US2199367A - Method of logging bore holes - Google Patents

Description

@awa-lu 5R QR" 9199,36? Hmm pril 30, 1940. F, ATHY ET AL 2,199,367

METHOD 0F LOGGING BORE HOLES Filed Aug. lO, 1938 6 Sheets-Sheet 1 /0 V e2. g/

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l//q n Weg/7 w 7' l l 4o INVENTOR BY g/'/fpg/v/ fa 5' ATTO NEY April 3o, 1949.

L. F. ATHY FAI.

METHOD OF LOGGING BORE HOLES i Filed Aug. l0, 1958 6 Sheets-Sheet 4 l WHY April 3G, 1940.

Search Raam L. F. ATHY Er AL METHOD OF LOGGING BORE HOLES Filed Aug. l0. 1938 6 Sheets-Sheet 6 ATTO NEY UNITED STATES @sa heb, in

l 2,199,367: PATENT OFFICE METHOD F LOGGING BOREHOLES Lawrence F. Athy and Harold R. Prescott, Ponca City, Okla., assignors to Continental Oil Company, Ponca City, Okla., a corporation of Dela- Waffe Application August 10, 1938, Serial No. 224,105

8 Claims.

Our invention relates to a method of logging bore holes drilled into the earth and more particularly to a method whereby the amount and direction of dip of the geological formations penetrated is recorded, rather than their depth as has been the practice in logging methods of the prior art.

In exploration for oil, gas, and other valuable mineral deposits, after a hole is drilled into the earth, it is customary to employ Various types of well logging methods to obtain accurate information of the character of the geological formations penetrated. This information can be plotted in the form of a log which canl be compared with the logs of other bore holes and correlated to obtain a comprehensive picture of the underlying formations.

Sinceoil or gas occurs on a crest of an anticlinal fold or on the updip portion of a structure, if we can ascertain the amount and direction of the dip of geological formations, we may determine the updip direction from a dry hole drilled on a flank of a structure and thus be enabled intelligently to locate subsequent test wells.

One object of our invention is to provide a novel method of determining the dip or slope of rock layers through which a bore hole has been drilled.

Another object of our invention is to provide a novel method of determining structure by ascertaining the dip or the slope of the rock layers at several holes drilled in an area and plotting such dips to obtain a structure map.

Another object of our invention is to provide a method of bore hole logging in which the amount and direction of the dipy of geological formations penetrated is recorded.

Other and further objects of our invention will appear from the following description.

In the accompanying drawings which form part of the instant specification and are to be read in conjunction therewith and in which like reference numerals are used to indicate like parts in the various views Figure 1 is a simplied diagrammatic view, used in connection with the explanation of the manner in which magnitude and direction of dip of geological strata pierced by a bore hole may be measured, in the case of a horizontal bed.

Figure 1a is a vector diagram of the voltage relationships along and across a horizontal bed.

Figure 2 is a simplified diagrammatic View used in connection with the explanation of the manner in which magnitude and direction of dip of geological strata pierced by a bore hole may be measured, in the case of a bed sloping upwardly to the right.

Figure 2a is a vector diagram of the voltages along and across the bed shown in Figure 2.

Figure 3 is a simplified diagrammatic view used in connection with the explanation of the manner in which magnitude and direction of dip of geological strata pierced by a bore hole may be measured, in the case of a bed sloping downwardly to the right.

I Figure 3a is a vector diagram of the voltage relationships along and across the bed shown in Figure 3.

Figure 4 is a plan view of the surface of the earth showing the arrangement of electrodes about the bore hole which pierces the geological strata.

Figure 5 is a diagrammatic view of an eastwest cross section of a bore hole showing strata pierced thereby, the recording apparatusrand a record strip obtained using alternating current.

Figure 6 is a diagrammatic viewl of a northsouth cross section of a bore hole showing strata pierced thereby, the recordingapparatus and a record strip obtained using alternating current.

Figure 7 is a diagrammatic view of a portion of the recording apparatus, a section of the geological strata across an east-west line and a record strip made using direct current.

Figure 8 is a diagrammatic view of a portion of the recording apparatus, a section of the geological strata across a north-south line and a record strip made using direct current.

Figure 9 is a detailed view of a particular geological strata showing the manner in which the potential of the electrodes in the bore hole may be used to indicate the dip of the bed.

