Saturday, 24 August 2013

How did we get to be of interest? Surely there is no shale gas here in Herefordshire?

How did we get to be of interest? Surely there is no shale gas here in Herefordshire?

Well, actually, there might be.

In the course of my studies into this I came across an interesting research paper, whose data was used in the DECC report - with more information about potential sites and more.

 The British Geological Survey (BGS) carried out a basic geological study of shale gas basins  through the use of conventional oil and gas well data to identify potential targets.

This report is basically  looking at lots of geological information to find a UK version (analogue) of the US shale gas rich Barnett Shale region. It is packed full of information and, if you look, the map on page 19 identifies Fownhope and Fowlet Farm (near Eastnor) as Cambrian Shales wells. This map also shows the main areas where hydrocarbon source rocks can be found in the UK.

Main hydrocarbon source rocks (outcrops). Wells reaching Tremadoc to Cambrian in England and hydrocarbon
 wells in northern Ireland which tested a tight gas Carboniferous play in several phases (Griffith 1983) as recently as 2001
The report states that
Satellite basins of the Worcester Graben  beneath the Bristol Coalfield and in Berkshire to the east (Mississippian strata are feebly developed in the latter area) provide the closest UK tectonic analogues to the Fort Worth Basin.

The report also specifically mentions Fowlet Farm and Fownhope boreholes SW of the Malverns as having proven Upper Cambrian black shales. The report details how, in these boreholes
 ~68 m of black shale has been intruded by dolerite sills; the shales have high gamma ray values and represent a potential source rock. Outcrop measurements of TOC support this interpretation, with values of ~5% recorded by Parnell (1983)

Obviously there is a world of difference between "potential source rock" and an actual drilling site, but the report does show why E. Herefordshire has become of interest and maybe why it was included in the recent DECC report on Unconventional Hydrocarbon resources

Still can't find any mention of Much Marcle, though!

If you are interested, the abstract for the report says
Organic rich shale contains significant amounts of gas held within fractures and micro pores and adsorbed onto organic matter. In the US shale gas extracted from regionally extensive units such as theBarnett Shale currently accounts for ~6% of gas production. Shale gas prospectivity is controlled by the amount and type of organic matter held in the shale, thermal maturity, burial history, microporosity and fracture spacing and orientation. 
The main UK organic rich shale sequences have been mapped at the surface and in the subsurface using a combination of outcrop, well and seismic data. Potential targets range in age from Cambrian to the late Jurassic: younger shales have been excluded because they have not reached the gas window, but they may possess a biogenic gas play. A GIS showing the distribution of potential reservoir units has been combined with information on hydrocarbon shows, thermal maturity, fracture orientation, gas composition and isotope data to identify potentially prospective areas for shale gas in the UK. These include Lower Palaeozoic shale basins on the Midland Microcraton, Mississippian shales in the Pennine Basin and Pennsylvanian shales in the Stainmore and Northumberland basin system

1 comment:

  1. Very important map of state of play in the UK, showing licenced areas, drilled sites, campaign groups etc.