US2685038A

US2685038A - Method of and means for measuring the depth of penetration of bullets within subsurface formations

Info

Publication number: US2685038A
Application number: US225164A
Authority: US
Inventors: Robert L Hoss
Original assignee: Individual
Current assignee: Individual
Priority date: 1951-05-08
Filing date: 1951-05-08
Publication date: 1954-07-27
Anticipated expiration: 1971-07-27

Description

July 27, 1954 RECOROEfl R. L. HOSS METHOD OF AND MEANS FOR MEASURING THE DEPTH OF PENETRATION 0F BULLETS WITHIN SUBSURFACE FORMATIONS Filed May 8, 1951 Robert L. Hosa- INVENTOR. I

Patented July 27, 1954 METHOD OF AND ME THE DEPTH OF P LETS WITHIN SUB ANS FOR MEASURING ENETRATION OF BUL- SURFACE FORMATION S Robert L. Hoss, Corpus Christi, Tex. Application May 8, 1951, Serial No. 225,164 10 Claims. (Cl. 250-83.6)

This invention relates to new and useful improvements in methods of and means for measur ing the depth of penetration of bullets within sub-surface formations.

As is well known, gun-perforating of well casing or pipe is general practice and the usual gunperforating operation involves the perforation of the casing by firing a selected number of projectiles or bullets through the wall of the casing in radial directions from the well bore. The bullets penetrate the well casing and the cement which cements said casing in place and enter the subsurface formation to thereby establish communication between the formation and the well bore. Although it has been heretofore recognized that the depth of penetration into th formation by the projectile or bullet affects the subsequent productivity of the formation, there is now no known satisfactory method for accurately determining the distance which the bullet has penetrated the formation.

In gun-perforating, the operator generally selects the particular size gun, the specific size bullet and the volume of the charge to be used in accordance with his past experience with the type of formation and in accordance with the size of the casing to be perforated so that actually the selection of the essential factors is on a more or less guesswork basis. After completion of the gun perforating operation, there is no way of knowing whether proper depth of penetration has been obtained. Even in those cases where the well produces after the gun-perforating operation, the operator is without knowledge that proper depth of penetration, which would provide maximum productivity, has been accomplished. In those instances, where no productivity is had subsequent to the perforating operation, it has been assumed that the formation is non-productive when, in fact, such non-productivity may have been due to failure of the bullets to properly penetrate into the formation or to properly perforate the casing and cement wall therearound.

It is, therefore, one object of this invention to provide an improved method for accurately determining the depth of penetration of a projectile or bullet which has been fired into a sub-surface formation by a perforating operation, whereby positive knowledge as to said depth of penetration is obtained.

An important object of the invention is to provide an improved method of determining the depth of penetration of a projectile into a subsurface formation wherein a controlled amount of radioactive material is incorporated within the projectile so that said projectile emanates radioactive radiations of a predetermined intensity at a known distance, and thereafter determining the depth of penetration of said projectile by measuring the intensity of the radiations at a point within the well bore.

Another object is to provide a method, of the character described, wherein the intensity measi urements are made in only a single horizontal plane Within the well bore, whereby accurate determination of the depth of penetration of each projectile may be accomplished even though the projectiles are relatively close to each other in horizontal planes.

F each projectile, and visibly recording the measurements at the surface.

A further object is to provide an improved apparatus for determining the depth of penetration of a projectile within a sub-surface formation and including, a Geiger-Muller counter or ionization chamber which is shielded in a manner to receive radiations in only a single restricted horizontal plane.

The construction designed to carry out the invention will be hereinafter described together with other features thereof.

The invention will be more readily understood from a reading of the following specification and by reference to the accompanying drawings forming a part thereof, wherein an example of the invention is shown, and wherein:

Figure 1 is a sectional view of a well bore illustrating the projectiles within the sub-surface formation and showing the detecting instrument lowered within said bore,

Figure 2 is a horizontal cross-sectional view taken on the line 2-2 of Figure 1,

Figure 3 is a sectional detail of a gun barrel assembly having a projectile which is employed in carrying out the method mounted therein, and

Figure 4 is an enlarged view of the indicating chart which records the measurements.

In the drawings thenumeral I0 designates a well bore having a well casing or pipe H extending therethrough. In accordance with the a w M-et the projectiles or bullets usual practice the well casing is cemented in place by cement [2.

