Onshore nodal seismic surveys: you asked, we answered

In May 2023, STRYDE hosted a webinar where expert geophysicists and geoscientists from DNO ASA and DUG discussed the valuable insights gained from recent nodal seismic surveys. The audience remained actively engaged throughout the webinar, bombarding the team with numerous thought-provoking questions.

You asked, we answered
The webinar

You asked, we answered

We have addressed some of the numerous questions posed by the audience during the webinar hosted by STRYDE, DNO ASA, and DUG in May 2023. Our expert geophysicists and geoscientists have provided detailed answers and insights to ensure that these queries are comprehensively addressed...

STRYDE nodes have massively changed the price point for seismic nodes. Its very hard to give any figures for costs of seismic surveys as STRYDE is not a seismic contractor. However, any survey using STRYDE equipment is proven to be significantly cheaper due to the much lower logistic and operational costs.

Field crew size really depends on the number of nodes to roll daily, receiver interval and the terrain. We typically see deployment speeds of 15 seconds per node for 25m receiver interval in desert. In arctic forested area in snow, we have seen 40 seconds per node for 25m interval. If you roll 2000 nodes per day in flat desert, then you would need 4 deployment team (12 people) and 4 retrieval teams (8 people). 2000 nodes can fit in a small light vehicle so logistics of rolling the nodes would be very easy.

No, the STRYDE Nodes™ are as sensitive as any other receiver system, The depth of investigation of any seismic survey depends mainly on the power of the source and the subsurface geology.

This is a complex problem based on the local geophysical data quality and survey parameters. In most surveys, nodes are deployed at half the receiver interval of the previous surveys. We typically see nodes being deployed at 10m, 12.5, 15m or 25m intervals. As was mentioned during the webinar, going denser allows much improved denoise and improved data quality.

Nothing special about deblending single-sensor nodal data. If anything, inversion-based deblending works better with highly sampled data as the thresholding in the FK becomes more reliable. Continuous recording plays a crucial role in enabling a completely free sim source acquisition where sources can fire at any time and reach very high operational efficiency, while still guaranteeing that all sources are captured, even the bad ones (important for good deblending). A very dense survey acquired by ADNOC in 2019 using the STRYDE Nodes™ and 16 Vibroseis shooting in ISS mode delivered an outstanding operational efficiency and the deblending was excellent. (https://doi.org/10.3997/2214-4...)

You are right, the 3D FKK was just an example to show how simple process like FKK can work very efficiently on HD data. Diffraction tails require another level of "care" in processing if they are to be preserved, although FKK filter designed for GR will only target certain frequencies which are usually lower than diffraction, there are other methods that can be more effective, for example modelling GR through SWI and removing them with adaptive subtraction ...etc. Diffraction has become the subject of a whole new way of processing (diffraction imaging) and high spatial sampling plays actually a crucial role in detecting them in the 1st place as they would usually be unrecognizable on sparse data.

Failure rates have been extremely low so far (<0.1%). The node has been kept very simple to reduce potential failures from a lot of electronics. We have had STRYDE Nodes™ operating now for around 5 years with very few issues. In the Compact and Pro system configurations, we supply a node test system which shakes the nodes with sine waves and impulses to check the node performance.

Yes, the data volumes are large but the system has been meticulously designed to handle huge data volumes. The raw data is harvested to Raid drives consisting of SSD drives. The receiver gathers are then generated from the raw data on the SSD raid array which is efficient due to fast read/write operations on the SSD drives. All data is backed up to NAS drives using 10GB/s ports. Clients can then copy data to tape 3592 drives. STRYDE system has data QC software to look at raw data, receiver and shot gathers. The seismic contractor needs to provide an infield QC system to make any brute stacks or other client deliverables.

We are using the standard procedures for high-density data as we mentioned during webinar. If you need any additional details about the processing please click here to contact the processing team: https://strydefurther.com/what...

STRYDE has massively reduced the price point for nodal devices enabling much higher density data at the same equipment cost as a conventional survey, and this is before the cost savings from operational efficiencies are factored in.

The GPS jamming did not affect then node timing as it happened only sporadically and the nodes were set up get a time fix every 2 hours so the nodes got enough fixes data to keep the time sync under control. The main operational issue with the GPS jamming was when it stopped the field crew deploying the nodes on the stakeless survey. If node positions were presurveyed in advance (i.e. marked by stakes) then there would be no deployment delays.

The nodes will get GPS signal even if buried under 1m of sand. We rarely see any loss of time sync's on desert crews. There have been various operation ways to deploy nodes in big dunes. The most successful method has been using a 1m fiberglass pole pushed into the sand and the nodes is tied to the pole. On the various jobs using this method, we have seen extremely low node loss. The crew can also set up verification teams. These teams can regularly visit the nodes and read node status (battery, memory, recording status etc).

3d refraction tomography has been used in O&G exploration for several decades, and although initially aimed at modeling the near surface to calculate statics, it later became an an essential part of the PSDM model bulding workflow. the 3D model is also used to detect cavities or near surface features that are too shallow to be imaged by reflection seismic. We are also seeing an outstanding resolution reached by 3d RT when high density data is used mainly because of the huge number of rays crossing the inverted model allowing teh use of smaller size voxels with still a high hit count. So the expertise and the tools are available. At, STRYDE we produce these type of models routinely for O&G and Geothermal projects, and we can certainly help with this project.

Higher modes can potentially be captured better with higher spatial sampling, in fact we have seen many examples with STRYDE deployed at 2m where some ground roles modes were still aliased!

However, the presence of high modes is not guaranteed as surface wave can be very complex in certain geological settings. The same challenges as in picking and inverting the other modes will still remain, but it certainly brings additional information to the inversion if it's there.

The node uses an accelerometer with a low frequency response down to 1Hz (-3dB point). So it will easily record low frequency seismic data from any vibrator.

The STRYDE Node™ is a blind node. You can visit the node regularly to see if it is operational ok (battery, memory, recording etc). There is no way to see any seismic data real-time as this requires radio comms which adds cost to the node. During harvesting, there are a lot of quality checks done on the seismic data and node health. Certain attributes are saved in a database (CHEQ) that keeps the history of the nodes. If attributes are out of specification then the operator is alerted to take out the node and test again.

We have numerous developments in R&D to help with lost nodes, however, our experience so far suggests that using a precise deployment with RTK GPS almost no nodes are lost, on one recent 60k node project in a desert environment with sand dunes, the crew lost just 1 single node. If the node is displaced through theft, or animals relocating it then any near-field telemetry will not be useful anyway.

It is correct that there is no current tilt measurement even though the node records data no matter what angle sits. The decision whether to include a tilt measure is with our engineering team and we should be able to share our solution soon. Our node is almost never constrained by memory when recording at 2ms, the battery will expire after 28 days before our 16Gb memory is full.

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