US2700897A - Continuous electrical logging - Google Patents

Description

Feb. l, 1955 J. J. ARPS 2,700,897

CONTINUOUS ELECTRICAL LOGGI'NG' Filed Sept. 2C, 1950 2 Sheets-Sheet l Ff/Mj.

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gil/n Feb. l, 1955 J. J. ARPS CONTINUOUS ELECTRICAL LOGGING 2 Sheets-Shee?l 2 Filed Sept. 20, 1950 INVENTOR JAW Jaco 142/25,

ATTORNEY United States Patent Office 2,700,897 Patented Feb. 1, 1955 CONTINUOUS ELECTRICAL LOGGING Jan J. Alps, Tulsa, Okla.

Application September 20, 1950, Serial No. 185,849

8 Claims. (Cl. 715-152) This invention relates in general to electrical exploration of the geological strata traversed by earth boreholes and more particularly to methods and apparatus for the lslinliultaneous electrical logging and drilling of well boreo es.

In the conventional methods of electrical logging of earth boreholes as heretofore usually practiced, a source of electric current has been located at the surface of the earth outside of the borehole and a current therefrom has been applied, through an insulated cable lowered into the borehole, to a portion of the penetrated geological strata to be explored, and the results of such exploration transmitted back up the borehole to the earth surface through the same or separate insulated conductors in the cable. The provision of insulated conductors in a drilling well together with the drill pipe in such manner that drilling and electrical logging operations can be carried on simultaneously, has been found to be of doubtful practicability. Therefore, the usual practice has been to interrupt the drilling operation at intervals to permit the removal of the drill pipe from the borehole and the running of the logging apparatus suspended from a conductor cable in the borehole in the absence of the drill pipe.

This has the disadvantage that the precise control of the depth of drilling with respect to certain formations is difficult, with the result that in many cases the desired shale body or the possible productive formation may have been drilled through or passed up, possibly necessitating subsequent time consuming and expensive corrective measures before the next intended steps in the process of continued drilling or completion of the well can be undertaken.

Another disadvantage in the before described usual method of electrical logging resides in the well known fact that the liquid from the drilling fluid invades the penetrated formations surrounding the borehole, thereby changing the electrical characteristics of such formations for a substantial distance laterally from the borehole axis. Such invasion is progressive with time and if permitted to continue for an appreciable length of time, results in sufficient contamination of the formations to cause possible confusion in the correct interpretation of the electrical characteristics of the formations thus measured.

The before described difficulties are largely overcome by the present invention which does not require insulated conductors in the borehole at any time but provides for the transfer of the results of the electrical logging operations or other similar operations within the borehole to the earth surface without employing the usual interconnecting insulated conductors, and this can be accomplished while the drill pipe is in the well borehole and during drilling operations. The system of the present invention furthermore permits the electrical logging apparatus to be embodied in or contained within the drilling tools, and the process of electrical logging to be carried on simultaneously with the drilling of the borehole whereby the electrical logging measurements can be made of the freshly penetrated formations before excessive invasion of drilling fluid into the formation takes place.

Another advantage of the present invention resides in the substantially simultaneous drilling and logging of a formation which it provides, thereby permitting a continuous and more accurate determination of the depth of the borehole relative to the formations penetrated thereby, than is possible by the intermittent, alternate drilling and logging operations heretofore usually employed. In other words, by employment of the method and apparatus of the present invention an electrical log may be made and observed while drilling operations are in progress and the drilling operations modified as desired or stopped immediately at the time the electrical log being recorded indicates the desirability of such modication or stoppage.

Accordingly, an object of this invention is to provide a method and apparatus for electrical logging of geological strata traversed by a borehole in which the necessity of using an insulated conductor extending into the borehole to the logging apparatus within the borehole is avoided.

Another object of this invention is to provide an electrical logging system which permits the conducting of electrical logging operations and drilling operations simultaneously.

Another object of this invention is to provide a system for transmitting information from a point within a well borehole to a point outside of the borehole during drill- 'ng1 and while the drilling tools are present in the bore- The objects of this invention are attained, in brief, by utilizing the circulating drilling uid to carry hydrogen tracer gas to the top of the borehole. This hydrogen tracer gas is generated by electrolysis of the liquid portion of the drilling fluid at the exploring electrode, by the action of and in proportion to the exploring current which flows between such electrode and the adjacent surrounding borehole formations. Upon arrival of the thus generated hydrogen at the top of the borehole as conveyed in the circulating drilling fluid, it is separated and measured by means of a suitable hydrogen gas detector. Measurements thus obtained provide indirect continuous measurements of the exploring electrode current and therefore are indicative of the conductivity or resistivity gf 1the formations opposite the electrode within the bore- Other objects, advantages and features of novelty will be evident hereinafter in the more detailed description of the invention.

