WO2000053891A1

WO2000053891A1 - Scalloped gun body with improved tolerances for underground well perforating, and process of manufacturing the same

Info

Publication number: WO2000053891A1
Application number: PCT/US2000/004997
Authority: WO
Inventors: Bruce A. Gillis; Rick E. Swope
Original assignee: Titan Specialties, Ltd.
Priority date: 1999-03-10
Filing date: 2000-02-25
Publication date: 2000-09-14
Also published as: AU3504100A

Abstract

Scallops are cut into a tubular gun body for use in underground jet perforation by measuring with a sonic or like probe the wall thickness of the tubular gun body at the location or locations where the scallops are to be machined on the exterior of the gun body. The measured wall thickness is inputted into a central processor which also has input of data defining the desired thickness of the web to remain in the tubular gun body after scalloping. The computer utilizes an algorithm to calculate how much metal needs to be removed by a machine tool from the tubular wall to obtain the desired web thickness. In the step of actually cutting the scallop the cutter of the machine tool, directed by the computer through robotic machinery, 'senses' the zero point, that is the beginning of the wall, by sensing a surge in current load (amperage) as the cutter touches the wall and begins removing metal from it. The sensed zero point is inputted into the central processor which thereafter directs the cutter to remove the calculated thickness of metal from the wall. The web that remains after the scallop has been cut has dimensions with tolerance on the basis of the accuracy of the measuring and cutting process and not on the basis of the manufacturing tolerance of the tubular gun body. Web dimensions having tolerance limits of approximately ± 0.20 inches or less, preferably approximately ± 0.005 inches or less, are attained in this manner even with gun bodies that have been made by hot finished manufacturing process.

Description

SCALLOPED GUN BODY WITH IMPROVED TOLERANCES FOR UNDERGROUND WELL PERFORATING, AND PROCESS OF MANUFACTURING THE SAME

BACKGROUND OF THE INVENTION

1. Field of the Invention The present invention is in the field of a gun assembly used for underground jet perforating while exploring for oil, gas, steam or other minerals, and extracting the same from underground. More particularly, the present invention is directed to a tubular gun body having scalloped areas with improved manufacturing dimensional tolerances, and to a process of manufacturing such gun bodies. 2. Brief Description of the Background Art It has been common practice for a long time in the oil, gas and related mineral production industry to perforate the wall of the oil or gas well casing at locations where entry of oil or gas from the surrounding formation into the casing is desired. The prior art has created gun assemblies containing shaped explosive charges for this purpose. The gun assemblies include a tubular gun body wherein the charges are placed. The charges are detonated by passing current through a blasting cap that ignites the charge through a detonating fuse. The force of the explosion first creates an opening in the wall of the tubular gun body and thereafter penetrates the well casing, the concrete that surrounds the well casing and thereafter the formation. Further background art pertaining to gun assemblies for underground jet perforating and the description of a gun assembly using resistive blasting caps can be found in United States Patent Nos. 5,531,164 and 5,700,969. Most perforating gun bodies manufactured in accordance with the state-of-the-art include areas in the tubular gun body where the wall of the gun body is deliberately thinner than in the rest of the body. The thinner- walled weakened areas are created by a machining process called scalloping and the areas are called scalloped areas. The scalloping procedure removes a pocket of metal in the side wall of the gun body directly over the future location of the shaped charge. The area that remains after scalloping is called a "web" and it follows that it is easier for the shaped charge to penetrate the web than it is to penetrate the full wall thickness. This allows the energy released by the shaped charge to more efficiently penetrate the well casing and formation. The oil, gas and related mineral exploration industry has been utilizing shaped charges since about the 1940's and the shaped charges have undergone continuous improvement since that time. In accordance with the present state-of-the-art, some shaped charges are capable of penetrating 49 inches, or more, of concrete. As the shaped charges have improved to their present level of performance the point has been reached where peak performance of the charges is hindered in a significant