Oil and gas exploration in the Weald - A Case Study
Geological History
When exploring for hydrocarbons, it is important to know the geological history of an area before any geophysical work is undertaken. For an oil reservoir to be present there are three main requirements of the geology:
- A suitable source rock is in the vicinity. This needs to be rich in organic material and of a suitable age that the changes of hydrocarbon maturation can have taken place.
- A suitable reservoir quality rock is present. This rock needs to have sufficient permeability and porosity to allow it to hold significant quantities of oil and gas.
- A cap rock or a structural trap is present to keep the hydrocarbons within the reservoir and not allow them to migrate away.
The first information comes from geological mapping of the surface. If we look at the solid geology map we can see that in our area of interest there are several types of rock, and some structures too. From this a cross section can be created. This cross section and the map only show the geology near the surface.
Look at the stratigraphic column for the south of England and see which of these rocks occur on the solid geology map.
Now look to see which rocks in the stratigraphic column are organic rich and so potential source rocks for hydrocarbons.
The geology at the surface does not necessarily show any of the rocks or structures at depth, which could well be different. It is then that geophysical methods can help to reveal what is deep below.
Click here to see a geological cross section of the area derived from seismic studies.
Download high resolution versions of cross section and stratigraphic column