In the drawings which illustrate a preferred embodiment and mode of operation of the invention and in which like reference characters designate the same or similar parts throughout the several views:

Figure l illustrates the general arrangement of the apparatus of the invention as applied to a drilling well borehole.

Figure 2 illustrates alternative apparatus to be employed in connection with the apparatus of Figure l.

Figure 3 illustrates a modified form of the apparatus of Figure 1.

The apparatus is as follows:

Referring primarily to Figure l, a longitudinal section of a typical well borehole is shown, by way of example, having a loweruncased portion 10 and an upper portion in which a surface string of casing 11 has been set. Within the borehole is shown conventional rotary drilling apparatus comprising adrill bit 12, adrill collar 13 and a drill stem ordrill pipe 14 connected at its upper end through asquare kelly 15 to aswivel 16, which is in turn supported by ahook 17 suspended from a suitable drillingline traveling block 123 and from well dei-rick apparatus thereabove (not shown). The square kelly 15 passes through conventional gripping means in a rotary table 20 which is adapted to be rotated by means of the usual beveled gear and pinion drive illustrated at 21 and 22 respectively. Thepinion 22 is arranged to be driven, in accordance with usual practice, throughshaft 23 by a suitable prime mover.

The circulation passage through the drill stern andswivel 16 is connected throughflexible hose coupling 25 and piping 26 to a suitable drillingfluid circulating pump 27, the suction of which is taken, throughsuction inlet pipe 28, from a mud settlingpit 29. The upper end of the surface casing 11 which provides a return path for circulating drilling fluid from the borehole, is provided with a lateral outlet pipe 31 which extends into the upper end portion of a closedseparator chamber 32. The said lateral pipe 31 is provided inside of the separator chamber with a downwardly curved elbow 33. Below the elbow 33 and within theseparating chamber 32 are provided a plurality of oppositely positioned, inwardly slopingbafties 35. The lower end of theseparating chamber 32 is provided with aconical bottom 36 which leads into anoutlet pipe 37 which in turn extends downwardly and laterally into atrough 39 leading to the top of the settlingpit 29. C

Theseparator chamber 32 is connected to suitable hydrogen detecting and measuring apparatus as hereinafter described.Chamber 32 is connected at the top end by way ofpipe 40 and through avalve 42 to acham ber 43, containing an electrically conductiveheater fila ment 44, and thence through connecting piping to theinlet 46 of a suitable exhaust fan orblower 47 having a discharge oroutlet connection 48. Thebeforementioned inlet 46 of theblower 47 is also connected through anotherbranch pipe connection 49 to achamber 50, similar tochamber 43, containing an electrically conductingheater filament 51 similar tofilament 44, and thence the connection extends through connection 52 andvalve 53 into a lower portion of theseparator charnber 32 at 54.

The electrically conductingheater lament 44 is supported withinchamber 43 by means ofconductors 55 and 56 which pass through suitable sealed lead-ininsulators 57 and 58 in the walls thereof, and the electrically conductingheating filament 51 is similarly supported within chamber Si) by means of conductors 60 and 61 3 which pass through sealed lead-ininsulators 73 and 74. Conductors and 61 leading from thefilaments 44 and 51, respectively, make common connection at 62, andconductors 56 and 60 leading from the opposite ends of the filaments make connection with substantiallyidentical resistors 64 and 65 which in turn are connected throughconductors 66 and 67, respectively, to opposite ends ofresistor 68. A conventional voltmeter or galvanometer V is connected betweenconnection 62 and acontactor 69 which makes sliding contact with theresistor 68. The circuit thus formed is, in effect, that of a conventional Wheatstone bridge arrangement, Current is supplied to the bridge circuit, from asuitable battery 69, throughconductors 70, 71 and a variable resistor 72.Voltmeters 75 and 76 may be connected across thefilaments 44 and 51, respectively.Filaments 44 and 51 are preferably made of a material which has a high temperature coefficient so that small changes in temperature will cause comparatively large changes in the electrical resistance thereof. Suitable materials for these filaments are preferably those not subject to oxidation and may be, for example, a noble metal such as platinum, gold, nickel or alloys thereof.