way when measurable differences occur in the web thickness left by the scalloping process. Under carefully controlled tests it has been observed in the state-of-the-art that performance varies unacceptably when there are variations of the magnitude of .090" or more in the thickness of the web. Specifically, charge designs common 10 to 15 years ago were capable of penetrating the formation ("shooting") 20 to 30 inches and with these charges variations in web thickness did not, on a percentage basis, affect the penetration results severely. It has been observed that with these or former shaped charges of the prior art a non- scalloped gun might have reduced penetration of the formation by approximately 4 to 5%, but present state-of- the-art charges that "shoot" 49 inches are impacted by a much higher percentage - possibly 10 to 20% - depending upon the variation in the thickness of the web. This, in turn created a need in the art for providing scalloped tubular gun bodies where the thickness of the web is controlled within small tolerances. Another relatively recent development in the state-of-the-art pertains to how the tubular gun bodies are manufactured. This more recently employed manufacturing technique has further increased the need for scalloped tubular gun bodies where the thickness of the web is controlled within small tolerances. Specifically, gun bodies used to be made by a cold finishing machining process that resulted in the tubular body that had dimensions within acceptable tolerances. Typically for an exemplary and typical gun body of 4.5 " diameter with typical 0.375 " wall the manufacturing accuracy is approximately within the range of ± 0.056 inches. More recently however, gun bodies are frequently made by the less costly hot finishing process that provides gun bodies, prior to scalloping, with significantly less accurate dimensions and lesser accuracy of concentricity; for example variations from the nominal dimensions of a hot finished tubular gun body may be as large as 0.100 " or more. Because of their lesser cost, however, the industry is very interested in and frequently prefers or would prefer to use hot finished gun bodies for underground j et perforating. Standard, state-of-the-art techniques for the scalloping process is to measure from the outside surface of the tube and to create machining tolerances based upon control from surface of the tube to the floor of the individual scallop. Typically a 4 ^lA " gun body with a specified wall thickness of say 0.375" might have scallops machined with depths of .250" with a remaining web of 0.125". Thus, this state-of-the-art process involves, in principle and in the above given example, the use of a machine tool to remove in the center of the scallop 0.250" of metal from the nominally 0.375" thick cylindrical body. Those skilled in the art realize however that the resulting web would vary by the tolerance factor of the gun tubing. In case of the cold finished products this variation is usually not enough to cause serious degradation in the performance of most shaped charges. However, in case of hot finished gun tubes made with less accurate dimensions, the variations in the web thickness can seriously degrade the performance of the modern shaped charges, even though the industry generally prefers or would prefer to use the less costly hot finished gun tubes. In light of the foregoing, there is a serious need in the art for scalloped tubular gun bodies for underground jet perforation where the web remaining after scalloping is within fine tolerances, and particularly for such gun bodies that are made by the hot finished manufacturing process. There is also the need for a process for making such scalloped gun bodies having fine tolerances of the web. The present invention satisfies this need. SUMMARY OF THE INVENTION It is an object of the present invention to provide scalloped tubular gun bodies for underground jet perforation where the webs remaining after scalloping have dimensions within tolerance limits which is approximately ± 0.020 inches or less, preferably approximately ± 0.005 inches, or less. It is another object of the present invention to provide scalloped tubular gun bodies for underground jet perforation that have ben made by a hot finishing manufacturing process and where the webs remaining after scalloping have dimensions within tolerance limits which is approximately ± 0.020 inches or less, preferably approximately ± 0.005 inches or less. It is still another object of the present invention to provide a manufacturing process for making scalloped tubular gun bodies for underground j et perforation that meet the foregoing obj ectives . These and other objects and advantages are attained by a scalloped tubular gun body that has been manufactured in a