Figure 9a is a vector diagram of the voltages across respective electrodes in Figure 9.

Figure 10 is another detailed View of a particular geological strata showing the manner in which the potential of the electrodes in the bore hole may be used to indicate the magnitude and direction of the dip' of the strata.

Figure 10al is an electrode diagram of the potentials across the electrodes in Figure 10.

Figure 11 is a sectional view of our bore hole electrode assembly.

Figure 12 is a diagrammatic View showing a section of the electrodes assembly taken along the line l2-l2 of Figure 11, connected to the amplifiers, the rectifier unit and the recording unit.

Figure 13 is a dip diagram obtained by the method of our invention.

Figure 14 is another dip diagram.

Figure 15 is another dip diagram.

' Figure 16 is a further dip diagram.

Figure 17 is a diagrammatic View of the amplier for the bore hole electrodes for use with direct current or with interrupted direct current at the surface electrodes.

Figure 18 is a diagrammatic view of an amplier for the bore hole electrodes for use with alternating current at the surface electrodes.

Referring now to the drawings, Figure 1 shows an electrical conductor I of homogeneous material which carries a currentin a. lateral direction indicated by the arrow 2. The voltmeter 3 indicates a Voltage drop along the conductor between points 4 and 5 separated by a linear distance a, the voltmeter being connected to points 4 and 5 by conductors 6 and 1.

It will be obvious to those skilled in the art that the magnitude of the voltage e1 recorded by the Voltmeter 3 will be an index of the quantity of current owing through the conductor I and the direction of current flow will be indicated by the direction of the indication of the voltage e1. In other words, if the voltmeter 3 indicates that the conductor 6 is positive with respect to conductor 1, then obviously current will be flowing as indicated by the arrow 2 in Figure 1.

Along a line I3, at right angles to a line connecting points 4 and 5, across points 8 and 9, we connect a voltmeter I0 by means of conductors II' and I2. It will be obvious that, since points 8 and 9 are directly above one another and the conductor I is horizontal, there will be no voltage drop between these points since it is assumed that the material I is homogeneous.

Referring now to Figure 1a, it will be observed that the inclination of the direction of a line drawn through points 4 and 5, with respect to a line normal to a line drawn through points 8 and 9, will be indicated by the angle whose tangent is SIS In this case, since e2 is 0, the tangent will be 0 and the angle 4) will be 0.

Referring now to Figure 2 (in which reference numerals similar to those used in Figure 1 are employed) it will be observed that point 8 is now further to the right than point 9. In other words, the line I3 drawn through points 8 and 9 forms an angle qa with a line I4 normal to the direction of the current, along which no potential difference exists. The potential difference between points 8 and 9 is the same as that which would exist between points 9 and I5, because the line I4 is that of 0 potential change. The actual distance between points 9 and I5=a tan qb. The potential drop between points 9 and I5 varies as a function of a tan b. In other Words ez=Ka' tan p, where K is a constant depending upon the current and the impedance of the conductor. Similarly ei=2 (e1)-Ka. tan qS-Ka el The above relations are shown in Figure 2a by a vector diagram in which The polarity of point 9 in Figure 2 with reference to point I5 (and hence point 8) will indicate the direction. Furthermore, since and e1=Ka, tan p is independent of Ka, since tan qb may be represented as the ratio It will be obvious from the foregoing, to those skilled in the art, that the results obtained will be independent of either K or a. In other words, the determination of the angle i by means of its tangent is independent of the quantity of current used, the receptivity of the conductor involved or of the separation between points 4 and 5 (a).

In order to be able to determine the angle qs, it is required only that the conductor be homogeneous in the region of points 4, 5, 8 and 9 and that a be equal to a or, if different values are employed for a and a', that the necessary computation steps are taken to reduce voltages e2 and e1 to values corresponding to equal values of a and a', (it being understood that a is the vertical separation between points 8 and 9, as indicated in the gures).

Figure 3 is similar to Figure 2 but point 8 is connected at a point farther to the left than point 9. In other words, qb is in a diiferent direction to the horizontal than 1 in Figure 2. This is indicated by the fact that, though the magnitudes of e1 and e2 are the same in Figure 3 as in Figure 2, the polarity is reversed.

Figure 3a is a diagrammatic view similar to Figure 2a, showing the vector diagram of the potentials.

