US3517756A

US3517756A - Methods and apparatus for procuring formation samples from well bores

Info

Publication number: US3517756A
Application number: US769790A
Authority: US
Inventors: Jack P Goss
Original assignee: Schlumberger Technology Corp
Current assignee: Schlumberger Technology Corp
Priority date: 1968-10-23
Filing date: 1968-10-23
Publication date: 1970-06-30
Anticipated expiration: 1987-06-30

Description

June 30, 1970 J R G058 3,517,756

METHOD AND APPARATUS FOR PROGURING FORMATION SAMPLES FROM WELL BORES Filed 001;. 25, 1968 z/Zrck R 60;:

INVENTOR.

United States Patent METHODS AND APPARATUS FOR PROCURING FORMATION SAMPLES FROM WELL BORES Jack P. Goss, Lake Charles, La., assignor to Schlumberger Technology Corporation, New York, N.Y., a corporation of Texas Filed Oct. 23, 1968, Ser. No. 769,790 Int. Cl. E21b 49/04 US. Cl. 175-4 15 Claims ABSTRACT OF THE DISCLOSURE In accordance with the new and improved methods disclosed herein, a coring bullet is impelled into an earth formation with sufiicient force to drive a columnar sample thereof into the axial bore of the bullet. To retract the bullet from the formation, it is at least partially rotated and, preferably simultaneously therewith, pulled in a generally-rearward direction away from the formation. A preferred embodiment of the invention is provided by connecting two flexible cables of unequal length between a suitable tool and circumferentially-spaced points on each coring bullet so that longitudinal movement of the tool will initially tighten the shorter cable and twist the bullet about its longitudinal axis as it is being pulled rearwardly. When the longer cable is subsequently tightened by continued movement of the tool body, an added pull will be imparted to the bullet to complete its withdrawal.

It is, of course, quite common to obtain samples of earth formations traversed by a borehole by means of any one of a variety of so-called coring bullets. Such sample-taking or coring bullets are typically comprised of a tubular body having an open axial bore adapted to receive formation materials cut away by a hardened cutting edge on the forwardmost portion of the body. In the usual situation, these coring bullets are respectively mounted in lateral chambers spaced longitudinally along a suitable tool body adapted for suspension in a borehole. Explosive charges are disposed in each of the bullet chambers so that, upon detonation, the coring bullets will be explosively impelled into the face of an adjacent earth formation with suflicient force to drive a generallycolumnar formation sample or core into the axial bore of each bullet. One or more flexible cables or tethers are usually used to securely connect each bullet to the tool body so that, after the bullets have been fired, they will be withdrawn from the formation as the tool is retrieved. Thus, whatever formation materials have been captured by the bullets may be recovered at the surface for examination and testing.

Although coring bullets of this nature are usually quite effective, it is not at all uncommon for a small, but still significant, number of these bullets to be left behind when the tool is retrieved. In particular, it has been observed that the loss of bullets seems to be more common in the harder earth formations. As a result, it is generally believed that those bullets which are lost are so tightly embedded in a hard formation that their respective connecting cables will fail before a sufiicient amount of the formation immediately surrounding the bullets can be torn away to free the bullets.

Accordingly, it is an object of the present invention to provide new and improved methods and apparatus for more reliably obtaining samples of earth formations. This and other objects of the present invention are attained by impelling a typical core-taking bullet into the exposed face of an earth formation. Then, once the bul- 3,51 7,7 56 Patented June 30, 1970 "ice let has been at least partially embedded into the earth formation, the bullet is withdrawn therefrom by conjunetively rotating it about its longitudinal axis as a retracting force is being applied thereto. In the preferred manner of imparting these rotative and retractingforces to a typical coring bullet, two flexible tethers of unequal length are respectively connected between the tool body carrying the bullet and circumferentially-spaced portions of the bullet. Thus, as the tool body is progressively displaced in relation to the embedded bullet, the shorter tether will first be tightened to angularly rotate the bullet about its longitudinal axis as well as to apply a reversely directed retracting force thereto. Then, if necessary, continued displacement of the tool body will tighten the longer tether so that the two tethers will ultimately both apply reversely-directed retracting forces to the bullet to complete its withdrawal from the earth formation.

The novel features of the present invention are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may be best understood by way of the following description of exemplary apparatus and methods employing the principles of the invention as illustrated in the accompanying drawings, in which:

FIG. 1 depicts a typical sidewall coring tool in which a preferred embodiment of new and improved apparatus has been provided for practicing the method of the present invention;

FIG. 2 is a cross-sectional view of the illustrated coring tool taken along the lines 2 of FIG. 1; and

FIG. 3 is a fragmentary isometric view of the tool shown in the preceding drawings as the present invention is being practiced.