Referring now to the lower end of the drill stem, thedrill collar 13 is provided with an outside insulating covering 77 which may be composed of an inner instilating sleeve ortubing member 78 fitting snugly over the full length of the drill collar from the top of thedrill bit 12 to the upper end of the drill collar. A pair ofspacedapart electrode rings 81 and 32 are carried by the insu- )ating sleeve 78 and are insulated from thedrill collar 13 thereby, said electrodes being normally exposed to contact with surrounding drilling fluid. These electrode rings may be made of platinum or a similar noble metal. Theinsulating sleeve 78 is covered above, below and between theelectrode rings 81 and 82 by a plurality of protective insulating ring members placed end-to-end as shown at 79. Such rings are preferably made of rubber or the like material and are of such thickness as to protect the recessed electrodes S1 and S2 and theinsulating sleeve 79 from abrasion by the borehole walls. Conventional casing protector rings may be here employed. Thedrill collar 13 is provided on its interior with a suitable fluid tight container or cavity schematically designated at 83 for containing abattery 84 and switching apparatus as hereinarter described.

Thebattery 84 has its positive terminal connected throughconductor 55, fluid circulation pressure operatedswitch 86 and conductor S7 with abrush 88. The negative terminal of the battery S4 is connected through conductor S9 with a brush 90. Brushes 38 and 90 are positioned to make electrical contact at diametrally opposite points with a reversingcommutator 91 having a pair of opposite,conductive commutator segments 92 and 93 insulated from one another and each of which extend around slightly less than half the circumference of theinsulating commutator disc 94. A pair of diametrally oppositebrushes 95 and 96 are positioned to make contact with thecommutator 91 at right angles to the diametral line of Contact ofbrushes 88 and 90, saidbrushes 95 and 96 being connected throughConductor 100 and 101 respectively with thebeforementioned ring electrodesl 81 and 82.

Thecommutator 91 is coupled for rotation, through a shaft 103 to amotor 104. Themotor 104 is adapted to be supplied with current frombattery 84 throughconductors 105 and 106 fromconductors 89 and S7 respectively Whenswitch 107 is closed. The iiuid circulation pressure operatedswitch 86 may be constructed in a manner similar to that disclosed in copcnding Arps application, Serial No. 68,930, now Patent No. 2,658,284.

Referring now primarily to Figure 2, recording apparatus is there illustrated employing a voltmeter or galvanometer V1 which may be the same or similar to the galvanometer or voltmeter shown at V in Figure l, theconductors 62 and 69 being adapted to make connection atjunction point 62 andmovable contact 69 respectively, in the hydrogen detection and measuring apparatus of Figure l. Thehand 110 of the voltmeter or galvanometer V1 carries at its outer end a pen which bears upon a chart or strip ofgraph paper 111 adapted to be moved betweenrollers 112 and 113 for the purpose of tracing a curve or making a graph as illustrated at 115. Thechart 111 may be driven by asuitable motor 116 coupled throughshaft 117 to one of the rollers such as theroller 113. The rate of drive of theroller 113 may be such that thechart 111 is moved at a given constant rate with respect to time or preferably at a rate or having a motion proportional to the longitudinal motion of thedrill stem 13 and accompanyingelectrodes 81, 82, into or out of the well borehole. This proportional motion may be accomplished by various suitable means such as, for example, employing aline 120 passing overpulleys 121 and 122 and extending between the travelingblock 123 and adrum 124, said drum being coupled to a Selsyn generator 12E: and the Selsyn generator in turn being coupled through suitable electrical connections, as shown at u, b and c, to a Selsyn motor at 116. Another apparatus suitable for this purpose is illustrated in Figure 2 of copending Arps applications Serial No. 619,629, filed October l, 1945, now Patent No. 2,524,031, and Serial No. 269,568, tiled Feb. l, 1952.

