Cable Telemetry Synchronization System and Method

Abstract

Cable telemetry synchronization systems and methods. The synchronization can involve positioning downhole equipment into a wellbore via a cable operatively coupled to a surface module that can include a telemetry system master clock. The downhole equipment can include a toolbus master node and at least one slave node module having a node clock operatively coupled to the toolbus master node. The synchronization can also involve sending a frame start command to the at least one slave node module from the toolbus master node at predetermined intervals, receiving a clock value from each of the at least one slave node module, calculating a clock offset for each of the at least one slave node module, and sending an absolute clock value and the calculated clock offset for each of the at least one slave node module via a downlink synchronization command to the at least one slave node module.

1 . A cable telemetry synchronization system for a wellsite having a rig positionable about a borehole penetrating a subterranean formation, comprising:
 a surface module comprising a telemetry system clock;   downhole equipment deployable into a wellbore via a cable operatively coupled to the surface module, the downhole equipment comprising:
 at least one slave node module, each of the at least one slave node module having a node clock and interface packet; and 
 a downhole master node module comprising a toolbus master node clock synchronized to the telemetry system clock, and the downhole master node module sends a frame start command to each of the at least one slave node module to synchronize the node clock(s) to the toolbus master node clock. 
   
     
     
         2 . The cable telemetry synchronization system according to  claim 1 , further comprising a global positioning system (GPS) clock; wherein the telemetry system clock and the toolbus master node clock further synchronize to the GPS clock. 
     
     
         3 . The cable telemetry synchronization system according to  claim 1 , wherein the downhole master node module determines, for each of the at least one slave node module, a clock offset based on a function of an arrival time for the frame start command and a response time for a return uplink packet from each of the at least one slave node module in response to the frame start command. 
     
     
         4 . The cable telemetry synchronization system according to  claim 3 , wherein, upon determining the clock offset for each of the at least one slave node module, the downhole master node module sends an absolute clock value and the clock offset for each of the at least one slave node module to a relevant one of the at least one slave node module, and each relevant one updates the node clock based on the absolute clock value and the clock offset for the relevant one. 
     
     
         5 . The cable telemetry synchronization system according to  claim 3 , wherein the interface packet for each of the at least one slave node module, upon receipt of the absolute clock value and a clock offset time, time stamps slave node event data based on the absolute clock value and the clock offset time for the at least one slave node module; and wherein the slave node event data is obtained by at least one downhole tool coupled to the at least one slave node module. 
     
     
         6 . The cable telemetry synchronization system according to  claim 1 , wherein each of the at least one slave node module further comprises a clock and data recovery (CDR) module that, upon receipt of an uplink message at the at least one slave node module, detects a preamble of the uplink message indicative of a coding scheme used by at least one lower node of the at least one slave node module for the uplink message, and locks the at least one slave node module to the detected coding scheme of the preamble. 
     
     
         7 . The cable telemetry synchronization system according to  claim 1 , wherein each of the at least one slave node module further comprises a clock recovery (CR) module that, upon receipt of a downlink message, detects the frame start command. 
     
     
         8 . The cable telemetry synchronization system according to  claim 1 , further comprising a numerically controlled oscillator, the toolbus master node clock being driven by the numerically controlled oscillator. 
     
     
         9 . A method for synchronizing a cable telemetry synchronization system of a wellsite having a rig positionable about a wellbore penetrating a subterranean formation, comprising:
 positioning downhole equipment into the wellbore via a cable, the downhole equipment comprising a toolbus master node and at least one slave node module operatively coupled to the toolbus master node, each of the at least one slave node module having a node clock;   sending a frame start command to the at least one slave node module from the toolbus master node at predetermined intervals;   receiving a clock value from each of the at least one slave node module;   calculating a clock offset for each of the at least one slave node module; and   sending an absolute clock value and the calculated clock offset for each of the at least one slave node module via a downlink synchronization command to the at least one slave node module.   
     
     
         10 . The synchronization method according to  claim 9 , wherein calculating the clock offset further comprises determining, for each of the at least one slave node module, the clock offset based on a function of an arrival time for the frame start command and a response time for a return uplink packet from each of the at least one slave node module in response to the frame start command. 
     
     
         11 . The synchronization method according to  claim 9 , further comprising:
 obtaining slave node event data by at least one downhole tool coupled to the at least one slave node module; and   upon receipt of the absolute clock value and a clock offset time, time stamping the slave node event data based on the absolute clock value and the clock offset time for the at least one slave node module.   
     
     
         12 . The synchronization method according to  claim 9 , further comprising updating the node clock of a relevant one of the at least one slave node module based on the absolute clock value and the clock offset for the relevant one slave node. 
     
     
         13 . The synchronization method according to  claim 9 , further comprising determining, for each of the at least one slave node module, a phase-lock adjustment based on a function of an arrival time for the frame start command. 
     
     
         14 . The synchronization method according to  claim 9 , further comprising synchronizing the toolbus master node and the at least one slave node module to a global positioning system (GPS) clock.