US2153802A - Method and apparatus for continuous exploration of bore holes - Google Patents

Description

April 11, 1939.

J. J. JAKOSKY METHOD AND APPARATUS FOR CONTINUOUS EXPLORATION OF BORE HOLES File'd Nov. 25, 1956 2 Sheets-Shaet l i 1939- J. J. JAKOSKY METHOD AND APPARATUS FOR CONTINUOUS EXPLORATION. OF BORE HOLES 2 Sheets-Sheet 2 Filgd. Nov. 23, 1936 0 OOOO0O OOOOO OOO 2 l Patented Apr. 11,1939

UNITED STATES PATENT OFFICE METHOD AND APPARATUS FOR CONTINU OUS EXPLORATION OF BORE HOLES John Jay Jakosky, Los Angeles, Calif. Application November as, 1936, Serial No. 112,207

This invention relates to a new method and apparatus constituting an improvement in the art of determining the character and nature of the strata traversed by a bore hole, and more particularly to the determination of the characteristics of the strata traversed by a bore hole while the drilling operations are in progress.

A prior method has been suggested for this work, embodying a drill pipe having an insulated internal conducting tube, or an insulated-conductor extending down inside of a drill pipe, and a bit which is insulated from the drill pipe. The current flows from this insulated bit into the strata. The other terminal of the current cir- "cult is at the surface of the ground near the mouth. of the hole, or it may be the drill pipe itself. Suitable measuring instruments are included in this circuit for measuring variations in current and/or potential as'the bit descends the hole. After repeated and extensive tests at commercial operations the method has proven to be of limited use due to the difliculty of properly insulating the drill pipe from the bore hole itself, or of passing an insulated wire down the inside of the drill pipe. Another practical 'diificulty in the latter method is to obtain proper insulation of the bit from the drill pipe. Insulating materials oi this type are not usually of sufiicient mechanical rigidity and ruggedness to withstand the severe conditions encountered in drill work. In the method which is described in accuracy.

An object of the invention. is to provide a method and apparatus which will give a visible, instantaneous, and preferably permanent record at the surface, as the drilling operations progress. Such records are of great value during drilling operations, especially in areas where the drilling must be stopped at a known horizon or strata, as for instance when drilling into a high pressure oil sand, or when drilling through an oil sand, and where water may be encountered by a stratum underlying the oil sand. By means of the present method and apparatus suitable A further object of the invention is to provide means for measuring the natural earth potentials and other potentials while minimizing the effect of the horizontal component of the natural earth currents. V 1 5 More specifically, the subject of this invention comprises an electrical method of underground surveying, wherein the electric current flows from the drilling bit of an ordinary drilling apparatus, through the subsurface, to a distant electrode located on the surface of the ground remote from the drilling apparatus. The method and apparatus of this invention is an improvement on my pending application Serial No. 94,063, filed August 3, 1936. In the present invention 'conductive efiects of the fluid in the drill hole may be minimized by the employment of fluids of relatively low conductivity, such as oil-clay suspensions, or other oil or drilling fluids of low conductivity.

An important feature of this invention is the employment of the distant electrode, the advantages of which have been brought out in my pending application Serial No. 55,600, filed December 21, 1935. It will be seen that if an electrode adjacent the hole were employed, or a direct connection made to the surface casing as in present conventional methods of electrically exploring bore holes or portions thereof after they have been drilled, that the current would largely flow between the near-surface and surface drilling apparatus, and the adjacent surface electrode. Under such conditions, a suflicient portion of the current would not flow from the drill itself to give a readable or detectable change on the total current flowing in the circuit, as different strata are penetrated. I

While the foregoing practical advantages of .this improvement are of major importance, the

' bore hole and drilling apparatus for -use in accordance with this invention;

Fig.2 is a diagrammatic illustration of one form of electrical circuit which may advantageously be employed in conjunction with various types of drilling apparatus such as that shown inFig. 1;

Fig. 3 illustrates an arrangement which may be employed for directly recording the relationship between depth and electrical characteristics; 56

formof electri Fig.4 is-a proper source of motive power la. The rotary table, by means of the Kelly joint 2, transmits a rotary motion to the drill stem 3 extending within the drill hole H. At the end of the drill stem is the drilling bit 4. The Kelly joint is supported at its upper end by the swivel head ll. These parts constitute the usual type of rotary drilling equipment and need not be described in detail herein. A connection terminal ii is in electrical contact with the swivel head and associated drilling mechanism including the drill stem! and bit I, and is connected to one side of a suitable electrical energizing and circuit, such as hereinafter described.

