In the oil & gas and renewables sectors, applied acoustics sparkers are a go-to option for ultra-high resolution geophysical surveys. This year especially, we’ve seen a high demand for our Dura-Spark 400+400 and accompanying CSP units.
We’ve also had many enquiries from customers, already in possession of aae equipment; who are looking to upgrade to the stacked sparker. However, these customers are often unsure what the benefits of the stacked sparker system are and if their existing equipment is compatible.
A common line of enquiry is:
- What are the advantages of the Dura-Spark 400+400 over single deck sparkers?
- How do I power the unit?
- which CSP works best with the stacked sparker?
- can I use my existing CSP unit?
Here, we endeavour to explain and clarify these points for customers considering the Dura-Spark 400+400.
What are the advantages of a stacked sparker?
The key advantage of the two-deck, stacked sparker system is the ability to fire the unit in different modes: Flip-Flop, Fire-Delay and Split-Fire. These modes describe the number of tips per shot, in use, and the deck fire sequence used to produce the source pulse. By engaging different fire modes, the source fire rate can be increased or the pulse frequency content fine-tuned.
In this mode, we fire one deck at a time, alternating between the top and bottom deck with each trigger signal. This requires two separate CSPs, one to power the top unit and a second to power the bottom. The key advantage is the ability to fire the source at twice the max shot interval, possible with a single CSP unit. In this way, we can greatly increase the shot density of a survey and in turn, the horizontal resolution.
As with Flip-Flop mode, fire delay requires two CSP units; one for each deck of the sparker. However, in this mode instead of firing the top and bottom deck at separate intervals; they are fired in very close succession (~200μS delay).
Firing in this way has two advantageous effects. Firstly, by timing the firing of the second deck correctly, we are able to suppress the negative effects of the secondary pulse oscillations (‘bubble pulse’). This gives us a shorter duration, higher amplitude pulse; than can be produced by a single deck sparker.
By further tweaking the power levels, the number of tips, time delay and sparker depth; Fire-Delay also gives the user the ability to fine-tune the frequency content of their source pulse.
This mode in practice is very similar to Fire-Delay. However, instead of upper and lower decks firing in close succession; arrays on the same deck are fired with a very small time delay. Again, the purpose of this mode is to give the user the ability to fine-tune the frequency content of the source pulse; for example, lengthening the pulse and in turn, adding energy to lower frequency components. Split-Fire mode can be employed with any multi-array sparker. However, as with Fire-Delay, two CSP units are required.
Choosing a CSP (bangbox):
Customers looking to purchase our Dura-Spark 400+400 sparker, obviously want to make full use of the sparkers power levels and fire modes. We therefore recommend using the Dura-Spark 400+400 in conjunction with either the CSP-Nv 1200, CSP-Nv 2400 or CSP-SNv 1250. All of these CSPs have the Flip-Flop and Fire-Delay functions which enable them to be used in partnership with a second CSP, as either a ‘control’ or ‘slave’ unit.
[Note: older CSP units, i.e. CSP-N, can be used as ‘slave’ units in conjunction with a newer model, but only CSP-Nv 1200, CSP-Nv 2400 or CSP-SNv 1250 can be used as the control unit.]
The number in the CSP name relates to the max output energy possible for a single discharge: 1200, 2400 or 1250 Joules respectively. The Nv or SNv variations have differing charging rates of: 2000J/s or 4000J/s respectively.
When assessing the suitability of a CSP unit for your particular survey needs, it is critical to ensure that your unit’s charging rate, is greater than the shot power × shot frequency required for your survey operations.
Charging Rate (J/s) ≥[Output energy (J) ×shot frequency (Hz)]
The above equation is valid for single deck sparkers with one CSP operating in standard mode or Dura-Spark 400+400 sparkers, in standard or Fire-Delay mode. Be aware, that when using Flip-Flop mode; the charging rate of a single CSP is effectively doubled. (See below for some examples of this in practice).
Michael Calvert, our Geophysical Product Manager, tells us why geophysics gets him out of bed in the morning and shares his plans for our renewable energy offering.
How would you describe your role at applied acoustics?
