Mark Connolly, Onboard Geophysicist

11pm – time to get up and make the short commute from my cabin to the instrument room on a seismic research vessel operating in the North Sea. I am working the night shift as an onboard geophysicist for a marine geophysical data acquisition company. The data we acquire is used by our client oil & gas companies in their exploration for hydrocarbons deep within the earth’s crust.

A seismic survey is a 24/7 operation therefore we spend an extended period (typically 4-5 weeks at a time) in the field both living and working aboard the vessel. With around 15 different nationalities onboard it certainly makes for an interesting work environment!

There are only four geophysicists onboard so two of us are relieving the guys who have been on-duty for the previous 12 hours. Hand-over takes place and we discuss the previous and upcoming shifts. Tonight operations are shut down due to rough seas we’ve being having over the last few days. With terabytes of raw data being acquired during the survey we have plenty of keep us occupied though!

The technique used to get our data is called “reflection seismology”. We specialise in a type of seismic called OBC (Ocean Bottom Cable). 

Sound energy is sent into the earth where it undergoes a complex series of reflections through the various rock layers comprising the earth’s crust. 

Sensors embedded in arrays of cables stretching several kilometres along the sea-floor detect and measure this reflected energy as it returns to the earth’s surface. 

The data we acquire will be used to build a detailed 3D image of the subsurface which will aid in the recovery of oil or gas from the targeted reservoir.

Tonight I’m spending most of my shift analysing data quality. Among other things this involves checking for irregularities due to issues such as faulty equipment or seismic interference (i.e. noise). 

Highly significant issues may require data to be reacquired so it’s important that those found are thoroughly investigated and detailed records are kept.

Breakfast at 05:30 means it’s time for a break and a chance to watch the sun rise over the north sea....then it’s back to work.

We can use the seismic data to supply us with some valuable information, for example we determine the positions of the sensors on the seafloor to an accuracy of about +/- 1m...no mean feat considering they’re covered by 100m of sea! 

An analysis tool being set up will also use the data to help us determine a sound velocity model for the rock layers in the subsurface. It’s amazing what you can decipher from a few squiggles on a computer screen.

Apart from analysing data other tasks that need to be taken care of include maintenance, repair of equipment and safety monitoring. If something breaks out here you don’t have much option but to fix it yourself.

Shift ends with hand-over at 11:45. After shift I usually unwind by going to the gym, we have a 1.5 hour safety meeting later though so maybe not today...the joys of working the night shift!

Mark Connolly



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