As has been noted, it is the usual practice to employ a gun perforator which fires projectiles or bullets through the wall of the casing l l through the cement and into the sub-surface area or formation surrounding the well bore. It has been recognized that proper depth of penetration by must be accomplished in order to obtain maximum productivity from the formation but heretofore there has been no method for ascertaining whether or not proper penetration of the projectiles or bullets into the formation has been accomplished.

In carrying out the present invention, each projectile or bullet A may contain a known controlled quantity of radioactive material whereby said projectile or bullet will emanate radioactive radiations of a given intensity. All of the projectiles or bullets are constructed in an identical manner, that is, each of said projectiles contain substantially the same quantity of radioactive material, which means that all bullets emit radioactive radiations of the same intensity at the same distance. The particular construction of each projectile A is subject to variation and so long as said projectile contains a predetermined or measured quantity of the radioactive material, the purposes of the present invention may be accomplished. As illustrated in Figure 3, the projectile comprises the usual bullet l3 mounted within the bore of the gun barrel i l and said barrel housing Ida has the usual powder chamber l4b behind the bullet; the powder is ignited in any well known manner by the igniter cord Me. This is typical gun barrel assembly and forms no part of the present invention since any suitable gun perforator may be employed for pro jecting the bullet.

The body of the bullet contains the radioactive material it which may be radioactive salt, uraninite or any other material capable of emitting radioactive radiations, and said material may be disposed within the body of the bullet in any convenient manner. As shown, the bullet is bored out and the radioactive material is disposed within a capsule which is retained within the bore by a threaded closure I511.

When the casing II is to be perforated the gun perforator (not shown) is loaded with the projectiles A, each of which has embodied there in the controlled or known quantity of radioactive material l5. The gun perforator is then lowered into the well here and actuated in the usual manner to fire the projectiles through the wall of the casing H in a radial direction and thereby perforate said casing. In Figure l, the projectiles Al, A2, A3 and AA have been illustrated as having different depths of penetration and said projectiles horizontal planes or elevations. As shown, the lowermost projectile A! has penetrated a considerable distance into the sub-surface formation F, while the projectile A2 has not penetrated through the cement wall between the casing ii and the well bore. The projectiles A3 and Ad have penetrated the cement but their depth of penetration into the formation is dissimilar.

In order to determine the depth of penetration of the projectiles the measuring instrument B is lowered within the well bore by means of the usual conductor cable IS. The instrument includes a housing l! which is centered within the well casing H by the usual bowed centralizer springs l8. Mounted within the lower portion of are disposed in different ell) the housing is a Geiger-Muller counter or ionization chamber [9, and as is well known, this counter is responsive to radioactive emissions. In order to cause the counter to receive the radioactive emissions in only a single horizontal plane, the counter or ionization chamber is shielded by suitable lead sleeves or

collars

28 and 2| which are interposed between the chamber l9 and the housing I1. The shielding collars or sleeves are suitably secured within the housing ll and are spaced apart from each other to provide an annular entry slot 22 through which radiations originating from a source in the same plane as the plane in which said slot is located may be received. The upper end of the conductor cable I6 has electrical connection with any well known recording device which recordsv the measurements made by the Geiger counter [9.

Usually the instrument B is lowered to a point below all projectiles and is then moved upwardly; during such upward movement the instrument is operated to make the desired measurements. As the instrument B is raised within the well casing, the movement of the entry slot 22 in the lower portion of the instrument opposite the lowermost projectile Al will cause the radiation originating from the projectile Al to enter said slot and be received within the ionization chamber 1 9. Due to the shielding by the

members

20 and 2|, any radiation from the next adjacent projectile A2 will not affect the counter, and therefore, the operation of the counter will be controlled solely by the radiations of the projectile opposite or in the same horizontal plane as the entry slot 22. Because of the centralizing springs 18, the counter it will be maintained at substantially the axial center of the well bore.

The magnitude of the current flowing through the center wire of the ionization chamber [9 is inversely proportional to the square of the distance that the particular radioactive projectile is located from said ionization chamber. In other words, the intensity of radiation from the projectile Al at the center of the well bore where the Geiger counter is located is determined by the distance of the projectile from the counter, and this distance is obviously dependent upon the depth of penetration of said projectile. Therefore, the counter actually measures the intensity of the radiation from the projectile Al and this measurement may be converted into a visible reading representative of depth of penetration by means of the usual recording chart and stylus.

