Device for transmitting to the surface the signal from a transmitter located at a great depth

A device for transmitting signals from a transmitter at the bottom of a drill well to the earth's surface including means for transmitting signals from the transmitter at the bottom of the drill well to the earth's surface, said means comprising:

• a drill collar which extends in an axial direction;
• said transmitter disposed in said drill collar;
• a cylindrical metal sleeve for forming part of an antenna for electromagnetic wave transmission, said cylindrical metal sleeve being disposed around said drill collar and connected electrically to said transmitter, said cylindrical metal sleeve having a diameter greater than the diameter of said drill collar and having an axial length shorter than the axial length of said drill collar;
• and
• an insulating sheath disposed between said cylindrical metal sleeve and said drill collar, said insulating sheath having an axial length shorter than the axial length of said drill collar, an annular groove being provided in the outer peripheral surface of said drill collar and said insulating sheath and said cylindrical metal sleeve being disposed in said annular groove with the outer peripheral surface of said cylindrical metal sleeve being of a diameter no greater than the diameter of the outer surface of said drill collar, said cylindrical metal sleeve comprising a cylindrical metal sleeve of netting, said netting consisting of overlapping helical springs, each helical spring being interlaced with and in parallel with an adjacent helical spring to form said netting, said netting being embedded in said annular groove by means of a hardenable plastic or epoxy resin disposed between said netting and a surface of said annular groove.

A device for transmitting signals from a transmitter at the bottom of a drill well to the earth's surface including means for transmitting signals from the transmitter at the bottom of the drill well to the earth's surface, said means comprising:

• a drill collar which extends in an axial direction;
• said transmitter disposed in said drill collar;
• a cylindrical metal sleeve for forming part of an antenna for electromagnetic wave transmission, said cylindrical metal sleeve being disposed around said drill collar and connected electrically to said transmitter, said cylindrical metal sleeve having a diameter greater than the diameter of said drill collar and having an axial length shorter than the axial length of said drill collar;
• an insulating sheath disposed between said cylindrical metal sleeve and said drill collar, said insulating sheath having an axial length shorter than the axial length of said drill collar;
• and further comprising resistivity measuring means for measuring the resistivity of the terrain at the bottom of the drill well in the vicinity of said transmitter, said resistivity measuring means comprising a plurality of cylindrical rings surrounding said insulating sheath, said rings being spaced from one another along said axial direction, said rings being connected to said transmitter by a programmable switching device whereby capacitive measurements can be made for determining the resistivity of the terrain at a desired level at the bottom of the drill well.