As geophysical product manager, I have quite a varied role. Anything from product training and working on design and development, to organising product trials and answering customer questions and support requests. The whole spectrum.
My main purpose is to be a communications hub, organiser and fixer. With my background as a geophysicist, I can see our products from a customer’s perspective. I talk to engineers, customers and sales, linking them all together to deliver the best product possible.
Where did your interest in geophysics and subsea equipment start?
It was a less usual and more diverse route that led me to this role. Initially, after leaving secondary school, I worked as an electrician. Then, in my late twenties, I went back into full-time education, completing a foundation course in electronic engineering at the University of York.
I have always been a practical thinker, but with a keen interest in earth and life sciences too. I think the subject of geophysics appealed to me because it combines all of these aspects. Therefore, after my studies at York, I went on to complete an integrated Masters in Geophysics at the University of Southampton.
The great thing about working on geophysical surveys, especially marine geophysics, is that you’re often the first to see a part of the world that has never been seen before. That really appealed to my spirit of discovery.
Why did you join applied acoustics?
I’ve worked as an offshore geophysicist for several years (Gardline and EMGS) and it’s not always easy. You’re away from home for six months of the year or more, so I’d always planned to eventually find a shore-based role. The Covid situation this year caused a lot of disruption to offshore survey projects I was working on and provided me with an opportunity to re-assess my work-life balance.
The role at applied acoustics appealed to me because it brought together my knowledge of geophysics and skills from my electronic engineering background. applied acoustics is also a long-term supplier of survey equipment to companies like Gardline, so I already knew they were well-established and respected in the industry.
How would you summarise your experience of the renewables sector?
The majority of my renewables experience came at Gardline. I was involved in offshore wind farm projects in the UK, Europe and USA, working with the likes of Equinor (formerly Statoil) and Ørsted, one of the biggest companies in the offshore wind farm sector.
Some of the projects focused on UXO surveys and clearance, while others incorporated a combination of geophysical methods including seismic surveys, side scan surveys, magnetometers, bathymetry, geotechnical surveys and geohazard identification.
What unique challenges and opportunities do renewables projects offer?
Most windfarms tend to be sited in very shallow water settings, which can be particularly challenging for seismic surveys. These surveys are typically aiming to acquire ultra-high resolution (UHR) data for the near-surface portion of the seabed (first 50m or so).
To get the best results, the surveys depend heavily on highly accurate positioning of equipment (source and receiver), high-frequency sampling of data, and precise timing of events (shots points and arrivals). The combination of these factors mean the UHR surveys, particularly multi-channel surveys, have a very low tolerance for error.
There are also multiple stages to a renewables project, from assessing the viability of offshore construction sites through to construction, then ongoing monitoring and maintenance. As a result, renewables projects tend to be large in terms of geographic area and data volume, not to mention long-lived. This allows us to build relationships with clients over a number of years.
How are applied acoustics’ products designed to suit the needs and challenges of the renewables sector?
Many of our sparkers are designed to produce the high frequencies required for UHR seismic surveys. Our Dura-Spark 240/400 and 400+400 in particular give their users a great amount of flexibility when it comes to varying the source’s power level, pulse shape, frequency content and bandwidth.
Our USBL tracking systems and positioning beacons deliver accurate results in shallow-water and deep-water settings, with little interference. We recently launched our Easytrak Pyxis INS + USBL system, which was very much designed with shallow-water renewables operations in mind.
How are you looking to enhance applied acoustics’ support for renewables clients?
One of our main aspirations is to stimulate discussion and establish trust with everyone in the geophysical survey chain. Our primary relationship is usually with the acquisition company, but by engaging with data processors and the end clients, we can build an even greater understanding of the sector, how it is changing and how we can adapt to that.
We are looking to encourage collaboration at all stages of the process and develop “virtuous circles” with clients. If we can enhance our products to better suit a client’s needs, they can acquire high-quality surveys and in turn make good project decisions.
Granted it’s been a difficult year for building contacts and relationships, but like any problem, we can find a solution if we work together.
Please get in touch with our team today to discuss your renewables project, or reach out to Michael directly on MCalvert@appliedacoustics.com.