Referring now primarily to Figure 3, radioactivity of the formations may be measured by the apparatus modification there shown. A radioactivity radiation detector which may be of any conventional type such as the Geiger counter, ionization chamber or the like devices responsive to gamma rays, neutrons or the like radiations is connected throughbattery 131 acrossresistor 132.Resistor 132 is in turn connected throughconducotrs 133 and 134 across the input terminals of a suitable amplilier means A. One terminal of the output of the amplifier means A is connected throughconductor 135 to thebattery 84 and thence throughconductor 85. switch 86 andconductor 87 to the brush 38 of thecommutator 91. The other output terminal of means A is connected throughresistor 136 andconductor 137 to brush 90 of thecommutator 91. The amplifier device A may be of conventional design and such that the current fiow from battery through the output thereof bears a predetermined functional relationship to the input signal appearing acrossresistor 132, which in turn is representative of the radiation intercepted by thedetector 130.

The operation of the apparatus is as follows:

ln operation of the drilling apparatus of a drilling well, the drilling fluid which is usually an aqueous sus-A pension of clayey materials, is withdrawn from thepit 29 through thesuction pipe 28 and forced by means ofpump 27 throughpipe 26 andcoupling 25 into the top of theswivel 16 and thence down through the interior of thekelly 15,drill pipe 14,drill collar 13 and out through suitable discharge holes, as illustrated at S9, in thedrill bit 12. The circulating drilling 'fluid then News upwardly in the annular space formed between the borchole walls and the drill stem as indicated by arrow :33, and up through the surface casing 11, from the top of which it is finally discharged through the lateral discharge pipe 31 into the top of theseparator 32. in theseparator 32 the drilling uid passes or falls downward over thebaie plates 35 to the bottom of the chamber from where it is finally discharged throughpipe 37 into thetrough 39 from which it fiows into the top of the settlingpit 29 to complete the cycle of circulation.

Meanwhile, during circulation of the drilling fluid as hereinbefore described, the drill stem comprising thekelly 15,drill pipe 14,drill collar 13 anddrill bit 12, may be rotated by means of the rotary table 20 which is driven by the bevel gear andpinion 21 and 22 respectively, thepinion 22 being driven through theshaft 23 as beforementioned. Drilling operations in the borehole may thus be maintained.

During drilling operations or any other operations, when thedrill collar 13 is maintained in electrical contact with the drilling fiuid Within the borehole, and under conditions where the drilling fluid is being circulated, the fluid operatedswitch 86 is operated to close the circuit betweenconductors 85 and 87. A closed circuit is thereby formed across thebattery 84 permitting a continuous flow of current from the negative terminal of thebattery 84 throughconductor 89, brush 90,commutator segment 93,brush 96 and conductor 101, to electrode 82 and thence through the drilling fluid and through a portion of the adjacent formation and return through the drilling fluid to theelectrode 81,conductor 100,brush 95,commutator segment 92,brush 88,conductor 87, fluid operatedswitch 86 andconductor 85, to the positive terminal of thebattery 84. Since a portion of the formation surrounding the borehole adjacent theelectrodes 81 and 82 forms a part of the electrical circuit across thebattery 84, as before described, the current flowing in this circuit will consequently be directly proportional to or at least representative of the formation conductivity.

The passage of the direct current between theelectrodes 81 and 82 while immersed in the aqueous drilling fiuid will cause hydrogen gas to be generated by electrolysis and liberated at thecathode electrode 81. At the same time oxygen gas will be generated by electrolysis and liberated at theanode electrode 82. As is well known two volumes of hydrogen will be liberated at theelectrode 81 for each volume of oxygen liberated at the electrode S2. The amount of hydrogen gas which will be released at thecathode 81, per unit of time will be, in accordance with Faradays Law, proportional to the current passing betweenelectrodes 81 and 82, and consequently the amount of hydrogen released atelectrode 81 will be representative or indicative of the conductivity of the adjacent formation.

The conductivity of the drilling fluid in the vicinity of the electrodes S1 and 82 will of course also affect the total conductivity of the circuit across thebattery 84 to some extent but as is well known in this art, the effect of this conductivity is usually a substantially constant factor and its effect is relatively small as compared to the conductivity of the relatively large volume of surrounding formations. Actually the conductivity of the drilling fluid is often less than that of the surrounding formations. in any event, the effect of the conductivity of the drilling fiuid is substantially constant and can be corrected for. While thecommutator 91 has been shown and hereinbefore described as positioned to connect the positive and negative terminals of the battery respectively to theelectrodes 81 and 82 the commutator may obviously be positioned, by rotation 90 from the position shown to reverse these polarities, without affecting the mode of operation of the apparatus.

