ISS – Independent Simultaneous Sweeping

The technology is based on independent, simultaneous excitation by multiple groups of vibration sources with no synchronization between groups and the use of different sweep signals (e.g., different durations or frequency ranges). Each vibration source group excites vibration in its own area, independently of the other groups, thus increasing the productivity of the operation. To receive the oscillations, a nodal system of continuous recording is used at all times. Separation of recordings from different vibration source groups is done according to time-stamped files generated by the GDS II for each group. The control sweep signals from each group of vibration sources are recorded on the service channel of the block and used to correlate the vibration programs. To maximize the difference between sweep signals from different source groups, nonlinear broadband sweep signals (BroadSweep) of different durations, generated by the GDS II, are used. Because of the different durations of the nonlinear broadband sweep signals, the sources operate in different frequency bands due to the different speeds of the frequency-time sweep, even though they excite vibrations simultaneously.

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ISS

Application example:

In March 2022, Bashneftegeofizika, with the participation of experts from Spetsgeofizika, conducted work in the Yuzhno-Yamburgskaya area to evaluate the impact of working methods on the productivity of seismic surveys when using different types of sweep signals. The basic possibility of implementing ISS and Shuffle techniques with cable equipment was demonstrated (in the original version of the work on the ISS method, it was planned to be implemented with the Stride cableless system).

An area of 30 square kilometers (2000 shot points) was selected to conduct the experiment and methodology. Four groups of installation of a seismic signal were mined at this site. To mine the area, the type of sweep was selected and the number of sources in the group was determined (see fig. below). Registration was done in continuous recording mode on the Sercel 508XL* (99-second seismic slices). The vibrator control system GDS-II provided the ability to determine coordinates and registration times. Transcriber^® software was developed to allow processing of such data.

The following methods were chosen to compare performance:

Slip-sweep (manufacturing method), quasi-linear signal
Shuffle, pseudo-random signal
ISS, linear frequency modulated signal
ISS, Broadsweep Technology.

Characteristics of the compared methods and sweep geometries are shown below.

3. Methods and parameters

Shuffle

4. Result.

Vertical section fragment. 1142 ms slices — fault — «shrinkage crack» in Turonian clay deposit

Shuffle

Comparison of methods:

The first three methods do not differ substantially in vertical resolution; the resolution of the Broadsweep method is significantly higher, especially at the top of the cross section. On the other hand, the in-phase axis resolution and traceability do not decrease with depth as in the Shuffle and ISS methods, and are not inferior to the signal of the Slip-sweep method at extreme depths.
In the Broad Sweep Cube slice, the balance of dynamics and resolution makes small structural and lithologic heterogeneities and rock bodies most subtle and distinct, and often the targets of exploration (faults-»shrinkage cracks» in Turonian clay deposits, individual sand bodies in Cenomanian deposits, channels in deepwater Achimovian deposits, riverbeds and meanders in Jurassic deposits)..
A family of pseudorandom sweeps ensures that individual reactions are separated.
Mixing steps are generated individually by each vibrator according to the parameters of the central encoder.
Using Shuffle sweep on the same test line, performance quadrupled.
Raw Shuffle recordings are noisier than linear recordings, but the quality of the resulting sections is similar.

5. Performance of techniques

* Ph/Hour — physical observation per hour

Data on the performance of each method was obtained from seismic station operators' reports for a given section of the region where 2000 shot points were worked. This figure shows the performance indicators of the methods in their pure form, not taking into account downtime due to weather conditions, refueling, etc.

The performance gain with ISS technology is approximately 1.75 times that of Slip-sweep. The performance of Shuffle is twice that of Slip-sweep; as with ISS, the limit on the number of groups per seismic station is 32 groups.

6. Analysis of the results of applying different signals

The signal used in the Slip-sweep method allows modification of the radiation spectrum by low-frequency sweep coning (3-5 Hz) and negative nonlinear high-frequency sweeps (7-90 Hz) to attenuate the energy of the medium on the recorded data, especially the high-frequency component. At the same time, operating the vibrating units in groups provides more focused field data.
The Shuffled signal vibrograms are completely mixed (one vibrogram for each group of four). After the correlograms are split into individual ones, the noise level of mutual influence increases, limiting the depth of the survey to 5-6 km, along with the absence of low frequencies.
Broadsweep signals use the «dwell» mode instead of low-frequency corning and a positive nonlinear high-frequency sweep. Mutual effects are random and insignificant and are removed by standard noise reduction. As a result, Broadsweep provides a richer, more dynamic image while improving the depth of survey and spatial resolution of the seismic record. This is confirmed by both visual evaluation and by the frequency response of the seismograms and seismic sections.

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