System and method for communicating signals in a cased borehole having tubing

For use in an earth borehole which is cased with an electrically conductive casing and has electrically conductive tubing extending therethrough;

• a measuring and communication system for measuring downhole conditions and communicating the measured conditions to the earth's surface, comprising:
• a downhole measuring and communications subsystem mounted on said tubing, said subsystem including:
• means for measuring at least one downhole condition;
• downhole transmitter means responsive to the measured downhole condition for generating an antenna drive signal representative of the measured condition;
• and downhole toroidal antenna means responsive to the antenna drive signal for coupling electromagnetic energy in a TEM mode to the annulus between said casing and tubing;
• an uphole communications subsystem at the earth's surface, including:
• uphole antenna means for coupling electromagnetic energy in a TEM mode from said annulus, an uphole receiver coupled to said uphole antenna for receiving signals representative of the measured condition;
• substantially non-conductive fluid in said annulus in at least the region of said downhole antenna means and above;
• and
• conductive means below said downhole communications subsystem for electrically coupling said tubing and casing.

For use in an earth borehole which is cased with an electrically conductive casing and has electrically conductive tubing extending therethrough;

• a method for communicating between a downhole location and the earth's surface, comprising the steps of:
• encoding downhole information into a pseudorandom code signal;
• transmitting said code signal from downhole to uphole in the form of electromagnetic energy in a TEM mode;
• receiving the transmitted code signal uphole, and demodulating the received signal to determine the modulation function attributable to the transmission path;
• processing the received code signal with the determined modulation function;
• and
• decoding the processed code signal to recover the downhole information.

For use in a borehole which is cased with an electrically conductive casing and has electrically conductive tubing extending therethrough;

• a method for communicating from a downhole location to the surface, comprising the steps of:
• encoding downhole information into a pseudorandom sign-reversing code signal;
• transmitting a number of different code signals from downhole to uphole in the form of electromagnetic energy in a TEM mode;
• receiving the transmitted code signals uphole, and decoding said code signals by correlation with the patterns of said code signals;
• determining a characteristic of the transmission path from the received code signals;
• and
• sending a command signal downhole to select the best available code signal for the transmission path.

For use in an earth borehole which is cased with an electrically conductive casing and has electrically conductive tubing extending therethrough;

• a method for communicating between a downhole location and the earth's surface, comprising the steps of:
• inserting non-conductive fluid in said annulus in at least the region of said downhole location and above;
• electrically coupling the tubing and casing below the downhole communications subsystem;
• coupling information-carrying electromagnetic energy in a TEM mode from a toroidal antenna which is part of a subsystem at said downhole location to the annulus between said casing and tubing;
• and
• coupling information-carrying electromagnetic energy in a TEM mode to a subsystem at the earth's surface from said annulus.

For use in an earth borehole which is cased with an electrically conductive casing and has electrically conductive tubing extending therethrough;

• a method for communicating between a downhole location and the earth's surface while perforation, testing, stimulation, or production of the well is being implemented via the tubing, comprising the steps of:
• inserting non-conductive fluid in said annulus in at least the region of said downhole location and above;
• performing an operation of perforation, testing, stimulation, or production of the well, and during said operation carrying out the following further steps:
• coupling information-carrying TEM electromagnetic energy in a TEM mode from a subsystem at said downhole location to the annulus between said casing and tubing;
• and
• coupling said information-carrying electromagnetic energy in a TEM mode to a subsystem at the earth's surface from said annulus.

For use in an earth borehole which is cased with an electrically conductive casing and has electrically conductive tubing through the casing and spaced from the casing;

• a communication system for communicating between the earth's surface and downhole, comprising:
• an uphole communications subsystem at the earth's surfaces, including:
• uphole antenna means and an uphole transmitter, said uphole antenna means coupling electromagnetic energy in a TEM mode from said transmitter to the annulus between the casing and tubing;
• a downhole communications subsystem mounted on said tubing, said subsystem including:
• a downhole receiver and a downhole toroidal antenna means concentric the tubing for coupling electromagnetic energy in a TEM mode from the annulus to said receiver;
• substantially non-conductive fluid in said annulus in at least the region of said downhole antenna means and above;
• and
• conductive means below said downhole communications subsystem for electrically coupling said tubing and casing.