Seismic surveys appraise geological features below the earth’s surface, by sending acoustic sound waves into the various layers of rock and measuring and recording the strength of each returning wave and the time it takes to bounce back.
When on land, Vibroseis trucks are commonly used for collecting data. These are trucks which use steel plates to vibrate the ground through a range of frequencies to send the sound signal into the subsurface. An array of receivers (geophones) at the surface measure the time for the reflections from the subsurface geology to arrive. The geophones may be configured in a 2D array, usually comprising a cable with geophones at regular intervals as far as 20 kilometres, or in a grid formation to conduct 3D surveying.
To collect and document marine seismic data on the other hand, a vessel towing an airgun array is used. Seismic data can be acquired in three configurations: 2D, 3D and 4D surveys. 2D surveys involve the use of just one streamer cable behind a seismic vessel, 3D surveys utilise multiple streamer cables and provide multiple transects to cover a specific area in high detail, while 4D seismic surveys are 3D surveys which are repeated over the same location – usually years apart. These cables contain receivers (hydrophones) at regularly spaced intervals which enable a recording of a reflected sound wave that can be obtained at several points away from the source.
Oil and gas companies and organisations such as Geoscience Australia have used seismic surveys to map the geology of Australia’s marine regions for more than five decades. Seismic data has become crucial to understanding large-scale geological structures, but the possible impacts of offshore seismic surveys on marine life are not fully understood.
Several studies have found that the loud low-frequency noises caused by offshore seismic surveying has the potential to harm marine animal populations or ecosystems. One study found that the sound energy from seismic activity can injure or kill larvae less than five metres to a seismic source by causing injuries to their hearing, kidneys and heart, while another study found evidence that suggests seismic surveys cause significant mortality to zooplankton populations.
Therefore, it is suggested that the industry supports research into the environmental effects of seismic activity on natural habitats and/or continues to follow environmental standards such as those prescribed in the Environmental Protection and Biodiversity Conservation Act 1999 and the Offshore Petroleum and Greenhouse Gas Storage Act 2006, to ensure that potential environmental impacts are mitigated.
Whether the data is sourced offshore or onshore, seismic processing requires powerful hardware, sophisticated software and specialised skills. Once the seismic data has been processed, it must be interpreted. Interpretation of this kind requires specialised geophysicists, who study the earth using gravity, magnetic, electrical, and seismic methods. Usually, geophysicists will compare seismic results with other data such as rock samples, regional well results and known geology to enhance the accuracy of their interpretation.
Sector adapts technology
Due to the sector’s constant race to increase productivity and the sheer volume of seismic data that needs to be accessed, interpreted and stored for further analysis, the oil and gas industry has long transitioned from analogue data recording to digital data recording. To gain maximum productivity gains over competitors, seismic-based technologies are advancing and the industry is adapting continously.
Andy Alexander, part of the Seismic 2019 event’s organising committee explained the rate of change of technological innovations in geophysics is and has always been fast.
“Geophysicists and geoscientists have always tended to push the boundaries of technology to get faster and better solutions and this trend seems likely to continue. I know from working with our partners and contractors on various assets that there have been significant steps forward in seismic data acquisition, imaging, visualisation and analysis.”
Mr Alexander believes it is clear that the power at these scientists’ fingertips in terms of workstations, access to cloud computing and software evolution is allowing the geoscience community to evaluate more data quicker and with better integration with other data types.
“The volume and variety of geophysical data we acquire and deal with is enormous which makes it ripe for the emerging discipline of ‘data science’ to apply existing and modern machine learning algorithms,” he commented.
According to a recent report by Research and Markets, investments in the global seismic survey equipment market totalled $1.1 million in 2017 and is expected to rise to almost $2 million by 2026. This growth is likely to be attributed to the increased use of seismic technology in shale gas exploration and huge demand for oil (especially in emerging economies). Australia is doing its part in expanding this industry as well.
In October 2018, Australia’s longest single continuous onshore seismic line was completed in Western Australia’s Pilbara region, running 872 kilometres, from Kiwirrkurra to Marble Bar.
Conducted by the Department of Mines, Industry Regulation and Safety’s Geological Survey of WA and Geoscience Australia, the mammoth $4.75 million survey of the Kidson Sub-basin took 52 days to execute and involved 40 personnel, a convoy of three Vibroseis trucks and associated back-up vehicles.
Acting Mines and Petroleum Minister Francis Logan said the survey will aid in deepening the geological understanding of the region, encourage exploration investment and the creation of jobs for Western Australians.
“I’d like to congratulate the team for successfully running this complex project and breaking an Australian record, recording a seismic line up to 50 kilometres deep is quite an achievement,” he announced at the time.
The survey was co-funded by the Australian Government’s $100.5 million Exploring for the Future program and Western Australia’s Exploration Incentive Scheme.
Federal Minister for Resources and Northern Australia Matt Canavan added that the Australian Government is investing in projects like the Kidson Sub-basin seismic survey to build a bigger, better picture of the region’s mineral, energy and groundwater potential.
“Although it takes a few months to process the raw data from the survey, the results will be worth the wait. All data collected as part of the Exploring for the Future program is made freely available online by Geoscience Australia, an invaluable resource for exploration companies looking to invest in Northern Australia,” the Minister commented. Geoscience Australia plans to release the results in May 2019.
Sources: Australian Petroleum Production and Exploration Association, 2018; Geoscience Australia; Widely used marine seismic survey air gun operations negatively impact zooplankton, Robert D. McCauley et al.; Guide Implementation of seismic surveys on the Norwegian Continental Shelf
