- 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.
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.
|Midland Valley||Dart Energy||367||655 bcf||?||655|
|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|
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|
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|
|Tyneside||Five Quarter||400||2 BTons||8,000|
|Firth of Forth||Thornton/Riverside||240||1 BTons||4,000|
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