Turning now to FIGS. 1-3, sidewall sample-taking apparatus 10 incorporating the principles of the present invention is shown suspended from a typical suspension cable 11 in a borehole 12 and adjacent an earth formation 13 from which one or more sample cores are desired. As is typical, the sample-taking apparatus 10 includes an elongated body 14 having a plurality of longitudinally-spaced lateral chambers 15 respectively receiving the base of a typical coring bullet 16 such as, for example, any of those shown in Pat. No. 3,072,202, Pat. Nos. 3,220,490 through 3,220,493 or in Pat. No. 3,329,- 217. O-rings 17 around the rearward portions of the bullets 16 fluidly seal a small charge of a propellant explosive as at 18 in each lateral chamber 15 behind the rear or base portion of each coring bullet. An electrically-responsive igniter, as at 19, is operatively inserted into each chamber 15 and connected to conductors in the cable 11 for selectively detonating the explosive charges 18. Inasmuch as the sample-taking apparatus 10 as has been described so far is typical, it is believed unnecessary to devote further attention to its description.

When it is desired to obtain one or more core samples from the earth formation 13, the tool 10 is positioned in the usual fashion in the borehole 12 immediately adjacent to the formation. One or more of the igniters 19 are then selectively energized from a power source (not shown) at the surface to impel a corresponding number of the bullets 16 into the exposed face of the formation 13 for procuring a desired number of formation cores.

As previously mentioned, the nose portions of the coring bullets 16 will be at least partially embedded in the earth formation 13, with the depth of their penetration, of course, being governed by the character of the formation. Generally speaking, however, for a given type of bullet and quantity of explosive 18, the bullet 16 will be more deeply embedded in a softer formation than in a harder formation. In any event, withdrawal of the bullet 3 12516 generally requires a substantial rearwardly-directed orce.

Accordingly, in accordance with the present invention, withdrawal of each of the bullets 16 is more reliably accomplished than has been possible heretofore by at least partially rotating the bullet about its longitudinal axis and, preferably simultaneously therewith, pulling on the bullet in a generally-rearward direction with sufiicient force to retract it from the formation 13. It will be appreciated, therefore, that by conjunctively rotating each bullet 16 about its longitudinal axis as it is being retracted, the force required to withdraw the bullet will be less than that required by simply pulling the bullet out of the formation.

Although various devices can, of course, be devised for accomplishing the joint rotation and retraction of the bullets 16, the preferred embodiment of the apparatus for accomplishing this is best illustrated in FIG. 3. As seen there, the bullet 16 has been propelled into the formation not shown in FIG. 3) to obtain a core sample 20. To connect the bullet 16 to the tool body 14, flexible cables or

tethers

21 and 22 are secured in the usual fashion to opposite sides of the bullet and respectively connected at their opposite ends to the tool body. The

tethers

21 and 22 are, of course, of sufficient length to allow the bullet 16 to be propelled out of the chamber and travel a short predetermined distance before the tethers are fully extended. As is typical, recesses or

grooves

23 and 24 are arranged along the tool body 14 on opposite sides of the chamber 15 to respectively receive the

tethers

21 and 22 which, for convenience, are usually neatly coiled (as best shown in FIG. 2) in these grooves so as to be smoothly payed out as the bullet 16 is propelled out of the chamber.

Instead of employing tethering cables of equal length as has been typical heretofore, in the present invention the

tethers

21 and 22 are of unequal lengths. Accordingly, as depicted in FIG. 3, to withdraw the bullet 16, it is necessary only to either lower or (as shown by the arrow 25) raise the tool body 14. In this manner, such longitudinal movement of the tool 10 will first tighten the shorter tether 21 to begin rotating the bullet 16 (as shown by arrow 26) about its longitudinal axis 27 and, either simultaneously or shortly thereafter, begin pulling the bullet rearwardly (as shown by the arrow 28). Then, upon continued longitudinal movement of the tool 10, the longer tether 22 will also be tightened to increase the rearwardly-directed pulling force on the bullet 16 if this is necessary.

It will be appreciated, of course, that a single tether, such as the tether 21, connected eccentrically to the bullet 16 would provide the combined rotative and rearward movements of the bullet. Such a single tether will, however, most likely unfavorably affect the flight of the bullet 16 as it is impelled against an earth formation. Thus, to avoid such undesirable effects as well as to provide a more-secure connection between the body 14 and bullet 16, two tethers as at 21 and 22 are preferred. Although the type of bullet as well as its size will have some influence upon choosing the difference in lengths of the two

tethers

21 and 22, it has been found that for typical bullets such as those shown in the aforementioned patents, a difference of only about %-inch in the efiective lengths of the two tethers will be sufiicient for the purposes of the present invention. Thus, a partial rotation of the bullet 16 will be made, which, if necessary to complete the withdrawal, will be quickly followed by equal pulls on opposite sides of the bullet once the longer tether 22 tightens.

Accordingly, it will be appreciated that by employing the principles of the present invention, coring bullets may now be more-reliably withdrawn from earth formations to achieve a significantly higher rate of recovery than has been possible heretofore. By at least partially rotating the bullet as it is pulled rearwardly, it has been found that even a tightly-embedded bullet will usually be loosened and withdrawn more easily from an earth formation. In the preferred manner of accomplishing this, the otherwise typical tethering cables are made of slightly different effective lengths so that longitudinal movements of the sample-taking tool will initially tighten only the shorter tether to partially rotate the bullet and begin withdrawing it. Then, if the bullet has not yet been completely withdrawn, once the longer tethering cable also becomes taut, the two cables will pull equally on opposite sides of the bullet to complete the retraction of the bullet from the earth formation.