When the instrument B is moved upwardly to locate the entry slot 22 in the same plane as the second projectile A2, the counter 19 is re sponsive to the radiations emanating from this projectile. As illustrated, this projectile has not penetrated the cement and is therefore much closer to the axial center of the well bore or closer to the Geiger counter than was the projectile Al. Since the projectile A2 contains the same quantity of radioactive material as does the projectile Al it willbe evident that the intensity of the radiations received by the counter I 9 from projectile A2 will be considerably greater than the radiations previously received from the further removed projectile Al. This difference in intensity which is actually measured by the counter will, of course, be recorded and indicated at the surface. It is noted that because of the shielding arrangement the counter I9 will be shielded from any extraneous radiation from either of the adjacent projectiles AI and A3. In

this regard, it might be noted that inugun perforating the difference in elevation between projectiles may be a matter of inches, and therefore it is important that the counter or ionization chamber be properly shielded to receive the radiations from only one projectile at any one time.

As raising of the instrument is continued, the entry slot 22 of said instrument is moved opposite the projectile A3 to measure the intensity of the radiations therefrom and is thereafter raised opposite the projectile A4 to measure intensity of radiation from this lowermost projectile. Although four projectiles are illustrated in Figure 1, any desired number may be projected through the wall of thecasing and the intensity of the radiation of each will be measured in turn as the instrument is raised past said projectiles. Because all of the projectiles contain the same quantity of radioactive material and because the intensity of the radiation of each projectile varies in accordance with its distance from the ionization chamber, it is evident that an accurate determination of the depth of penetration of each projectile may be made.

The particular recording mechanism 23 which is located at the surface is, as has been stated, subject to variation. However, it is preferable to employ the well known recording chart and stylus arrangement, and in Figure 4, a view of the chart 24 is illustrated. The length of the chart is representative of the depth of the instrument and the chart will be driven in synchronization to the lowering and raising of the cable 16. The transverse width of the chart may be calibrated in distance representative of depth of penetration. The recording or indicating line 25 is made by a suitable stylus which is controlled by the operation of the Geiger counter as the latter measures the intensity of the radiations emitted by the various projectiles. As illustrated in the chart, the initial oiTset 26 in the recording line 25 is indicative of the depth of penetration of the first projectile Al. Because the projectile Al is a considerable distance from the counter I9, the offset 26 is relatively small since the intensity of radiation at the point of reception is not too great.

The second offset 21 illustrated on the chart is representative of the depth of penetration of the projectile A2, and since this projectile has not penetrated the cement wall the intensity measurement is quite high thereby resulting in a relatively large-offset in the indicating line 25. The offset 28 on the chart is indicative of the depth of penetration of the projectile A3 and this penetration, although through the cement wall I2, is not too deep into the sub-surface formation F. The offset 29 on the chart is representative of the depth of penetration of the projectile A4 which has entered the formation about the same dis tance as projectile Al.

From the foregoing it will be evident that a simple and accurate method and apparatus for measuring the depth of penetration of projectiles is provided. Each projectile has incorporated therein a predetermined known or measured quantity of radioactive material with the result that if all projectiles were exactly the same distance from the counter or ionization chamber IS, the intensity measurements made by said counter would be identical. With this arrangement the variation in distance between each projectile and the counter results in a variation in intensity which is inversely proportional to the square of e the distance and the intensity measurements made by the counter are a measure of said distance. This intensity measurement is transposed into a visible record calibrated in depth of penetration and provides accurate knowledge as to the exact distance which each projectile has been projected into the sub-surface formation. The shielding of the counter or ionization chamber IS in a manner to permit reception of radiations inonly a single horizontal plane is important because in gun perforating the projectiles are relatively close to each other with respect to horizontal elevations or planes; as a matter of fact, it is not uncommon for the projectiles to be fired within four to six inches of each other in different horizontal planes and in order to permit accurate determination the counter or ionization chamber must be shielded against the effects of any radiation other than that from the particular projectile being investigated. It is also important to the present invention that the counter or ionization chamber be maintained in the same relative position within the well bore throughout the measurements made with respect to all of the projectiles, since this assures that any variation in distance between the counter and the projectile. is due solely to the difference in the depth of penetration of each projectile as compared to the other projectiles.

It is pointed out that the radiation from the radioactive projectile is of such a high order of magnitude as compared to the intensity of natural earth radiation that natural radiation will not be recorded on the penetration record. The particular measuring instrument B is constructed to be substantially insensitive to natural radiation whereby when said instrument is at any point in the well bore other than opposite the projectiles the stylus forms the substantially straight line 25 on the indicating chart.

