Researchers in Stavanger, Norway, have developed a theory which can be important for future oil and gas exploration.

The Golden Zone is the name of a an underground zone where temperatures range between 60 and 120 C. The name refers to a new discovery that 90 per cent of the world's oil and gas reserves are to be found just there.

The theory has been tested and verified against a global database containing 120 000 oil fields under production, This gives geologists a tool that makes it simpler and cheaper to find new offshore oil and gas reserves.

The theory of the Golden Zone has come as a surprise to the petroleum industry. The theory has been developed over a period of ten years by the former senior researcher, now dean, Per Arne Bjørkum at the Faculty of Technology and Science at the University of Stavanger, and the researchers Paul Nadeau and Olav Walderhaug at Statoil.

This tool makes the work easier because the companies can now concentrate their resources on exploration at this temperature range. Outside this interval of 60 to 120 C, particularly above 120 C, the chances of finding oil and gas are much slimmer.

Earlier it was assumed that the formation of oil and gas was related to temperature. The new discovery is that temperature decides where most of the lighter oil and gas is trapped in the reservoirs.

The increase of temperature downward into the reservoirs varies from place to place. Therefore the zone is to be found at different depths. On the Norwegian continental shelf it is located at depths ranging from two to four kilometers, while in other reservoirs it may be found somewhere between one to two km. These are the so-called warm reservoirs. In cold reservoirs the zone is located at about four to eight kilometers down.

The fact that oil and gas coexist within the same temperature zone is a new discovery and a surprise. Gas is formed at higher temperatures than oil. Consequently it has been a standard rule that there should be more gas than oil the deeper one drilled into the reservoir. The reason why this is not the case is covered by the new theory which predicts that both oil and gas escape through fissures formed at 120 C. But nobody had checked it, Bjørkum says.

Obviously it had to be like that according to the new theory, he says.

The hope of finding much more oil the deeper we drilled into the basement of the sedimentary basins, is about to fade. Not everybody likes to hear this because they want to keep up hope. The main theory about the location of oil and gas in reservoirs was developed at the beginning of research more than ten years ago. In our opinion the theory was both complicated and inconsistent. The Golden Zone has been discovered because we now think differently, Bjørkum says.

He adds that there is also a good deal of oil in sediments of temperatures lower than 60 C, but the oil there is heavier and of poorer quality. It is referred to as heavy oil because bacteria eat the lighter and liquid oil components.

Even if the price of oil is now so high that we can produce more heavy oil, there are great environmental problems linked to it. It is difficult to refine, and for the time being there is no treatment capacity. It takes more than ten years to build new refineries.

However, there is enough coal in the world to last for several hundred years of energy consumption. If we can find an efficient and environmentally friendly way of producing oil and gas from coal it could be our way out, Bjørkum adds.

Bjørkum thinks that the greatest challenge just now is to produce enough oil and gas for the next ten years.

Right now the companies do not find enough oil and gas to replace what they produce. During the last 25 years exploration has not managed to match the quantity produced. When exploring it is important to be as realistic as possible. That is why we are depleting our resources and makes it mandatory to extract as much as possible from our finds. In this way we may contribute to postponing the crisis many see coming, and that is also the starting point for research at UiS. The new knowledge concerning the whereabouts of oil and gas makes us more efficient in our exploration than earlier.

Bjørkum thinks that the world may easily find itself in a situation of fighting wars over the access to oil and gas.

The likelihood of war increases if serious shortage comes earlier than the world expects. In that perspective sound knowledge about where oil and gas are located may also contribute to preserving world peace.