Method and apparatus for producing parallel boreholes

Telemetry apparatus for parallel boreholes, comprising:

• a first borehole having an entrance location;
• a guide cable in said first borehole, said guide cable extending from said entrance location a predetermined distance into said first borehole;
• a source of current connected to said guide cable for producing a guide current in said guide cable and a corresponding magnetic guide field surrounding said cable;
• a drill stem for drilling a second borehole within said magnetic guide field;
• a sensor probe in said drill stem responsive at least to said magnetic guide field to produce output data signals corresponding to said magnetic guide field;
• a transmitter within said drill stem connected to said sensor probe for transmitting said data signals from said sensor to said guide cable;
• and
• means connected to said guide cable for receiving said data signal for use in controlling said drill stem.

A method for producing substantially parallel boreholes, comprising:

• drilling a first borehole through the Earth using drilling equipment;
• pulling a guide cable into said first borehole by means of said drilling equipment simultaneously with drilling said first borehole for use in providing a reference magnetic field;
• retaining said cable in said first borehole as said drilling equipment is withdrawn, and
• drilling a second borehole guided by said magnetic field.

Telemetry apparatus for borehole, comprising:

• a drill stem for drilling a borehole;
• a sensor probe within said drill stem for producing data signals to be transmitted;
• a drill stem transmitter responsive to said data signals to produce a corresponding first magnetic field;
• a telemetry cable within and responsive to said first magnetic field to produce corresponding magnetically induced voltages;
• and
• a receiver connected to said cable to detect said voltages.