Wells, Wells And More Fracking Wells

Summary

  • Fracking requires large numbers of wells
  • Conventional well can drain large area
  • For impermeable rock many wells required
  • Often 8 wells per square mile or more
  • Tens of thousands drilled in US already
  • Largest onshore gas field in UK was 8 wells
  • Fracking companies play down the scale
  • What they say to investors most accurate
  • Well numbers can be estimated from reserves
  • Adds up to tens of thousands of wells across UK
  • Plus pads, pipelines, compressor stations etc.

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A critical aspect of the exploitation of unconventional gas which is often not fully appreciated is that, not only is the extraction process for an individual well much more intense (hydraulic fracturing etc.), but the number of wells that have to be drilled is much larger. This is principally because unconventional gas is trapped in impermeable rock, and so the gas cannot easily flow through it. A conventional gas field can drain gas from a large area through a small number of wells because the gas can flow through the permeable rock of the reservoir. For shale gas or coalbed methane (CBM) wells need to be drilled wherever the gas is, at regular intervals, since the gas cannot flow through the shale or coal. Well spacings of 8 wells per square mile (or even higher) are common in the US and Australia, where large areas have been coated in wells and supporting infrastructure. Over 45,000 shale gas wells and 55,000 coal-bed methane (CBM) wells have been drilled in the US and over 5,000 CBM wells in Australia.

In the UK and Ireland we have hardly seen any onshore oil and gas development at all, with an average of around 20 wells drilled per year, mostly test wells which did not find anything and were quickly capped. This is not remotely comparable to the unconventional gas extraction that is now being envisaged. The largest onshore conventional gas field to date in the UK, Saltfleetby in Lincolnshire, had 8 wells. Because shale and CBM produce much less gas per well than conventional gas, an unconventional gas field would require hundreds of wells to produce the same amount of gas per day as Saltfleetby. To produce as much gas as a large North Sea field would require thousands of wells, covering hundreds of square miles of countryside. Bradford County in Pennsylvania, where in the 4 years starting in 2008 through 2012 around 2000 shale gas well were drilled in an area which is about 80 percent the size of Sussex, shows the . Along with the well pads comes huge amounts other infrastructure including pipelines, compressor stations, waste storage ponds and treatment facilities.

Fracking companies are usually very reticent about the number of wells their proposed developments would eventually require and tend to like to concentrate attention on the handful of test wells they are currently trying to drill, especially when talking to local people. However when they are communicating with their shareholders and potential investors, their focus is entirely the opposite, the long term potential rather than their short term plans. While this bragging is about amounts of gas which they might potentially be able to extract, it is trivial to estimate the number of unconventional gas wells that would be needed to produce a given amount of gas. It should be noted that these are estimates and not precise calculations, since the amount of gas produced by unconventional wells varied enormously. Since the reserve estimates produced by the companies involved are highly uncertain anyway, the uncertainties in the conversion to wells numbers are not that important. The well numbers should provide a good order of magnitude estimate of the potential i.e. they will answer the question: to produce the amounts of gas that the companies are bragging about would hundreds, thousands or tens of thousands of wells be required?

To construct the graphic above reserve estimates produced by licence owners were used as the starting point. These estimates are highly variable in their precision and potential accuracy. In some cases where only ‘gas in place’ values are available these had to be converted into an estimate of recoverable gas using typical recovery factors (10 percent). To convert to number of wells the amount of gas was divided by the total amount of gas produced by unconventional gas wells. For shale gas we use an average total production of 1 billion cubic feet (bcf) per well, while for coalbed methane (CBM) we use 0.5 bcf. For tight (shale) oil a value of 150,000 barrels per well was used. These values, which are again very variable, are estimate from this research by the US Geological Survey. In the case of underground coal gasification (UCG) a value 250,000 tons of coal per well was used. Since full scale UCG has never been undertaken this is very uncertain, but should be a good order of magnitude estimate. The number of wells calculated was capped at a density of 16 wells per square mile (40 acre spacing) for shale gas, shale oil and CBM, since drilling at higher densities than this has not happened to date. Where this has been done the number is shown in brackets. In general this is probably an indication that the company is being over optimistic about the amount of gas that can be extracted.

See sites like Marcellus-Shale.us and West Virginia Host Farmsto get an idea of what all these well pads, pipelines and compressor stations would look like. The table below contains the data used in making the graphic.

Region Company Area Reserve/ Resource Type Wells
Shale Gas
Midland Valley Dart Energy 367 655 bcf ? 655
Lancashire Cuadrilla 1,186 20,000 bcf ? a (7,300)
Cheshire/Lancashire IGas Energy 300 10,200 bcf ? a (4,800)
Cheshire Dart Energy 708 3,055 bcf ? a 3,055
South Wales Eden Energy 806 12,799 bcf ? (5,000)
East Midlands Dart Energy 1,235 4,760 bcf ? a 4,760
Sussex Celtique/Magellan 1,094 10,000 bcf ? (6,700)
Fermanagh Tamboran 746 2,200 bcf ? 2,200
Letrim/Caven Tamboran 986 2,000 bcf ? 2,000
Total
31,900
Shale Oil
Merseyside Aurora 100 80 mmbbl ? 530
Sussex Celtique/Magellan 1094 125 mmbbl ? 830
Total
1,360
Coal-Bed Methane (CBM)
Midland Valley Dart Energy 367 597 bcf 2C 1,194
Solway Basin Dart Energy 295 123 bcf 2C 246
North West IGas 1,556 1,811 bcf 2C 3,622
Cheshire Dart Energy 708 1,683 bcf 2C 3,366
Northern England Alkane Energy 133 385 bcf ? 770
East Midlands Dart Energy 1,413 1,218 bcf 2C 2,436
Staffordshire Dart Energy 325 686 bcf 2C 1,372
South Wales Dart Energy 442 320 bcf 2C 640
South Wales Eden Energy 247 980 bcf 2C (1,500)
Somerset UK Methane 450 1,155 bcf ? b 2,310
Kent Coastal Oil and Gas 371 952 bcf ? b 1,904
Total
19,360
Underground Coal Gasification (UCG)
Swansea Bay Clean Coal 77 1 BTons 4,000
Cromer Clean Coal 100 260 MTons 1000
Humberside Clean Coal 81 200 MTons 800
Sunderland Clean Coal 97 260 MTons 1000
Solway Firth Clean Coal 41 107 MTons 400
Holdness/S.Humber Europa 200 1.35 BTons 5,400
Tyneside Five Quarter 400 2 BTons 8,000
Firth of Forth Thornton/Riverside 240 1 BTons 4,000
Total
24,600

a Calculated from gas-in-place using recovery factor on 10 percent

b Calculated from difference of South Wales and all UK resources for Eden Energy’s licences, split between Somerset and Kent based on license area

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