A logging system 2 is described in which an input signal value is compare by a signal processor 12 to a trigger-band 34 and an inner-band 36 centre about a previously logged value 34 and changing at a previously determined rate of change. When the trigger-band is exceeded at point 40, intermediate points are logged representing the maximum and minimum points since the last logged point and the point at which the inner-band was left. The intermediate points enable a more accurate subsequent reconstruction of the actual signal to be made from the logged values.
The specification discloses a method of maintaining a historical database of information. The method describes up to eleven segments, each segment corresponding possibly to a different data logging rate in the historical database. Points, whether measured or calculated parameters, are grouped into segments based on which points may have their data logged at the same frequency. The points, in turn, contain pointers to logs, with entries in the log data corresponding to a time-stamp or tag of the segment to which the log belongs. Thus, points (and their corresponding logs) in different segments may be logged at different rates. The specification also discloses a method for dynamically resizing the historical database.
The present invention is directed to methods and systems for taking measurements relating to subterranean formations. The methods and systems effectively compress data and thus facilitate more efficient data transmission. The methods and systems are capable of automatically varying data compression rates during a measurement operation. The variable data compression capability facilitates reliable collection of measurement data at faster and/or constant logging speeds. The data compression methods and systems may be applied to any measurement operation relating to subterranean formations, including, but not limited to: acoustic wireline logging measurements, acoustic logging-while-drilling measurements, electromagnetic measurements, nuclear magnetic resonance measurements, and resistivity measurements.
A logging system 2 is described in which an input signal value is compared by a signal processor 12 to a trigger-band 34 and an inner-band 36 centered about a previously logged value 34 and changing at a previously determined rate of change. When the trigger-band is exceeded at point 40, intermediate points are logged representing the maximum and minimum points since the last logged point and the point at which the inner-band was left. The intermediate points enable a more accurate subsequent reconstruction of the actual signal to be made from the logged values.
