Undiscovered Oil and Gas in the Midlands of England: A USGS Assessment

U.S. Geological Survey Fact Sheet 2018–3028, National and Global Petroleum Assessment. By the Midlands Area Assessment Team: Christopher J. Schenk, Marilyn E. Tennyson, Tracey J. Mercier, Cheryl A. Woodall, Thomas M. Finn, Stephanie B. Gaswirth, Phuong A. Le, Michael E. Brownfield, Kristen R. Marra and Heidi M. Leathers-Miller.

Using its geology-based method, the USGS estimates mean undiscovered, technically recoverable resources of 319 million barrels of oil and 8.3 trillion cubic feet of gas in the Midlands of England — both continuous (unconventional) and conventional.

The geology

The Midlands' structure is complex, shaped by a series of tectonic events:

• Late Devonian to Carboniferous stretching opened rift basins (grabens) where organic-rich shales of the lower Bowland and Hodder formations were laid down. Later, as the region slowly subsided, organic-rich shales of the upper Bowland and river-delta sandstones of the Millstone Grit Group followed. The Bowland and Hodder shales are the Midlands' best source rocks.
• Late Carboniferous and Early Permian north-directed compression lifted and inverted many of the old rift structures.
• Late Permian to Jurassic subsidence buried the shales under kilometres of sediment, maturing their organic matter and generating oil and gas.
• Up to 4 kilometres of uplift and erosion in the Paleogene may have breached traps and let oil and gas escape. That possible loss is the biggest geological uncertainty in the assessment.

What was assessed

Three total petroleum systems (TPS), divided into seven assessment units (AUs):

• Bowland-Hodder TPS — oil and gas still held in the shales themselves, in four units: upper and lower Bowland-Hodder shale gas and shale oil. The lower shales are up to 3,000 metres thick, the upper up to 900 metres, and both reach gas-generating maturity (vitrinite reflectance above 1.3 percent). The model assumes some oil or gas stayed in the shales after the Paleogene uplift.
• Carboniferous TPS — oil and gas from the same shales, and perhaps from Westphalian coals, that migrated into (1) inversion structures with possible sandstone and carbonate reservoirs — the Midlands Conventional Oil and Gas AU — and (2) low-permeability sandstones and siltstones of Namurian and Westphalian age in the Cleveland and Cheshire subbasins — the Namurian–Westphalian Tight Gas AU.
• Carboniferous Coal TPS — coalbed gas in Westphalian coals in two main areas mapped by the UK Department of Energy and Climate Change, with up to 40 metres of net coal where unmined. Current and former mines and coal-mine-gas areas are excluded.

Well drainage areas, success rates and recoveries for the unconventional units were based on analogues in the United States.

The four shale assessment units. Base map from the National Park Service. USGS.

The tight gas, coalbed gas and conventional assessment units. USGS.

Results

Mean estimates, with the F95–F5 range (a 95 percent chance of at least the first figure, 5 percent of at least the second):

• About 97 percent of the oil — 308 million barrels — is potential shale oil.
• About 97 percent of the gas — 8,006 billion cubic feet — is unconventional: shale gas (54 percent), tight gas (22 percent) and coalbed gas (21 percent).

Mean results by assessment unit (oil in million barrels, gas in billion cubic feet; the probability that the unit holds at least one accumulation in brackets):

Sources

• Schenk, C.J., and others, 2018, Assessment of undiscovered oil and gas resources in the Midlands area, England, 2018: U.S. Geological Survey Fact Sheet 2018–3028. https://doi.org/10.3133/fs20183028 · https://pubs.usgs.gov/publication/fs20183028
• The maps, the results by unit and the assessment team come from the fact sheet's PDF. Its landscape photograph is from a stock site and is not reproduced here.
• Rewritten in hubnx's own words.