With the bit  16  at or near the wellbore bottom, clean fluid is circulated through the tubing and circulation mandrels of the perforation assembly and up through the annulus  20  between the pipe string  10  and the casing  18  bore wall. Conversely, fluid may be reverse circulated by being pumped down the annulus  20  and back up the pipe string. 
         [0037]    This circulation process is continued until the operator is satisfied with the degree of debris flushing accomplished. When the flush circulation is complete, the pipe string  10  is positioned to align the perforation assemblies with the corresponding geologic production zones. With all other preparations complete, the fluid pressure within the wellbore is raised, usually by control of the circulation pumps, to the predetermined value for shearing the pins  80 . In particular, the wellbore fluid pressure bearing against the cross-sectional area of the firing pin piston  70  is raised until the net force value of the fluid pressure on the piston  70  overcomes the shear strength of the shear pins  80 . This pressure value will be characterized here as the detonation pressure. 
         [0038]    When the detonation pressure is reached, the firing pin piston drives the firing pin  74  into the percussion initiator  86 . Impact of the firing pin against the percussion initiator  86  activates shock sensitive compounds within the percussion initiator which decompose explosively. In turn, the hot explosive gases of the percussion initiator  80  activate the detonation booster  92  which ignites the detonation cord  94 . 
         [0039]    The detonation cord  94  is connected along its length to the base of each shaped charge  102 . Upon ignition by the booster  92 , a deflagration front from travels the length of the detonation cord  94  to successively ignite each of the shaped charge  102 . Resultantly, a jet of hot gas and molten material erupts from the shaped charges to pierce the casing  18 , any surrounding cement collar and a limited distance into the geologic formation forming the production zone. The production zone penetration channel created by the shaped charge jet serves to increase the area of fluid production face from the production zone. Such fluid production follows the channel through the casing wall perforation into the wellbore annulus. The fluid production may be extracted at the surface from either the wellbore annulus or from the pipe string  10  flow bore which remains in place for production. 
         [0040]    Supplementally, after the casing and production zone perforation, well treating frac-fluid such as zone specific formation fracturing acid or proppant comprising fluidized particulate or sand mixtures may be pumped down either the pipe string bore or the wellbore annulus to enhance the perforation channel productivity. Following the frac-fluid treatment, the well may be flushed with clean circulation fluid initially or again if flushed previously. 
         [0041]    Throughout these several well preparation processes, the pipe string has remained in place. When the last procedure has been completed, the well pressure is allowed to return to the natural state and the in situ formation fluid allowed to enter the casing bore through the perforations. Formation fluid may be extracted from either the well bore annulus or the production tube. In the latter case, the in situ fluid enters the production tube bore from the casing annulus through the bit  16  jet apertures. 
         [0042]    Although the invention has been described in terms of specified and presently preferred embodiments which are set forth in detail, it should be understood that this is by illustration only and that the invention is not necessarily limited thereto. Alternative embodiments and operating techniques will become apparent to those of ordinary skill in the art in view of the present disclosure. Accordingly, modifications of the invention are contemplated which may be made without departing from the spirit of the claimed invention. Directional orientation terms such as “upper”, “lower”. “up” and “down” are not to be to be interpreted as terms of operational limitations but only as descriptive devices for facilitating Applicants&#39; invention disclosure.

Summary:
A well completion method and apparatus comprises a pipe string having a bottom attached boring bit and scraper or reamer. Above the bit at designated well fluid production locations, perforation assemblies are integrated into the pipe string. Each perforation assembly comprises a by-pass circulation mandrel and a perforation gun. The circulation mandrel and perforation gun are both secured to respective arms of a Y-adapter. The Y-adapter leg receives the pin end of a traditional drill or production pipe. In one downhole trip, the wellbore casing may be scraped and the bottom-hole cement plug drilled out. Without removing the pipe string, the wellbore is flushed by a circulation of clean fluid down the pipe string bore, through the circulation mandrels and out the bit tooth cleaning jets into the wellbore annulus. Subsequently, the wellbore pressure is raised to detonate casing perforating shaped charges in the perforating gun. After perforating, the well may be additionally treated with fracturing fluids such as acid or fluidized abrasives such as sand.