What does tight oil extraction involve?

Aerial View Of Hydraulic Fracturing Operation On A Bakken Shale Pad In North Dakota (Click To Enlarge)

For threatened communities, tight oil extraction is pretty much identical to shale gas extraction. As with all unconventional fossil fuels, it involves much larger amounts of extraction effort, with the associated increased environmental and social impacts this entails. Unlike conventional oil which is trapped in permeable rock by impermeable rocks above, tight oil is trapped within low permeability rocks through which it cannot easily flow. This has a number of consequences. Massive slickwater hydraulic fracturing is needed to crack the rock. Horizontal wells (typically with very long laterals) are needed. But most importantly, large numbers of wells are required. Even with horizontal drilling and hydraulic fracturing a single well can only drain a small area.

In North Dakota, a typical tight oil well has a 1.8 mile (2.9 km) horizontal section running through the Middle Bakken formation. It is fracked in up to 40 separate stages along its length. Initially wells in the Bakken were drilled with a wide spacing (1 or 2 wells per square mile) but companies are now moving towards denser drilling patterns of up to 4 wells per square mile (160 acre spacing). It is unclear whether this might evolve to even higher well densities in the future; shale gas wells are often drilled on an 8 wells per square mile spacing (80 acre spacing). Over 10,000 tight oil wells have been drilled in the Bakken Shale so far, and around 150 drilling rigs are were operating there (until the recent oil price crash) drilling about 1,800 wells a year. Tens of thousands more wells would need to be drilled to extract the quantities of oil that is claimed to be recoverable.

Aerial view of Bakken Shale well pads in the Williston Basin, North Dakota (Click To Enlarge)

The social, safety and environmental impacts on North Dakota of this intense extraction effort have been huge, but it should be noted that North Dakota has one of the lowest population density states in the US with around 10 people per square mile. Less than 700,000 people live in an area larger than England and Wales. In comparison the population density of the UK is over 660 people per square mile, and Sussex has a population density of over 1,100 people per square mile. It is in the eastern US, in states like Pennsylvania, where the population density is 28 times higher than North Dakota (though still only a third of that in the UK), that the largest numbers of people have been significantly affected by unconventional oil and gas extraction.

In the UK, even before the recent flow testing at Horse Hill, UK Oil & Gas Investments (UKOG) had commissioned studies into how it might exploit this tight oil. The details are sketchy and focus is on the concept of a single pad. It carefully avoids any question of how may pads and wells this could mean across the region, but does mention that sites across the Weald are already being identified. The two non-commercial appraisal sites which Cuadrilla is fighting to impose on Lancashire have 4 wells per pad, but even so their impact is far from insignificant. The Weald concept pad has 12 horizontal wells (with provision for 4 more) and an additional production processing facility larger than the pad itself. The concept assumes that the oil will be transported to the Fawley Oil Refinery in Hampshire by road tanker; a highly dangerous prospect (for more details of the impacts of Bakken Shale oil transport see How could the Weald be affected by fracking?).