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Method and apparatus for producing parallel boreholes

  • US 5,725,059 A
  • Filed: 12/29/1995
  • Issued: 03/10/1998
  • Est. Priority Date: 12/29/1995
  • Status: Expired due to Fees
First Claim
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1. A method of drilling parallel, generally horizontal boreholes, comprising:

  • drilling a first borehole from an entrance location to an exit location;

    pulling a guide cable into said first borehole while withdrawing the drill string used to drill the first borehole;

    supplying a first guide current to said guide cable to produce a first magnetic field surrounding the guide cable;

    drilling a second borehole within said magnetic field;

    measuring selected parameters including parameters of said first magnetic field within said second borehole;

    producing a second current in said second borehole and modulating said second current in accordance with the measured parameters to produce a corresponding modulated second magnetic field;

    detecting said modulated second magnetic field at said guide cable to produce in said guide cable a third current corresponding to said measured parameters;

    determining from said measured parameters the distance and direction from one of said boreholes to the other of said boreholes; and

    controlling the direction of drilling of said second borehole in accordance with said determined distance and direction.

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