Core samples: An insight into depths of thousands of meters

They provide insights into the earth’s history, but they also reveal important information about oil and gas reservoirs. Anja Kobstädt is a sedimentologist at the OMV lab in Gänserndorf and explains how to draw answers from a rock.

Anja Kobstädt picks up a magnifying glass. On the table in front of her lies a meter-long piece of dark gray rock. “This is a core sample from Pakistan,” explains the young sedimentologist and bends down to have a closer look at her sample. “It is still quite fresh and was just recently delivered.”

“Fresh” is relative in this context: Here, in a storage building at OMV Austria in Gänserndorf, Lower Austria, dozens of meters of several million-year-old core samples lie on metal tables. “They come from our wells around the world—Yemen, Tunisia, Austria, and, like this one, Pakistan—and they are important documentation material.” These samples tell us about millions of years of geological history and thus the formation of oil and gas reservoirs.

The core samples do not only provide important information in the search for hydrocarbons, they are also a key puzzle piece that helps us better understand the earth’s history.
Anja Kobstädt, Sedimentologist at the OMV lab in Gänserndorf

A core sample sees the light of day

But before she and her colleagues from the Formation Characterization department can start their work, the core sample must first be extracted from the ground. And that is quite a project: Usually, a well is worked around the clock. When the decision has been made to extract a core, regular operations have to be stopped and the well has to be stabilized. This is only possible thanks to the great cooperation with the drilling team on site. Then it is pulled up out of the ground with special equipment. This can take several days. Most of the cores are up to 27 meters long and they can be extracted from depths of several thousand meters. The deepest well ever drilled by OMV dates back to 1983 and had a depth of 8,553 meters. Once extracted, they are then cut into lengths of about one meter and sent to the OMV lab in Gänserndorf.
 

Every core sample examined in painstaking detail

Anja Kobstädt leads her visitors through the corridors of the lab and the sedimentologist explains that there are inspection rooms left and right. Experts in the lab draw important information from the rock. What kind of stone is it? Is it porous? How was it formed? What microfossils is it made up of? To answer these questions, Anja Kobstädt and her colleagues perform a number of complex analyses on the core sample.

First the natural nuclear radiation (gamma ray) emitted by the core is measured. The differences in radioactivity allow analysts to draw conclusions about any possible oil and gas deposits. “Put simply, lower radiation means a higher probability of oil and gas deposits. After all, shale-free sandstones and carbonates are potential reservoir rocks in a conventional sense. They emit less radiation than shaly sandstones and shales, which in turn contain more radioactive elements,” explains Anja Kobstädt.

Photos under UV light reveal areas containing oil-bearing horizons. Oil is organic in origin and shows a fluorescent glow under UV rays, as seen in bright glowing sections. In contrast, blue, non-fluorescent areas do not hold any oil. Now the cored rocks will be examined piece by piece, first with the naked eye and then under a microscope. “Just the description of one core can take up to three or four days,” explains Anja Kobstädt. “After that comes the detailed analysis. The amount of work required for this varies depending on the issues and complexity of the rock.”

Crucial answers about the reservoir rocks

It’s worth the effort: Important conclusions can be drawn about the formation and possible distribution of reservoir rocks using their analyses. “This helps our colleagues plan future wells and optimize production from reservoirs,” says Anja Kobstädt. Therefore, the results of research help reduce risk when making important decisions: Like whether it pays off to continue drilling.

A library of core samples

A core sample does not only contain important information for today, but also for future generations: Using new technology to reanalyze an existing sample can reveal valuable new findings, explains Anja Kobstädt. And so it happens that colleagues uncover new potential in what were presumed to be less attractive fields. That’s why every single piece of core is always carefully wrapped, numbered, and organized in the archive of the core laboratory according to their place of origin after the analyses. They are right next to Anja Kobstädt’s desk, namely in the store rooms adjacent to the lab. It is basically like a massive library, says the sedimentologist as she wanders between the rows and rows of samples. “If necessary, samples which have been here for decades can be retrieved and analyzed again”. In addition to the core samples, hundreds of kilos of “so-called drill cuttings”—the broken bits of rock acquired during the drilling process—are sent to the lab, which also provide important information after being analyzed.

The archive now holds about 50,000 meters of core and even more drill cuttings, which have been collected since the 1940s. When asked about the value of the rock, Anja Kobstädt smiles: “A core sample may appear unremarkable at first glance, but the value it holds for us cannot be put into words.”

Anja Kobstädt

has been working in the OMV lab in Gänserndorf, Lower Austria, since spring 2015. Before this the 27-year-old worked as a reservoir geologist in Germany, Spain, and the UK. As a sedimentologist in the Formation Characterization department, the native-born German is responsible for closely analyzing core samples and drill cuttings— this includes the sedimentological description and interpretation of the rocks and a detailed analysis of its components.

Details on the core sample archive

• The lab and the core sample storage have been in Gänserndorf since 2008. Before that, the core samples were stored in Neusiedl an der Zaya.
• About 40 OMV experts from the fields of geology, chemistry, petrophysics, high-pressure technology, corrosion, and materials science work in the lab.
• The heart of the lab is the geology department. Cores or drill cuttings are extracted at every drill site and shipped to the OMV lab in Gänserndorf, Lower Austria.
• All samples are closely analyzed and stored in the archive for later analysis.
• Around 50,000 meters of core and even more drill cuttings are currently stored there.