Natural gas – a bridge too far

Is natural gas a bridge to a low carbon future?  Not if you look more carefully.

Spend some time looking into the environmental impact of shale gas production using hydraulic fracturing and you quickly come to the conclusion that natural gas isn’t a bridge to anywhere useful. In fact it’s not a bridge at all.

By focusing only on the combustion of natural gas in a modern power plant, the proponents of this ‘clean fuel’ conveniently forget the substantial footprint that the production, collection, and processing of this fuel leaves indelibly imprinted on the environment.

Start with fracking.

Approximately 1 million wells have been hydraulically fractured since the technique was first developed in the late 1940s.  Around 25,000 to 30,000 new wells were drilled and hydraulically fractured in the US each year between 2011 and 2014, in addition to existing wells that were fracked to increase production.

Multi-stage fracturing involves injecting a fluid: usually water plus chemicals and proppants (which ‘prop up’ the fractures) at extremely high pressure into a shale formation in a number of places (stages) along the wellbore. This fractures the rock and creates a network of open fractures through which the gas can flow and be collected.

What is new is the combination of these technologies: the use of greater amounts of water, sand and chemicals; and the higher injection rates and pressures employed to fracture a much larger volume of rock.

The scale of the development is also what differentiates shale gas development from conventional gas production. Although both conventional and shale gas development requires the construction of well pads, work camps, roads, and pipelines–shale gas development requires more of these activities. Even with multi-well pads, shale gas development will generally lead to more pads being built and more wells being drilled than would be needed to produce the same volume of gas from conventional gas reserves in high-permeability reservoirs.

Hydraulic fracturing requires large quantities of water. Some wells in the US use as much as 7 million gallons per fracture. In British Columbia, fracturing can reportedly require as much as 25 million gallons.[i]  Providing this amount of water to a wellsite requires hundreds of trips by diesel-engine tanker trucks transporting water to the site.  In principle, a lot of this water could be reused, but the proportion of water used in fracking that comes from reused wastewater is low.  A EPA report on the fracking water cycle states that the median percentage of the injected fluid volume that comes from reused wastewater was only 5% between 2008 to 2014.

However, the absolute quantities of water withdrawn are often less important than the times and rates at which water is extracted. Fracking uses a lot of water over a short period of time—several days. If several fracking operations happen sequentially, as they would in a multi-well pad, or concurrently on different pads, the demand could exceed the local unallocated supply for that period. Based on the US average  of 19,000 m3 per well, a well pad with eight wells could use some 150,000 m3 of water within two to three months.

But it is the mix of chemicals that are an essential part of the hydraulic fracturing process that is most alarming. The US EPA report identified over 1,000 chemicals that were reported to have been used in fracking fluids between 2005 and 2013. A given well will use anywhere from 4 to 28 chemical additives in a fracking operation.  Three chemicals: methanol, hydrotreated light petroleum distillates, and hydrochloric acid were used in 65% of the wells reporting to the Fracfocus database.

These chemicals are transported to the well site and stored on site until they are mixed with the base fluid and proppant and pumped down the production well. While the quantities added to the fracking fluid are very small, the amounts stored at the well site are not. Thousands of gallons of chemical additives can be stored on site for use during the fracking process.

Spills and leaks are inevitable.

The EPA reported 151 spills of fracking fluid or additives in 11 states between 2006 and 2012.  The mean quantity of fluid released was 1,600 liters, but the largest spill was over 73,000 liters. Thirteen of these spills polluted local surface waters. In Pennsylvania, between 2008 and 2013, 10 spills of over 1500 liters that polluted surface waters were documented.  The spills ranged from 13,000 liters to one which was over 850,000 liters.

During fracking, a well is subjected to very high pressures. The fracking fluid is pumped into the well until the targeted rock formation fractures—then pressure decreases. The well casing, cement, and other well components must be able to withstand these pressures so that the fracking fluid can flow to the targeted rock formation without leaking.

Older wells that are fracked may not be able to withstand these pressures. Older wells may also be fracked at shallower depths, where cement around the casing may be inadequate or missing. There have been several documented failures of this type. In one case, the fracking of an inadequately cemented well in Bainbridge Township, Ohio, contributed to the flow of methane into local drinking water resources. In another case, an inner string of casing burst during fracking of an oil well  near Killdeer, North Dakota, resulting in a release of fracking fluids and formation fluids that polluted a groundwater resource.

In rural areas where homes rely on private wells for water, fracking operations pose a particularly high  risk.  Pennsylvania regulators have confirmed at least 260 instances of private well contamination from fracking operations since 2005. Independent journalists exploring the issue have documented over 2,300 complaints of pollution of private wells in 17 of the 40 Pennsylvania counties where fracking has taken place.

After hydraulic fracturing, the injection pressure applied to the well is released and the direction of flow reverses, causing fluid to flow out of the well. The fluid that initially returns to the surface after fracking is mostly fracking fluid and is sometimes called ‘flowback’.  The fluid that returns to the surface during gas production is similar in composition to the fluid naturally occurring in the targeted rock formation and is typically called ‘produced water’.

