This efficient acquisition and processing method has significant environmental advantages compared to traditional acquisition. eSeismic utilizes continuous source and receiver wavefields to produce broadband subsurface images.
eSeismic uses continuous source and receiver wavefields to fundamentally change the way that marine seismic data are acquired and processed. Seismic data is continuously recorded for as long as it takes to acquire the sail lines. The sources are also operated continuously. A significant decrease in sound pressure levels is achieved, meaning less environmental impact and improved sampling, without compromising efficiency.
A field trial in Brazil confirms the potential benefits of recording of continuous source and receiver wavefields including reduced environmental impact, improved efficiency and better data quality. eSeismic development is funded by The Research Council of Norway, Equinor and PGS.
- Environmental: Peak sound pressure levels (SPL) can be significantly reduced by distributing the emitted signals from the sources in time
- Environmental: Sound exposure levels (SEL) integrated over time can also be reduced
- Efficiency: There are no speed limitations since the method does not require the seismic recording or the sources to be triggered with specific spatial intervals, and since no listening time is needed
- Efficiency: Rapid coverage of the target during the acquisition by operating several sources simultaneously, and increasing the spread width of the sources
- Quality: Continuous wavefields may deliver uplifts in data quality and spatial sampling of source positions.
The continuous source wavefields can be generated with either marine vibrator technology or with traditional airguns. Individual airguns are triggered in a near-continuous fashion with short randomized time intervals to generate a continuous wavefield. The emitted signals approach the properties of white noise making it possible to deconvolve the data with the total source wavefield.
Field Trial in Brazil
A small-scale trial survey was acquired in 2018, with 16 x 8100-meter multisensor GeoStreamers with 100 m streamer separation. A constant streamer tow-depth of 15 m was used. The source set-up consisted of six sub-arrays of airguns, where each sub-array was equipped with six airguns. Individual airguns were triggered with a mean interval between consecutive triggerings of several shots a second. The nominal separation between the sub-arrays of airguns was 16.67 m. Since the source deconvolution using the proposed method can solve for one point-source per sub-array with six point-sources in the crossline direction, the nominal cross-line bin size for this survey is 8.33 m. In the inline direction, the receiver gathers have a trace spacing of 12.5 m. For comparison, a conventional dual-source acquisition with the same streamer geometry would deliver a cross-line bin size of 25 m.
eSeismic (right) provides significantly reduced values of sound pressure and sound exposure levels but yields comparable imaging results to a dual-source setup (left).
Lower Noise Emission, Increased Sampling, Greater Efficiency
One of the main potential benefits of eSeismic is a reduction in the environmental impact of marine seismic sources. The peak sound pressure levels are significantly reduced by triggering one airgun at a time compared to triggering an array of several airguns simultaneously. Sound exposure levels are also reduced. The peak sound pressure levels are approximately 20 – 22 dB lower for the proposed method compared to conventional, whereas the sound exposure levels are 8 – 9 dB lower for eSeismic.
Sampling is increased by 300% and dense crossline CMP spacing is achieved without compromising the acquisition efficiency. The 800 m wide sail-line is sampled with 96 common midpoints, compared to 32 with a standard dual-source configuration. The bin size of the 3D migrated volume is 12.5 x 12.5 m.
From an efficiency standpoint, there are minimal vessel speed limitations, since this method does not require the seismic recording (or the sources) to be triggered with specific spatial intervals. Limitations imposed by shot cycle-time and record length are now relaxed.
Imaging Continuous Wavefields
On the receiver side, all the continuous data are processed at once to maintain the continuity of the data. After receiver motion correction of each measured component, the measured data are in stationary receiver positions and the deconvolution of the emitted source wavefield can be performed. This is done by computing the entire emitted source wavefield that can contribute to each stationary receiver location. In order to enable a stable deconvolution of the source wavefield, the source wavefield needs to be as 'white' as possible, without deep notches in the spectrum.
In addition to continuous seismic recording, nearfield hydrophone data needs to be recorded continuously, in order to be able to determine the wavefield emitted by the individual source elements.
Shallow time slices show improved lateral resolution, especially in the crossline direction (vertical axis), for eSeismic (right) compared to conventional dual-source data (left).