Thedrillstemisshownprovidedwithprotectors P spaced atintervals along the length thereof for the purpose of minimizing or preventing electrical connection between the drill stem and the wall of the hole H. Such protectors may comprise rings of oil-resistant rubber or other insulating material placed about the drill stem at convenient intervals. Commercially available protectors are satisfactory and I have found it preferable to employ solid rubber protectors rather than the composite rubber-metal type which are usually constructed with metal clamps for engaging the drill stem and with rubber projections extending from the clamps. However, it is within the scope of this invention to use protectors of any type which will properly space and insulate the drill stem from the wall of the hole.

The bore hole H is shown as filled or substantially filled with an insulating or poorly conducting liquid medium F, which completely surrounds the drill stem 3 throughout substantially its entire length and insulates said drill stem from the wall of the hole. The liquid medium F may advantageously comprise a poorly conducting drilling fluid, such as a suspension of clay or other colloidal or weighting material in oil or other poorly conductive liquid. It will be appreciated that although I find it preferable to utilize the protectors P to prevent or minimize contact of the drill stem with walls of the bore hole, such protectors may in some cases be dispensed with and satisfactory results may still be obtained. The oil drilling fluid or other non-conductive fluid will in general form a relatively non-conductive mud sheath along the walls of the drill hole, es-

pecially if the wall rock-is not highly impregnated with water, so that even if the drill stem comes in contact therewith at one or more points along its length, the electrical path afforded by such contact will in general be highly resistant and will have little effect on the electrical measurements taken in measuring circuits which will be sub sequently described.

The present invention is also applicable to various types of rotary drilling equipment and drilling bits, including various devices for obtaining rock samples, and to core-bits. In addition, the invention may be applied to cable drilling apparatus wherein a heavy bit assembly impacts andcutsintotheearthbybeingalternately raised and lowered on a steel cable. The inven tion may also be applied to hydraulic drilling methods employing a pipe, extending into the bore hole, from which liquid under high pressure is being discharged. In short, the method and apparatus of this invention may advantageously be employed with any exploring and/or drilling apparatus which employs electrically conductive drilling equipment and an insulating or poorly conductive fluid around the drill stem.

One type of electrical circuit which may be employed for measuring the changes in resistance or impedance, as the drill penetrates the earth, is illustrated in Fig. 2. It will be understood, however, that any of the conventional circuits may be employed for measuring changes in ourrent, potentiahreslstivity, impedance, or otherresistance) in the case of direct current, or ad-,

mittance (the reciprocal of impedance) in the case of alternating current.

Electrical connection to the rotary drill stem may be made by means of terminal Ii, as above described, and the other contact to the earth is made by means of a large surface electrode 5, placed a considerable distance from the hole.

.This distance is preferably one-thir'd (or more) of the contemplated depth of the hole or of the depth through which measurements are to be taken for any given position of the electrode 5. The distant electrode 5 is firmly imbedded in the earth in such a manner as to minimize the contact resistance. It is essential that this resistance be of a fixed nature, inasmuch as any variation in it will cause variations in the recorded data. I have found that the electrode should preferably 'be placed a distance of two to five feet-below the surface of the ground, in order to prevent changes in conductivity due to changes in temperature between night and clay, and changes caused by drying out of the soil or its wetting after a rain. I One arm of the conventional Wheatstone bridge indicated generally at W is a variable resistor 8 which may be adjusted to equal the raistance of thewell-distant electrode circuit at the start of the drilling and measuring operations. The power supply means l3 for the Wheatstone bridge may be any source of constant potential supply, either direct current, or low frequency or high frequency alternating current. In a majority of cases, it is convenient to employ the 60 cycle alternating current available at the rig, In the latter case, it is preferable to employ a small, well insulated transformer, in order to isolate the measuring circuit from the alternating current supply which is oftentimes grounded. The power supply is impressed across the bridge circuit at points cd. An ammeter 'l is employed for showing the total current flowing in the bridge circuit,-

and a second ammeter 8 shows the current flowing in thetwell-distant electrode circuit. Connected across the arms of the bridge, between points a -b, is a vacuum thermocouple 9, which measures the changes in potential produced across the bridge, as the conductivity of the aicasoa continuously recording meter I 2, which usually records variations in the bridge potential versus time. In case the potential supplied by source It is subjected to material fluctuation, I prefer to employ'a compensating thermocouple 9' whose input is connected in shunt with a variable resistance It in the line leading to the bridge andwhose output is connected in series with the output of thermocouple 9, but in reverse relation thereto. a