Figure 4 is a plan View looking down at the earths surface upon a bore hole I6. The current Stake I1 is due West of the bore hole I8. The current stake I8 is due east of the bore hole I6. The current stake I9 is due north of the bore hole I6, and the current stake 20 is due south of the bore hol-e I6. It will be noted that the electrodes I1, I 8, I9, and 28 are placed at equal distances from the bore hole I6 in Figure 4. This is not absolutely necessary. The distances between the current stakes and the bore hole should be such that a suicient current will penetrate to the deepest geological strata to be investigated. It is also desirable to make the distances between the bore hole and the current stakes of a rather large order in order that the current in the geological strata pierced by the bore hole Awill flow along the beds with substantially no curvature in the region of the bore hole. In order to accomplish this result, we have found that the distance between an electrode and the bore hole should be from one to one and a half times the depth of the deepest geological strata to be investigated.

Referring now to Figure 5, which is a section through the bore hole IB taken on an east-west line, it will be noted that the bore hole pierces a plurality of layers 2|, 22, 23, 24, 25, and 26. 'I'he layer 2| is the surface or weathered layer. The bed 22 is a high conductivity bed. The bed 23 is a medium conductivity bed. The bed 24 is a low conductivity bed, while the bed 25 is another medium conductivity bed. The east and West bore hole electrodes are connected across the output of an alternator 21 by means of conductors 28 and 29. It is to be understood that observations are made across one plane, that is either in a north-south, or east-west direction, at one time. The electrode system 38, shown in greater detail in Figures 11 and 12, is lowered into the bore hole by means of a cable 3I, normally wound upon a reel 32. The cable 3l is provided with conductors. These conductors are connected to slip rings 33, 34, 35, 36 and 31. Slip ring 33 is connected to amplifier 38 by conductor 39. Slip ring 34 is connected to amplifier 49 by conductor 4I. Slip ring 35 is connected to amplifier 42 by conductor 43. Slip ring 3B is connected to amplifier 44 by conductor 45. The return circuits for the amplifiers 38, 40, 42, and 44 is by way of conductor 41 to slip ring 31. The output of the amplifiers is led by conductors 48, 49, 50, 5I, and 52 to a rectifier unit 53. The output of the rectiiier unit 53 is impressed by conductors 54 and 55 upon oscillograph element 58 suspended in the field of a magnet 51. The oscillograph element 56 carries a mirror upon which light from an incandescent lamp 59 is focused by lens 68 for reflection along path 6| upon the sensitized record strip 62 to form a trace 63. Two of the conductors are connected to slip rings 84 and 85, which are, in turn, connected by conductors 86 and 61 to the input of an amplifier 68. The output of amplier 68 is impressed by conductors 69 and 18 upon an oscillograph element 1| positioned in the field of a magnet 12. The oscillograph element 1| carries a mirror 13 upon which light from an incandescent lamp 18 is focused by a lens 15 for reflection along path 16 upon the record strip 82 to form oscillograph trace 11. A resistance 18 is placed in the conductor 29 across the output of the alternator 21. One side of the resistance 18 is connected by conductor 19 to an oscillograph element 88, positioned in the field of a magnet 8|. The other side of the oscillograph element 88 is connected by conductor 82 and adjustable arm 83 to a point upon resistance 18, since the arrangement described will cause oscillograph element 88 to measure the IR drop between the point of connection of conductor 19 and the point of contact of adjustable arm 83 of resistance 18. Since the resistance at any given time will be fixed, the IR drop will vary as a function of the current and hence oscillograph element 88 will measure the current flowing through conductor 29. The oscillograph element 88 carries a mirror 84 upon which light from an incandescent lamp 85 is focused by lens 86 for reflection along path 81 upon the record strip 62 to form oscillograph trace 88.