process where the wall thickness of the tubular gun body is measured at the location or locations where scallops are to be machined on the exterior of the gun body. The actual measured wall thickness is inputted into a computer or central processor which also has input of data defining the desired thickness of the web to remain in the body after scalloping. The computer utilizes an algorithm to calculate how much metal needs to be removed by a machine tool from the tubular wall to obtain the desired web thickness. In the step of actually cutting the scallop the cutting knife or cutter of the machine tool, directed by the computer through robotic machinery, "senses" the zero point, that is the beginning of the wall, by sensing a surge in current load (amperage) as the cutter touches the wall and begins removing metal from it. The sensed zero point is inputted into the computer or central processor which thereafter directs the cutter to remove the calculated thickness of metal from the wall. Therefore, the web that remains after the scallop has been cut has dimensions with tolerance on the basis of the accuracy of the measuring and cutting process and not on the basis of the manufacturing tolerance of the tubular gun body. Web dimensions having tolerance limits of approximately ± 0.020 inches or less, preferably approximately ± 0.005 inches or less, are attained in this manner even with gun bodies that have been made by hot finished manufacturing process . The features of the present invention can be best understood together with further objects and advantages by reference to the following description, taken in connection with the accompanying drawings, wherein like numerals indicate like parts. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a plan view, partly in cross-section of a scalloped tubular gun body that has been made by a hot finishing process. Figure 2 is a cross-sectional view of the scalloped tubular gun body of Figure 1, the cross-section being taken on lines 2,2 of Figure 1. Figure 3 is a partial plan view, partly in cross-section of a scalloped tubular gun body having a scallop with tolerance limits in accordance with the present invention. Figure 4 is a cross-sectional view of the scalloped tubular gun body of Figure 3. Figure 5 is partial plan view of the scalloped tubular gun body of Figure 3. Figure 6 is a schematic view of the apparatus used in the process of the present invention, showing a step of measuring the wall thickness of the tubular gun body with a sonic probe. Figure 7 is another schematic view of the apparatus used in the process of the present invention, showing a step of placing the rotating cutter of a machine tool on the tubular gun body. Figure 8 is a graph showing change in the load on an electric motor driving the cutter when the cutter begins and continues cutting metal from the gun wall. Figure 9 is a diagrammatic view showing the steps in the process of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS The following specification taken in conjunction with the drawings sets forth the preferred embodiments of the present invention. The embodiments of the invention disclosed herein are the best modes contemplated by the inventors for carrying out their invention in a commercial environment, although it should be understood that various modifications can be accomplished within the parameters of the present invention. Referring now to Figures 1 and 2 of the appended drawings, a tubular gun body 20 including a shaped explosive charge 22 of the type normally used in gun assemblies for underground jet perforation is shown. A general description of a gun assembly (not shown) for underground jet perforation, that provides a disclosure how such a gun assembly is used, can be found in United States Patent Nos. 5,531 , 164 and 5,700,969, the specifications of which are incorporated herein by reference. As is known, gun assemblies for underground jet perforation are used in well casings (not shown) and well casings vary in diameter. Accordingly, the diameter of the of gun assemblies and more specifically of the scalloped gun bodies which can be constructed in accordance with the present invention are limited only in the sense that they must fit into the well casings in which they are intended to be used. Presently contemplated diameter of the tubular gun bodies which can be made in accordance with the present invention is in the range of approximately 1.5 to 7.0 inches. For the purposes of the preferred embodiments of the invention a typical gun body can be considered having a diameter of 4.5 inches. A typical range of the thickness of the cylindrical wall 24 of the gun body 20 is approximately 5/32 (0.156) to 5/8 (0.625) inches, and an example of 0.375 inches for the wall thickness represents