Eppo Oomkens and the Discovery of Groningen Gas

American Association of Petroleum Geologists (AAPG)

The Netherlands is renowned for its giant Groningen gas field, which contains about 100 TCF of gas (figure 1) and has a total life expectancy of about 100 years. Discovered in 1959 by the Shell/Esso company NAM (Nederlands Aardolie Maatschappij), its huge size was recognized in 1963.

Important in this respect was a junior well-sitter named Eppo Oomkens.

Eppo, of course, did not decide where important wells were to be drilled, but his observations on cores and cuttings in 1963 were important in interpreting the desert facies of a key well. This well confirmed the Groningen field as Europe’s biggest.

This is all the more remarkable because Eppo was company trained. After only one year at Delft University (mining engineering) in 1948-49 he was conscripted into the Dutch army. He then joined Shell and went to New Guinea, where he contracted malaria and was nursed back to health by Anneka, whom he married in 1957.

He subsequently joined Shell Research (KSEPL, 1957-68) as a geological assistant.

A tall man standing six-foot-six, Eppo’s private transport was a Citroen Deux Chevaux, the only car with a roof high enough for him to sit in while driving. For all other cars he had to sit half-sideways in the back seat.

First Impressions

Immediately after World War II, the occasional hydrocarbon discoveries in Netherlands were mostly confined to Jurassic and Cretaceous reservoirs. A 1952 wildcat in the greater Groningen area found 180 meters of water-bearing Permian Rotliegend (red layers) Sandstone, and four years later at Ten Boer (figure 2, page 64), the main target in the area, the overlying Late Permian Zechstein dolomites had only gas shows.

It was presumed there were no prospects within or beneath the Rotliegend (figure 3, page 64).

The Groningen gas field was discovered by NAM in 1959 with the well Slochteren-1. At that time, it was considered too small to be commercially viable in a land where every small town had its own coal-gas plant.

With further drilling to the north, however, it was realized there was a gas column filling the entire 180-meter thickness of the Rotliegend, and all its wells seemed to have the same gas-water contact at a depth of about 2,900 meters.

As that gas-water contact possibly enclosed an area approaching 1,000 square kilometers, it looked as if this gas field could be huge.

To check this observation, it was decided in 1963 to deepen the Ten Boer well (figure 2), which penetrated the reservoir near its gas-water contact and confirmed the size of the field.

Eppo then studied the Rotliegend cores and cuttings from this well – and not only did he suggest their desert origin, but he also noticed the depositional bedding dipped mostly to the west, thus indicating a possible extension of the reservoir sands beneath the North Sea (figure 1).

A study of modern deserts was considered essential, and although Eppo was obviously very clever, with no university degree he was not allowed to take charge of any geological research.

Rather unexpectedly, my involvement followed.

Making a Connection

By 1963 my early Shell career had taken me to New Zealand and the Canadian Arctic. In both areas I had come across a type of sea-floor sediment named “turbidites” in 1962 by the Dutch researcher (and eventual AAPG Sidney Powers award winner) Arnold Bouma.

On leaving Canada I had spent the winter of 1962-63 walking the Himalayan foothills of Nepal with AAPG member Martin Ziegler. After a trip to Spain looking at turbidites in the spring of 1963, Shell decided that I should lead a turbidite research team.

On reporting for duty in my new role at the beginning of November, I was shocked to be told, “It is all changed – you are now our desert expert and had better learn fast.”

Although Shell had worked in various desert countries over the previous 50 years, no one had studied their surface sediments – and a study of modern deserts was considered essential.

My experience of deserts was limited to 1947-48 army service in Libya.

We all felt the most efficient way to learn about deserts was to visit one. Shell had an operating company in Libya, and Eppo was allowed to join me on a visit.

I learned a lot from him there, as he recognized many sedimentary features seen in Groningen cores that we could now study in the field.

On returning to Shell Research, Eppo and I were told to take part in discussions with our partners Esso at the neutral locality of a hotel. Esso did not support NAM’s interpretation of a desert origin for the Rotliegend reservoir rocks, preferring instead to follow that of their American consultant, a specialist on the Mississippi delta.

The meeting began with NAM’s chief geologist presenting basic data, including photos of cores from one of the wells. Then the consultant took over. According to him, the Groningen reservoir sands were deposited in a delta of Mississippi type – and if not Mississippi then of Mackenzie, Ganges or Indus type.

It happened that I was the only person present who had ever seen the Mackenzie Delta – before going to Nepal I had spent two summers (1959-61) with Shell Canada mapping between the Arctic Circle and the Arctic Ocean, first in the Northwest Territories, which included the Mackenzie Delta, and then in the Yukon.

Borrowing a few slides from the two previous speakers, I compared them with photos taken during my trip with Eppo to the Libyan desert.

When I had finished, the consultant said that, although he did not believe me, it was clear that Esso had to learn something about deserts.

Other members of the Esso team, however, told me that I had won “hands down.”

Six weeks later Eppo and I came across an Esso geologist in northeast England studying the British equivalent of the Rotliegend. Although much more Rotliegend core has been studied since then, a desert interpretation for the upper part of the Rotliegend still stands.

Lasting Recognition

Following several months assisting in field research, Eppo’s abilities eventually were confirmed:

  • He was assigned to the United States (Ventura, Houston, New Orleans) from 1968-71.
  • From 1971-77 he was an exploration team leader in London followed by time in Jakarta, Indonesia (1977-78), Perth, Australia (1979-80) and The Hague (1980-82).
  • He was working for NAM in Assen when he retired in 1989.

He is known to have been living in Drouwen (south of the Groningen field), when he died in January 2012.

Author’s note: Thanks to Koen Weber and Willem Niewenhuys for adding some previously unknown details about Eppo’s career (and to Caroline Hern for removing typing errors). Jenny Jones, at Aberdeen University, drew the figures for me.

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