Rosalena

Imaging Geophysicist

"What I enjoy most working at CGG is the friendly and relaxed environment, the high quality training material and teachers & the new technologies being developed and tested continuously."

MSc in Exploration and Applied Geophysics, University of Pisa; BSc in Geology, University of Bari.

Current focus: Velocity model building and Full Waveform Inversion involving joint inversion of towed streamer and ocean bottom seismic data.

I come from Puglia, in Southern Italy. I am a lover of art and food, and I love to have my friends over and cook for them. I am also a yoga enthusiast and try to practice as regularly as I can.

I have always been fascinated by how you can read the Earth’s history simply by looking at an image or a landscape, so I started studying geology. My personal interest and inclination naturally shifted towards earthquakes, seismology and signal processing. When I saw for the first time what quality of image it is possible to achieve – right into the earth’s depths, I was hooked to Geophysics already.

My interest in CGG started when I participated in a company recruiting event, right when I was about to decide which way to go for my MSc: Geology or Geophysics? The quality of the images shown during that event and the description of the company’s technology really caught my imagination and my final choice was made. From then on, I studied and worked towards getting to look at and process high-quality images of the earth.
What I enjoy most working at CGG is the friendly and relaxed environment, the high quality training material and teachers & the new technologies being developed and tested continuously.

Although I am now working on building earth models in depth for final imaging my first experience at CGG was working on time signal processing of 4D seismic monitoring data.

What is 4D seismic monitoring?

Once wells have been drilled and oil is being produced, the challenge for engineers is to understand the behaviour of the reservoir, identify locations for infill drilling and design enhanced oil recovery programs. 4D seismic obtained by repeating 3D seismic surveys at regular time intervals and looking for differences in the reservoir response, allows any change to be monitored at high resolution across the whole field.

The act of taking oil and gas out of the reservoir causes changes in fluid flow, saturation and pressure and these alter the elastic properties of the affected rocks, which in turn causes measurable changes to the travel-time and amplitude of seismic waves. In order to visualise and quantify these changes a repeat seismic survey using the exact same acquisition parameters (even down to shot location) is acquired. This new survey is known as the monitor and the original is labelled the baseline. This gives us our fourth dimension which is time.

Sometimes the monitor is processed in exactly the same way as the baseline even down to resurrecting old versions of programs used in the original processing; often both surveys are processed with the latest available technologies. The aim of 4D processing is to attenuate the 4D noise caused by changes in acquisition parameters such as more modern recording equipment or from different environmental conditions such as water currents, and to emphasise the actual differences, the 4D signature, caused by the changes in fluid, pressure and stress.

A key philosophy in 4D processing is to optimise for the 4D difference. Often if you optimise the processing of each individual dataset you end up with a worse 4D result. 4D cost functions are often used to allow a trade-off between what is best for processing and what gives the best 4D difference.

The image shows the change in the probability of oil being present from the original baseline survey in 1992 to the 2003 monitor survey indicating quite effective production from the field (extraction of oil) at well A.