The future of seismic data acquisition

Seismic surveys have for decades been a key part of offshore exploration, producing comprehensive imagery of sub-bottom rock formations that allow the location and evaluation of oil and gas deposits.

They also find their use in assessments of the seabed for offshore construction, installations of renewable energy infrastructure, academic studies of the geology as well as civil engineering projects.

Conventional seismic acoustic surveys are carried out with a vessel that tows the so-called air gun array and one or multiple streamers – an array of hydrophones on a system of long cables.

These hydrophones capture acoustic waves which bounce off the sub-bottom structures and travel back to the sea surface.

The acquired data is then reprocessed, revealing the details about the structures beneath the seafloor.

Other types of seismic acquisition techniques include using ocean bottom cables, now mostly replaced by usually ROV-deployed ocean bottom nodes (OBNs), and emerging solutions such as the robotic nodes in the form of autonomous underwater vehicles (AUVs).

The latter is becoming more and more popular as oil and gas exploration companies are looking to keep up with the energy transition by trying to reduce overall environmental footprint as well as boost OBN efficiency.

Overall, seismic surveys have always been described as highly complex operations, however rising energy demand in the past has driven exploration into more challenging environments that require new and even more complex approaches.

When it comes to which of the seismic data acquisition technologies has the edge over the other, bottom line is still the economics behind it.

Exploration companies have in the past selected traditional data acquisition options by towed streamers.

Aside from cost, streamers advantage is also the coverage and speed. They only need one vessel to tow them and do not require any retrieval of equipment.

However, we need to point out that the larger the survey and streamer spread, the larger the cost.

Cables and nodes have predominantly been used for reservoir characterisation and monitoring and compared to streamers are said to deliver much clearer data, but also have their own disadvantages, such as depth limit for cables and operational cost for nodes.

It is also true that a lot of headway has been made with each of the above-mentioned seismic acquisition technologies.

Energy firms are continuously working to refine OBNs, boosting their battery life as well as increasing the gap between which nodes need to be placed to get accurate readings.

Robotic nodes, which are still in the R&D stage, are envisioned to be able to swim to and from the pre-plot receiver location without the need for a separate deployment vehicle.

However, so far, the biggest challenges for this technology has been the node weight, positioning and ultimately its retrieval.

Survey autonomous underwater vehicles (AUVs) have been in commercial use for quite some time now, with the oil and gas industry as the largest user of this technology.

In the offshore energy industry, AUVs are usually tasked with pipeline inspection missions and cable route surveys.

As the modern seismic industry was shifting toward longer streamers, higher streamer counts, tighter streamer spacing which yield faster production rates, but obviously come at a cost, an EU-funded project was launched in 2015 with a goal to use AUVs for seismic surveys.

The so-called WiMUST (Widely scalable Mobile Underwater Sonar Technology) project has delivered a system of streamer-towing cooperating AUVs that simplify seismic surveying.

Namely, the short streamers of small aperture are towed by AUVs, which act as sensing and communication nodes of a reconfigurable mobile acoustic network, and the whole system behaves as a distributed sensor array for recording data, obtained by illuminating the seabed and the sub-bottom with acoustic waves from a source installed onboard a support vessel.

The project involved several European partners from Italy, Germany, Holland, France and the UK.

Some time has passed since WiMUST and industry players moved forward looking to maximise efficiency of subsea survey operations.

As an example, marine robotic company Ocean infinity this year delivered the industry first in which geophysical, geotechnical, and seismic data has been gathered at the same time.

This was achieved through simultaneous operations of Ocean Infinity’s AUVs with geotechnical and seismic equipment based from one surface vessel.

The 28-day project conducted 2D ultra high-resolution seismic surveys and seabed soil sampling offshore Angola.

We’ve already discussed how the low oil price has led energy companies to scale back near-term investment plans significantly, and how 2020 has proven to be a very challenging year for the marine seismic industry.

Market analysts predicted that seismic industry will take the biggest hit in the offshore oilfield services arena with revenues falling between 50 per cent and 80 per cent.

The hardest-hit area is the acquisition of new geological and geophysical studies in recently acquired blocks and work on exploration wells yet-to-be-approved.

Adding COVID-19 pandemic and energy transition from fossil fuels to this scenario has made the situation even worse, forcing seismic players to adjust their business plans to better prepare themselves for this downturn.

The oil & gas industry is still the main backer of seismic technology advancements. Nevertheless, long-term projections for seismic industry and fossil fuels remain limited and we could soon see seismic companies target other alternatives such as acquiring data for potential carbon and hydrogen storage sites.

This still remains to be seen as people advocate that fossil energy industry is going to be the key driver for the energy transition.

We also need to remember that seismic industry has managed to adjust to one major downturn before this one.

Before the Covid-19 pandemic and the oil price slump we saw the industry shifting towards development of ocean bottom node (OBN) seismic technologies with aim to maximise their productivity.

Seabed acquisition is a rapidly growing area of the seismic market, leveraging novel techniques and technologies to achieve improved cost and quality.

