The Carboniferous Bowland Shale gas study: geology and resource estimation

Andrews, I.J.. 2013 The Carboniferous Bowland Shale gas study: geology and resource estimation. London, UK, British Geological Survey for Department of Energy and Climate Change, 64pp.

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The assessment of shale gas resources in the UK is in its infancy. This report summarises the background geological knowledge and methodology which has enabled a preliminary in-place gas resource calculation to be undertaken for the Bowland-Hodder (Carboniferous) shale gas play1 Marine shales were deposited in a complex series of tectonically active basins across central Britain during the Visean and Namurian epochs across a large area of central Britain (Figure 1). 2 The marine shales attain thicknesses of up to 16,000 ft (5000 m) in basin depocentres (i.e. the Bowland, Blacon, Gainsborough, Widmerpool, Edale and Cleveland basins), and they contain sufficient organic matter to generate considerable amounts of hydrocarbons. Conventional oil and gas fields around most of these basins attest to their capability to produce hydrocarbons. of the Carboniferous (c.347-318 Ma). In all of these basins, deep-water marine shales pass laterally into shallow-water shelf limestones and deltaic sandstones. Contemporary basins extend offshore beneath the East Irish Sea and the Southern North Sea. The organic content of the Bowland-Hodder shales is typically in the range 1-3%, but can reach 8%. The maturity of the Bowland-Hodder shales is a function of burial depth, heat flow and time, but subsequent uplift complicates this analysis. Where they have been buried to sufficient depth for the organic material to generate gas, the Bowland-Hodder shales have the potential to form a shale gas resource analogous to the producing shale gas provinces of North America (e.g. Barnett Shale, Marcellus Shale). Where the shales have been less-deeply buried, there is potential for a shale oil resource (but, as yet, there is inadequate geotechnical data to estimate the amount of oil in-place). In this study, shales are considered mature for gas generation (vitrinite reflectance > 1.1%) at depths greater than c. 9500 ft (2900 m) (where there has been minimal uplift). However, central Britain has experienced a complex tectonic history and the rocks here have been uplifted and partially eroded at least once since Carboniferous times. Because of this, the present-day depth to the top of the gas window is dependent on the amount of uplift, and can occur significantly shallower than 9500 ft. The total volume of potentially productive shale in central Britain was estimated using a 3D geological model generated using seismic mapping, integrated with outcrop and deep borehole information. This volume was truncated upwards at a depth of 5000 ft (1500 m) below land surface (a suggested US upper limit for thermogenic shale gas production) or the depth at which the shale is mature for gas generation (whichever was the shallowest). The volume of potentially productive shale was used as one of the input parameters for a statistical calculation (using a Monte Carlo simulation) of the in-place gas resource (see Appendix A).

Item Type: Publication - Report
Funders/Sponsors: Department of Energy and Climate Change, NERC
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Date made live: 13 Nov 2013 16:11 +0 (UTC)

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