While a particular embodiment of the present invention has been shown and described, it is apparent that changes and modifications may be made without departing from this invention in its broader aspects; and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

What is claimed is:

1. A method for obtaining a sample of an earth formation traversed by a well bore and comprising the steps of: positioning a tubular formation-coring bullet in a well bore adjacent to an earth formation from which a sample is to be taken so that the longitudinal axis of said bullet intersects the formation; impelling said bullet forwardly along its said axis into the earth formation to at least partially embed the forward portion of said bullet therein and force a portion of the earth formation into said bullet; turning said bullet about its said longitudinal axis to loosen the embedded forward portion of said bullet in relation to the earth formation thereabout; and pulling said bullet rearwardly to withdraw said embedded forward portion thereof from the earth formation.

2. The method of claim 1 wherein said turning and pulling steps are in conjunction with one another.

3. The method of claim 1 wherein said turning step rotates said bullet only a portion of a complete revolution.

4. A method for obtaining a sample of an earth formation traversed by a well bore and comprising the steps of: positioning a tubular formation-coring bullet in a well bore adjacent to an earth formation from which a sample is to be taken so that the longitudinal axis of said bullet intersects the formation; impelling said bullet forwardly along its said axis into the earth formation to at least partially embed the forward portion of said bullet therein and force a portion of the earth formation into said bullet; pulling in a generally-reverse direction on one side of said bullet to at least partially twist said bullet about its said longitudinal axis and loosen said bullet in relation to the earth formation as said bullet is being retracted therefrom.

5. The method of claim 4 further including the subsequent step of: pulling in a generally-reverse direction on the other side of said bullet to augment the retraction thereof from the earth formation.

6. Apparatus adapted for obtaining a sample of an earth formation traversed by a well bore and comprising: a support adapted for suspension in a well bore; a tubular coring bullet on said support and having a longitudinal bore terminating at an opening in the forward end of said bullet and formation-cutting means adjacent to said forward end thereof; and means connecting said bullet to said support including first and second flexible members of unequal length respectively secured to said support and to circumferentially-spaced portions of said bullet.

7. The apparatus of claim 6 further including: means operable for longitudinally impelling said bullet forwardly against an earth formation with sufficient force to cut away a portion of such a formation.

8. The apparatus of claim 6 further including: explosive means adapted for longitudinally impelling said bullet forwardly against an earth formation with sufficient force to cut away a portion of such a formation;

and means selectively operable from the surface for detonating said explosive means.

9. Formation-sampling apparatus comprising: a support adapted for suspension in a well bore; formationsampling means including a tubular coring bullet on said support and having a longitudinal bore terminating at an opening in the forward end of said bullet and formationcutting means adjacent to said forward end thereof adapted for cutting away a portion of such a formation; and means connected to said bullet and said support and responsive to longitudinal movement of said support in relation to a well bore for at least partially rotating said bullet about its said longitudinal axis and retracting said bullet from an earth formation from which a portion has been cut away by said formation-cutting means.

10. The apparatus of claim 9 wherein said movementresponsive rotating and retracting means include a flexible member respectively secured to said support and to an eccentrically-located portion of said bullet.

11. The apparatus of claim 9 wherein said movementresponsive rotating and retracting means include first and second flexible members of unequal length respectively secured to said support and to circLunferentially-spaced portions of said bullet.

12. Apparatus adapted for obtaining a sample of an earth formation traversed by a well bore and comprising: a support adapted for suspension in a well bore and having at least one chamber therein defined about a lateral axis and with an opening on one side of said support; formation-sampling means on said support and including a cylindrical coring bullet coaxially disposed in said lateral chamber and having a forward end projecting from said chamber opening adapted to be impelled against an earth formation; and means connecting said bullet to said support and responsive only to longitudinal movement of said support in relation to a well bore after said bullet has been impelled against an earth formation for imparting a force to said bullet tending to at least partially turn said bullet about said lateral axis and retract said bullet from an earth formation.

13. The apparatus of claim 12 wherein said connecting means include first and second flexible members of unequal length respectively secured to said support and to circumferentially-spaced portions of said bullet.

14. The apparatus of claim 12 wherein said formation-sampling means include explosive means in said lateral chamber adapted for axially impelling said bullet forwardly against an earth formation with sufiicient force to cut away a portion of such a formation; and means selectively operable from the surface for detonating said explosive means.

15. The apparatus of claim 14 wherein said connecting means include first and second flexible members of unequal length respectively secured to said support and to circumferentially-spaced portions of said bullet.

References Cited UNITED STATES PATENTS 2,055,506 9/ 1936 Schlumberger 4 2,944,791 7/1960 Le Bus 175--4 3,220,493 11/1965 Urbanosky 175 -4 3,280,922 10/ 1966 Bannister 175-4 DAVID H. BROWN Primary Examiner