One side of oscillograph element 89 is connected through variable resistance 98 to conductor 19. The other side of oscillograph element 89 is connected by conductor 9| to one side of the output of amplifier 68 at conductor 10. A conductor 92 connects the other side of the output of amplier 88, that is conductor 69, to conductor 82. In other words, oscillograph element 89 is interconnected with oscillograph elements 1| and 88 to record the instantaneous summation of the voltages influencing these oscillograph elements. In this manner, the relative phase of the voltages recorded by oscillograph element 1| with respect to the voltages recorded by oscillograph element 88 will be recorded by the trace of oscillograph element 89. This trace is formed by the reflection along path 93 of light from incandescent lamp 95 by mirror 95 to form trace 99. When the amplitude of trace 99 is high, the voltages impressed upon oscillograph elements 1| and 88 are in phase. When the amplitude of the trace 99 is small, the voltages impressed upon oscillograph elements 1| and 88 are out of phase. The sensitivity of the oscillograph element 89 is arranged to be much greater than the sensitivity of oscillograph element 1| or oscillograph element 88 and the resistance 98 is used in series with oscillograph element 89 to minimize the current flowing through this element. This permits the oscillograph element 89 to record appreciable amplitudes with a current which will give substantially no deflection to oscillograph elements 1| and 88. It will be seen that our arrangement permits the oscillograph element 1| to record substantially nothing but the output of the amplifier 68. It permits oscillograph element 88 to record substantially nothing but the Search output from the resistance 18 (the current-output of the alternator). At the same time, oscillograph element 89 will record the summation of the outputs impressed upon oscillograph elements 1| and 88.

The initial connections are made so that traces 11 and 88 are in phase when the beds are higher under electrode i8, the east electrode, when surveying in an easterly-westerly line. Similarly, the initial connections are such that the traces 11 and 88 are in phase when the beds are higher under the south electrode 28.

oscillograph trace 99 is normally arranged to give the same amplitude as oscillograph trace 88 by adjustment of the resistance 98, when the amplitude of trace 11 (e2) is 0. When trace 11 (e2) shows that potential exists across the vertically spaced electrodes of the receptor 38, the oscillograph 99 will increase if traces 11 and 88 are in phase. Likewise, the oscillograph trace 99 will decrease if traces 11 and 88 are out of phase. The oscillograph element 89 and the 0scillograph trace 99 are needed only where an alternator is used as the current source. With direct current, the oscillograph 89 may be disconnected.

The connections to the oscillographs are shown on a larger scale in Figure l2 in which like reference numerals are used to indicate like parts.

The reel 32 is rotated to move electrode assembly 38 into and out of the bore hole by means of a motor |88. The motor |88 is a synchronous m0- tor and connected in parallel with motor which drives the roll |82 which moves the record sheet 62 through reduction gearing |83. By this arrangement, the record sheet will move as a function of the motion of the electrode assembly so that the record sheet will furnish a graph from which the inclination and direction of dip of the beds may be read at their respective depths. The key |84 is adapted to complete the circuit to the electrodes I1 and I8 from the alternator 21. If desired, the key may be momentarily closed in order to give transient impulses.

Referring now to Figure l1 in which there is shown an enlarged view of electrodes assembly 30, the body member |85 is made out of any suitable insulating material and contains adjacent its upper portion a conducting ring |88 separated a predetermined distance from a conducting ring |81. Connected to conductor ring |86 is oonductor |88 of the cable 3|. Connected to conductor ring |81 is the conductor |89 of the cable 3|. Conductors |88 and |89 are connected to slip rings 64 and 65 which are connected by conductors 66 and 61 to the amplifier 68. The potential difference existing between rings |86 and |81 is voltage ez, that is the voltage drop between two vertically separated points.

The measuring electrode arrangement to obtain e1 is more complicated due to the fact that it must record a voltage drop between two hori- Zontal points irrespective of orientation. In order to accomplish this, we provide adjacent the lower portions of body |85 a plurality of conducting points H8, IH, H2, H8, H4, H5, H8, H1, H8, H8, |29, and |2l, disposed about a central conducting element |22. Electrode points H9, |28, and |2| are connected as a group to conductor 89 leading to amplier 38. Conducting points H8, |H, and H2 are connected as a group to conductor 4| leading to amplifier 98. Conducting points H3, H8, and H are connected as a group to conductor 83 leading to amplifier 42.