a typical embodiment. As is known, the length of the tubular gun body used in underground jet perforations can also vary greatly depending on the requirements of the specific underground exploration or production. The length of the gun body can also be related to the number of explosive charges incorporated in the gun assembly, as few as one and as many as 400 charges may be used; for example but not by way of limitation a gun body is approximately 3 to 30 feet long. As it was noted in the introductory section of the present application for patent, it is common practice in the art to provide a thinned area called a "scallop" 26 in the wall 24 in the region where an explosive charge 22 is to be placed in the gun assembly. The number of scallops 26 in a gun body can vary as much as the number of explosive charges 22, although not every explosive charge 22 is necessarily placed adjacent to a scallop 26. There can be as few as one scallop 26 and as many as 24 (or more) scallops 26 per linear foot of the gun body 20. When there are a plurality of scallops 26 in a gun body 20, they may be lined up with one another, but typically they are not lined up, as is shown in Figure 1. Figure 1 of the appended drawings shows a tubular gun body that has been manufactured by the so called hot finishing process, and therefore, as is known in the art, has relatively large tolerances in terms of wall thickness and concentricity. In some extreme but not totally unusual cases the thickness of the wall 24 may vary as much as 0.10" from the nominal dimension. This is shown in an exaggerated form by the areas bearing the reference number 28 in Figure 1. When viewed in a plan view the scallops 26 usually have the configuration of a circle, and the bottom of the scalloped area, that is the outer surface of the remaining "web" 30 is normally flat. It follows from this geometry, as it is well understood in the art that the amount of metal to be removed from the cylindrical wall 24 of the tube 20 is not uniform within the circle. As is usual in the industry, the dimensions (fraction of inches) of metal that is to be removed from the wall 24 to make the flat-bottomed scallop 26 refers to the center of the circle. The same consideration applies to the thickness of the web 30 that remains when the scallop 26 is formed. This is readily apparent on Figures 2 and 4. It is also apparent from the drawings that if a scallop 26 were to be cut in the tube 20 in the area shown by reference numeral 28 in Figure 1 in accordance with the prior art, that is by removing, for example 0.250" of metal from a nominally 0.375 " thick wall 24, then the remaining web 30 would be significantly thicker than the desired and nominally calculated 0.125 ". In accordance with the present invention, however, the scallops 26 shown in the drawing figures are manufactured by removing sufficient metal from the wall 24 of the tube the thickness of which has been measured, so as to arrive to a wall thickness of the web 30 which is desired, and which is controlled by the tolerance limits of the measuring and scallop machining process and not by the tolerance of the tube manufacturing process. Referring now primarily to Figures 6 and 9, a machine tool 32 is shown schematically that is connected with and can be controlled by a central processor or computer 34. Inasmuch as machine tools controlled by a central processor or computer in general, and even those which are used for cutting scallops in tubular gun bodies for underground jet perforation are well known in the art, the machine tool 32 and central processor 34 are described here only to the extent necessary to describe the present invention. Thus, the machine tool 32 includes a vise 36 in which the tubular gun body 20 is held in position appropriate for the desired work to be performed. The machine tool 32 includes a rotating spindle 38 in which the cutting knife or cutting tool 40 is held. The spindle 38 is moved by a slide 42 of the machine tool 32, as directed by the central processor 34. Power to rotate the spindle 38 is provided by an electric motor that is not specifically shown in the drawing figures. Figure 6 also illustrates schematically a probe for measuring the wall thickness of the gun body 20. In the presently preferred embodiment of the invention the wall thickness probe is an ultrasonic probe and in the following description the wall thickness probe is named an "ultrasonic probe" or simply a "sonic probe" 44. It should be understood, however, that the function of the wall thickness probe 44 is to measure the actual wall thickness of the tubular gun body 20 at the location or locations where the scallop or scallops 26 are to be formed in the gun body 20. Whereas sonic probes are well suited for this purpose, there are other