A geologist's paradise
11/03/2005 The geological archives of the Norwegian Petroleum Directorate hold sand, gravel and clay from 3000 km of drilling on the Norwegian shelf.
A huge hall, called "Steinlageret" (the rock storehouse) holds drill cores and drill cuttings from all of the exploration wells drilled on the Norwegian shelf. For geologist and principal engineer in the Norwegian Petroleum Directorate (NPD), Robert W. Williams, this is a veritable paradise.
"What a wonderful place to be! You could say that I am crazy about rocks, but then you could say that about most of the people who work in geosciences. In terms of pure palaeontology, the storehouse holds enough research material for several thousand doctorates! The Steinlageret forms the very foundation for everything we know about the Norwegian shelf. If we did not have this information, we would not be able to produce oil and gas from the shelf," says Williams.
An exploration well is drilled to prove a potential deposit of petroleum, or to obtain information to delimit a proven deposit. Exploration wells include wildcat wells and appraisal wells. All companies who are to drill an exploration well on the Norwegian shelf must submit a portion of all drill cores and drill cuttings that are extracted. This rule has been in effect since the very first exploration well was drilled in 1966, and it still applies today.
Not to be discarded
The core sample is a cylindrical sample taken from a rock formation during core drilling. The entire length of the drill cores must be submitted, but not for the full diameter. The requirements call for submission of just one-quarter longitudinal section from exploration wells, and one-half longitudinal section from production wells. The length of the core may vary from about five to 300 meters.
Drill cuttings are crushed rock from the drill bit which is brought up through the borehole together with the drilling fluid (drilling mud). In addition to 123 kilometres of core samples, the NPD has about 600,000 bags of drill cuttings. Together, this makes up 3000 km.
The Steinlageret also contains liquid samples from most of the discoveries on the Norwegian shelf. These are stored in a refrigerated room kept at a temperature of -20 C (so that volatile hydrocarbons will not evaporate). The samples are analysed and stored on the NPD's premises, which requires a huge amount of space. Nevertheless, the samples may not be discarded.
"Researchers constantly find new techniques that allow us to discover more when we analyse geological data. There is always something to learn when we go back and analyse older samples using new techniques. This allows us to obtain new knowledge that we would not have been able to obtain using the old techniques. That is why it is so important that we keep all of the samples," says Williams.
The rock collection is large and fascinating. Williams confesses that he would love to spend more time in Steinlageret.
"I visit there often, but not as often as I would like. In the laboratory we are always working on preparing samples and microfossil analysis. We go to the storehouse when we need to select samples that can help answer whatever problem we are trying to resolve."
A costly affair
Drilling wells is expensive. An exploration well costs about NOK 100 million. Coring costs about NOK 50,000 per meter, thus making an already expensive operation even more costly. Normally, only reservoirs are cored. (A reservoir is a delimited mass underground where the rocks are so porous or so fractured that they hold large volumes of a liquid or gas that can be exploited). This is important in order to obtain an estimate of the volume of hydrocarbons that can be produced from the source rock.
Drill cuttings come up with the drilling fluid. These samples are taken continuously, and are therefore not so expensive.
"Even though the samples do not have a market value, they are, financially speaking, irreplaceable. If we had not taken care of them, we would have had to drill more than 1000 new wells, which would have cost hundreds of millions of kroner. If we take into account improved recovery, new oil and gas discoveries and more efficient (cheaper) exploration as a result of core studies, the value of the cores is quite astronomical," says Williams.
To be used in projects
All samples are exempt from public disclosure for two years after they were taken. After this, they can be borrowed for studies and sampling. Universities, consultant firms and oil companies often apply for access to the samples for use in various projects. The applications are processed by the NPD, and the samples are lent out on the condition that the NPD receives a copy of the final reports from the projects. This ensures that the NPD has access to the analyses that have been performed.
The Steinlageret facility was first completed in 1986. Since that time, the building has been expanded twice during the course of the 1990s. And even though the hall is a whopping 2870m² in size and the samples are stacked on top of each other, Steinlageret is in the process of bursting its seams once again.
[How to apply for access to the samples ]
Contact in the NPD:
Robert W. Williams, tel. +47 51 87 64 72