Electrode points H8, H1 andH8 are connected 75 as a group to conductor 45 leading to amplifier 44. The center electrode |22 is connected by conductor 41 to one side of al1 four amplifiers 38, 40, 42, and 44, as can readily be seen by reference to Figure 12. The conductors are housed in cable 3| which leads into a bore |23 formed in the body of the electrodes assembly. The cable passes out of the bore |23 through a stuffing box assembly as can readily be seen by reference to Figure 11. The lower member |24 of the stufiing box assembly is threaded or otherwise secured to the top of the body member |05. The upper member of the stuffing box |25 is adapted to squeeze packing |26 against the outside of cable 3| tightly to secure the cable to the member |24 which in turn supports the body member |05 and the electrodes assembly. The central electrode |22 closes lower end of bore |23 and prevents the ingress of bore hole fluid into the bore, which might result in the short circuiting of the electrodes. The output of amplier 38 is impressed through conductor 48 upon the anode |21 of duo-diode vacuum tube |28. The output of amplifier 40 is led by conductor 49 to anode |29 of duo-diode vacuum tube |28 of the rectifier unit 53. The output of amplilier 42 is conducted by conductor 50 to the anode |30 of the duo-diode vacuum tube |3| of the rectifier 53. Conductor 5| is adapted to impress the output of amplifier 44 upon the anode |32 of the duo-diode vacuum tube |3| of the rectifier 53. Each anode will pass current whenitbecomes positive and will permit current to flow to its respective cathode. For example,when anode |21oftube |28 becomes positive with respect to the cathode |33, current will flow from the anode |21 to the cathode |33 through conductor |34 through resistance |35 through conductor |36 through conductor |31 which is the common cathode return to all amplifiers. It will be noted that the other side of each amplifier is connected to conductor |38 which is connected to conductor |31.

In parallel with the resistance |35 we place a variable condenser |39 which is adjusted to filter out individual pulsations when alternating current is employed. The capacity of condenser |39 and the resistance |35 are adjusted to give a time constant sufficiently large that individual pulsations of alternating current will be smoothed out, but sufliciently small that variations in amplitude of potential across the electrodes, a very short time later, will be indicated by a similar variation of potential upon the grid |40 of the vacuum tube |4|.

It will be obvious from a view of Figure 12, that a similar flow of current through resistance |35 and common return conductor |31 will take place when any of the anodes |21, |29, |30, or |32 becomes positive with respect to their respective Cathodes. Battery |42 furnishes energy for filament |44 which heats the cathode |45 of tube I3|. Cathodes |33 and |45 are interconnected by a conductor |46 to which grid |40 is connected by conductor |41. It will be obvious that the potential impressed upon grid |40 will be the integral of the rectified potentials from all four amplifiers. A B battery |48 is connected through the plate |49 of tube |4| through oscillograph element 56. The other side of B battery |48 is connected by conductor |50 to the cathode |5| of tube |4|. The filament heater |52 for the cathode is furnished energy from the battery |42. A C battery |53 furnishes bias for the cathode |5|.

From the foregoing, it will be obvious that the oscillograph element 56 will move as a function of the rectified potential from all four amplifiers 38, 40, 42, and 44, in view of the manner in which the electrodes ||0, ||2, ||3, ||4, ||5, H6, ||1, ||8, H9, |20, and |2| are arranged around the central electrode |22, as shown in Figure 12. The potential impressed upon the grid |40 of the tube 4| by conductor |41 will be substantially independent of the orientation of the horizontal electrode system. It will be further obvious that the oscillograph 58 is controlled by the potential between the central electrode |22 and the peripheral electrodes. This potential is potential e1. It will be clear to those skilled in the art that the horizontal electrode system may be made nondirectional to a greater extent by the use of more electrodes disposed about the perpiheral, and more ampliers on the corresponding rectifier tubes.

The output of amplifier 68 will vary as a function of potential e2. This is impressed by conductors 69 and 10 upon oscillograph element 1| as hereinabove described. The electrode spacing may be any convenient spacing which is much less than the thickness of the geological strata to be investigated. Since electrode spacing is considerably less than the thickness of the strata, the ratio of the two potentials will represent values Within a single stratum and Will therefore represent dip.

The electrode system with its amplifiers may be pre-calibrated by calculation. We prefer to suspend the electrode system in a fluid between a pair of immersed conducting plates. We then pass current between the two conducting plates and place the electrode system at known angles with reference to the conducting plates, and adjust amplier gains until is equal to the tangents of the various known angles.

