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Special Digest

Shale Oil coming in the Weald?

13/11/2013

DECC focus in the south switches from shale gas to shale oil.

An interesting Q/A extracted from the ongoing Lords enquiry. Toni Harvey is a senior geoscientist in DECC responsible for onshore development.

There are two points of interest to me. Firstly Ms Harvey seems to be relying on to a great extent the USGS estimates for well productivity. This is important because these are significantly LESS than estimates that the industry quotes. This will have impact on the number of wells needed to be drilled, suggesting that our (my own and Refracktions estimates) should move upwards.

Secondly the news is that in the south DECC is now expecting more of an outcome from the survey currently farmed out to BGS of shale prospects in the South of England is likely to focus on shale oil rather than shale gas. We need to bone up more on shale oil, perhaps.

Apart from any similarities of the processes of extracting unconventional oil and shale gas, the argument against continuing mining for oil must be a strong one- no possible excuse from the frackers regarding climate change impact.

"Lord Griffiths of Fforestfach: My question is about how you go from an estimate of a resource to an estimate of a reserve. My immediate instinct would be say that it depends on how many resources people in companies put into a resource to try to convert it into a reserve. There might also be something scientific and technical that prevents that. Even if companies put more resources in, it would not be easy to move from one to the other. Could you explore that a little for us?

Toni Harvey: The conventional way to calculate a reserve number is to calculate a resource and a recovery factor. A certain percentage, say, could be recovered, and then you would fine tune that recovery factor. The experience in North America, particularly in the US, is that the USGS has developed a different methodology for coming up with resource assessments, and ultimately reserves. They found that that old recovery factor method just did not work. For unconventional reservoirs, it is how much each individual well can produce; it is the estimated ultimate recovery of a well. Then you just decide how many wells you are going to drill. They have also found that the estimated ultimate recovery changes quite a bit throughout a basin, so you need to narrow it down to what the sweet spots are in that basin. The USGS do all their work now by looking at the decline rates on the wells that they have drilled and put into production. From that, they extrapolate to say what the entire basin will be. We just do not have the data yet to be able to do that.

Lord Griffiths of Fforestfach: The report that you held up then is about shale gas. It is not about tight oil. Could tight oil also be a substantial addition to the UKs shale resource?

Toni Harvey: When DECC commissioned the report, we were focused on shale gas. It came somewhat as a surprise to us, because we thought that Bowland shale was going to be very deeply buried and entirely in the gas window, but there actually is some Bowland shale in the oil window, which is less deeply buried. So again, back to this figure of 42, the light orange is the Bowland shale that is in the oil window, and the dark orange is the Bowland shale that is in the gas window. Because most of it was in the gas window and we had not scoped out the report to do an oil estimate, we stopped at gas. DECC has now commissioned the BGS to do a report on the Weald basin in southern England, because that basin has not been buried as deeply and is likely to be mostly liquids. In that case, we will probably come out with a shale oil estimate, and we might not go to the effort of doing a shale gas estimate.

Lord Griffiths of Fforestfach: And you have no initial idea of what that might be?

Toni Harvey: No, we are still doing the seismic mapping, log analysis and core rock evaluation. There is a lot of work to be done."

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