In sands deposited on sandy beaches and in rivers pores often account for 40-45 per cent of the volume. In other words, the sands' porosity is 40-45 per cent. As deposits of overlying sediments gradually accumulate on top of the sands and they are subjected to increasing pressure and temperature, they eventually become compacted into sandstones which are less porous. Under these conditions, porosity is usually reduced to 10-20 per cent. The porosity of sandstone reservoir rock is a vital factor which helps determine how much oil can be recovered from each rock volume.
Porosity is therefore of decisive financial significance to operations.
Our aim is to be able to predict the porosity and permeability of rock types, providing oil companies with a basis on which to calculate production capacity if they discover oil or gas. Porosity of sands decreases as the overburden increase as a result of both physical compaction of the sand grains and chemical dissolution and precipitation of minerals in the pores. We are currently studying the physical compaction of sand in cooperation with the Norwegian Geotechnical Institute in a project financed by the Research Council of Norway. We have been studying reservoir rock from the North Sea and from Haltenbanken for many years to help us understand why some sandstones are far more porous than expected at a certain depth. Several of the fields on the Haltenbank contain sandstones which have porosity of 20-25 per cent at a depth of more than five kilometres.