It will be seen that any type of measuring arrangement may be employed, but the vacuum thermocouple as described constitutes a particularly stable system I for measuring these ratus, an electric current is supplied to the circhanges during the drilling operation. The vacuum thermocouple has a suillcient time lag, which minimizes the minor and unimportant variations caused by changes in electrical conductivity as the drill stem and drill momentarily come in contact with diiferent portions of the drill-hole wall and easing, as the drill and drill stem rotate. As pointed out above, the contact of the drill stem and the wall of the bore hole will ordinarily not cause any substantial variation in the current flow, due to the insulating mud sheath employed. However, the use of insulating protectors on the drill stem will tend to prevent such, contacts. Due to the low power output of the vacuum thermocouple, it is preferable to employ it in conjunction with some type of sensitive galvanometer and photographic recording sy m In tamng measurements with the above appacuit from source It, said current flowing through the formation penetrated by the drilling apparatus. The drill bit 4' normally makes good electrical contact with the bottom or walls of the bore hole and serves as one electrode, while the drill stem is substantially insulated from contact with,the walls of the hole throughout its length, by the poorly conducting fluid medium surrounding said drill stem, either with or without the ditional spacing and insulating effect of the spacers P.

Application of this invention to conventional drilling operations may be summarized briefly as follows:

Measurements y be made at any e after drilling operations have started. The measurements should begin, however, at a time when the strata exhibit characteristic electrical changes which may be employed for correlation pses. In some areas, important electrical markers (strata which may readily recognized by characteristic changes in electrical properties) manifest themselves many hundreds of feet above the oil sands, while in other areas important markers are encountered adjacent to the oil sands. In metal mining operations, the measurements should begin prior to the time the drill penetrates the mineral-be formations. For location of water-bearing horizons the measurernents also should begin prior to the time the bit penetrates the water-bearing formation.

The electrical i apparatus, diagrammatically illustrated in Fig. 2, is connected to the drilling mechanism and the distant electrode by means of suitable insulated wires. The bridge resistor 8 is adjusted to give a suitable position of the recording pen or light beam on the recording sheet of the meter 12. If variations in power supply are noticeable, the resistor it should be adjusted to minimize'these variations.

It will be recognized that when the drill is penetrating a medium of homogeneous conductivity, the recording line will tend to follow a general substantially straight course having a certain slope, due to gradual and uniform change in the potential across the bridge between the points a-b as the bit descends. When the drill penetrates a stratum of different electrical conductivity there will be a change in the direction of the recording line, due to the resulting difference in the rate of change of the potential across the bridge. If, for instance, the drill passes out of a good conducting medium into a highly resistant medium, or vice versa, there will be a change in the slope of the line, due to the change in resistance between the drill bit and the distant electrode. Interpretation of the data will necessitate, however, that consideration be giventhe diiferent rates of penetration of the drill in strata of different degrees of hardness. For instance, the-drill will penetrate 10.0 feet of a soft shale formation in less time than it will penetrate 10 feet of a harder formation. As a result the slope of the line is dependent as much upon the rate of drill penetration as upon the electrical properties of the strata. Before interpretation may be made of the record, under the extreme conditions Just mentioned, the depth of penetration of the drill at given time intervals must be obtained from the driller's records. Final interpretation is therefore based upon changes .in slope versus depth of penetration.

It should be noted that there are two major earth circuits which influence the readings, one circuit from the drill bit electrode to the distant electrode, andanother circuit from the surface equipment, the rig, etc., to the distant electrode.

Due to the great spacing between the drilling apparatus and the distant electrode, the diner-ence in potential between the drill bit and the drill rig is negligible compared to the potential difierence between the distant electrode and the drill rig so that there will be practically no current flow through the earth between the bit and the rig. Furthermore, the electrical properties of the circuit between the rig and other surface equipment, and the distant electrode will remain constant for any position of the drill bit; therefore, the changes in electrical properties of the earth circuit in cluded between the distant electrode and the drill bit electrode will appear as variations in the readings obtained on the electrical measuring inst r' a cute.

