Abstract:
A low profile high energy gas fracturing device, comprising a closed steel tube having a uniform wall thickness, except for having thinned areas that are designed to rupture when subjected to pressure greater than a predetermined level. Propellant is packed into the said steel tube sufficient to create high pressure above said predetermined level, when ignited. Finally, an ignition mechanism passes through said tube, to ignite the propellant.

Description:
BACKGROUND 
     Deposits of valuable fluids, such as crude oil, natural gas and even water, frequently occur in geologic formations having limited permeability. Although the initial perforating of the sides of an oil well typically opens up this type of deposit for initial exploitation, the well may soon experience a drop in production and require further treatment. To address this situation, a number of different fracturing techniques have been developed including explosive fracturing, hydraulic fracturing and high energy gas fracturing (HEGF). Each of these techniques is designed to fracture the underground geologic formation, thereby increasing permeability. 
     HEGF appears to have an advantage over the other fracturing techniques when certain conditions exist in a well. Test observations have shown that HEGF can create several radially extending fractures, thereby increasing the chance of significantly increasing permeability of nearby rock. 
     One type of HEGF uses a propellant that must be kept dry and contained during combustion. In this version, a strong container bearing a charge of propellant (i.e. a low explosive) is lowered into a partially liquid filled well and the propellant is ignited. The container keeps the charge dry and constrains it to obtain the full explosive force. 
     One type of propellant container that has been used is a steel tube defining a series of apertures, each capped. When the propellant is ignited the caps are blown off and the propellant, now in gaseous form, pours out of the apertures and fractures the rock sides of the well, thereby creating fissures through which oil can flow. 
     Unfortunately, the protruding caps made this mechanism too thick to fit into some narrow wells. Wells that are too narrow to accept the 3.375 inch profile of the original HGEF device offered previously are found in Mexico and other developing countries, and in the United States, when a portion of a tube mechanism in a well (associated with a sucker pump) the upper part of well cannot be removed, or is too long to be removed economically, it is impossible to use a 3.375 inch profile device. Narrowing the tube to permit clearance for the caps reduces the volume of the tube to the point where the effectiveness is reduced. The thickness of the steel is necessary to resist the expansive forces of the propellant, once ignited. 
     SUMMARY 
     The following embodiments and aspects thereof are described and illustrated in conjunction with systems, tools and methods which are meant to be exemplary and illustrative, not limiting in scope. In various embodiments, one or more of the above-described problems have been reduced or eliminated, while other embodiments are directed to other improvements. 
     In a first separate aspect, the present invention may take the form of a low profile high energy gas fracturing device, comprising a closed steel tube having a uniform wall thickness, except for having thinned areas that are designed to rupture when subjected to pressure greater than a predetermined level. Propellant is packed into the steel tube sufficient to create high pressure above the predetermined level, when ignited. Finally, an ignition mechanism passes through the tube, to ignite the propellant. 
     In a second separate aspect, the present invention may take the form of a method of fracturing a narrow well that is partially filled with water. The method makes use of a low profile high energy gas fracturing device, which includes a closed steel tube having a uniform wall thickness, except for having thinned areas. Propellant is packed into the steel tube, an ignition mechanism passes through the tube, to ignite the propellant and a line wire extends from the tube, and is in electrical contact to the ignition mechanism. This device is passed into the narrow well until it is submerged in the water and a signal is transmitted through the line wire to activate the ignition mechanism, causing it to ignite the propellant, thereby creating pressure inside the tube sufficient to rupture the tube at least at some of the weakened area, thereby permitting gas to escape at a high energy. 
     In a third separate aspect, the present invention may take the form of a round steel tube, including a circular wall, having a sequence of holes formed in its exterior, extending partially through the circular wall. 
     In addition to the exemplary aspects and embodiments described above, further aspects and embodiments will become apparent by reference to the drawings and by study of the following detailed descriptions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments are illustrated in referenced drawings. It is intended that the embodiments and figures disclosed herein are to be considered illustrative rather than restrictive. 
         FIG. 1  is an isometric view of a high energy gas fracturing cylinder, according to the present invention. 
         FIG. 2  is a longitudinal sectional view of the cylinder of  FIG. 1 , showing a detail view of a weakened area. 
         FIG. 3  is a cross-sectional view of the cylinder shown in  FIG. 1 . 
