Design and Implementation of a High Precision Time Synchronization Method for Borehole-surface Microseismic Monitoring

Borehole-surface monitoring can effectively improve the accuracy of the microseismic event location. It is necessary to strictly synchronize the acquisition time of borehole and surface monitoring nodes. However, the synchronization signal transmission through the logging cable will cause a delay. In this paper, a calibration method designed to compensate for the deviation of time synchronization due to long-distance transmission on the logging cable. First, the transmission delay of the pulse per second (PPS) is measured in the delay measurement stage. The delay from the global positioning system (GPS) module to all monitoring nodes can get in sequence. Second, In the delay compensation stage, each monitoring node is delayed for a particular time to ensure that all nodes start working simultaneously. Finally, a high-precision clock source is designed to drive the analog-to-digital converter (ADC) to avoid the crystal oscillator’s accumulated error. To verify the accuracy of the calibration method, the modules were tested separately. The length of the logging cable used is 3000 meters. Through experimental verification, the method in this paper can be used to accurately control the time synchronization of different monitoring nodes in the borehole and on the surface within 1us.