instruments which are also suitable and can be used in the performance of the process of the present invention. For example, a magnetic probe could also be used. In fact, any instrument that can measure the wall thickness with the desired accuracy of ± approximately 0.005 inches and can input the data into a central processor or computer, and can be directed by the central processor on a robotic arm, is suitable for use in the process of the present invention. The sonic probe presently used in the process of the present invention is a T-Mike EZ Ultra Thickness Gauge, FCC ID: EJG 57M T-Mike and is available from Stresstel Corporation, Ultrasonic Testing Equipment Scotts Valley California, 95066. This instrument has the capability of measuring wall thickness with an accuracy of ± 0.002 inches, provided it is calibrated in accordance with manufacturer's recommendations. A robotic arm that is controlled by the central processor 34 and carries the sonic probe 44 is shown in Figure 6 and bears the reference numeral 46. As is shown schematically in Figure 6, both the slide 42 of the machine tool 32 that carries the spindle 38 and the robotic arm 46 that carries the sonic probe 44 input data and/or receive commands from the central processor 34. In the performance of the process of the present invention the sonic probe measures the actual thickness of the wall 24 at the location or locations where scallops are to be formed and the resulting information i. e. wall thickness data, are fed into the central processor 34. The actual measured data of the wall thickness are to be contrasted with the nominal wall thickness of the tube 20 that is provided by its manufacturer, and which in cases of a hot finished gun body may differ as much as 0.1" from the nominal thickness. In accordance with the preferred embodiment of the process of the invention, wall thickness is measured by the probe for locations of several scallops. Preferably the wall thickness of as long a section of of the tube 20 is measured that can be covered by the probe 44 without changing the position of the tube 20 in the vise 36 or like gripping device. The measured data are fed into the central processor 34. Input of the measured data is schematically illustrated in Figure 6 by the arrow on the line connecting the sonic probe 44 with the central processor 34. The central processor 34 includes in its memory the data defining the thickness of the web 30 which is to be present in the scallops 26 of the scalloped gun tube 20. It should be understood that the intended thickness of the webs 30 may not be the same for each of the scallops 26 even in a single tube 20. The central processor 34 includes an algorithm that calculates the thickness of metal that needs to be removed from wall to obtain the intended web thickness. This calculation is based on the data of the intended web thickness and on the actually measured wall thickness at the locations of each intended scallop 26. If necessary, the central processor 34 then commands the robotic arm 46 to move the sonic probe 44 out of the way so that the cutting tool 40 can access the gun tube 20 at the intended locations, and commands the slide 42 carrying the cutting tool 40 in the spindle 38 to commence the cutting operation. This and the following steps are explained with reference to Figures 7, 8, and 9. Input of data regarding position of the slide 42 and control of the same by the central processor 34 are schematically illustrated in Figure 7 by arrows on the line connecting the spindle 38 with the central processor 34. As the cutting tool 40 moves downward, carried by the slide 42, it makes contact with surface of the gun body 20 and begins cutting metal. At the point of contact the load on the electric motor (not shown) increases sharply. The apparatus senses the sudden sharp increase or surge in the load and records the position of the cutting tool 40 where the surge of load occurred as the zero or reference point at which the cutting process begins. Whereas several types of circuitry and associated equipment as well as software may implement the step of "sensing" the sudden surge on the load of the electric motor (not shown) as the zero or reference point, in the presently preferred embodiment this step is implemented as follows, and on the basis of the following considerations. The electric motor (not shown) driving the spindle 38 is monitored by a current to voltage converter (not shown) that outputs an analog voltage proportional to the current load of the motor. The output voltage is in the range of zero (0) to 10 VDC in the preferred embodiment and it is converted to a digital signal in the range of zero (0) to 4095 bits by an analog to digital converter (not shown) that is included in the central processor 34. In this