Another type of measuring and indicating apparatus which has proven satisfactory utilizes a triode vacuum tube, having its input (grid-filament) circuit connected across the arms a-b of the bridge, in place of the vacuum thermocouple 9., The plate circuit of the vacuum tube is connected to a recording chart, for recordingvariations in current versus time. arrangement has the advantage of giving more power, which may be employed for actuating a heavier type of recording mechanism. If the trlorie tube is used, a pen actuated stylus may be employed, giving a direct, visible reading of the The vacuum tube nected as described in the above paragraph. A record of this type gives considerable information to the drilling superintendent, besides merely the electrical properties of the strata passed through. For instance, all informationrelative to actual time of drilling, time consumed in going in and out of the hole; and time idle, is shown clearly on the chart. Sharp breaks in the recorded curve, or deviations from the general direction thereof, will indicate variation in the electrical characteristics of the strata penetrated by the drill, and differences in the slope of different portions of the curve will indicate difierences in conductance or other electrical characteristics of the strata at two corresponding depths. I

It will readily be seen that instead of using the continuous roll-type paper recording system, it is possible to employ the conventional circular'rebreak or change in direction of the spiral.

Since the chart records time versus electrical properties, it is necessary to obtain from the driller's log the depth which the drill has reached for any 'certain period of time. In this man- 'ner the changes in electrical properties of the strata at difierent depths can be ascertained.

This invention also contemplates a recording method showing the relationship between electrical properties and actual depth. This may comprise a depth-recording system utilizing a measuring wheel: frictionaliy held against the drill pipe'as it descends the hole. This measuring wheel may actuate a gear system which in turn drives the recording paper.

between electrical properties and actual depth is" diagrammatically illustrated in Fig. 3. In this figure, the drilling assembly comprising 9. Kelly joint 2, supported by the swivel head II, and the drill pipe and bit in the hole is supported by a sheave wheel it. Steel cables I! are threaded through the sheave wheel over the crown block 20 at the top of the derrick 2|. A small steel flexible cable 22 is connected to the sheave wheel II. This cable passes over idler pulleys 23 and 23a, to the recording mechanism which is located at a convenient place on the derrick floor. The recording mechanism is actuated by movement of the cable 22 as the sheave block 18 moves upward and downward during the drilling opera-- tions. The actuating mechanism comprises a drum 24 on which the flexible cable 22 is wound.

A sufiicient number of turns are placed on the drum in order to allow the sheave block it its full extent of travel during drilling operations. Two ratchet pawls 25 and 25a are employed for obtaining the proper direction of rotation for the recording paper 26. When the drilling operations are in progress, that is, when the bit is on the descent, the pawl 25a engages the ratchet wheel 3|. This ratchet wheel drives a sprocket wheel 3! which meshes with perforations along the edge of the recording paper 2!. As thebit descends the hole the paper 28 is moved forward and a record made by means of the pen recorder, shown diagrammatically at 32, which may-be comparable in function to the recording meter l2 and may be connected in the measuring circuit in the same manner as said meter I! in Fig. 2. An idler wheel 29 is employed for rig dly supporting the paper as it passes the recording pen. The unused paper is on spool 28 and the used paper, is on spool 21. Both of these spools are driven by means of proper spring belts connected to the driving assembly 30 and 3|. The idler I! is preferably placed from 12 to l8 inches from the drive sprocket Si in order that visual observations may be made of the record as the drilling progresses. When-the pawl 25a engages the ratchet wheel ll, it will be seen that the paper is moved forward as the bit descends the hole. After the desired increment of drilling operation has been acompleted and it is desired to come out of the hole, the pawl 25a is manually disengaged from the ratchet wheel Ill. The Kelly joint is now disengaged from the drill stem, and another section of drill stem inserted in the assembly. The bit is now lowered to the bottom of the hole and the pawl 25a again engaged. As the drilling operations are resumed, the record is continued. When it is desired to come out of the hole, the

pawl a is disengaged. In some instances it is desirable to reverse movement'of the paper, and this may be accomplished by engaging pawl 25. By means of an interlocking control between the pen recorder 32 and the pawl contacts, 'no record is usually made on the paper when its direction of movement is reversed;

When it is desired to record natural earth'potentials, the drilling system and the distant electrode are. connected to the input circuit of any suitable measuring system, for instance, to the input circuit of a vacuum thermocouple, the outi put circuit being connected to a recording meter in a manner comparable to that above described. Changes, and often reversals, in the natural earth potentials'are obtained as'the drill penetrates different strata. These changes in potential are probably due to (l) the non-uniform distribution of lateral flowing current with depth, and (2) differences in chemical properties of the natural earth waters in the various strata.

