Fracking

What fracking is

Fracking, or hydraulic fracturing, is the extraction of natural gas or petroleum from shale rock by hydraulic fracturing. The gas is called shale gas and it is mostly methane. It does not sit in a large open cavity in the rock: it is held in the tiny pore spaces of the shale. It came to be there because fine mud, rich in the remains of plankton and other micro-organisms, was laid down on a sea floor, was buried and compacted into shale, and was then heated enough for those remains to break down into gas and petroleum.

The difficulty is that shale is impermeable. Its grains are far too fine for gas to move through the pore spaces, so a well drilled into shale would collect almost nothing, because the gas cannot travel through the rock to reach the borehole. Fracking solves that by creating permeability where none exists. Water, sand and a small amount of chemical additives are pumped into the shale at very high pressure until the rock cracks, and the cracks join together into a network of pathways that drains gas towards the well.

This is why shale gas is described as an unconventional resource. In a conventional gas field the gas has migrated out of its source rock into a permeable sandstone or limestone and is trapped beneath a cap rock, so it flows to the well under its own pressure. Shale gas has never left its source rock, so the permeability has to be manufactured before anything will flow. The same technology applied to shale oil gives shale oil, and the rock layer itself is called the shale play.

How a shale gas well is drilled and fractured

Everything begins on a well pad, a flat area of a few hectares that is cleared, drained and surfaced, with access roads, water storage, pipelines and power brought to it. Because the wells are drilled directionally, one pad can carry many wells, which keeps the surface footprint far smaller than it would be if each well had its own site. The rig drills a vertical well down through the overlying rocks, usually 1 to 3 km, until it reaches the shale.

As the bit goes down, steel casing is lowered into the hole and cement is pumped into the space between the casing and the rock, so that the well is sealed off from every rock layer, and every aquifer, that it passes through. The well is then drilled horizontally through the shale for a kilometre or more, steered with a downhole motor and monitoring equipment so that the horizontal section runs along the layer that holds the gas. This is the section that makes the difference, because a horizontal well meets far more of the shale than a vertical one ever could.

Fracturing is done in stages along the horizontal section. A perforating gun is lowered into the first stage and fires small explosive charges through the casing to open holes into the shale. Fracking fluid, which is more than 99 per cent water and sand with a small amount of chemical additives, is then pumped in at very high pressure. The pressure opens fractures in the shale, and the proppant carried in the fluid - the sand or small ceramic grains - is left behind inside them. When the pumps stop and the pressure falls, the fractures would close up again, but the proppant holds them open, leaving a permanent network of pathways. A plug seals that stage off and the process is repeated further along the well.

When the plugs are removed, gas flows back up the well and is separated at the surface from the flowback water and the salty produced water that come up with it. The gas goes into a pipeline, while the water is treated, recycled into the next well, or disposed of by injection into a deep disposal well. Because a well has to be drilled, cased, fractured in many stages and then connected to pipelines and roads, developing a shale play is slow, capital-heavy work rather than a quick operation.

The benefits of fracking

The strongest arguments for fracking are economic. Drilling and fracturing a well employs drilling crews, engineers, drivers, water hauliers and site staff, and a shale play keeps them in work for years rather than months. Governments gain tax and licence revenue, landowners and farmers gain rent and royalties for the gas taken from under their land, and local businesses gain from the wages that are spent locally. Where the gas replaces imported fuel, the country's import bill falls and its energy security improves, because supply comes from inside its own borders rather than through a pipeline or by tanker from someone else.

There is an environmental argument as well, and it is the reason several governments have treated shale gas as a transition fuel. Burning methane to generate electricity produces roughly half the carbon dioxide of burning coal for the same output, and gas-fired stations can be started and stopped quickly, so they can back up wind and solar farms when the wind drops and the sun sets. Where gas has displaced coal, as in the United States, carbon dioxide emissions from power stations have fallen sharply. Gas is also cleaner in other ways than coal: it releases almost no sulphur dioxide and far less particulate matter, so it improves urban air quality.

The social benefits matter too. Shale gas has been developed in regions that lost their heavy industry and where the remaining work was farming or tourism, and the wages and royalties have kept families and services in those areas. In countries with large shale reserves but expensive imported energy, such as Argentina and China, developing the resource gives industry a cheaper and more reliable fuel, and reduces the risk that a foreign supplier can turn the tap off. Supporters also argue that gas bought from a stable trading partner is preferable to gas bought from a state that may use supply as a political weapon.

• Jobs and wages: drilling crews, engineers, drivers and site staff, plus the local businesses that supply and serve them.
• Government and landowner income: taxes, licence fees and royalties shared with the owners of the land above the shale.
• Cheaper and more secure energy: domestic gas replaces imported gas or coal and improves the balance of payments.
• About half the carbon dioxide of coal for the same electricity, and quick start-up to back up wind and solar power.
• Cleaner air than coal: almost no sulphur dioxide and much less particulate matter.
• Regeneration of regions that have lost their traditional industry.