embodiment, zero volts and zero (0) bits would be equal to 0% motor output and ten volts and 4095 bits would be equal to 100 % motor output. However, it is known that due to parasitic losses the electric motor consumes current when it runs idly without machining (cutting). The percentage of the current in idle mode relative to maximum load varies due to several factors, such as temperature. For example, when the machine is first started the current use in idle mode is usually higher than later, because lubrication oil is not yet flowing as well as later, the bearings are not up to operating temperature and other factors. Later on, when everything is up to normal operating temperature the idle current load is lower. This results in what is termed a floating current load or draw. Because of this, a current baseline is determined by the central processor 34 prior to the machining every scallop 26. Thus, the varying current draw is averaged by the processor 34 and used in the algorithm as a baseline to determine when the cutter 40 contacts the gun body 20 or work piece. When the cutting tool 40 contacts the work piece, the current draw rises sharply. In the preferred embodiment when the processor 34 sees the motor current, transformed to digital signals as described above, rise 400 bits past the computer averaged baseline current, (10% of 4095 bits) then the processor 34 considers the position of the cutter 40 to be at the zero or reference point. Usual time frame of the current rise is in the range of 40 to 60 milliseconds. The actual time frame for machining the scallop 26 varies approximately in the range of 12 to 28 seconds depending upon its depth and the hardness of the material of the gun body 20. Figure 8 illustrates the rise in current load versus relative time of the scallop cutting operation. In the figure the current load is shown in terms of percentage of the maximum (100 %) load after the current load has been converted to analog voltage and then to digital signals. Based on the above-described establishment of the zero or reference point the central processor 34 directs the cutting tool 40 to remove the calculated thickness of metal from the wall 24 relative to that zero or reference point. After the intended amount of metal has been removed, the slide 42 withdraws the cutting tool 40 and the process comprising the steps of lowering the cutting tool 40 at the intended location of another scallop 26, observing a zero or reference point by the surge in load, and subsequent removal of metal is repeated one or several times, until it becomes necessary to readjust the positioning of the tubular gun body 20 in the machine tool 32 so as to access another section of the tube 20. At that point the entire process may be repeated, commencing with the step of the sonic probe 44 measuring the thickness of the wall 24 in the next section of the tube 20. The steps of the process of making the scalloped gun body in accordance with the present invention are diagrammatically illustrated in Figure 9. Optionally, the sonic probe 44 may be directed by the central processor 34 to return to the scallop 26 after it has been cut, and measure the thickness of the web 30 that just had been formed. After being fed into the central processor 34, the resulting data may be used in a printed report regarding the finished scalloped gun body. Measurements of the web 30 obtained during the operation while cutting one scallop can also be utilized as feed-back to the central processor 34 to make adjustments in cutting depth to obtain more accurate results. The programming or preparation of software to perform the operations described in connection with this invention is within the skill of the practitioner in the art, based on the foregoing disclosure. The scalloped gun body has webs 30 the thickness of which is within a tolerance limit of ± 0.020 inches, and preferably within ± 0.005 inches. In this regard it is noted that a tolerances of ± 0.020 inches are the expectation of the industry, however these expectations were, generally speaking, not met in the prior art, especially not with respect to tubular gun bodies made by the hot finishing manufacturing process. The scalloped gun bodies of the present invention, however, satisfy and even exceed these expectations. Therefore, both the manufactured product as well as the above-described process of making the same satisfy a long-felt need in the art and are believed to be novel and inventive. Several modifications of the above-described embodiments and invention may become readily apparent to those skilled in the art in light of the foregoing disclosure. Therefore, the scope of the present invention should be interpreted solely from the following claims, as such claims are read in light of the disclosure.