' Referring toFig. 4, I have shown a circuit arrangement .whereby earth potential measurements may be taken between-a drill bit and a distant ,potential electrode alternatively with measurements of potential between said distant electrode and an electrical energizing circuit established between a distant energizing electrode and the drill bit. Distant potential electrodes E1 and E: located at a considerable distance from the drill hole H are shown connected through suitable insulated conductors 4| and 42 to a common conductor 43 which is connected to the variable tap of a potentiometer 52. A drill bit 44 is shown in contact with the bottom of the hole H and is in electrical connection with a drill stem 45 which is connected through a suitable conductor to one side of a measuring device M, the other side of said measuring device being connected to the other side of the potentiometer 52 through a conductor 41. The potential between the con- *ductors l3 and 41 may be made variable by com necting a battery 5| across the potentiometer and varying the potentiometer 52 according to wellknown methods. It will be noted that no insulating protectors are shown about the drill stem ll. Protectors as shown in Fig. 1 may be usedif desired; however, under some conditions the awaeoe strata for a short distance and will tend to term a high resistant layer along the hole H which will satisfactorily insulatethe length of the drill stem 55 from the hole The utilization of two or more potential electrodes connected together at a common point, such as the electrodes E1 and E2, connected together bythe conductors ti and 2 to the common conductor 63, is one important feature of this invention. Such an arrangement tends to eliminate potential variations due to changing earth currents, which currents are ordinarily a varying source of error and are present atv all times, making it practically impossible to duplicate survey results. This feature has been particularly pointed out in my pending application Serial No. losses, filed September 28, 1936, and it will sumce to say that the reference electrodes such as E1 and E2 should be spaced with respect to hole H and connected together in such manner that the'horizontal component of the natural earth currents in the neighborhood of the bore-hole will have no efiect on the reference potential no matter what the direction or magnitude of the earth currents. In areas where extreme variations in earth currents are encountered, more than two potential electrodes may be advantageously employed. It has been found that normal earth currents flow substantially horizontal, and have a very minor vertical component. It will be appreciated'that in the example illustrated, Fig i, the electrodes E1 and E2 are substantially equidistant irom the drill hole H and at a considerable distance therefrom, and that E1, E2, and H are substantially in a line-with one another, although this symmetrical arrangement is not entirely necessary.

The natural earth potential between the reierence points E1 and E2 and the bottom of the drill hole, at the position of the drill bit dd, may now be measuredwith the portion oi the electrical circuit described above. Since the electrodes E1 and E2 are located at a considerable distance from the drill hole and are connected together through conductors ti and 412, the juncture of said conductors and the conductor dd is at a more or less average potential of the points E1 and E2 and is considered as a reference potential and measurements may be taken with the measuring device M, which may comprise a recording potentiometer, which are indicative of the vertical commnent of the earth potential at the position of the drill bit dd. In order to establish a suitable zero level on the recording meter record which is indicated at dl in Fig. 5, the potentiometer 52 may be adjusted to bring the indication of the earth potential to any convenient point on the recording medimn it. It will he appreciated that as the bit at bores into the earth, the potential will vary and it may he necessary at time to time to readjust the potentiometer 52 to keep the potential readings onthe record; also it may he necessary to reverse the polarity of the battery oil in some instances to maintain the desired control of the recording.

I have also shown the distant energizing electrode E3 connected through an insulated condoctor as including an ammeter A to a source or variable potential S, the other side of said source S being connected to one side of a switching means M and the-other side of said switching means being connected through a conductor dd to the conductor dd which is connected to the drill stem 45. The, source S is ,preferablyo constant current generator provided with suitablemanuai or automatic means for maintaining a constant current reading on the ammeter A. The switching means 5d may comprise stationary quadrants 55 and t6 and a rotor bar or connected to a suitable time-operated shaft so that if, for example, the time-operated rotor ti is turning atfthe rate of one revolution in do minutes, connection will he established between the quadrants dd and 55 by the her tll every 2d minutes and the connection will he maintained for ten minutes.

