A method includes receiving data indicative of outputs of first and second seismic sensors. The outputs include components corresponding to the detection by the first and second seismic sensors of first and second seismic signals. In addition, the method includes identifying, relative to a first clock in the first seismic sensor, a first time associated with a time of arrival of the first seismic signal at the first seismic sensor, and a second time associated with a time of arrival of the second seismic signal at the first seismic sensor. Further, the method includes identifying, relative to a second clock in the second seismic sensor, a third time associated with a time of arrival of the first seismic signal at the second seismic sensor, and a fourth time associated with a time of arrival of the second seismic signal at the second seismic sensor. Still further, the method includes determining an offset of the first clock relative to the second clock using the first, second, third and fourth times.

A seismic system that includes a seismic source configured to generate a first seismic signal and a second seismic signal in a formation adjacent the seismic source. A first downhole sensing device disposed in a first borehole configured to detect the first seismic signal and the second seismic signal in the formation; and a first surface acquisition system is in communication with the first downhole sensing device. The first surface acquisition system is configured to: determine a first reference transit time based at least in part on detection of the first seismic signal by the first downhole sensing device; a first subsequent transit time based at least in part on detection of the second seismic signal by the first downhole sensing device; and

whether a synchronization variation is expected to be present based at least in part on the first reference transit time and the first subsequent transit time.

A technique facilitates accumulation of information via arrays of seismic tools to enable improved assessment of subterranean reservoirs. A plurality of seismic tool arrays may be combined to increase the quantity of downhole seismic tools, e.g. sensors. The seismic tool arrays are synchronized, via downhole clock synchronization technology, in a manner which enhances seismic data collection via the combined seismic tool arrays. In drilling applications, the seismic tool arrays may be combined with a bottom hole assembly. For example, multiple seismic tool arrays may be combined in a logging-while-drilling platform.

A time synchronization system includes: a position information acquisition unit configured to acquire installation position information related to an installation position of a time synchronization target whose time is synchronized; a time synchronization signal acquisition unit configured to receive a positioning signal transmitted from a positioning satellite as a time synchronization signal and acquire, from the time synchronization signal, transmission position information related a position of the positioning satellite and transmission time information at timing when the time synchronization signal is transmitted; and a signal processing unit configured to calculate synchronized time information for the time synchronization target based on the installation position information of the time synchronization target and the transmission position information and transmission time information from the time synchronization signal, and transmit the synchronized time information to the time synchronization target.

In some embodiments, an apparatus and a system, as well as a method and an article, may operate to receive a derived clock signal downhole, the derived clock signal being derived from a surface clock signal (associated with a surface clock), such that the frequency of the derived clock signal is less than the frequency of the surface clock signal. Further activity may include measuring the frequency of the derived clock signal in terms of an uncorrected downhole clock frequency (associated with a downhole clock) to provide a measured frequency equivalent, and correcting time measurements made using the downhole clock, based on the measured frequency equivalent, or based on an actual frequency of the downhole clock determined according to the measured frequency equivalent. Additional apparatus, systems, and methods are described.

In a logging system (100), multiple receiver units (106) are synchronized over a control area network (CAN) bus (110) without use of separate differential lines. A ready for synchronization command is received over the CAN bus (110). In response to receiving the ready for synchronization command, a start synchronization interrupt is enabled. A start synchronization command is then received over the CAN bus (110). In response to receiving the start synchronization command, the start synchronization interrupt is triggered for capturing formation signals which are produced responsive to excitation signals from a transmitter unit (104).

In a logging system (100), multiple receiver units (106) are synchronized over a control area network (CAN) bus (110) without use of separate differential lines. A ready for synchronization command is received over the CAN bus (110). In response to receiving the ready for synchronization command, a start synchronization interrupt is enabled. A start synchronization command is then received over the CAN bus (110). In response to receiving the start synchronization command, the start synchronization interrupt is triggered for capturing formation signals which are produced responsive to excitation signals from a transmitter unit (104).

Method, apparatus and system for calibrating and synchronizing a seismic acoustic source array (50) by taking into account both a time-break signal (500) and a near-field signal (504). A time delay between the time-break signal and the near-field signal is used to calculate an offset for adjusting the shooting of the source elements of the source array.

Method, apparatus and system for calibrating and synchronizing a seismic acoustic source array (50) by taking into account both a time-break signal (500) and a near-field signal (504). A time delay between the time-break signal and the near-field signal is used to calculate an offset for adjusting the shooting of the source elements of the source array.

A downhole repeater network timing system for a drilling rig including a drillstring extending subsurface downwardly from a surface wellhead. The system includes a node located at the drillstring lower end and including a sensor adapted for providing a signal data set output corresponding to downhole drilling conditions. Multiple nodes are located downhole between the Bottom Hole Assembly (BHA) and the wellhead and are associated with the drillstring. The nodes are adapted for receiving and transmitting the signals. The timing control system is adapted for controlling all times within a timeframe according to pre-configured constants known to all nodes. A downhole low rate linear repeater network timing method uses the system.