In some cases it may be desirable to apply an intermittently or periodically reversed current to theelectrodes 81 and 82 in order to avoid polarization effects or the deposition of colloids upon the positive electrode. In such cases theswitch 107 is closed manually prior to lowering the drill string into the borehole or by other suitable means after lowering the drill string into the borehole. Closing of theswitch 107 energizesmotor 104 which in turn drives thecommutator 91 through the coupling shaft 103. Rotation of thecommutator 91 results in periodic switching and reversal of the polarity of the potential applied from thebattery 84 to theelectrodes 81 and 82. The rate of rotation of the commutator and hence the frequency of reversal of the current or voltage applied to theelectrodes 81 and 82 should be sufficiently low to permit the desired electrolysis and Suitable frequencies for this purpose may be of the order of 0.1 to 10 cycles per second. The potential applied to the electrodes by the battery may be from a few volts above the polarization potential of 1.2 to 1.7 volts, to as high as 100 volts depending upon the current density used, the geometry and arrangement of electrodes, type of drilling fluid employed and other conditions.

The hydrogen gas which is liberated atelectrodes 81 or 82 in the case of the use of D.C. or atelectrodes 81 and 82 in the case of the use of intermittently or periodically reversed polarity, such liberation being in quantities representative of the conductivity of the adjacent formation as before described, is conveyed in the circulating drilling mud to the top of the well bore and up through the annular space in the surface casing 11 in the direction indicated byarrow 102 from where it passes through the lateral outlet pipe 31 and into the top of theseparator chamber 32. The drilling fluid containing the hydrogen gas is directed downwardly through theseparator chamber 32 by the elbow 33 from which it falls down through the chamber over the bafe plate 3S in counter-current contact with upwardly owing air, and finally the drilling fluid from which hydrogen has been removed, is discharged from the bottom of the separator chamber throughpipe 37 into thetrough 39 through which it ows in return to the settlingpit 29.

The air which passes upward in counter-current contact with the downwardly flowing drilling fluid within the separatingchamber 32 as before described, enters at the bottom throughpipe 37 which is only partially filled with the outwardly flowing drilling fluid as indicated by thearrow 34 and passes out of the top of the separating chamber, together with separated hydrogen throughpipe 40 andvalve 42 and thence the air-hydrogen mixture flows through thechamber 43 and in contact with theheater filament 44. The air, after passing through thechamber 43 and in contact with thefilament 44, flows on throughpipe 45 to theinlet 46 of theblower 47 and is finally exhausted from theblower outlet 48. At the same time a substantially equal amount of substantially hydrogen-free air is drawn into pipe 52 at apoint 54 from a lower portion of the separating chamber, and flows through thechamber 50 into contact with theheater filament 51 and thence throughpipe 49 to theinlet 46 of theblower 47 and is exhausted therefrom at 48 together with the air from theother branch pipe 45. By withdrawing air both from the top and from a lower portion of the separatingchamber 32 as before described, the air streams passing in contact with thefilaments 44 and 51 will thereby have nearly the same temperatures and humidities. These quantities of air may be equalized or otherwise adjusted as desired by means of thevalves 42 and 53.

The Whealstone bridge measuring circuit is initially adjusted by movement of the position of thecontact 69 upon theresistor 68 to a condition of balance under which the voltmeter V is zeroed. The current flowing through theheater filaments 44 and 51 are then adjusted by means of the variable resistor 72 such that these filaments are heated to a temperature below the point where any hydrogen mixture or any other of the conibustible gases passing over them will ignite. This ternperature can be carefully controlled, as before stated, by adjusting the variable resistor 72 and checking with thevoltmeters 75 and 76. The voltage applied will depend largely upon the total resistance of the heater filaments.

As before explained,filaments 44 and 51 are preferably made of a conductive material which has as high a temperature coefficient as possible so that a small difference in temperature between the filaments will cause a comparatively large difference in their electrical resistances, resulting thereby in a comparatively large unbalance of the measuring circuit which will be reflected in the meter V.

The thermal conductivities, expressed in calories per second per square centimeter per degree centigrade per centimeter, of the gases most likely to be encountered in the drilling fluid arc as follows:

Air 56.8 10*G Carbon dioxide 30.7X 106 Hydrogen, 0 C 327.0X10-6 liberation of hydrogen at each electrode to take place. Hydrogen, 100 C 369.0X10-6 arnese? Methane Nitrogen Oxygen (Handbook of Chemistry and Physics, 23rd edition, page 1456.)

