It is possible to record data continuously by using a recording length that is longer than the time interval between consecutive shots. This can be useful for imaging deep targets with long offsets, for example in salt-prone areas. Continuous recording can improve source sampling and have a positive impact on efficiency, particularly in the presence of strong currents.
By overlapping shot records, the recording length chosen for a survey can be longer than the time interval between consecutive shots. This is comparable to continuous recording as a continuous data stream can be extracted.
- Overcome large water depths
- Increase acquisition speed
- Improve efficiency especially when acquisition is affected by strong currents
- Image deeper targets
- Improve noise removal and minimize edge effects
This technique was utilized for the full-azimuth Triton survey in the Gulf of Mexico, where it increased the recording period without increasing the shot interval between consecutive signals. Longer recording lengths are better for imaging of deep sub-salt targets with long offsets, a common feature in the Gulf.
Combining continuous recording and overlapping shot records also speeds up acquisition, as well as improving efficiency in the presence of strong currents. This method of recording is a requirement for triple source acquisition.
Optimal Acquisition Parameters
A number of factors come into play when calculating the optimal acquisition parameters.
- Water depth in the survey area
- Target depth(s)
- Velocity model
- Intended shot point interval
- Intended record length
- Expected average acquisition bottom speed
- Current strength relative to acquisition direction, if available
The results of this assessment will typically provide the optimal record length and the maximum achievable shot overlap. An alternative shot point interval may also be considered. Nucleus+ is used to design and model the survey.