Tight Oil and the Weald

The flow testing that has just finished at Horse Hill has drawn attention to the potential for large-scale unconventional oil drilling in South East England.

While some were slow to understand the significance of the Horse Hill tests, campaigners have tried to open local people’s eyes to what they could lead to. This blog post is based mainly on information from campaign group Frack Off – see links at the end of this post.

“very much like an industrialised process…”

This two-minute video contains clips from several interviews with Stephen Sanderson, Chairman of both Horse Hill Developments Ltd and its largest stakeholder, UK Oil and Gas Ltd (UKOG), about oil prospects in the Weald (the area between the North and the South Downs, including large parts of Sussex and Surrey and part of Kent).

Talking about the oil deposit, which he says extends over 1,200 square miles or more, Sanderson says, “this type of oil deposit very much depends on being able to drill your wells almost back to back so it becomes very much like an industrialised process … Generally you have to drill a lot wells close to each other so you can maintain a certain level of production.”

The “industrialised process” Mr Sanderson refers to could mean typical densities of four to eight wells per square mile. Along with the associated support infrastructure of pipelines, processing plants and waste facilities, and the heavy traffic for construction and transporting oil, this would completely change the character of our area. Hints of what to expect can be seen in Texas, Pennsylvania and Queensland.

Tight oil

At Horse Hill, the companies were looking both for conventional oil, which could provide small returns, and unconventional oil, which, while a much riskier prospect, could produce massive returns.

The conventional target is the Portland Sandstone, a small, local oil deposit which could be drained by one or a small number of wells. At nearby Brockham, Angus Energy is producing an average 21 barrels of oil a day from the Portland.

The major unconventional target is the Kimmeridge Clay shale formations, which cover a large part of the Weald. This is ‘tight oil’ or ‘shale oil’.

Tight oil is oil trapped in low permeability rocks. Extracting it usually requires similar techniques to shale gas: the drilling of long horizontal laterals, hydraulic fracturing or acid stimulation, and the drilling of a densely-spaced patterns of wells. These processes are colloquially known as fracking, though the government recently changed the definition of fracking to exclude low-volume operations and those above 1,000 metres depth.

At Horse Hill, the companies tested two layers within the Kimmeridge Clay. UKOG claims to have flowed more than 450 barrels per day (bopd) from the Lower Kimmeridge Limestone and 900 bopd from the Upper Kimmeridge Limestone. They say an additional 168 bopd flowed from the Portland Sandstone.

The next steps

The next stage will be to apply for planning permission to “drill a horizontal sidetrack and conduct long term production tests”.

Sanderson has complained that the planning process is too slow and says he is talking to the government “at a high level” about how to fast-track the planning process.

From the objector’s point of view, a shortcoming of the situation is that planning applications are always judged on their individual merits, so it’s not easy to object to one drill site on the grounds that it’s opening the door to the industrialisation of the whole area.

What’s in store?

UKOG say there may be up to 124 billion barrels of “oil in place” in the Weald Basin. Even if this is correct, oil in place is not the same as oil which can be extracted. And for unconventional resources the difference can be very large indeed. For instance, the current recovery factors for the Bakken Shale (a formation in North Dakota similar to the Kimmeridge) are estimated at about 3.5%. With this assumed recovery factor, the notional accessible oil becomes a still improbable 4.3 billion barrels. Given that the total production of a tight oil well is around 125,000 barrels, it would require tens of thousands of wells to extract this much oil.

There are other estimates of the unconventional oil in the Weald: 4.4 billion barrels of oil in place according to the British Geological Survey (BGS) and 17 billion according to the US Energy Information Administration (EIA), 700 million barrels of which could possibly be extracted. Applying a recovery factor of 3.5% to the BGS estimate, 154 million barrels could be extracted from the Weald. This would still require more than 1,200 wells.

UK oil consumption currently stands at around 1.6 million bopd – so the BGS estimate would supply the equivalent of just 96 days’ use. The EIA’s estimate is equivalent to 437 days’ use and even UKOG’s highly dubious 4.3 billion barrels only to seven years’ use, assuming we managed to drill the 34,000 wells required.

How could the Weald be affected?

Exploitation of tight oil is an entirely new industry in the UK so it is impossible to say exactly what the impacts will be. But experience in the US and Australia shows there are numerous risks, including air and water pollution, toxic and radioactive waste disposal issues, heavy traffic, and health impacts for people and animals.

Some downsides are given: such as the massive amounts of extra road traffic (particularly heavy good vehicles) it will involve.

Other risks are small for an individual well – but when thousands are being drilled it becomes a near certainty that some of those wells will have an impact. For instance, industry data shows that around 6% of wells leak in some way as soon as they are constructed; once you drill more than a few dozen wells it is almost certain that at least one of them will leak.

Some impacts, such as air pollution and truck traffic, are worst during the drilling and stimulation phase, while others, such as leaking wells, may get worse over decades. This article contains a good overview of the various risks from fracking and associated technologies.

As more and more wells are drilled, the impacts accumulate and it is the cumulative impacts of this industrialisation which eventually becomes the dominant factor.

Frack Free Surrey – and many of the people living round Horse Hill – will oppose any further testing here.

Read more on the Frack Off website:








One Response

  1. Ken Wilkinson says:

    It is odd that you use ‘Frack-Off’ as a source of information. A bit like using ‘Britain First’ to comment on race relations!

    Its difficult to see what not to like about these results. These are natural flow rates of a substantial amount from a vertical well. The horizontal drilling will allow much more to be accessed, so very large flows from a single well could result in much more flow, and thats without pumping. No one on the surface would know about this, and its all in naturally fractured rock. The N Sea provided huge amounts of tax revenue andf jobs for the UK for decades. This could have a great effect as well. The price is low at the moment but will surely rise at some point. Thats an issue for UKOG however.

    As for fracking, its not allowed shallower that 1000m, and if the formation is flowing without fracking there would appear to be no reason why it would ever be proposed. Other stimulation methods are available, but it appears this is not needed. (Its difficult to build up the pressure to frack in a permeable formation!)

    All the other stuff, trucks etc, apply to the 13 oilfields around your area. They have been operating for decades with no issues, till the anti frack people got involved. Only non hazardous chemicals are permitted, its all covered by great science and experience, so whats the problem? I bet everyone around there has a car and heats their home using fossil fuels.

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