Methods and apparatus for multi-well ranging determination

A drilling system for multi-well ranging, comprising:

• a transmitter antenna to transmit a first electromagnetic signal into a surrounding formation and a receiver antenna to receive response signals from the surrounding formation, wherein the transmitter antenna and receiver antenna are included on a drilling collar or a downhole logging tool positioned within a drilling well;
• excitation sources positioned along multiple target wells to transmit various electromagnetic signals into the surrounding formation from different target wells;
• a controller operably connected to the transmitter antenna and the excitation sources to instruct the transmitter antenna and the excitation sources to transmit the first and various electromagnetic signals into the surrounding formation, and wherein the controller is configured to:
• apply a joint-inversion among azimuthal signals received from different excitation sources;
• determining azimuthal directions from the drilling well to multiple target wells based at least in part on the joint-inversion;
• decoupling formation signal and casing signals from the multiple target wells by the obtained azimuthal directions;
• and
• determining distance from the drilling well to the multiple target wells after determining the azimuthal directions from the drilling well to the multiple target wells.

A downhole ranging tool that comprises:

• a transmitter antenna to transmit a first electromagnetic signal into a surrounding formation;
• a receiver antenna to receive response signals from the surrounding formation;
• and
• a controller operably connected to the transmitter antenna and the receiver antenna to instruct the transmitter antenna to transmit the first electromagnetic signal into the surrounding formation, receive a first response signal from the surrounding formation in response to transmitting the first electromagnetic signal, receive a second response signal from the surrounding formation in response to a second electromagnetic signal transmitted from a target well, and determine an azimuthal direction from the downhole ranging tool to the target well based at least in part on a joint-inversion among response signals received at the receiver antenna.