Solving the chalk mystery in Stavanger

 Following the experimental observations performed in the lab, Aksel Hiort and Merete Vadla Madland are now developing a completely new model for calculating the water weakening effect, based on chemical equations.

Following the experimental observations performed in the lab, Aksel Hiort and Merete Vadla Madland are now developing a completely new model for calculating the water weakening effect, based on chemical equations. Photo: Uis.no.

A piece of chalk in a laboratory at the University of Stavanger in Norway may be the key to unlock a great mystery. If the mystery is solved, it will generate billions in additional income for the oil industry.

Associate Professor Merete Vadla Madland at the Department of Petroleum Engineering at the University of Stavanger is leading a group of geologists, petroleum engineers, rock mechanics, physicists, mathematicians and chemists who are now switching between modelling and experimental testing at the chalk laboratory.

They are about to uncover the mechanisms behind water weakening. The answer to this riddle is crucial knowledge for oil companies to be able to predict the reservoirs’ behaviour.

It was just before Christmas, an excited post doctor at the International Research Institute of Stavanger (IRIS) spotted something quite extraordinary through the scanning electron microscope she was using. Tania Hildebrand-Habel immediately called the manager of her research team to tell her the news: A dense layer of recently precipitated minerals had formed on the chalk grains she had been studying for some time.

To appreciate the importance of this discovery, we need to go back in time to an event which has sparked a lot of brain wringing within the oil industry. In 1984, it was revealed that the North Sea oil field Ekofisk, situated 70 metres below sea level, had subsided by 1-2 metres. This was not the first time in history that a reservoir had compacted as a result of oil and gas extraction.

But the scale of the seabed subsidence was unprecedented. The explanation to this phenomenon lay in the specific rock formation in this particular field. The Ekofisk rock reservoir is mainly made of chalk, as is the neighbouring Valhall field. The oil contained in the reservoir was subjected to high pressure and contributed to uphold the layers above. As the reservoir was depleted, the chalk had to withstand an increasing weight.

IRIS now knows that the stress became too big, and the chalk formation eventually gave in.

Read more on: Uis.no

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