Patent Document ID: 20040027131
Application ID: 10616429
Patent Flag: 0

Claim One:
1. A tool for steering a downhole drilling apparatus with respect to a geological bed boundary in an earth formation, said tool having a tool axis and comprising: a first transmitter antenna disposed within a plane oriented at a first angle with respect to the tool axis for transmitting a first transmitted electromagnetic wave into said formation, wherein said first transmitted electromagnetic wave induces a first electric current in said formation, and wherein said first electric current generates a first induced electromagnetic wave in said formation; a second transmitter antenna spaced apart from said first transmitter antenna along the tool axis and disposed within a plane oriented at a second angle with respect to the tool axis for transmitting a second transmitted electromagnetic wave into said formation, wherein said second transmitted electromagnetic wave induces a second electric current in said formation, and wherein said second electric current generates a second induced electromagnetic wave in said formation; a receiver antenna located between said first and second transmitter antennas along the tool axis and disposed within a plane oriented at a third angle with respect to the tool axis, said third angle being different from said first and second angles, for receiving said first and second induced electromagnetic waves and generating first and second response signals based upon said first and second induced electromagnetic waves, respectively, said first and second response signals being proportional to the electrical resistivity of a portion of said formation; and a processor in communication with said receiver antenna for (a) receiving said first and second response signals and (b) generating an output signal as a function of borehole depth based on said first and second response signals, wherein said output signal is indicative of the relative position of said tool with respect to said geological bed boundary as said tool approaches said geological bed boundary.