Drilling Tools

Abstract

A drilling tool has been provided which has a gastight cavity therein, the entrance of which cavity is preferably positioned away from a wear surface of the tool and which cavity contains krypton .sup.85 as a wear indicating means either for a bearing wear surface or for an abrasive drilling wear surface. The indicating means are activated when, because of wear, the cavity is punctured and krypton .sup.85 escapes or is expelled by means of auxiliary agents. The method of marking the tools as well as the tools thus marked are within the scope of the invention. Further, the improvement in the method of drilling deep bore holes with a tool possessing these indicating means is similarly within the scope of the disclosed invention.

Description

The present invention relates to the marking of tools and instruments used for deep drilling with radioactive tracer substances which serve to indicate the occurrence of the critical wear.

When using the drilling instruments which are generally applied for geological and industrial deep drilling, for example, roller bits, diamond bits, drilling turbines, reamers and smoothing instruments, it is necessary to know with a high degree of certainty when a predetermined, namely the highest permissible, amount of wear has occurred upon the tools and instruments, which are exposed to a high stress. In roller bits, for example, an excessive wear on the roller bearings which are exposed to a very high degree of abrasion causes the rolls to be out of a true alignment and this may result in the destruction of the cutter head of the drill bit. Extensive and expensive locating and catching operations are then necessary as a result. When the reamers and smoothing instruments have undergone excessive wear the well bores obtained are badly sized and this requires a time-consuming additional treatment.

Up to now it has to be judged by experience and feeling whether or not the highest tolerable service life of such tools and instruments has been reached. When the tools or instruments are brought to the surface for visual inspection it turns out in most cases that they could have been used for a much longer period or that they should have been replaced already a long time ago because a dangerous amount of wear has occurred. The removal of the tools or instruments requires much time and expenditure, especially when the well is very deep.

It has previously been proposed to indicate to the driller that his bit has worn away the highest admissible amount by providing the instruments for drilling deep wells with recesses into which a radioactive tracer substance is embedded, the recesses being closed in such a manner that the tracer substance is released as soon as the highest tolerable amount of wear has occurred whereupon the radioactive tracer substance becomes suspended or dissolved in the circulating drilling fluid and is brought in it to the earth's surface where it is detected by a measuring and indicating instrument. It has also been proposed to embed in the recesses provided for this purpose in addition to the tracer substance, a propellent which when coming into contact with the drilling fluid decomposes with the evolution of gas and expels the tracer substance from the recess. It has further been proposed to mark the propellent itself by a radioactive substance for example, to use as the propellent sodium amide containing nitrogen.sup.13 or tritium, an alanate or boranate containing tritium, carbon dioxide containing carbon.sup.14 or a carbide containing carbon.sup.14. It has also been proposed to use water-soluble radioactive tracer substances, for example, a chloride containing chlorine.sup.36 or a radioactive cation such as potassium.sup.42 , sodium.sup.24 or cesium.sup.134.

The hitherto known processes have not been used for practical drilling. Soluble tracer substances cannot be used because they contaminate the drilling fluid and this has to be avoided at all costs. Ionogenic tracer substances are not reliable as indicators in the processes concerned since they may be retained in the well bore by ion exchange or other interferring effects. Besides, many of the tracer substances which have been proposed for marking purposes emit gamma particles which must be prevented from penetrating into the well bore for they would very much complicate the measurement of natural radioactivity which has to be carried out during the drilling operation.

The substances emitting beta particles which have hitherto been proposed are either not suitable for the marking of drilling instruments for one of the aforesaid reasons as is for example, the case with the ionogenic chlorine.sup.36, or they are difficulty accessible substances such as, for example, carbon.sup.14, which are too expensive for use in practice or they are substances having too short a hair life, as is the case with nitrogen.sup.13, or they are substances emitting very soft beta particles, for example, tritium, which can only be detected by means of sensitive measuring instruments which are expensive and not able to withstand the hard usage at drilling sites.

The present invention provides a process for indicating the occurrence of the critical amount of wear upon instruments and tools by means of a radioactive tracer substance in which the radioactive tracer substance is krypton.sup.85. The tracer substance is advantageously used in the form of an inclusion compound. It is particularly advantageous to use krypton.sup.85 in the form of its clathrate with hydroquinone.

