Environmental Engineering Reference
In-Depth Information
resources published in 2003 by the Oil and Gas Directorate of the Depart-
ment of Trade & Industry.
12
The 6
th
Petroleum Geology Conference on the
Global Perspectives of North West Europe was held later in the same year. The
three-day programme concluded with a session on non-conventional pet-
roleum. This included a presentation on the UK's shale gas resources and
provided a platform to disseminate updated conclusions of the Imperial
College research of some 15 years previously. The advances in US shale gas
exploration and production technology could now be applied to the UK.
13
In
2008 the British Geological Survey began to review UK shale gas resources
and delivered a presentation on their results at the 7
th
Petroleum Conference
in March 2009. Subsequently, the Department of Energy & Climate Change
commissioned the BGS to prepare a report on The Unconventional Hydro-
carbon Resources of Britain's Onshore Basins - Shale Gas.
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The result of this was that several companies started to look at shale gas
sites within the UK at the time of the announcement of the 13
th
onshore
round of UK licences in 2006. In 2008 Wealden Petroleum Developments Ltd
was awarded a license that covered large parts of the Weald, an area in South
East England situated between the parallel chalk escarpments of the North
and the South Downs, for exploration. Additionally, Cuadrilla Resources
Corporation was awarded a licence that includes areas of the North West of
England.
2
Shale Gas Production and Reserves in the UK
2.1 Overview
2.1.1 Shale Gas Production Process. As noted, horizontal drilling and
hydraulic fracturing are the two technologies that together have the potential
to unlock the tighter shale gas formations.
Hydraulic fracturing (also known as ''fracking'') is a well-stimulation tech-
nique which consists of pumping a fluid and a propping agent (''proppant''),
such as sand, down the wellbore under pressure to create fissures in the
hydrocarbon-bearing rock. Propping agents are required to ''prop open'' the
fracture once the pumps are shut down and the fracture begins to close. The
ideal propping agent is strong, resistant to crushing, resistant to corrosion,
has a low density and is readily available at low cost. The products that best
meet these desired traits are silica sand, resin-coated sand (RCS) and ceramic
proppants. The fractures start in the horizontal wellbore and can extend for
several hundred metres while the sand holds the fissures apart, allowing the
gas to flow into the wellbore. Recovery of the injected fluids is highly variable,
depending on the geology, and ranges from 15 to 80%.
15
Horizontal drilling allows the well to penetrate into the hydrocarbon rock
seam which can be typically 90 m thick in the US, but can be up to 1000 m
thick in some of the UK shale gas seams. Horizontal drilling maximises the
rock area that, once fractured, is in contact with the wellbore and therefore
maximises the volume of shale gas that is released.
