Patent Publication Number: US-10760384-B2

Title: Method of creating and finishing perforations in a hydrocarbon well

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. Non-Provisional patent application Ser. No. 14/585,956, filed on Dec. 30, 2014, and set to issue as U.S. patent Ser. No. 10/024,145 on Jul. 17, 2018, the disclosure of which being incorporated herein by reference in its entirety for all purposes. 
    
    
     BACKGROUND 
     Field of the Disclosure 
     Embodiments herein pertain to creating and finishing perforations in a hydrocarbon well. 
     Background of the Disclosure 
     A hydrocarbon well (oil or gas) is typically finished using a device known as a perforating gun. This device includes a steel tube containing a set of devices, typically referred to as “shaped charges” each of which includes a charge of high explosive and a small amount of copper. The tube is lowered into the well, and the high explosive charges are detonated, fragmenting the copper and accelerating the resultant copper particles to a speed on the order of 30 mach, so that it blasts through the wall of the steel tube, through any steel casing forming the wall of the well, and perforates the surrounding rock, thereby permitting oil or gas or both to flow into the well. 
     Unfortunately, the resultant perforation has some characteristics that inhibit the flow of liquid or gas into the perforation from the surrounding rock. As the copper particles push into the rock it pushes the rock immediately in its path rearward and to the side, and also heats this rock, resulting in perforation surfaces that are less permeable to the flow of liquids and gasses than would otherwise be the case. 
     SUMMARY 
     Embodiments herein pertain to a method of creating and finishing perforations in a hydrocarbon well having a well wall that may include one or more of: shooting a high velocity jet of metal particles into the well wall, thereby creating a perforation in the well wall; pushing a gas blast into the perforation, for a blast time duration, the gas blast creating an increasing pressure at the perforation, until a maximum is reached, the pressure of the gas then undergoing a period of rapid decline to a level of less than 50% of the maximum pressure. 
     In aspects, the period of rapid decline takes less than one-sixth of the blast time duration. The time pattern of speed and pressure of the gas blast may result in a higher maximum pressure at the perforation than would have happened had the maximum pressure been reached midway through the gas blast, thereby resulting in localized fracturing, emanating from the perforation. This may permit a greater flow of hydrocarbons into the perforation and from the perforation into the well. 
     The period of rapid decline may take less than one-tenth of the blast time duration. The gas blast may flow at an increasing speed, as the pressure increases. 
     Other embodiments herein pertain to a method of creating and finishing perforations in a hydrocarbon well having a well wall that may include one or more of: operating a perforation assembly to cause a high velocity jet of a material to shoot into the well wall, thereby creating a perforation in the well wall. 
     The perforation assembly may include: a tube having a tube wall; a plurality of shaped charges disposed within the tube and adapted to shoot the high velocity jet through the tube wall and into the well wall; a propellant also disposed within the tube, the propellant having a surface area; and a detonating cord operable to ignite the shaped charges and the propellant. 
     In aspects, the propellant may be configured to undergo a combustion until it is substantially consumed by the combustion. The propellant may initially combust slowly enough that the combustion of the propellant does not interfere with functioning of an at least one of any of the plurality of shaped charges. 
     The method may further include introducing a gas blast into the perforation for a blast time duration, the gas blast eventually reaching a maximum pressure. The method may include allowing a pressure of the gas blast to undergo a period of rapid decline to a level of less than 50% of the maximum pressure. 
     The period of rapid decline may take less than one-sixth of the blast time duration. 
     Still other embodiments herein pertain to a method of perforating a well wall that may include one or more of: providing a perforation creating-and-finishing assembly for use in a well having a well wall. The assembly may include: a tube having a tube wall; a plurality of shaped charges positioned within the tube; a propellant also positioned within the tube, the propellant having a surface area and being configured so as to combust at an increasing rate until substantially consumed; and a detonator disposed within the tube. 
     The method may include lowering the assembly into the well to a predetermined position. The method may include operating the assembly to ignite the detonator, thereby igniting the plurality of shaped charges and the propellant. The plurality of shaped charges may be configured to provide or facilitate the shooting of a high velocity jet of metal particles through the tube wall and into the well wall, thereby creating a perforation. 
     Yet still other embodiments of the disclosure pertain to a method of creating and finishing perforations in a hydrocarbon well having a well wall that may include one or more of: causing a high velocity jet of a material to shoot into the well wall, thereby creating a perforation in the well wall; introducing a gas blast into the perforation, for a blast time duration, the gas blast creating an increasing pressure at the perforation until a maximum pressure is reached; and allowing the pressure of the gas blast to undergo a period of rapid decline to a level of less than 50% of the maximum pressure. 
     In aspects, the period of rapid decline may take less than one-sixth of the blast time duration. 
     These and other embodiments, features and advantages will be apparent in the following detailed description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full understanding of embodiments disclosed herein is obtained from the detailed description of the disclosure presented herein below, and the accompanying drawings, which are given by way of illustration only and are not intended to be limitative of the present embodiments, and wherein: 
         FIG. 1  is a sectional view  5  of a portion of a hydrocarbon well having a perforation creating and finishing device, shown in a side view for ease of description. 
         FIG. 2  shows the environment and device of  FIG. 1 , during detonation of the device. 
         FIG. 3  shows the environment and device of  FIG. 1 , at a further stage of deployment, after a perforation in the well wall has been created. 
         FIG. 4  is an expanded sectional detail view of the well wall perforation of  FIG. 3 , taken along line  4 - 4  of  FIG. 3 . 
         FIG. 5  shows the environment and device of  FIG. 1 , at a final stage of deployment, showing the finished perforation. 
         FIG. 6  is an expanded sectional detail view of the finished well wall perforation of  FIG. 5 , taken along line  6 - 6  of  FIG. 5 . 
         FIG. 7  is an isometric view of a cylindrical carton filled with pieces of propellant. 
         FIG. 8  is a graph of combustion rate over time of the propellant in the device of  FIGS. 1-3 and 5 . 
     