The tracer substance is introduced in known manner into the bore holes with which the instrument is provided and which are cut open and release the tracer substance as soon as the critical amount of wear has occurred.

In cases in which the well bores are deeper than about 300 meters the proper pressure of the gas released from the inclusion compound is in general too small as compared with the pressure of the supernatant liquid column so that the gas cannot leave the bore hole in which it is embedded. Even in cases in which the gas is embedded as such in the bore hole the pressure cannot be increased to any desired degree since the increase of the pressure is limited by increasing tightening difficulties.

In such a case it is preferred to introduce into the tracer bore hole not only the tracer substance but also a propellent which when coming into contact with the drilling fluid decomposes with the evolution of gas. For this purpose there may be used, for example, mixtures of water-soluble acids and carbonates. There may also be used alkali metals, for example, sodium or potassium. It is particularly advantageous to use hydrides, in particular lithium hydride or calcium hydride, since these compounds enable a particularly high yield of gas to be obtained in comparison with the volume of solid substances introduced.

Embodiments of the invention will now be described by way of example only with reference to the accompanying drawing in which

FIG. 1 is a sectional view of a smoothing instrument which has been marked in accordance with the invention,

FIG. 2 illustrates a roller bit marked in accordance with the invention.

Referring to FIGS. 1 and 2 the tracer bore hole 1 contains the tracer substance 2 and, if desired or required, the propellent 3. The hole is closed by an appropriate closure 5, for example, a riveted screw or a shrinking closure, so as to be impermeable to gas. Numerals 4 designate the surfaces of the marked tool which are exposed to abrasion. The thickness of the material between the bore hole 1 and the surface 4 is so designed as to correspond to the highest tolerable amount of wear. As soon as such an amount of material has been abraded from the surface 4 that the bore hole 1 is cut open the drilling fluid penetrates into the bore hole 1 and the tracer substance 2 leaves the hole, is carried to the earth's surface by the drilling fluid and can there be determined by means of a known counter which by way of known devices can actuate an indicator, a warning signal or a stopping device.

When the external pressure is high, as is always the case when the drilling is carried out in a great depth, the discharge of the tracer substance 2 is supported by the propellent 3 which upon reacting with the drilling fluid that has entered develops a gas which expels the tracer substance 2 out of the bore hole 1.

In instruments and tools in which much material is available where the bore hole for the marking can be made, for example, in smoothing instruments, the tracer substance may be embedded in the bore hole in a relatively large, closed capsule which may also contain the propellent. In such a case the marking need not be carried out by the manufacturer. It is sufficient to provide the part to be marked with the bore hole and to introduce the capsule immediately before use.

The following example serves to illustrate the invention but it is not intended to limit it thereto.

EXAMPLE

The process according to the invention was tested in practice on a drilling site in a series of experiments. The results of a typical test will now be described.

Data of the Drilling

Core boring with a diamond bit;

depth: between 2345.3 and 2363.3 meters

tubing of the well to a depth of 2250 meters

diameter of the well bore in the depth according to the experiment: 216 mm;

geological formation: transition from Zechstein to carboniferous formation (layers of sandstone and argillaceous slate);

circulating fluid: fluid of clay and brine; total quantity 80 cubic meters;

speed of circulation of the fluid: 82 minutes per circulation; throughput of fluid: approximately 1 cubic meter/min. drilling load at the bottom of the well: 5 to 7 tons;

number of revolutions of the drill poles: 120 revolutions per minute;

arrangement of the drill poles from bottom to top: diamond head, core barrel, smoothing instrument, 12 heavy bars, the rest being normal drill bars.

Test Proceeding

Into appropriate pocket holes disposed in the three ribs of the smoothing instrument brass capsules were introduced in such a manner that their points were 1 millimeter below the surface of the ribs. The upper parts of the capsules were embedded in screws which had been hollowed by boring, the capsules being thus secured in the pocket holes. The parts of the screws projecting over the surface of the ribs were filed off so that the said surface was smooth. The brass capsules had walls 1 millimeter thick and a total length of 30 millimeters. In their front part which had a length of 20 millimeters they had a diameter of 5.6 millimeters and in their back part which was designed as a lock they had a diameter of 9 millimeters. In their front parts, which were next to the surface of the ribs, the capsules contained a mixture of about 100 millicuries of krypton.sup.85 in the form of hydroquinone clathrate (= 40 milligrams) and 150 milligrams of LiH which latter when reacting completely with water sufficed to produce at 100.degree. C. pressure of 1100 atmospheres in the capsule which had a volume of 0.5 cubic centimeter. At its end the capsule was closed with a conical lead plug which had been pressed into it by means of a threaded pin. The place into which the screw was introduced had been filled with a cold-setting plastic so that no gas could escape through the threads after the screw had been introduced.

