A method and system for determining first breaks of sonic waveforms

A non-transitory computer readable medium storing instructions executable by a computer processor, the instructions comprising functionality for:

• obtaining a sonic dataset from a sonic tool moveable within a wellbore, wherein the sonic tool comprises a source and a plurality of receivers each separated by a unique source-receiver distance, and the sonic dataset includes a plurality of traces each corresponding to a unique combination of one of the plurality of receivers and one of a plurality of source activation locations in the wellbore,
• determining a sonic slowness log from the sonic dataset;
• for each trace recorded by a subset of the plurality of receivers:
• determining an initial first break estimate for each trace, and
• determining a second first break estimate based on an energy ratio within a time window surrounding the initial first break estimate;
• for each of the plurality of traces in the sonic dataset:
• predicting a refined first break estimate based, at least in part, on the second first break estimates, the sonic slowness log, and an inter-receiver distance;
• and
• determining the set of final first breaks of the sonic dataset by applying a time shift to the refined first break estimates.

A system for determining a set of final first breaks of a sonic dataset obtained from a sonic tool moveable within a wellbore, wherein the sonic tool comprises a source and a plurality of receivers each separated by a unique source-receiver distance, and the sonic dataset includes a plurality of traces each corresponding to a unique combination of one of the plurality of receivers and one of a plurality of source activation locations in the wellbore, the system comprising:

• the sonic tool to acquire the sonic dataset;
• a logging acquisition system to record the sonic dataset;
• and
• a processor configured to:
• determine, a sonic slowness log from the sonic dataset;
• for each trace recorded by a subset of the plurality of receivers:
• determine an initial first break estimate for each trace, and
• determine a second first break estimate based on an energy ratio within a time window surrounding the initial first break estimate;
• for each of the plurality of traces in the sonic dataset:
• predict a refined first break estimate based, at least in part, on the second first break estimates, the sonic log, and an inter-receiver distance;
• and
• determine the set of final first breaks of the sonic dataset by applying a time shift to the refined first break estimates.