OBNs have been around for quite some time, but ever since oil & gas industry started tapping into this technology, they have dramatically advanced.

Specifically, an ocean bottom node is an autonomous recording device with a self-contained recording system, timer and a battery.  As there is no link with the surface, there is no restriction on length of the receiver line, no delay due to telemetry/power line collapses and no downtime associated with moving of the recording vessel.

However, seabed seismic surveys have not been widely used due to the higher acquisition costs.

Oil and gas majors recognised OBNs as technology of choice for reservoir characterization and monitoring, and decided to approach this elephant in the room.

In recent years, we’ve seen significant engineering efforts focused on increasing the efficiency of receiver deployment and retrieval in order to address this cost differential and open seabed receiver techniques to a wider range of seismic surveys.

In addition, efforts have been made to improve source efficiency and upgrade receiver inventories which, depending on the required geometry, may also impact overall survey efficiency.

Three main improvement targets have been identified. Namely, to re-engineer the existing ROV deployed node technique; use a node deployment similar to seabed cable systems, called node-on-a-rope technique (NOAR); and develop robotic ocean bottom nodes.

The idea of making nodes fly is not that new. Companies such as Autonomous Robotics Limited (ARL) has been developing the concept since 2013 following the acquisition of GO Science.

Reportedly, these flying nodes would deliver reduction in survey costs, more than half the cost of ROV deployed nodes.

Cabled nodes also provide a cheaper alternative in shallow water, but with compromises on the positioning accuracy compared to ROV-placed nodes.

ARL flying nodes are deployed and recovered by a cage, similar to an ROV launch and recovery system. Once the cage reaches the deployment depth, the nodes are released and guided to their position by and unmanned survey vessel (USV).

A couple of other players in the industry are developing robotic nodes. Some are propelled and AUV-like, such as the one from the UK-based Blue Ocean Seismic Services.

A Norwegian developer iDROP, on the other hand, has gone for a gravity-based solution, aiming to disrupt the ocean bottom seismic industry.

Called the Oceanid, a proprietary technology is purely based on gravity. The “drop-node” will autonomously glide laterally to a pre-plot position on the seafloor and plant a vertical low frequency seismic sensor. Post logging the node will drop a slurry ballast and ascend to an instructed location on the surface and be recovered onboard with a light weight floating conveyor system at the same rate.

The nodes can be operated from most vessel platforms, ideally on a hybrid seismic source setup, but can also be deployed manually in small quantities from a FRC or fully automated container system onboard a PSV, the company explains.

iDROP plans to upscale testing and demonstrate a scarce survey spread during the summer 2021, in parallel to further enhancing the seismic payload and acoustic positioning system targeting large scale time-laps acquisitions.

Kyrre J.Tjøm, CEO and co-founding partner of iDROP told Offshore Energy that in general the company’s view is that today’s seismic operations are inaccurate, slow and expensive, and due to lack of funds and a conservative approach, new ideas are held back and only fragmentally supported by the market.

He says that the industry funding is partly an indirect self-support to, and from, vessel owners, capitalizing on extensive surveys, comprising millions of manhours and a wide fleet of offshore units with dual WROVs and massive active heave-compensated LARS configurations etc.

When it comes to flying node systems, Tjøm question the realism in tackling the complexity related to underwater navigation challenges and vast energy consumption. He believes that for these systems, as well as their Oceanoid, the safe and efficient recovery method will be the success factor.

The above-mentioned Blue Ocean Seismic Services (BOSS) has recently landed a £10-million boost from bp Ventures, Woodside Energy and Blue Ocean Monitoring.

The investment should help continue the development of a fully integrated system which uses long endurance self-repositioning autonomous underwater nodes to conduct offshore seismic surveys for oil and gas exploration and reservoir optimisation, while also identifying and monitoring carbon storage opportunities under the seabed.

BOSS’ CEO, Simon Illingworth, highlighted that their solution simultaneously reduces the cost, carbon emissions, time and human life risk currently associated with underwater offshore exploration.

“Our pioneering technology is anticipated to lower exploration costs by an astonishing 50 percent and is powered by rechargeable batteries, which makes oil and gas exploration less carbon intensive.

Unlike traditional methods, thousands of these nodes can be deployed autonomously at a single time and stay underwater for nearly three months, Illingworth explains.

He told us that the company expects its first units to be rolled out between the middle to end of 2022.

Bottom line is that as the demands of the industry become more challenging, owing to the high costs of reservoir exploitation and exploration in more complex areas, as well as aim to optimize carbon and hydrogen storage, energy companies will continue to challenge providers to acquire higher quality, more cost-efficient seismic data. 

Ocean bottom seismic players have responded with a new focus on resolving the factors limiting the efficiency of the seabed seismic solution, both on the source and receiver side.

Ongoing engineering efforts, combined with operational innovation, have the potential to make a step change in seabed seismic efficiency and cost effectiveness, thereby opening up the seabed seismic solution to a much larger proportion of the contemporary seismic market.