    
    
     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. 
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , in a preferred method of creating finished perforations in the wall  10  of an oil or gas well, which is made up of steel casing  12 , cement  13  and underlying rock  14 , a perforating gun  15  is lowered into proximity of a portion of wall  10 , to be treated. Perforating gun  15  includes a charge tube  16 , which supports a number of shaped charges  18 , containers  20  of propellant  38  ( FIG. 7 ) and a detonating cord  22 , all encased in a fluid-impermeable sealed steel carrier  24 . 
     Referring to  FIGS. 2 and 3 , the detonating cord  22  is ignited, causing the shaped charges  18  to expel particles of metal  26  ( FIG. 2 —shown as an ellipse for ease of presentation) at a high velocity, within ten microseconds. Travelling at approximately 30 mach, the metal particles  26  penetrate through steel carrier  24 , creating a carrier perforation  27  ( FIG. 3 ) and into the wall  10 , creating a perforation  28  ( FIG. 3 ) through the steel casing  12 , and a further perforation  29  ( FIG. 3 ) in the rock  14 , thereby facilitating the flow of hydrocarbons into the well. 
     The movement of the metal particles  26  into the rock creates a perforation  29 , having walls  30 , which have been seared and made more dense by rock  14  that has been pushed to the side or pushed toward the back of the perforation  29 . Consequently, the perforation does not facilitate the flow of oil as much as might be possible. The containers  20  of propellant  38  combust over a period between 10 and 100 milliseconds, far more slowly than the action of the shaped charges  18 . 
     In one preferred embodiment, the rate of combustion  56  of the propellant  38  increases with greater pressure, causing the combustion rate to increase at a greater than linear rate  48  as some propellant  38  combusts and the gas thereby released creates a higher pressure; however, at least one additional piece  39  of propellant  38  may not combust at an increasing rate after being ignited. Referring to  FIGS. 5, 6, 7 and 8 , in a few milliseconds, the combustion has spread over the surface areas of the pieces  39  of propellant  38  ( FIG. 7 ), including the interior surface areas, created by a set of seven through-holes  40  in each piece  39  of propellant  38 . 
     As the through-holes  40  grow in diameter, due to the combustion, the surface area of each through-hole grows, just as the outer diameter of the piece  39  of propellant  38  is reduced over time. In one preferred embodiment, the pieces  39  of propellant  38  are packed together in groups, with each group including seven pieces  39  of propellant  38 , and being interposed between two shaped charges. 
     Referring to  FIG. 8 , as the propellant collectively combusts, the combustion rate  48  of propellant  38  reaches a maximum  50  ( FIG. 8 ), directly before the fuel is exhausted, resulting in a high maximum combustion rate  50 , followed by a rapid plunge  58  to zero  60 . In one preferred embodiment, the rapid decline  58  takes less than one-sixth of the blast time duration. In another preferred embodiment, the rapid decline  58  takes less than one-tenth of the blast time duration. Not only does the combustion rate increase due to through-holes  40 , but also because propellant  38  combusts more rapidly under higher pressure. 
     As the combustion progresses, a gas  70  is produced, which increases the pressure inside carrier  24  (and very quickly, outside of carrier  24 , as well). This increased pressure also causes propellant  38  to combust more rapidly, leading to the nonlinear combustion rate curve  48 . In a preferred embodiment, the period during which the combustion rate plunges from the maximum  50  to zero  60  (the combustion cessation period), takes less than one-tenth of the total time period of combustion  56 . For each piece  39  of propellant  38  the combustion cessation period is less than one-thirtieth of the period of combustion  56  (for the same piece  39  of propellant  38 ). 
     The hot gas  70 , that is the product of the propellant combustion is pushed rapidly and forcefully out of the tubing carrier perforations  27  with increasing speed that is proportional to the increasing pressure caused by the gas blast, and into well wall perforations  28  and  29 , which are still fairly well aligned with carrier perforation  27 , as the relatively massive perforating gun  16  accelerates and moves relatively slowly. In one preferred method, the pressure created by gas  70  increases until a maximum is reached before declining rapidly. Both the speed and the pressure of the gas  70  act to break apart the rock  14 , and create a star pattern of fissures  72  emanating radially from perforation  28 , thereby facilitating the flow of oil and gas into the well. 
     The through-holes  40  of propellant  38  result in a higher maximum combustion rate and a corresponding higher pressure at perforation  29 , than would be otherwise the case. Surprisingly, because of the through-holes  40 , the maximum pressure applied to the perforations  29  is high enough to be effective, even though large portions of steel carrier  24  are taken up by shaped charges  18 , and thereby not available for stowage of propellant  38 . 
     The propellant  38  includes its own oxidizer, and so does not need any external source of oxygen to combust. Further, propellant  38  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, 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. For example, one or more pieces of propellant that do not include through-holes could be included and combust at a decreasing rate, or that include a single through-hole and combust at a steady rate, could be included. It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions and subcombinations as are within their true spirit and scope.