Steerable magnetic dipole antenna for measurement-while-drilling applications

An antenna for creating or detecting a magnetic field in a constant direction relative to the major axis of a substantially cylindrical tool;

• said antenna comprising:
• (a) an essentially round hole disposed in the wall of said tool on a chord in a plane perpendicular to said major axis of said tool;
• (b) a ferromagnetic rod disposed within said hole;
• (c) non-conducting inserts terminating each end of said hole;
• (d) a slit extending radially outward between said hole and an outer surface of said tool;
• and
• (e) a single antenna wire with a section essentially parallel to said major axis of said tool and traversing said slit perpendicular to said slit.

A method for steering the drilling of a borehole by creating or detecting a magnetic field in a constant direction with respect to the major axis of a MWD tool, said method comprising:

• (a) providing a drill collar;
• (b) disposing a dipole antenna within said drill collar;
• (b) disposing a transmission-receiver circuit within said drill collar;
• wherein
• (c) said magnetic dipole antenna comprises
• (i) a first and a second set of grooved antenna elements wherein
• said first and said second sets of grooved antenna elements are axially spaced along said drill collar, and
• grooves comprising each said set of grooved antenna elements are essentially parallel to the major axis of said drill collar;
• and
• (ii) a first and a second set of hole antenna elements disposed axially in said drill collar between said first and second sets of grooved antenna elements wherein
• said first and said second sets of said hole elements are azimuthally spaced around the periphery of said drill collar, and
• holes comprising each said set of hole elements are essentially perpendicular to said major axis of said drill collar;
• and
• (d) said magnetic dipole antenna is electrically connected by a single antenna wire to said transmission-receiver circuit thereby creating or detecting a magnetic field in a constant direction relative to said tool.

A method for creating or detecting, with an antenna, a magnetic field in a constant direction relative to the major axis of a substantially cylindrical tool;

• said antenna comprising:
• (a) disposing an essentially round hole in the wall of said tool on a chord in a plane perpendicular to said major axis of said tool;
• (b) disposing a ferromagnetic rod within said hole;
• (c) terminating each end of said hole with non-conducting;
• (d) forming a slit extending radially outward between said hole and an outer surface of said tool;
• and
• (e) providing a single antenna wire comprising a section that is essentially parallel to said major axis of said tool and traversing said slit perpendicular to said slit.