         FIG. 4  is a exploded view of the cylinder of  FIG. 1 . 
         FIG. 5  is an isometric view of the cylinder of  FIG. 1 , as it is lowered into a well. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 1 , in a preferred embodiment a high energy gas fracturing device  10  is comprised of a steel tube  12 , having an inner diameter of 1.610 inches and an outer diameter of 2.03 inches, narrow enough to fit into a narrow well. A set of weakened areas  14  forms a helix about tube  12 . The wall thickness of tube  12  is generally 0.21 inches, but each weakened area  14  is created by machining a hole to a depth of 0.175 inches into the exterior of tube  12 , resulting in a weakened area  14  wall thickness of 0.035 inches. 
     A top-most weakened area  14  has a center that is a length  16  of six inches from a top-end  18  of tube  12 . Weakened areas  14  have center-to-center spacing  20  of 3.281 inches in the longitudinal dimension, and of 20 degrees, which translates to 0.156 inches, in the circumferential dimension. Each weakened area  14  is round and has a diameter of 0.75 inches. The weakened areas  14  extend over almost a meter. In an alternative preferred embodiment, the tube is longer and the weakened areas  14  extend over a two meter length. A line wire  22 , typically extending through the well to an electrical signal producing device at the well top, extends into tube  12 . A top cap or plug  24  covers the top of tube  12  and a bottom cap or bull plug  26  covers the bottom. 
     Referring to  FIGS. 2 and 3 , tube  12  encloses a tubular carton  30  packed with propellant  32  (also referred to in some literature as “low explosive”). The line wire  22  and an ignition cord  34  extend through a thin tube  36  defined by carton  30 , at its side. Carton  30  facilitates the placement of propellant into tube  12 , together with line wire  22  and the ignition cord  34 , which otherwise might prove an encumbrance, as they would have to be passed through before tube  12  would be filled with propellant, and the propellant would tend to damage these elements, as it was poured into tube  12 . 
     And blasting cap  38  permits an electrical pulse through the line wire  22 , connected to a ground  40 , to ignite the ignition cord  34 . The end cap  26  (“bull plug” in industry parlance) closes the end of tube  12 , and protects the blasting cap  38 . 
     Referring now to  FIG. 4 , a top joining element  50 , permits attachment of another unit, such as device  10 , for a longer section of well revitalization, or the top plug  24  ( FIGS. 1 and 5 ). A pair of top O-rings  52  seal the top joining element  50  to tube  12 . A soft steel spacer  54  permits line wire  22  to extend into the interior tube  12 . Finally a bottom pair of O-rings  56  seal tube  12  to bottom cap  26 . Referring to  FIG. 5 , device  10  is lowered into a well  60 . It may then be lowered thousands of feet, until it is covered with water. 
     The device  10  is lowered into the liquid, to a depth of at least 91 meters (300 ft). It should be noted that although 91 meters (300 ft) generally serves as the minimum depth to which device  10  must be submerged in order to work effectively, it can be made to work even in a dry well, if steps are taken to block the gas produced from the propellant combustion from leaking upwardly or downwardly, away from device  10 , once emitted. Moreover, device  10  may be very deeply submerged, to a depth at least on the order of 3,000 meters. 
     Next, the blasting cap  38  is ignited by the line wire  22 , which ignites the ignition cord  34 , which ignites all of the propellant  32  within approximately one millisecond. The gasses produced are contained by the column of liquid in the well  60  and burst out rapidly toward the sides of the well  60 , where perforations in the well casing are found and transited. The first gas to emerge through the perforations tends to blast debris out of the perforations, while immediately subsequent gas, at an even higher pressure and velocity due to the progressive combustion, opens up new cracks in the geologic formation. The combustion is completed in about 20 milliseconds. The pressure produced by the combustion of the propellant  32  deforms spacer  54 , permitting to act as a more effective barrier against the hot gasses, which might otherwise blast off the top cap  24 . 
     Propellant  32  may be either single-based (nitrocellulose), double-based (nitrocellulose and nitroglycerin), or triple-based (nitrocellulose, nitroglycerin, and nitroguanadine). These propellants may be available from BAE Systems, Inc., in Radford, Va. 
     While a number of exemplary aspects and embodiments have been discussed above, those possessed of skill in the art will recognize certain modifications, permutations, additions and sub-combinations thereof. It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions and sub-combinations as are within their true spirit and scope.