Referring now to Figure 9, the points |54 and |55 represent the vertical electrode system. Points |56 and 51 represent the horizontal elec- .trode system. It will be noted that the points are disposed within the bore hole |6. Before immersion, the bore hole is filled with a normal drilling fluid. The stratum |58 is a buried stratum being investigated. Electrode points |56 and |51 are connected to the means |59 for measuring and indicating magnitude and polarity of the voltage el obtained across conductors |56 and |51. Electrode pointsl |54 and |55 are connected to a means |60 for measuring and indicating the magnitude and polarity of the voltage e2 obtained across conductors |54 and |55. These electrode points or conductors are more or less vertically spaced, due to the fact that the electrode system is suspended. Conductors |56 and |51 are in the same general horizontal plane since they are placed at right angles to the axis of the electrode system assembly which is suspended by means of a cable.

The arrows |6| indicate the instantaneous direction of the current flow through the stratum |58. The current through the bore hole will parallel the geological strata as will readily be seen by reference to Figure 9. It will be obvious that the current will thus follow the strata if we consider the stratum |58, one of good conductivity, surrounded by beds of poor conductivity. The current will show a marked tendency to follow the good conductor laterally along the stratum and parallel to it.

The voltage e1 between points |56 and |51 will be the same as that'between point |56 and point |62. The linear distance between points |56 and |62 is a cos qs, where fp is the angle of dip and a is the linear spacing between electrodes |56 and |51. The voltage e1 therefore, is proportional to the distance a cos gb. In other words,

Similarly, the voltage e2 is measured by the measuring and recording means |60 which is connected to the vertical electrode points |55 and |54. The line |63 is one of equal potential, because it is drawn at right angles to the strata |58. By this is meant that an electrode positioned on line |63 will have the same potential as any other electrode positioned upon said line |63, though vertically displaced therefrom. From this, it follows that electrode |54 will have the same potential with reference to electrode |55 as point |64 haswith reference to point |55. The voltage e2 therefore is proportional to a sin qs, where a is the vertical interelectrode space and qb is the dip of the stratum |58. This may be expressed e2=Ka sin qb.

acosq asin Ka cos Q tan =Ka sin 4a e1 length of the arrows e1 and e2 indicate the respective magnitudes of the potential differences and the directions of the arrows indicate the po*- larity of the potentials.

Figure 10 is similar in al1 respects to Figure 9 except that the stratum |58 dips in the opposite direction, though a like amount. The magnitude and polarity of e1 will be the same as before. The magnitude of e2 will be the same as before. Its polarity, however, is changed. This is readily discernible by reference to Figure 10a which is similar to Figure 9a but in which e2 is plotted in the opposite direction, due to the fact that its polarity is the opposite.

When direct current or intermittent direct current is employed at the electrodes |1, I8, |9, and 2U, all of the amplifiers employed in the system are like that shown in Figure 1'1. The conductors 66 and 61 connected to bore hole electrodes through the cable are connected across resistance |65, one end of which is connected by conductor |66 to the cathode |61 of a vacuum tube |68 through a cathode biasing C battery |69. A cathode heater filament |10 is furnished energy from an A battery |1|, the grid |12 being connected by arm |13 to a point upon the resistance |65. The positive side of B battery |14 is connected to the plate |15 of tube |68 through an oscillograph element.

When alternating current or transient impulses are used, the amplifier shown in Figure 18 is employed throughout. Resistance |65 is connected across conductors 66 and 61, leading to the bore hole electrodes through the slip ring arrangement to the cable. The output of the first vacuum tube |68 is impressed upon the grid |16 of the output tube |11 through a high pass filter |18 and a low pass filter |19. The high pass filter rejects undesirable frequencies below that of the source frequency. The low pass filter |19 rejects undesirable high frequencies above that of the source frequency. The-primary |80 vof a transformer is placed in the plate circuit ofthe output tube |11. The secondary |8| of the output transment by conductors 69land-18.

