Just how much shale gas and shale oil – collectively know as unconventional hydrocarbons – is there in the Weald Basin?
In the light of the recent British Geological Survey (BGS) report on the unconventional hydrocarbon resources of the Weald Basin, we have produced an information note that presents a summary of the report's findings, illustrates its significance for our future energy requirements, and highlights the uncertainty and important caveats that should be attached.
Caveats and uncertainty
Despite all the media attention and hype generated by the prospect of large quantities of unconventional hydrocarbons just waiting to be extracted, it seems that, in the Weald at least, things may not be as straightforward as some of these reports suggest.
Firstly, the study indicates that there is no shale gas potential in the Weald Basin, principally because the shales of the region have not been buried sufficiently long for shale gas to be generated.
Secondly, although the study suggests the region's shale oil reserves may be significant (the mid-level estimate is 4.4 billion barrels), it also found that much of this oil is likely to be "immature", and thus difficult and costly to extract in commercial quantities. There may only be discrete locations – or "sweet spots" – in the Weald Basin where shale oil extraction is even viable.
Thirdly, due to the Weald Basin's geological complexity, hydrocarbon extraction will be far more challenging than in the vast, relatively homogenous, shale plays found in the US.
Finally, and perhaps most importantly, there is an enormous difference between so-called "in place" resource estimates (i.e. what actually exists in the rocks) and what is technically and economically recoverable. In the US – where conditions are geologically much more favourable – levels of recovery for shale oil tend to average around 5%. By assuming a 5% recovery factor, the High Weald AONB Unit's information note presents calculations of how long the region's shale oil reserves would supply UK energy demands (it turns out that it would only last 0.14 years).
Given the variety of other important caveats and uncertainties (see the information note), the prospect of a shale oil bonanza in the Weald seems far less likely than is some media reports suggest. However, as the BGS report says, the attractiveness of hydrocarbon extraction is constantly changing with technological advances and variable economic conditions, and the extent to which the region's shale oil is "producible" will only be more definitely known following further exploration and drilling. What does seem clear, however, is that unconventional hydrocarbons are unlikely to be the silver bullet of UK energy supply that they have sometimes been made out to be.