The foregoing disclosure and description of the invention is illustrative and explanatory thereof and various changes in the size, shape and materials, as well as in the details of the illustrated construction may be made, within the scope of the claims, without departing from the spirit of the invention.

I claim:

1. The method of determining the depth of penetration of projectiles into a sub-surface area surrounding a well bore including, depositing a plurality of projectiles each having identical radio ctive radiation emitting qualities into the su -surface area at different elevations therein, and thereafter measuring the intensity of the radiations emanating from each projectile in situ within the sub-surface area.

2. The method of determining the depth of penetration of projectiles into a sub-surface area surrounding a well bore including, depositing a plurality of projectiles each having identical radioactive radiation emitting qualities into the sub-surface area at different elevations therein, moving an instrument responsive to radioactive radiations within the well bore, and maintaining the instrument in the same position in a vertical plane Within the bore throughout its movement therethrough, and measuring by means of said instrument the intensity of the radiations emanating from each projectile, which intensity is a measure of the depth of penetration of said projectile.

3. The method as set forth in claim 2, together with the step of shielding the instrument from all radiations 'other than those from the projectile oppositezsaid measuring instrument.

4. The method of determining the depth of penetration of a plurality of projectiles into a subsurface area surrounding a v@ bore including, depositing the projectiles at various horizontal elevations in the sub-surface area, each projectile having the same predetermined quantity of radioactive material therein whereby said projectiles emit radioactive radiations, thereafter measuring the intensity of the radiations emanating from each projectile in situ within the sub-surface area, and transposing at the surface the measurements so made into visible indications of depth of penetration of each projectile into the sub-surface area.

5. The method of determining the depth of penetration of proj tiles into a sub-surface area surrounding a W l bore including, introducing into each projectile a measured quantity of radioactive material, thereafter depositing the projectiles into the sub-surface area at different elevations therein, and thereafter measuring the intensity of the radiations emanating from each projectile in situ within the sub-surface area.

6. The method of determining the depth of penetration of proje iles into a sub-surface area surrounding a w bore including, introducing into each projectile a measured quantity of radioactive material, thereafter depositing the projectiles into the sub-surface area at different elevations therein, thereafter successively receiving radiations emanating from each projectile at a predetermined point within the well bore, and measuring the intensity of the radiations received from each projectile, the reception point being successively varied in a horizontal plane to receive emanations from all projectiles but being maintained constant in a vertical plane with respect to the axis of the well bore.

7. The method of etermining the depth of penetration of projecxges into a sub-surface area surrounding a wel' bore including, introducing a measured quantity of radioactive material into each projectile so that all projectiles contain the same quantity, thereafter firing the projectiles into the sub-surface area at diiferent horizontal elevations therein, moving a measuring instrument responsive to radioactive radiations within the well bore while maintaining the instrument in the same vertical plane with respect to the axis of the bore to cause said instrument to successively move past each projectile, and measuring by means of the instrument the intensity of the radiations emanating from each projectile, which intensity is a measure of the depth of penetration of said projectile.

8. The method as set forth in claim 1,.together with the step of shielding the measuring instrument from all extraneous radiations other than those from the particular projective opposite said measuring instrument in a horizontal plane.

9. An apparatus for determining the depth of penetration of a projectile into a sub-surface formation-surrounding a well bore including, a projectile having a measured quantity of radioactive material incorporated therein, and an instrument adapted to be lowered through the well bore and responsive to radioactive radiations, and means within said instrument for measuring the intensity of the radioactive radiations emanating from the projectile after said projectile has been deposited within the subsurface formation.

10. An apparatus for determining the depth of penetration of a projectile into a sub-surface formation surrounding a well bore including, a prgFotfle having a measured quantity of radioac ve material incorporated therein, an instrument adapted to be lowered through the well bore and responsive to radioactive radiations, means within said instrument for measuring the intensity of the radioactive radiations emanating from the projectile after said projectile has been deposited within the sub-surface formation, and electrically operated recording means at the surface of the well bore and electrically connected with the instrument for transposing the intensity measurements into a visible indication of the depth of penetration of the projectile into the formation.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,228,623 Ennis Jan. 14, 1941 2,469 161 Russell May 10, 1949 2,508,772 Pontecorvo May 23, 1950 2,515,535 Thayer et a1. July 18, 1950 OTHER REFERENCES Radioactivity Well Logging," by E. N. Tiratsoo, reprinted from Petroleum, published by Leonard Hill, Ltd, Jan. 1948, 6 pages.