The distant energizing electrode E3 is preferahly placed at a considerable distance from the bore hole E, that is, a distance equal to or greater than jone third the depth to which the hit dd is carried; the electrode E3 is preferably placed outwardly oi the electrode E2 so that the electrode he lies between the electrode F3 and the hole H... The electrodes El, E2, E3 and the hole H are preferehly substantially in a line; however, this is not a requirement for operation, nor is it necessary for the electrode E3 to he further away from the hole H than the electrode E2. The electrodeEz may he at any position where suficient energy will flow inthe earth to create a measurable po tential hetween electrodes L; and E2, and the hit dllor drill stern It may he readily seen that current flow between the drill bit dd through the earth to the electrode Es will influence the potential of adjacent points on the surface of the earth and that the potential or any of said last-named points will he a function'or" the current distribution through the earth, which is indicative of the nature of the strata, and a function of the current in said circuit. By maintaining a constant current through the earth circuit interpretation will be greatly simplified, although results may be interpreted ii variations in current are recorded along with pomntial measurements. it variable current energization is employed, the meter A should preferably he or a recording type, to allow proper interpretation of the potential record made by recording meter when connection is estahlishw between the quadrants lid and so the measuring means M will give indications. which are indicative of the potential of he as influenced by the ciurent now from E to. the drill hit 65; these indications will also heinfluenced by the vertical component of the natural earth potentials but will not he annreclahly efiected hy the horizontal components of menstrual earth currents as pointed out alcove. When connection is hrolten between said quadrants the meter M will give indications of natural earth potentials as above descrihed.

Referring particularly to Fig. 5, I have shown an example oi. a record which may he obtained with the apparatus shown in Fig. The solid rotor oi the ssvltchine means it does not establish contact with the quadrants dill and'dt;

when the rotor Ell contacts said quadrants the stylus will move across the record as at tie and trace a record, for example of potential, at tic tor the length of time said connection is maintained. at the end of said time the contact will aid Fill

be broken and the stylus will move to the left along 62b and trace the curve 62a. Thus it may be seen that by dotting in the lines between the adJacent portions oi? the curves 62b and 620, a continuous record of the earth potential and potential indicative of earthconductivity and the nature and characteristicsof the strata may be plotted simultaneously on the single recording medium.

- Methods and apparatus in which measurements are taken indicative of the potential during successive energizing current pulses and during the intervals between such current pulses as described above are more fully described and claimed in my copending application Serial No. 230,963, filed September 21, 1938.

It will be appreciated that suitable compensating networks may be inserted in the circuit of'the measuring means M and in operative association with the switching means 54 for adjusting the relative positions and amplitudes of the earth potential curve 62b and potential curve 62c as will readily be apparent to those skilled in the electrical art.

It will be understood that since the chart shows electrical properties versus time, it will be necessary to obtain the depth for any given time from the driller's log in order to correlate the electrical data with depth of the drill hole.

It will also be understood that, instead of taking continuous electrical measurements as above described, a series of separate electrical measurements may be taken at suitable frequent intervals of time or depth, the purpose being, in general, to obtain measurements of the electrical characteristics of the portion of the earth included electrically between the drill bit and the remote electrode with the drill bit positioned at diflerent depths within the earth.

It will be further appreciated. that the metfibd and apparatus of the present invention, embodying the use of the drill bit as one electrode, another electrode connected to the earth at a position remote from the bore hole, and a poorly conducting fluid medium within the bore hole and around the drill stem, either with or without insulating spacers on the drill stem, may be employed in measuring variations in any desired electrical characteristic of the strata traversed by a bore hole. Thus, I may measure variations in natural earth potential, or variations accompanying the flow of an energizing current passed through the earth, and said energizing current may be applied between the same electrodes as those employed in taking measurements or between separate electrode means. Where an energizing current is employed, it may be either unidirectional or alternating high or low frequency, and measurements may be taken showing variations-ln resistance, impedance, conductivity, dielectric value, phase angle, power loss or other electrical characteristic, as set forth in my Patents No. 2,038,046 and No. 2,140,798 and in my pending application Serial No. 108,022.

I claim:

1. In the drilling of a bore hole with a drilling apparatus comprising a drill stem extending within the bore hole and a drill bit at the lower end of said drill stem, the method of exploring the strata traversed by the bore hole, which comprises: taking a measurement in an electrical circuit including the drill stem, the drill bit as one electrode, another electrode connected to the earth at a position remote from the bore hole,

and the portion of the earth included electricalbit electrode is moved to different depths in said bore hole.

2. In the drilling of a bore hole with a drilling apparatus comprising a drill stem extending within the borehole and a drill bit at the lower end of said drill stem, the method of exploring the strata traversed by the bore hole, which comprises: taking measurements indicative of electrical conductivity in an electrical circuit including the drill stem, the drill bit as one electrode, another electrode connected to the earth at a position remote from the bore hole, and the portion of the earth included electrically between said electrodes; and repeating such measurement to determine variations in the electrical conductivity of said included portion of the earth, with the drill bit electrode at different depths within the bore hole, while maintaining a body of poorly conductive fluid in thebore hole and around said drill stem, said other electrode being sufficiently distant from said bore hole so that variations in said measurements will be produced by changes in the electrical conductivity of the different portions of the earth included electrically between said electrodes as said drill bit electrode is moved to difl'erent depths in said bore hole.

