Patent GB-330876-A (GB)
Title: Improvements in apparatus for locating deposits of oil, gas and other dielectric subterranean bodies
IPC: G01V3/06
Filed: 1929-01-14
Abstract: 330,876. Marks, Sir G. C., (Oil Finding Corporation). Jan. 14, 1929. Prospecting for minerals ; current and pressure meters. - Oil or other dielectric deposit below the earth's surface is located by passing a highfrequency alternating current through relatively short and relatively long paths in the earth and indicating differences of characteristics between these paths. In the apparatus shown, high-frequency alternating current is supplied by a step-up transformer 27, the primary winding of which is connected in series with a battery 26 and buzzer 25, a choking-coil 29 and shunting condensers 30 preferably being included. The secondary winding of the transformer 27 is connected through the primary winding of a step-up transformer 31 to a stake 6 which is driven into the ground. The circuit is completed through one of two electrodes 8, 12 which are spaced trom the surface of the earth by insulating plates 9 so as to form condensers with the earth as the other electrode. The secondary winding of the transformer 31 is connected between the cathode and grid of a rectifying valve 32, in the plate circuit of which is an indicator such as a microammeter 38. In order to prevent a continuous current from passing through the indicator 38 when no alternating current is impressed upon the grid of the valve 32, an opposing voltage derived from the filament battery 40 through a potentiometer 39 is impressed on the indicator 38, fine adjustment being obtained by means of a second potentiometer 43. The filament voltage is indicated by means of a voltmeter 42 and is maintained constant by adjusting a rheostat 41. A voltmeter 47 may be connected by means of a two-way switch 48 either across the battery 35 and rheostat 37 in the plate circuit or across the grid biassing battery 44. By means of a threeway switch 11 the secondary circuit of the transformer 27 is closed through a condenser 14 of known capacity and the resulting reading of the indicator 38 observed. The switch 11 is then moved to connect the plate 8 in circuit and the alternating current passing through the long path between the electrode 8 and the stake 6 is observed on the indicator 38. The plate 12 is then substituted for the plate 8 by means of the switch 11 and a reading is taken of the alternating current flowing between the electrodes 6, 12. If this reading is appreciably the same as the last, the resistance of the long path through the earth is negligible compared with the impedance of the condenser 8, indicating that no oil or other dialectric deposit is below the area including the electrodes. If such deposit is present, the resistance of the long path between the electrodes 6, 8 is appreciable compared with the impedance of the condenser 8, causing the current to be lower than that passing between the electrodes 6, 9. When such a difference between the readings is accompanied by fluctuation of the intrument needle while measuring current in the long path, the prescence of natural gas is indicated. Alternatively, a constant alternative current may be transmitted through the short and long paths and the voltage required to produce this current through the long path compared with that required to produce the same current through the short path. The connections of the secondary winding of the transformer 31 are reversed with respect to the primary winding in order to prevent undesired coupling between the leads. Where the soil is exceptionally dry, the insulating plates 9 may be omitted.