Produced water is extremely toxic. It has been found to contain:

  • Naturally-occurring organic compounds including benzene, toluene, ethylbenzene, xylenes, oil and grease;
  • Naturally occurring radioactive materials including radium;
  • Metals including barium, manganese, iron and strontium;
  • Sodium, magnesium and calcium salts (chlorides, bromides, and sulfates);
  • Hydraulic fracturing chemicals, additives, and their derivatives


Produced water is usually stored in lined surface ponds or tanks before being either treated, used to fracture another well, or reinjected into a deep saline formation or, in the US, being reinjected into a Class II disposal well.  Lined ponds, even when built with double liners, are rarely free from flaws and can be expected to eventually leak.

Spills of produced water have been reported right across the US—ranging from 1300 to 3800 liters (the median values of several datasets).  However, much larger spills have occurred. In North Dakota there were 12 spills greater than 79,500 liters and, in 2015, one huge spill of 11 million liters.  Many of the reported produced water spills contaminated surface water resources: the EPA reported that 13 of 225 spills polluted local creeks, ponds, or wetlands. One spill contaminated ground water. A report from California showed that between 2009 and 2014, 18% of spills impacted waterways. In yet another incident, pits holding flowback fluids overflowed in Kentucky in 2007, contaminating the Acorn Fork Creek.

Saline produced water cannot be treated in typical municipal wastewater treatment plants because the high salinity negatively effects the activated sludge process. In addition, the naturally occurring radioactive elements brought to the surface in the produced water may be absorbed by the sludge or simply flow through the treatment plant and be discharged into the receiving waters. Hence, deep-well injection is generally the industry’s preferred option when the geology allows for this method of disposal.

And then there’s methane

Shale gas is mainly methane—which is a powerful greenhouse gas; much more powerful than carbon dioxide is contributing to climate change and a warming planet.  Just how powerful it is depends on how you measure its intensity.

In contrast to CO2, which can lingers in the atmosphere for decades, methane breaks down fairly quickly—within 12 years. However, the impact of CO2 on climate change has generally been measured over a period of a 100 years.  This is the convention which has been adopted by the IPCC–and which has been followed by many climate scientists.

The smaller emission factor tends to minimize the impact of methane as a greenhouse gas. In addition, it is hardly scientific to measure the environmental impact of a pollutant over a period of time during which it is not actually present in the environment. The global warming potential (GWP) of methane should be set at the upper level—a level that recognizes its substantial and immediate contribution to global warming when it is released.

Natural gas is being touted as a clean fuel: and it is certainly cleaner than coal in terms of its emissions of carbon dioxide when fueling a power plant to generate electricity.  Natural gas also produces much less particulate air pollution, lower levels of nitrogen oxides (which can lead to the ground level ozone), and less sulfur dioxide than coal. Emissions of vapor-phase mercury are also insignificant—if the mercury is removed during up-stream processing.  In other words, it burns relatively cleanly.

But if hydraulic fracturing and the production and processing of shale gas release significant quantities of methane, the advantages of natural gas over coal quickly disappear.

Both methane and carbon dioxide are released during fracking when:

  • Emissions of methane and carbon dioxide occur during drilling and well completion, mostly due to venting and flaring;
  • Emissions occur from plays where the gas contains significant amounts of carbon dioxide that has to be removed before the gas can be brought to market;
  • Fugitive emissions occur during production, processing, gathering, and transport to market;
  • Emissions occur from well seeps after abandonment.

There have been several attempts to accurately measure methane emissions from hydraulically fractured shale gas sites.  The results are variable, inconsistent, and often contradictory. This may be because methane leaks from frack sites are likely to be sporadic, intermittent, and to some extent unpredictable.  Surveys conducted at different times of the year and at different stages of the fracking process cycle will give different results. In addition, airborne releases are difficult to attribute to a specific site.

There is, however, absolutely no doubt that the hydraulic fracking of shale plays produces significant emissions of methane.

A detailed peer-reviewed study in 2015 by Robert Howarth at Cornell University came to the conclusion that when methane emissions from shale gas production were accounted for, shale gas is not quite the clean fuel many proponents claim.  Yes it burns cleaner.  But the upstream production processes–starting with drilling the well–leak a powerful greenhouse gas into the atmosphere: methane.  These emissions more than offset the advantage that shale gas has at the power plant in comparison to coal.

How does all this gas from the frack site wells get collected?

It’s what’s called the gathering system.  Every single one of the roughly 750,000 gas producing wells in the US and Canada has gas pipelines running from the well across the land to the nearest gas processing plant.  This so-called bridging technology requires an absolutely enormous network of local pipelines gathering the gas together and pumping it to a processing plant where it is cleaned up.

And that’s right, we have never met a pipeline that didn’t leak.

And why do we need a bridge anyway?  Just step right over.  Solar energy and wind power are right on your doorstep.  No emissions, no pipelines, no smoke, no groundwater pollution, no pollution of rural drinking water wells.

And no mercury.


Under the hood:

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