Since, as is apparent from the foregoing table of thermal conductivities of various gases, the thermal conductivity of hydrogen gas is relatively high as compared to air, oxygen or any other gases normally found in drilling mud and which may be liberated in the separatingchamber 32, the presence of hydrogen in the air from the drilling huid and which passes through thechamber 43 will result in withdrawal of a greater amount of heat fromtilament 44 than the relatively hydrogen-free air passing through chamber withdraws fromiilament 51, thereby causing a greater cooling or reduction in the temperature offilament 44 than that offilament 51. The resistance of thefilament 44 will thus undergo a greater reduction than that of filament with the result that the bridge measuring circuit will be unbalanced in such a way as to retlect that unbalance in the voltmeter V. The amount of unbalance thus indicated by the voltmetcr V will, therefore, be indicative or representative of the hydrogen content or" the gas stream owing from thegas separator 32.

By plotting the concentration of hydrogen gas measured in the before described manner. against or in correlation with the depth of the borehole, by means of the apparatus illustrated in Figure 2, a log as illustrated at 115 will be obtained representing the formation conductivily versus depth. ln such measurements suitable precautions can be taken to correct for the distance between the bottom of the drill bit and the eliective position ofelectrodes 81 and 82. Also it may be necessary or dcsirable to adjust the drive mechanism moving thechart 111 to compensate for the time necessary for a given volume of the drilling uid to travel from a point in the borehole opposite theelectrodes 81, 82 to the top ot' the well and through thegas separation chamber 32. Typical means for so adjusting the chart drive mechanism is disclosed in the applicants copending application Serial No. 269,568, tiled February l, 1952.

instead of employing two separate electrodes as shown at 81 and 82 in Figure 1 the bit itself may be used as one of the electrodes and in such case the structure of the drill collar. electrode and electrode bit may, for example, be made as shown in the article by David G. Hawthorn and .lohn E. Owen in the January i940 issue of the Petroleum Engineer, page 7l.

The principles of this invention can also, as hei-einbet'ore described, be applied to other measurements such us natural potential, drilling weight on the bit. bottom hole temperature or pressure or radioactivity ofthe formation, it being only necessary in order to accomplish this to regulate the ilow of current from thebattery 84 to theelectrodes 81 and 82 and therebetween through the drilling tiuitl in accordance with the beforcmentioned characteristics to be measured.

For example, the measurement of radioactivity within the well borehole can be accomplished by the hereinbetorc described apparatus of Figure 3. The operation of this portion of the apparatus is as follows: Radioactivity radiation intercepted by thedetector 130 results in a potential drop or in rapid potential pulsations acrossresistor 132 which are applied throughconductors 133 and 134 to the input of ampliiier device A. ln the output circuit ot' amplifier device A, current, which is a predetermined function ot` the radiation received bydetector 130, tiows frombattery 84 throughconductors 85 and .135 to the one output terminal of the device and thence throughresistor 136.conductor 137, brush 99 (and with commutator positioned as shown),brush 96 and conductor 101 toelectrode 82. Fromelectrode 82 the current flows through the tluid in the borehole to electrode 8l and returns throughconductor 100,brush 92.brush 88,conductor 87,switch 86 andconductor 85 and returns tobattery 84.Resistor 136 is made relatively' high so that differences in resistances of the current path betweenelectrodes 82 and Si through the borehole fluid and surrounding formations will have an inappreciable effect upon such current ilow. Whencommutator 91 is turned 90 from the position shown, the current flow insofar aselectrodes 81 and 82 are concerned will be reversed from that just' described.

The hydrogen gas liberated atelectrodes 81 and 82 in proportion to the current thus caused to ow therebetween in the operation of the apparatus of Figure 3 is carried in the drilling fluid to the top of the well where it is separated and measured as hereinbefore described in connection with the apparatus of Figure l.

