Digital Energy Journal- Advances in vibroseis and wireless seismic at INOVA Geophysical

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Advances in vibroseis and wireless seismic at INOVA Geophysical

Friday, July 15, 2016

US seismic equipment company INOVA Geophysical is known for its development of onshore source (vibroseis) and recording technology. Andy Bull, VP for emerging technology, explained what advances have been made to date.

Onshore wireless seismic recording is moving towards a third generation of technology, said Andy Bull, VP of emerging technology with INOVA Geophysical.

He was speaking at the Finding Petroleum forum in London on February 24, 'New Geophysical Technology'.

INOVA Geophysical was formed as a joint venture between US seismic company ION Geophysical and BGP of China.

Customer demand for wireless technology appears to be moving in two conflicting directions, with some people wanting data communicated in near real time from the wireless recording devices, and other people looking for higher trace density (so more data being recorded, leading to a clearer seismic image). These requirements are somewhat in conflict, because the more data you record, the more it costs to communicate it in real time.

A lower for longer oil price could drive more interest in onshore operations, because onshore oil drilling and production is usually much cheaper than doing it offshore. Studies have shown that 80 per cent of future deepwater projects are likely to be uneconomic at an oil price of below $60, he said, but many onshore projects will still be robust at that price, he said.

Vibroseis Techniques

There is growing industry interest in a technique known as Dispersed Source Arrays which uses high productivity techniques in conjunction with vibrators shaking dedicated frequency bands (low, mid, high) at different spatial intervals. This technique is based on research from the Delphi Consortium, in the Netherlands, showing that it can help to get a better understanding of the subsurface.

Typically, generating low frequencies requires having a specially tuned 'custom sweep' of the seismic signal, with the seismic source signal starting slowly at low frequencies and going gradually to a linear sweep of the higher ones. But research by INOVA indicates that it may be preferable, especially with the DSA technique, to use shorter linear sweeps for low frequency operations, he said. You can deliver more energy into the ground this way, and it also takes less time, improving operational efficiency.

This low frequency linear sweep method is made possible by advances in source controller technology, which automatically limits the stroke at low frequencies and reduces the risk of damage to the vibrator.

Low Frequency Energy

There is also technology development going into improving the low frequency energy which the Vibroseis truck can deliver while maintaining a more stable wavelet which improves data quality and can give additional insight into the subsurface.

INOVA is developing a vibroseis which can almost double the amount of low frequency force energy delivered into the ground. The force from a vibrator can basically be calculated using Newton's 'F=ma' - the vibrator has a reaction mass, which travels towards the ground, and the bigger the travel distance, or stroke, the more acceleration it can gather.

'We've been working on a new vibrator design,' he said. 'We've increased the weight of the reaction mass, we've significantly increased the stroke length and we've redesigned the base plate and hydraulic system.'

It has extensively tested this vibroseis' capability at low frequencies, in one test using geophones installed in a well at 7,500 feet depth, recording high energy seismic between 1 and 4 Hz.

Source controllers

INOVA is also developing its 'source controller' technology, which provide complex feedback control to the vibrator as it executes each sweep.

The quality of source controllers on the market today can vary. In a test INOVA compared a recording from its most recent model with another on the market, and found phase and amplitude control varied significantly and led directly to a much more stable wavelet, depending on controller type, even when both were configured for the same sweep in the same location. There were also differences in how the controllers managed harmonic distortion.

'The wavelet with controller A is more stable and uniform,' he said.

Cableless

Looking now at cableless seismic recording, the market may now be approaching a third generation of equipment, he said.

The first generation, introduced in the 1990s, had a low battery life and limited channel count. The second generation, which was introduced around 2005, had a higher channel count and better battery life but has struggled to seriously challenge cable systems across all regions.

The third generation, will almost certainly be smaller and lighter and probably cheaper. They will take advantage of ongoing improvements in power consumption, energy density, GPS performance and high sensitivity sensors.

It was worth noting that today's second generation systems already achieve a very high level of reliability, which can be measured in terms of a trace yield of over 99 per cent, he said.

While the cost of cabled systems is still coming down, it may soon hit a floor, because of the underlying cost of copper, he said. Cable-less systems currently cost around 1.5x to 2 x as much as cabled systems but this multiple is likely to reduce over time.

Managing communications infrastructure for real-time cableless recording systems gets substantially more complex, as the amount of data and the number of channels increases. This problem also gets much worse in complex terrain or high canopy environment, where, ironically, the benefits of cableless are stronger compared to an easier 'open desert' environment, he said.

The company recently did a project in a tree-covered hillside area of the Marcellus Shale, US, using 2678 autonomous nodes. If a radio communications infrastructure had been required for real time data transmission, it would have needed about 60 radio masts, which would have been operationally complex to install, move and maintain without disrupting production or infringing on permit restrictions. Radio communications infrastructure like this can take 'a lot of trial and error to optimise,' he said. 'While the idea of real time data is seductive, it does have its challenges.'

Trace density

Meanwhile, other parts of the market are looking more closely at the benefits of improving trace density, with experts saying that the increase in trace density has been one of the biggest contributors to the improvement in seismic data quality over the past few years.

Having a high trace density means that the impact of noise such as 'air blast' - when noise from the source travels through the air to the receivers - can be much reduced.

In a study, INOVA found that for a synthetic 45 fold survey with 1800 traces per km2, the suppression of air blast noise was 'not that great'. By doubling the fold to 180, with 7200 traces per km2, there was 'immediate improvement in air blast suppression. Going to 700 fold, 20,000 traces per km2, meant that the noise suppression is 'very effective,' he said.

This approach could offer significant advantages compared to radio-based systems but requires some significant improvements in cableless technology and reductions in per channel cost.

Audience comment

After the talk, one audience member noted exploration managers are successful if they manage to find something which other people haven't found (even though they were exploring the same part of the world) - and one way to do that can be to use a higher trace density than your predecessor did. 'It is pretty well proven that trace density gives you that difference,' he said.

One audience member noted that geophysicists are getting much less concerned about real time quality control of wireless seismic recording, as they get more confident in it.

One audience member noted that a big driver in higher resolution onshore seismic surveys is multiclient projects, where a seismic company determines what form the survey should take, rather than a single client.

Many seismic contracts issued by oil companies are made around acquisition specifications for 2D recording, originally written in the 1970s, and haven't evolved since then.

Another audience member said the data processing capability can also be a limitation on how much seismic data you can record. 'There's not many people who have had too much experience in processing of this data,' he said.

One audience member noted that the 'pull' in the market for higher processing is often coming from Middle Eastern National Oil Companies, who are more comfortable giving out long term contracts, to make it viable for manufacturers to develop the technology.

Associated Companies
» Inova Geophysical

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