Search Room Referring now to Figure 7, there is vshown a record strip V62 vmade with. direct current. The oscillograph .element 56 records potential e1. The value of e1 for the various beds is shown by trace 63. Oscillograph element 1| gives the potential e2. The value of e2 as the electrodes assembly 3l) is lowered through the bore hole is given by trace 11. Oscillograph element 8.0 gives trace 88 which indicates the current in the surface electrodes |9. It will be observed that e2 has the same direction of motion (polarity) as indicated by trace 11 as trace 88. This means that the bed is higher under electrode |8, the east electrode, than it is under the west electrode. That is, bed 22 is dipping downward toward the west by an angle whose tangent is which, in the case inustratea, would be an anglel whose tangent is .213, or an angle of l2 degrees. This is shown in Figure 13 where arrow |82 is drawn toward the west a length proportional to 12 degrees. Similarly, bed 23 is higher under electrode I8 and the value of is .23. The angle whose tangent is .23 is 13 degrees. Arrow |83 in Figure 14 is a plot of this value. In the same manner, we obtain from record strip 62 of Figure '1 that the value of for bed 24 is .25. The angle whose tangent is .25 is 14 degrees. Since the trace v88 is in the same direction as trace 11, bed 24 is higher under electrode |8. The vector |84 in Figure 15 is pointed from the bore hole Westerly a value representing 14 degrees. From the record strip 62, the value of for bed 25 is found to be .268. The angle whose tangent is .268 is 15 degrees. Trace 88 being in the same direction as trace 11, the bed is higher under electrode |8 and the vector |85 in Figure 16 indicates the east-west component of bed 25.

Referring now to Figure 8, the record strip 62 in this gure is taken on a north-south line. The value of e1 is given by trace 63; the value of e2 is given by trace 11; and the value and direction of the surface electrode current is recorded b-y trace 88, Examining the record strip in Figure 8, it will be observed that the trace 63 is in the opposite direction from trace 11; This means that the beds are lower under the south electrode 20 than under the north electrode |9. From the record strip, the'value of in the Vicinity of bed 22 is .052. The angle whose tangent is .052 is 3 degrees. The vector |86 in Figure 13 is plotted a distance proportional to 3 degrees in a direction indicating that the beds are dipping from north to south. lin the same manner, the value of for bed 23 in Figure 8 is .087.

The angle whose tangent is .087 is 5 degrees, the dip again being from north to south. The vector |81 in Figure 14 is. plotted a distance through the surface electrodes.

proportional to degrees in a direction pointing from north to south. The value of for bed 24 in Figure 8 is .105 or the tangent of 6 degrees. The vectorv |88 in Figure 15 illes south a length proportional to 6 degrees. Similarly, from the record strip, we obtain a value of 8 degrees for bed 25,

e1 being .141. The vector |89 in Figure 16 flies south a distance proportional to 8 degrees.

Figure 13 shows the east-west component and the north-south component of the true dip in bed 22. The resultant vector |90 in Figure 13 indicates the extent and direction of the true Ydip of bed 22. In Figure 14, the resultant vector I9I indicates the true dip and direction of dip of bed 23. The resultant vector |92 in Figure l5 indicates the true dip of bed 24, both in direction and amount, while the resultant vector |93 of Figure 16 indicates the true dip both in direction and amount which exists in bed 24 in the region of bore hole I6. The same information as hereinabove described with respect to the use of direct currents is obtained with alternating currents.

Referring now to Figure 5, where the record strip 62 shows the traces obtained, trace 63 is proportional to the value of e1. 'Irace 'l1 is proportional to the value of e2. Trace 88 indicates the value of the alternating current passing through the surface electrodes I 'I and I8, while trace 99, as described above, indicates whether the value of e2 is in phase with the value of the surface electrode current. It will be seen by comparing trace 'I'I and trace 99 that, when trace I1 increases in amplitude, trace 99 also increases in amplitude, clearly showing that the current ez is in phase with the current passing This indicates that the beds are higher under electrode I8. Since trace 63 is the rectified horizontal component e1 it will be noted that trace 63 of the record strip in Figure 5 is substantially the same as trace 63 in the record strip shown in Figure 7. The value of e2 is given by the amplitude of the trace 'I1 and substantially the same information is obtained from the record strip shown in Figure 5 as that shown in Figure 7 and the eastwest electrodes and their directions are ob-tained and plotted as described above.

Referring now to Figure 6, which is similar to Figure 5, except that readings are being taken in a north-south direction, it will be seen by reference to the record strip 62 that, when the amplitude of trace 11 increases, the amplitude of trace 99 decreases. This indicates that e2 is out of phase with the current passing through the surface electrodes` I9 and 20. This indicates that, in a north-south direction, the beds are deeper under electrode 20, that is, the beds are dipping from north to south. The same information is obtained from the record strip 62 of Figure 6, which is obtained from the record strip 62 shown in Figure 8. Trace 63 being the rectied horizontal component, e1 is the same as trace 63 of Figure 8. The amplitude of trace 'I1 indicates the value of e2.

