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04.08.2017

Five weeks on a seismic vessel

At the beginning of 2017, Troy Collier got the chance to experience offshore life on a seismic vessel in New Zealand as part of the OMV Integrated Graduate Development program. Five exciting weeks in the life of a graduate geoscientist and this is what he has taken away on impressions:

Interpreting seismic data is deeply ingrained into my work as a geologist, but to fully appreciate the data you must also fully appreciate how it was acquired. Geophysical textbooks cover acquisition and processing in great detail, but there is nothing like the real experience of five weeks offshore on a seismic vessel.

Troy Collier

Graduate Geoscientist at OMV New Zealand

Troy Collier: My Offshore Seismic Diary

At the end of 2016 one of the largest seismic vessels in the world began acquiring a 16,000 km2 marine 3D seismic survey over the East Coast Basin of New Zealand. And the best about it: I was given the chance to be part of it. But let me start from scratch.

My five-week offshore journey began with a helicopter flight to the seismic vessel. This was the first time I had flown to work. Not many people can say that they have done that.

But before you can travel offshore you must complete a Basic Offshore Safety Induction and Emergency Training (known as BOSIET for short). This involves Safety Induction, Helicopter Safety and Escape (HUET), Sea Survival and First Aid, Fire Fighting and Self Rescue – to make sure you are prepared for worst-case scenarios on the vessel. The training is very informative, exhilarating and involved, especially when you are belted into the seat of a model helicopter that is upside down and filling with water!

Safety is also number-one priority once onboard the seismic vessel. First of all I was given a comprehensive safety induction pointing out the muster locations and life jackets, fire extinguishers, how to respond to a man-overboard scenario, the ship’s various alarms and use of the Personal Protective Equipment (PPE) including steel capped boots, reflective overalls, safety gloves and glasses.

After that, my work as a geoscientist could start. Geoscientists are continually trying to unravel the geological history of sedimentary basins and we use the most advanced seismic techniques to reveal the scientific secrets of the subsurface. In my case this process involved an offshore 3D seismic acquisition and it brings back loads of information about the geology of a basin, and with it a good basis for assessing the likelihood to find oil and gas below the sea ground.

What is seismic acquisition?

Seismic acquisition uses elastic sound waves that reflect off interfaces such as beds of rock or deposits of oil or gas, which return to the surface and are recorded by hydrophones. Geophysicists can then interpret and map to reveal drilling targets, and help provide scientific knowledge about the offshore geology. The vessel acquired seismic data 24/7 for more than six month. Once the data have been collected it takes a year of processing and then another year of interpreting it. Interpreting seismic data is deeply ingrained into my daily work as a geologist, but to fully appreciate the data you must also fully appreciate how it was acquired and processed. This is something that I had little knowledge about. Geophysical textbooks cover acquisition and processing in great detail, but there is nothing like the real experience of five weeks offshore on a seismic vessel, fully immersed in the acquisition of the 3D seismic survey.

Watch our video for more information: What is seismic reflection?

Offshore life

Onboard a seismic vessel, each member of the seismic crew has a specific department that they work: Acquisition, Navigation, Handling and In-Field Geo. To get a feel for the departments and how they contribute to seismic acquisition I spent a week with each of them, learning the ins and outs of their roles and how they ensure a high-quality end product.

In my first week I stayed with the In-Field Geo team, whose aim it is to process the seismic data. They do so to attain the highest possible signal-to-noise ratio by attenuating as much noise as possible without altering the primary signal of the reflected waves. Starting off with them was a little unconventional, as the In-Field Geo team is the last in the chain. But as a geologist I was quite keen to see the raw data being processed as it was coming in and being written to tape. It was exciting to see a brute stack (an initial approximation of the seismic data) and think “I am one of the first sets of eyes to witness this part of the earth for the first time in human history”.

Seismic vesselIn the following week I joined the Acquisition team. They must make sure that the acoustic source is operating within the survey area. More than that, they are in charge of maintaining the integrity of the in-sea streamers, as well as recording and quality-check of the seismic data. The Acquisition team regularly gets to participate in workboat operations, to change parts of the streamer, which I found very exhilarating to be a part of. The work is very hands-on and dynamic. One minute you’re in front of the computer to screen the data, and a few minutes later you’re out kilometers behind the seismic vessel fixing the streamers for shark bites.

In week 3 I moved on to the Navigation team. They are responsible for keeping the vessel on course whilst battling against external elements such as the weather, ocean currents, and feather angles, so that data is acquired along the pre-plotted seismic lines. They must also ensure that the streamers are sampling the same positions of the subsurface over and over again to ensure there is enough data to increase the signal-to-noise ratio. Navigators are also in charge of the maintenance of all GPS units used on the seismic vessel. These are vital for providing an accurate position for every source activation location. After a seismic sequence is done, the navigators produce the P190, which is the processed navigation data that is passed on to the In-Field Geos to position the resultant seismic in space and time.

In my next offshore week, I moved on to the Handling team. The Handling team is responsible for the maintenance of the acoustic source array, and anything else mechanical on board. This includes hydraulic winches, hydraulic systems, welding, high-pressure air systems or monowings. Ensuring that the seismic equipment is well-maintained and operating within the specifications outlined in the survey is integral to the entire acquisition operation – without a seismic source there is nothing to record.

Health, Safety and Environment are top priority

Marine seismic acquisition requires the utmost adherence to health and safety protocols. The operational environment can be harsh, and the ocean is unforgiving. Staff can be working at heights or at the mercy of dynamic ocean conditions out on the small workboats. It is for these reasons that all employees must be aware of the HSE (Health, Safety & Environment) principles and practise these in their day-to-day tasks. Onboard each seismic vessel is an appointed Safety Officer who serves as an ambassador for the HSE system. Before any team operation is undertaken, a HARC (Hazard Assessment and Risk Control) is performed to identify possible hazards and provide evaluations of the risks.

While the safety of the people working onboard is a top priority, great care is also taken with regards to the protection of wildlife. OMV has strict internal standards to protect marine mammals in the area of the seismic survey. “Mitigation zones” are defined as an area from the centre of the source array. If any “species of concern” (SOC) comes within the defined radius, operations are shut down immediately. There are qualified Marine Mammal Observers (MMOs) and Passive Acoustic Monitoring (PAM) operators onboard to take care of this. MMOs work from the bridge during daylight hours using high-powered binoculars to identify SOCs coming within the mitigation zone. The MMOs have total authority to shut down the seismic operation until the mammals leave the mitigation zones. PAM operators work 24 hours a day, and serve as the “eyes” when darkness falls. They are listening for the clicks and whistles of mammals and detect how close they are. MMOs and PAM operators together ensure that the well-being of marine mammals is respected whilst the survey is being conducted.

The end is just the beginning

After five weeks of invaluable marine acquisition experience my Offshore Seismic Diary ends here. The onshore version, however, is to be continued. Now that I have learned how 3D seismic is acquired, back in the office my technically-excellent colleagues will teach me how 3D seismic is interpreted. In doing so, whilst continually applying my learnings from the OMV Integrated Graduate Development program, I hope to help find some oil and gas!

And special thanks to the WesternGeco crew for welcoming me onboard as an offshore rookie.

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