Wellsite System and Method for Multiple Carrier Frequency, Half Duplex Cable Telemetry

Abstract

Methods and systems for multiple carrier frequency, half duplex cable telemetry for a wellsite. The methods involve generating a first type of bi-directional message in a first propagation mode, generating a second type of bi-directional message in the first propagation mode and in a second propagation mode, transmitting over a cable operatively coupling a surface modem and a downhole modem the first and second types of bi-directional message sequentially in a plurality of time periods across a single frequency bandwidth, and separating each of the first and second types of bi-directional message from a most subsequently transmitted one of the first and second types of bi-directional message by a quiet time sample during which no message is transmitted.

What is claimed is: 
     
         1 . A method for multiple carrier frequency, half duplex cable telemetry for a wellsite, comprising:
 generating a first type of bi-directional message in a first propagation mode;   generating a second type of bi-directional message in the first propagation mode and in a second propagation mode;   transmitting the first and second types of bi-directional message over a cable operatively coupling a surface modem and a downhole modem sequentially in a plurality of time periods across a single frequency bandwidth; and   separating each of the first and second types of bi-directional messages from a most subsequently transmitted one of the first and second type of bi-directional message by a quiet time sample during which no message is transmitted.   
     
     
         2 . The method according to  claim 1 , wherein the cable comprises one of a heptacable, a monocable, a coaxial cable, a wired drill pipe conductor, and a slickline. 
     
     
         3 . The method according to  claim 2 , wherein the first propagation mode comprises a T5 propagation mode. 
     
     
         4 . The method according to  claim 2 , wherein the second propagation mode comprises a T7 propagation mode. 
     
     
         5 . The method according to  claim 1 , wherein the first type of bi-directional message comprises downlink and the second type of bi-directional message comprises uplink. 
     
     
         6 . The method according to  claim 1 , wherein a length of the quiet time sample is determined based on one or more of: a length of the cable, a time interval sufficient for a cross-talk ECHO to dissipate, a travel latency time sufficient to avoid overlap of the first and second types of bi-directional message, and a variable user input. 
     
     
         7 . A system for multiple carrier frequency, half duplex cable telemetry for a wellsite, comprising:
 a surface modem that generates one or more downlink messages in a first propagation mode;   one or more downhole tools that obtain measurements relating to at least one of borehole characteristics and formation characteristics, the one or more downhole tools coupled by a toolbus to a downhole modem, the downhole modem generating one or more uplink messages in the first propagation mode and in a second propagation mode;   a cable electrically coupling the surface modem and the downhole modem;   wherein the downlink and uplink messages are transmitted over the cable sequentially in a plurality of time periods across a single frequency bandwidth, each of the downlink and uplink messages is separated from a most subsequently transmitted one of the downlink and uplink messages by a quiet time sample during which no message is transmitted.   
     
     
         8 . The cable telemetry system according to  claim 7 , wherein the cable comprises one of a heptacable, a monocable, a coaxial cable, a wired drill pipe conductor, and a slickline. 
     
     
         9 . The cable telemetry system according to  claim 8 , wherein the first propagation mode comprises T5 propagation mode; and wherein the second propagation mode comprises T7 propagation mode. 
     
     
         10 . The cable telemetry system according to  claim 7 , wherein a length of the quiet time sample is determined based on one or more of: a length of the cable, a time interval sufficient for a cross-talk ECHO to dissipate, a travel latency time sufficient to avoid overlap of two types of bi-directional message, and a variable user input. 
     
     
         11 . A system for multiple carrier frequency, half duplex cable telemetry for a wellsite, comprising:
 a surface acquisition unit operatively coupling to a surface modem that generates one or more downlink messages in a first propagation mode;   a downhole modem that generates one or more uplink messages in the first propagation mode and in a second propagation mode;   a downhole toolstring comprising one or more downhole sensing tools that obtain measurements relating to at least one of borehole characteristics and formation characteristics, the downhole toolstring operatively coupled to the downhole modem via a toolbus;   a cable electrically coupling the surface modem and the downhole modem;   wherein the downlink and uplink messages are transmitted sequentially in a plurality of time periods across a single frequency bandwidth, each of the downlink and uplink messages is separated from a most subsequently transmitted one of the downlink and uplink messages by a quiet time sample during which no message is transmitted.   
     
     
         12 . The wellsite system according to  claim 11 , wherein a length of the quiet time sample is determined based on one or more of: a length of the cable, a time interval sufficient for a cross-talk ECHO to dissipate, a travel latency time sufficient to avoid overlap of the two types of bi-directional message, and a variable user input.