In actual use, some general information of the direction of the dip will be known from geological information. This furnishes an additional check as to the direction of clip.l Generally, this information is not necessary but, in the case of small dip angles, that is where the beds are nearly horizontal, it furnishes a check on the adjustment of the apparatus.

Normally e2 will be quite small compared to er since obviously the dip will never be as great as 90. In practice We amplify e2 about ten times as much as e1 in order to obtain a record strip which can be more clearly read. The amplication is taken into account in computing the value of the tangents of the dip angle. 'Ihis enables us to obtain more reliable measurements of ez and makes our readings more accurate.

Our method may be used in connection with core drilling or other shallow drilling or drilling conducted solely for explorative purposesy to determine structure of the shallow beds in order to properly locate prospect holes. Our method may also be used in conjunction with other commonly employed well logging methods to supplement the information there gained.

It will be observed that we have accomplished the obects of our invention. We have provided a novel manner of obtaining the amount and direction of the dip of buried geological strata from which structure maps may b-e plotted. We are able to locate the portions of structures and are therefore able intelligently to locate wells.

It will be understood that certain features and sub-combinations are of utility and may be employed without reference to other features and sub-combinations. This is contemplated by and is within the scope of our claims. It is further obvious that various changes may be made in details within the scope of our claims without departing from the spirit of our invention. It is, therefore, to be understood that our invention is not to be limited to the specific details shown and described.

Having thus described our invention, we claim:

1. A method of logging bore holes to determine the dips of the strata pierced thereby, including the steps of passing a current through the geological section pierced by the bore hole, observing the potential diierence between horizontally disposed electrodes positioned in' a bore hole adjacent a stratum being investigated, simultaneously observing the potential difference between vertically spaced electrodes positioned within the bore hole adjacent the stratum being investigated, and ascertaining the dip of the stratum from said potential differences.

2. A method of logging bore holes including the steps of passing a current in a given direction through the geological section pierced by the bore hole being investigated, lowering horizontally and vertically spaced groups of electrodes into said bore hole, simultaneously moving a record strip as a function of the movement of said electrode groups, recording the potential difference between said horizontally spaced electrodes, simultaneously recording the potential difference between said vertically spaced electrodes and determining the dips of the various strata past which the electrodes are moved by the ratios of the horizontal and vertical potential differences.

3. A method of logging bore holes including the steps of passing a current in a given direction through the geological section pierced by the bore hole being investigated, lowering horizontally and vertically spaced groups of electrodes into said bore hole, simultaneously moving a record strip as a function of the movement of said electrode groups, recording the potential difference between said horizontally spaced electrodes, simultaneously recording the potential diference between said vertically spaced eleotrodes, determining respective components oi the dips of the various strata past which the electrodes are moved by the ratios of the. horizontal and vertical potential diierences, then passing current through the geological section being investigated in a direction at an angle to said rst direction, repeating the above steps to obtain another component of the dips of the geological strata past which the electrodes are moved, and obtaining the resultant of said dip ycomponents to ascertain the true dips of the strata through which the bore hole is sunk.

4. A method as in claim 1 in which the current is direct current.

5. A method as in claim 1 in which the current is alternating current.

6. A method as in claim 1 in which the current is alternating current of a predetermined frequency, including the steps of rejecting potential differences above said predetermined frequency, rejecting potential differences below said predetermined frequency, amplifying and observing potential diiferences of said predeteramasar mined frequency and determining the desired dip from said amplified potential diiferences.

7. A method as in claim 1 in which said current passing step is conducted momentarily to obtain transient current.

8. A method of logging b-ore holes to determine the dips of the strata pierced thereby, including the steps of passing an electrical current through the geological section pierced by a bore hole, receiving the potential differences between a point and a plurality of surrounding points disposed in a plane adjacent a stratum being investigated, amplifying each of said potential differences between said central point and one of said surrounding points, rectifying the amplied potential diiierences, integrating the rectified amplified potential differences and observing the integrated potential diierence, simultaneously observing the potential difference existing between a point above said plane and a point below said plane extending from said first point in a line at right angles to said plane, and ascertaining the tip of the stratum from said second potential difference and said integrated potential diierence.

LAWRENCE F. ATI-IY. HAROLD R. PRESCOT'I.

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