The terms measuring the quantity of hydrogen as cmployed herein in the specification and claims are not to be limited in meaning to actual quantitative determination of such values but are to include the actuation of any indicator or recorder means or device such as the voltmeter or galvanometcr V or V1 or the like device whereby a visual indication or graphical record ot a measure of such values or an indication or graphical record of a value which is indicative of or representative ot` the amount of hydrogen present in the separated gases or present in the drilling fluid may be obtained.

lt is to be understood that the foregoing is illustrative only and that the invention is not limited thereby but may include various modifications and changes made by those skilled in the art without distinguishing from the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

l. A method of logging a well borehole comprising: applying a potential difference between a pair of spaced electrodes, vertically shil'table within said borehole and in electrical contact with aqueous tluid therein whereby hydrogen is generated in said I'luid at said electrodes by electrolysis in quantities which are representative of the conductivitics of the formations surrounding said borchole adjacent said electrodes; circulating said fluid containing said hydrogen to the top of the well borehole and there separating hydrogen gas therefrom; and measuring the quantity of the separated gas relative to time.

2. A method for logging a well borehole comprising: applying a D.C. potential difference between a pair of spaced electrodes, vertically shiftable within said borehole and in electrical contact with aqueous tiuid therein whereby hydrogeu is generated in said luid at one of said electrodes by electrolysis in quantities which are representative of the conductivity of the formation surrounding said borehole adjacent said electrodes; circulating said iluid containing said hydrogen to the top of the well borehole and there separating hydrogen gas therefrom: and measuring the quantity of the separated gas relative to time.

3. A method for logging a well borehole comprising: applying a D.C. potential difference between a pair of longitudinally spaced electrodes, vertically shiftable within said borehole and in electrical contact with aqueous tiuid therein whereby hydrogen is generated in said fluid at one of said electrodes by electrolysis in quantities which are representative of the conductivity of at least a portion of the formation surrounding said bore hole adjacent said electrodes; circulating said tluid containing said hydrogen to the top of thc well borehole and there separating hydrogen gas therefrom; continuously measuring the quantity of the thus separated gas relative to time; and correlating the resultant measurements with the well borehole depth.

4. The method according to claim 3 including the step of periodically reversing the polarity of the potential applied to the electrodes.

5. A method for logging a well borehole comprising: applying a D.C. potential diierence between a pair of longitudinally spaced electrodes. vertically shiftable within said bore hole and in electrical contact with aqueous iluid therein whereby hydrogen is generated in said tluid at one of said electrodes by electrolysis in quantities which are representative of the conductivities of at least a portion of the formations surrounding said borehole adiacent said electrodes; circulating said fluid containing said hydrogen to the top ot the well borehole and there separatA ing hydrogen gas therefrom; continuously measuring the ouantitv of the separated gas relative to time; and recording said measurements relative to the well borehole depth.

6. A method of logging a well borehole comprising: passing a variable current between a pair of spaced electrodes vertically shiftable within said borehole and in electrical contact with aqueous fluid therein whereby said current flows through said uid between said electrodes and hydrogen is generated in said liuid at at least one of said electrodes by electrolysis in quantities which are representative of the values of said current; varying said current in response to and as a function of the values of a quantity to be measured within the borehole, circulating said fluid containing said hydrogen to the top of the well borehole, and there measuring the quantity of separated hydrogen in said uid.

7. A method for logging a well borehole comprising: passing a variable D.C. current between a pair of spaced electrodes vertically shiftable within said borehole and in electrical contact with aqueous uid therein whereby said current flows through said iluid between said electrodes and hydrogen is generated in said uid at one of said electrodes by electrolysis in quantities which are representative of the values of said current; varying said current in response to and as a function of the values of a quantity to be measured within the borehole, circulating said uid containing said hydrogen to the top of the well borehole, and there measuring the quantity of the hydrogen in said iuid; and correlating the resultant measurements with the well borehole depth.

8. A method of logging a well borehole comprising: passing a variable current between a pair of spaced electrodes vertically shiftable Within said borehole and in electrical contact with aqueous tluid therein whereby said ured; circulating said fluid containing said hydrogen to the top of the well borehole, and there measuring the quantity of the thus separated hydrogen relative to time; and correlating the resultant measurements with the well borehole depth.

References Cited in the le of this patent UNITED STATES PATENTS 1,819,923 Schlumberger Aug. 18, 1931 2,238,903 Lieneweg Apr. 22, 1941 2,296,030 Hall Sept. 15, 1942 2,341,169 Wilson et al. Feb. 8, 1944 2,380,520 Hassler July 31, 1945 2,388,141 Harrington Oct. 30, 1945

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