The Fracking Process

FRACK UK considers below the nature of shale gas, and the exploitation method used to extract it.

1.1       Shale gas

‘Shale gas comprises methane recovered from mudrocks and shales which have previously been considered too impermeable (‘tight’) to allow economic recovery of gas’[1].

Gas which can be economically extracted by drilling a normal borehole into the rock formation, where the rock is sufficiently porous to allow gas to flow to the surface, is known as ‘conventional gas’.   The UK’s current North Sea gas assets are made up of this conventional gas.

Shale gas on the other hand, which is where natural gas is effectively trapped within shale rock strata, is known as ‘unconventional gas’ or ‘shale gas’[2]. 

 1.2            Hydraulic fracturing

Whilst many perceive hydraulic fracturing as a relatively new technique, it was in fact first utilised in Oklahoma in 1949[3], and has been practised on land in the UK at over 200 sites during the last 30 to 40 years[4].

Initially the fracturing methods used were not advanced. It was only until approximately ten years ago that hydraulic fracturing for shale gas took off in earnest in the USA with the introduction of new technology which allowed for horizontal drilling.  Indeed, ‘The ability to economically produce natural gas from unconventional shale gas reservoirs has been made possible recently through the application of horizontal drilling and hydraulic fracturing’[5].

This technique involves drilling a vertical borehole to the depth where the shale formations exist, and using horizontal drilling techniques to then drill horizontally into the shale.  During this process the well bore is cased and cemented in place. 

The Royal Society, in its report entitled Shale Gas Extraction in the UK: a review of hydraulic fracturing[6] (“Royal Society Report”) explains that subsequently ‘Explosive charges fired by an electrical current perforate holes along selected intervals of the well within the shale formation’[7].  A mixture of water, chemicals and sand (known as ‘fracking fluid’) is then pumped at high pressure into the well bore which then passes through these perforations and fractures the surrounding shale rock creating fissures.   The chemicals in the fracking fluid are used to make a ‘highly viscous, low friction fluid’[8] which facilitates the sand entering the fissures during the stimulation process.

The sand then becomes trapped within these fissures, thus holding them open and allowing the gas to flow back to the surface. This is known as ‘stimulation’ and detail of the technique is shown in the diagram above and in the video below.

Fracturing usually needs to be re-visited once every 4-5 years to ensure continued gas production[9], but in the meantime all drilling rigs and associated equipment can be removed leaving very little plant on the site.

Immediately after a successful fracture commonly 40-60% of the fracking fluid flows back up the well bore, and is known as ‘flowback fluid’.  This is then recovered for subsequent treatment or in some cases re-use.

For two videos on the fracking process, click here, and on the youtube video below. 

[1] British Geological Survey, Mineral planning Factsheet – Alternative fossil fuels (2011), page

[2] see L. Magoon, Petroleum Systems of the United States (United States Government Printing Office, 1988), page 48

[3] see J.B. Clark, ‘A Hydraulic Process for Increasing the Productivity of Wells’ (1949) 1(1) Journal of Petroleum Technology 1-8; see Canadian Society for Unconventional Resources, Understanding Hydraulic Fracturing (2010), page 5

[4] C. Lowbridge, ‘Fracking confusion: How UK has been ‘fracked’ for decades’ (BBC News, 22 August 2013)

[5] D. Rahm, ‘Regulating hydraulic fracturing in shale gas plays: the case of Texas’ (2011) 39(5) Energy Policy 2974, 2974; see also J. Curtis, ‘Fractured shale-gas systems’ (2002) 86(11) AAPG Bulletin 1921, 1937

[6] Royal Society, Shale Gas Extraction in the UK: a review of hydraulic fracturing (June 2012), (“Royal Society Report”)

[7] Royal Society Report, ibid., page 9

[8] Canadian Society for Unconventional Resources, Understanding Hydraulic Fracturing (2010), page 19 

[9] British Geological Survey, ibid., page 8