3. In the drilling of a bore hole with a drilling apparatus comprising a drill stem extending within the bore hole and a drill bit at the lower end of said drill stem, the method of exploring the strata traversed by the bore hole, which comprises: taking measurements indicative of electrical impedance in an electrical circuit including the drill stem, the drill bit as one electrode, another electrode connected to the earth at a position remote from the bore hole, and the portion of the earth included electrically between said electrodes; and repeating such measurement to determine variations in the electrical impedance of said circuit with the drill bit electrode at different depths within the bore hole, while maintaining a body. of poorly conductive fluid in the bore hole and around said drill stem, said other electrode being suflicientiy distant from said bore hole so that variations in said measurements will be produced by changes in the electrical impedance of the difi'erent portions of the earth included electrically between said electrodes as said drill bit electrode is moved to difierent depths in said bore hole.

4. In the drilling of a bore hole with a drilling apparatus comprising a drill stem extending within the bore hole and a drill bit at the lower end of said drill stem, the method of exploring the strata traversed by the bore hole, which comprises: takingmeasurements indicative of electrical resistance in an electrical circuit including the drill stem, the drill bit as one electrode, another electrode connected to the earth at a position remote from the bore hole, and the portion of the earth included electrically between said electrodes; and repeating such measurement to determine variations in the electrical resistance of said included portion 01' the earth, with the drill bit electrode at different depths within the bore ma'wmie maintaining a body of poorly conductive fluid in the borehole and around said drilljstem, saidother electrode being suiiiciently distant from said bore hole so that variations in said measurements will be produced by changes in the electrical reof said drill stem, the method of exploring the.

diflerent depths in strata traversed by the bore hole, which oom-' prises: passing an electric current through the earth between the drill bit as one electrode and another electrode connected to the earth'at a position remote from the bore hole, and measuring variations in an electrical characteristic of the earth within the path of such current flow as said drill stem is extended to diflerent depths,

while maintaining a body of poorly conductive fluid in the bore hole and around said drill stem, said other electrode being sumciently distant from said bore hole so that variations in said measurements will be produced by changes in an electrical characteristic of the diiferent portions of the earth included electrically between said electrodes as said drill bit electrode is moved to different depths in said bore hole. 6. In the drilling of a bore hole with a drilling apparatus comprising a drill stem extending within the bore hole and a drill bit at the lower end of said drill stem, the method of exploring the strata traversed by the bore hole, which comprises: passing an electric current through the earth between the drill bit as one electrode and another electrode connected to the earth at a position remote from'the bore hole. and. measuring variations in edectrical conductivity of the earth within the path of such current flow as said drill stem is extended to different depths, while maintaining a body of poorly conductive fluid-in-the bore hole being sumciently distant from said bore hole so that variations in said measurements will be produced by changes in the electrical conductivity of the different portions of the earth included electrically between said electrodes as said drill bit electrode ismoved to diflerent depths in said bore hole.

position remote from the bore hole, and measuring variations in electrical resistance of the earth within the path of such current flow as said drill stem is extended to difierent depths, while maintaining a body of poorly conductive fluid in the bore hole and around said drill stem, said other electrode being sufiiciently distant from said bore hole so that variations in said measurements will be produced by changes in the electrical resistance of the different portions of the earth included electrically between said electrodes as said drill bit electrode is moved to different depths in said bore hole;

8. In the drilling of a bore hole with a drilling apparatus comprising a drill stem extending withand around said drill stem, said otherelectrode in the bore hole anda drill bit at thelowerend of said drill stem, the method of exploring the strata traversed by the bore hole, which comprises: passing alternating current through the earth between the drill bit as one electrode and another electrode connected to the earth at a position remote from the bore hole, and measuring variations in an alternating current characteristic oi the earth within the path oi such current flow as said drill stem is extended to diiierent depths, while maintaining a body oipoorlycon ductive fluid in the bore hole and around said drill stem, said other electrode being sufliciently distant from said bore hole so that variations in said measurements will be produced by changes in 'an alternating current characteristic-oi the difl'erent portions of the earth included electrically' between said electrodes as said drill bit electrode is moved to different depths in said bore hole.