After the smoothing ribs had undergone an abrasion of 1.5 to 2 millimeters during the drilling operation the point of the capsule was opened, drilling fluid entered the capsule, dissolved the clathrate and by reacting with the propellent produced hydrogen which expelled the krypton.sup.85 from the capsule, so that it entered the ascending fluid. The krypton.sup.85 distributed in the fluid, one-third of the total quantity of krypton being contained in the first, uppermost cubic meter of fluid and the rest being contained in diminishing concentration in the remaining 9 of the 10 cubic meters. Immediately behind the fluid funnel a large area counter tube was arranged which had a surface of 260 sq. centimeters and was mounted on a float. The measuring arrangement comprising counter tube, cathode follower, cable and ratemeter had a blind counting rate of 600 impulses per minute.

Result

After the first capsule had been perforated by abrasion in the earth's formation 3.4.times. 10.sup.4 impulses per minute were first indicated. After the first circulation (82 minutes) only 4.times. 10.sup.3 impulses per minute were indicated had further dropped to 1.2.times. 10.sup.3, no considerable increase of the degree of mixing with the fluid taking place. The experiment shows that 10 millicuries of krypton.sup.85 which corresponds to five times the blind counting rate are sufficient to produce an alarm. Also, after another three or four circulations the activity drops to 1 percent of the value first indicated, so that further indications will not be disturbed.

Claims

We claim:

1. A drilling tool containing in a closed cavity therein krypton.sup.85 or a compound thereof, as a gaseous nonionogenic the cavity being so positioned in the tool that the krypton.sup.85 or the compound thereof is liberated when the tool has been subjected to the highest permissible amount of wear.

2. A tool as claimed in claim 1, wherein the krypton.sup.85 is present in the form of an inclusion compound.

3. A tool as claimed in claim 1, wherein the krypton.sup.85 is present in the form of a hydroquinone clathrate.

4. A process for marking a drilling tool to indicate when the highest permissible amount of wear has taken place, the improvement of which comprises inserting in a cavity in the tool krypton.sup.85 or a compound thereof as a gaseous nonionogenic indicator.

5. A process as claimed in claim 11, wherein the krypton.sup.85 is present in the form of an inclusion compound.

6. A process as claimed in claim 11, wherein the krypton.sup.85 is present in the form of a hydroquinone clathrate.

7. In a process for marking tools and instruments for drilling deep wells with the aid of a circulating drilling fluid using radioactive tracer substances which serve to indicate the occurrence of the highest permissible amount of wear and which are embedded in bore holes in the tools or instruments in such a manner that upon the occurrence of the highest permissible amount of wear, these tracer substances occur in the circulating fluid and with it are carried to the earth's surface, the improvement which comprises using krypton.sup.85 as a gaseous nonionogenic radioactive tracer substance in conjunction with a propellant expelling the same from the tool into the fluid.

8. A process as claimed in claim 7, wherein the krypton.sup.85 is present in the form of an inclusion compound.

9. A process as claimed in claim 7, wherein the krypton.sup.85 is present in the form of a hydroquinone clathrate.

10. In a process for drilling deep bore holes by means of a drilling tool containing indicating means said drilling being aided by a fluid, the improvement which comprises:

a. placing in the tool in a gastight cavity krypton .sup.85 and an agent to expel from the tool krypton.sup.85 if needed, said cavity being placed at a distance away from a wear surface with a filling opening away from said wear surface for filling said cavity in the tool, said distance corresponding to the permissible amount of wear of said surface,

b. indicating a permissible amount of wear of the drilling tool by puncturing said compartment by abrasive wear of said tool, and

c. recording a wear indicating occurrence of said krypton.sup.85 aided by the drilling fluid acting as a carrier for krypton.sup.85.