Claims

WHAT IS CLAIMED IS: 1. An article of manufacture adapted for assembly with at least one shaped explosive charge for underground jet perforation, comprising: a tubular metal body having an exterior surface, an interior surface and a wall between said exterior and interior surfaces, said wall defining an interior lumen wherein said shaped charges can be contained, and at least one scallop formed in the exterior surface of the metal body, the scallop being configured as a depression in the wall whereby in the scallop the wall of the metal body between the exterior and interior surfaces is substantially thinner than the wall outside the scallop, said thinner wall having a predetermined nominal thickness, the thinner wall being within less than approximately 0.020 inches of the predetermined nominal thickness. 2. The article of manufacture in accordance with Claim 1 wherein the thinner wall is within less than approximately 0.05 inches of its predetermined nominal thickness. 3. The article of manufacture in accordance with Claim 1 wherein the scallop is configured as a substantially circular depression. 4. The article of manufacture in accordance with Claim 1 comprising a plurality of scallops. 5. A substantially tubular gun body adapted to be assembled in a gun assembly containing at least one shaped explosive charge for underground jet perforation, the tubular gun body having an exterior surface, an interior surface and a wall between said exterior and interior surfaces, said wall defining an interior lumen wherein said shaped charges can be contained, at least one scallop formed in the exterior surface of the metal body, the scallop being configured as a depression in the wall whereby in the scallop the wall of the metal body between the exterior surface and interior surfaces is substantially thinner than the wall outside the scallop, the thinner wall having manufacturing tolerance limits less than approximately 0.020 inches, the scallop having been made by the process comprising the steps of: measuring the actual thickness of the wall of the gun body at the location where the scallop is to be formed to obtain data reflecting the actual thickness of the wall at the location; calculating the thickness of metal that is to be removed from the wall of the gun body at the location to obtain the scallop of a predetermined desired wall thickness, the step of calculating being based on the measured data reflecting the actual thickness of the wall at the location; lowering a powered rotating cutting tool to the gun body at the location, sensing a sudden increase in load when the cutting tool commences removing metal from the gun body, the linear positioning of the cutting tool relative to the gun body being considered a reference point when said sudden increase in load is sensed, and continuing to remove the calculated thickness of metal with the cutting tool relative to said reference point. 6. The gun body in accordance with Claim 5 wherein the thinner wall has manufacturing tolerance limits less than approximately 0.005 inches. 7. The gun body in accordance with Claim 5 having a plurality of scallops made in accordance with the process defined in Claim 5. 8. The gun body in accordance with Claim 5 wherein the process of making the scallop further comprises the step of feeding the data reflecting the measured thickness of the wall at the location into a central processor having an algorithm, said central processor being supplied with data reflecting the desired wall thickness of the scallop at the location, the step of calculating being performed by the central processor in accordance with the algorithm. 9. The gun body in accordance with Claim 8 wherein the process of making the scallop further comprises the steps of obtaining data regarding the linear position of the cutting tool at the reference point, and feeding said data into the central processor, and wherein the step of continuing to remove the calculated thickness of metal with the cutting tool relative to said reference point is directed by the central processor. 10. The gun body in accordance with Claim 9 wherein in the process of making the scallop the step of measuring the actual thickness of the wall of the gun body at the location is performed by a sonic tool. 11. A substantially tubular gun body adapted to be assembled in a gun assembly containing at least one shaped explosive charge for underground jet perforation, the tubular gun body having an exterior surface, an interior surface and a wall between said exterior and interior surfaces, said wall defining an interior lumen wherein said shaped charges can be contained, at least one scallop formed in the exterior surface of the metal body, the scallop being configured as a depression in the wall whereby in the scallop the wall of the metal body between the exterior surface and interior surfaces is substantially thinner than the wall outside the scallop, the thinner wall having manufacturing tolerance limits less than approximately 0.020 inches, the scallop having been made by the process comprising the steps of: measuring with a probe the actual thickness of the wall of the gun body at the location where the scallop is to be formed to obtain data reflecting the actual thickness of the wall at the location; inputting the data reflecting the actual thickness of the wall at the location into a central processor having an algorithm, said processor having data defining a predetermined desired wall thickness in the scallop at the location; calculating the thickness of metal that is to be removed from the wall of the gun body at the location to obtain the scallop of the predetermined desired wall thickness at the location, the step of calculating being performed in the processor utilizing the algorithm and based on the inputted data reflecting the actual thickness of the wall at the location; lowering under the control of the processor an electrically powered rotating cutting tool to the gun body at the location, sensing a sudden increase in load when the cutting tool commences removing metal from the gun body and inputting into the processor data reflecting the linear positioning of the cutting tool relative to the gun body when said sudden increase of load is sensed, said position being a reference point, and continuing under the control of the microprocessor to remove the calculated thickness of metal with the cutting tool relative to said reference point. 