9. In'the drilling of a bore hole with a drilling apparatus comprising a drill stem extending within the bore hole and a drill bit at the lower end of said drill stem, the method of exploring the strata traversed by the bore hole, which comprises: passlng alternating current through the earth between the drill bit as one electrode and another electrode connected to the earth at a position remote from the bore hole, and measuring variations in electrical impedance of the earth within the path of such-current flow as said drill stem is extended to different depths, while maintaining a body of poorly conductive fluid in the bore hole and aroundsaid drill stem, said other electrode being sufiiclently distant from said bore hole so that variations in said measurements will be produced by changes in the electrical impedance of the diflerent portions of the earth included electrically between said electrodes as said drill bit electrode is moved to difi'erent depths in said bore hole.

10. In the drilling of a bore hole with a drilling apparatus comprising a drill stem extending within the borehole and a drill bit at the'lower end of said drill stem, the method of exploring the strata traversed by the bore hole, which comprises: passing alternating current through the earth between the drill bit as one electrode and another electrode connected to the earth at a position remote from the bore hole, and measuring variations in phase angle accompanying such current flow and'resulting from changes in electrical characteristics of the earth within the path of such current flow, as said drill stem is extended to diiferent depths, while maintaining a, body of poorly conductive fluid in the bore hole and around said drill stem, said other electrode being sufilciently distant from said bore hole so that variations in said measurements will be produced by changes in ,anelectrical characteristic of the diiierent portions of the earth included electrically between said electrodes as said drill bit elec trade is moved to different depths in said bore hole.

11. An apparatus for electrical exploration of bore holes during the process of drilling, which comprises: a drill bit electrode in electrical connection with the earth within a bore hole; a drill stem electrically connected to said drill bit} a body of poorly conducting fluid in said bore hole in position to partially insulate said drill stem from said borehole; an electrode connected to the surface 'of the earth at a position remote from said bore hole; and electrical measuring means named electrode for indicating changes in an electrical characteristic of the earth included between said drill bit electrode and said last-named electrode as said drill bit electrode is moved to diflerent depths, said other electrode being suflicientiy distant from said bore hole so that variations in said measurements'g will be produced by changes in an electrical characteristic of the difierent portions of the earth included electrically between said electrodes as said drill bit electrode is moved to different depths in said bore hole.

12. An apparatus as set forth in claim 11, and further comprising insulating protector means secured to said drill stem at intervals along the length thereof for preventing contact of said drill stem with the sides of said bore hole.

13. An apparatus for electrical exploration of bore holes during the process of drilling which comprises: a drill bit electrode positioned within a bore hole and in electrical connection with the earth therein; a drill stem electrically connected to said drill bit electrode and in electrical connection with the drilling apparatus on the surface of the earth; a body of poorly conducting fluid within the bore hole and around the drill stem in position to partially insulate the same from the bore hole; a plurality of reference electrodes connected to the surface of the earth and connected together and so positioned as to minimize the varying earth potentials produced by the horizontal components of the earth currents; and measuring means connected between said last-named electrodes and said drill stem for indicating variations in the vertical component of the natural earth potentials between said drill bit electrode and said other electrodes as said drill bit electrode is moved to different depths in the bore hole. I

14. An apparatus set forth in claim 13 and i'urther comprising: an energizing electrode connected to the surface oi the earth outwardly of said reference electrodes from said bore hole; power supply means connected to said energizing electrode and to said drill stem through switching means operable to alternately connect and disconnect said power supply means to said drill stem; said measuring means being operable to indicate variations in natural earth potentials when said switching means is in disconnected position and operable to indicate variations in an electrical characteristic of the earth included between said energizing and drill bit electrodes when said switching means is in connected position, as said drill bit electrode is moved to different depths within the bore hole.

15. In the driliing of a bore hole with a drilling apparatus comprising a drill stem extending within the bore hole and a drill bit at the lower end of said drill stem, the method of exploring the strata traversed by the bore hole, which comprises: passing an electric current through the earth between the drill bit as one electrode and another electrode connected to the earth at a position remote from the bore hole; and measuring variations in an electrical potential between two points within the path of such current flow as said drill stem is extended to different depths, while maintaining a body of poorly conductive fluid in the bore hole and around said drilistem, said other electrode being suiliciently distant from said bore hole so that variations in said measurements will be produced by changes in an electrical characteristic of the diiiferent portions of the earth included electrically between said electrodesas said drill bit electrode is moved to diii'erent depths in said bore hole.

JOHN JAY JAKOBKY.

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