12. The gun body in accordance with Claim 11 wherein the thinner wall has manufacturing tolerance limits less than approximately 0.005 inches. 13. The gun body in accordance with Claim 11 having a plurality of scallops made in accordance with the process defined in Claim 11. 14. The gun body in accordance with Claim 11 that prior to cutting the scallops has been manufactured by a hot finishing process. 15. The gun body in accordance with Claim 11 wherein in the process of making the scallop the step of measuring with a probe is performed with a sonic probe. 16. A process for making a scallop in a substantially tubular gun body adapted to be assembled in a gun assembly containing at least one shaped explosive charge for underground jet perforation, the tubular gun body having an exterior surface, an interior surface and a wall between said exterior and interior surfaces, said wall defining an interior lumen wherein said shaped charges can be contained, and at least one scallop formed in the exterior surface of the gun body, the scallop being configured as a depression in the wall whereby in the scallop the wall of the gun body between the exterior surface and interior surfaces is substantially thinner than the wall outside the scallop, the thinner wall having manufacturing tolerance limits less than approximately 0.020 inches, the process comprising the steps of: measuring the actual thickness of the wall of the gun body at the location where the scallop is to be formed to obtain data reflecting the actual thickness of the wall at the location; calculating the thickness of metal that is to be removed from the wall of the gun body at the location to obtain the scallop of a predetermined desired wall thickness, the step of calculating being based on the measured data reflecting the actual thickness of the wall at the location; lowering an electrically powered rotating cutting tool to the gun body at the location, sensing a sudden increase in load when the cutting tool commences removing metal from the gun body, the linear positioning of the cutting tool relative to the gun body being considered a reference point when said sudden increase in load is sensed, and continuing to remove the calculated thickness of metal with the cutting tool relative to said reference point. 17. The process of Claim 16 further comprising the step of feeding the data reflecting the measured thickness of the wall at the location into a central processor having an algorithm, said central processor being supplied with data reflecting the desired wall thickness of the scallop at the location, the step of calculating being performed by the central processor in accordance with the algorithm. 18. The process of Claim 17 further comprising the steps of obtaining data regarding the linear position of the cutting tool at the reference point, and feeding said data into the central processor, and wherein the step of continuing to remove the calculated thickness of metal with the cutting tool relative to said reference point is directed by the central processor. 19. A process for making a scallop in a substantially tubular gun body adapted to be assembled in a gun assembly containing at least one shaped explosive charge for underground jet perforation, the tubular gun body having an exterior surface, an interior surface and a wall between said exterior and interior surfaces, said wall defining an interior lumen wherein said shaped charges can be contained, at least one scallop formed in the exterior surface of the metal body, the scallop being configured as a depression in the wall whereby in the scallop the wall of the metal body between the exterior surface and interior surfaces is substantially thinner than the wall outside the scallop, the thinner wall having manufacturing tolerance limits less than approximately 0.020 inches, the process comprising the steps of: measuring with a probe the actual thickness of the wall of the gun body at the location where the scallop is to be formed to obtain data reflecting the actual thickness of the wall at the location; inputting the data reflecting the actual thickness of the wall at the location into a central processor having an algorithm, said processor having data defining a predetermined desired wall thickness in the scallop at the location; calculating the thickness of metal that is to be removed from the wall of the gun body at the location to obtain the scallop of the predetermined desired wall thickness at the location, the step of calculating being performed in the processor utilizing the algorithm and based on the inputted data reflecting the actual thickness of the wall at the location; lowering under the control of the processor an electrically powered rotating cutting tool to the gun body at the location, sensing a sudden increase in current load when the cutting tool commences removing metal from the gun body and inputting into the processor as a reference point data reflecting the linear positioning of the cutting tool relative to the gun body when said sudden increase of current load is sensed, and continuing under the control of the microprocessor to remove the calculated thickness of metal with the cutting tool relative to said reference point. 20. The process of Claim 19 wherein the process the step of measuring with a probe is performed with a sonic probe. 21. The process of Claim 19 wherein the thinner wall has manufacturing tolerance limits less than 0.005 inch. 22. The process of Claim 19 used for making a plurality of scallops in the gun body. 23. The process of Claim 19 wherein the gun body has been manufactured by a hot finishing process.