The limitations of fracking

The environmental objections start with water. Fracturing a horizontal well can use tens of thousands of cubic metres of fresh water, and in a dry region that water competes directly with drinking supplies and irrigation. Most of it stays underground and is never recovered, so it is lost from the local water cycle. The water that does return, the flowback water and the salty produced water, is contaminated with salts, heavy metals, hydrocarbons and the chemical additives used in the fluid, and it also brings up naturally occurring radioactive material from the shale. A spill at the surface, or a leak from a cracked storage pit, can reach a stream or a shallow aquifer, and where well casing and cementing have failed, methane and fluid can travel up the outside of the well into groundwater.

Air is the second front. Methane escapes during drilling, during fracturing, and from valves, compressors and pipelines. Methane is a potent greenhouse gas, far more powerful than carbon dioxide over the short term, so a leakage rate of a few per cent can wipe out the climate advantage of burning gas instead of coal. Diesel engines on rigs, pumps and trucks release nitrogen oxides and fine particles, flaring of waste gas releases carbon dioxide and black carbon, and the silica dust produced by handling sand is a hazard to workers.

The third is induced seismicity, earthquakes caused by human activity. Fracturing itself usually produces earthquakes far too small to be felt, but the far bigger problem is the disposal of the wastewater. Pumping millions of litres of salty water into a deep disposal well raises the pressure in the pore spaces of the rock, and if that rock contains a fault, the extra pressure can allow the fault to slip. Oklahoma went from a handful of felt earthquakes a year to hundreds, and researchers linked the rise to wastewater injection; the state regulator cut the volumes that could be injected and closed some wells, and the number of felt tremors fell. Earthquakes associated with shale gas operations have also been recorded in the Sichuan basin in China. Even small tremors crack plaster, damage foundations and frighten people.

Finally there are the land, nuisance and social costs. Each pad needs roads, water pipelines, compressor stations and constant heavy traffic, and a well can be drilled and fractured around the clock, so nearby homes get noise, dust, diesel fumes and floodlighting at night. House prices and the peace of the countryside fall, and communities divide between those who have signed a lease and those who have not. Money invested in gas can also delay investment in the renewable energy that will be needed in any case, and if a company goes bankrupt its wells can be left orphaned - still leaking, with nobody paying to seal them.

Managing the risks of fracking

The first decision a government makes is whether to allow fracking at all. Some have chosen prohibition: France banned hydraulic fracturing in 2011 and revoked permits that had already been issued, and Bulgaria, the Netherlands and Ireland, together with Scotland and Wales, have bans or moratoria of their own. The United Kingdom lifted a moratorium in 2018 and reimposed it in 2019 after further tremors at a site in Lancashire. A ban removes the risk completely at the site, but it does not remove the demand: the gas is then imported from somewhere else, so the emissions, the water use and the earthquakes simply move to the producing country. That is why the alternative is to permit fracking but regulate it hard.

Where fracking is allowed, the standard package of controls begins with a full environmental impact assessment and public consultation before a licence is granted, and with permits that limit how much water may be taken and set out how waste water must be handled. Operators must disclose the chemicals added to the fluid, as they do on the FracFocus register in the United States. Well integrity is the key to protecting groundwater: several layers of steel casing, cement pumped from the bottom of the well up past the shallowest aquifer, and pressure tests to prove that the seal holds. Water in nearby wells and springs must be tested before drilling starts, so that a later change can be proved rather than guessed, and a setback distance is kept between the well and homes, water wells, streams and known faults.

Operational controls reduce the other impacts. Water is recycled from one well to the next, or taken from brackish sources instead of fresh supplies, and flowback water is stored in closed tanks rather than open pits to cut the risk of spills. Gas that would once have been flared is captured and sold through a green completion, and leak detection and repair programmes hunt down the valves and compressor seals that lose the most methane. Earthquakes are managed with a traffic light system: a network of seismometers watches the site, work may continue below a set threshold, must pause and be reviewed at a medium reading, and stops altogether above a higher one. In the United Kingdom the threshold at which work had to pause was a tremor of magnitude 0.5.

Every one of these strategies has a limitation, and that is where the marks are. Recycling leaves a concentrated brine that still has to be disposed of, and in Oklahoma it was the disposal wells themselves that caused the earthquakes. A traffic light system sets a threshold that is a political judgement rather than a scientific certainty, and it can only react after a tremor has already happened. Baseline water testing is only useful if it was carried out before drilling, which is often not the case, and methane occurs naturally in many aquifers, so the source of any methane found is disputed. Regulators may lack the staff to inspect thousands of wells, small operators resist spending money on leak repair, and a financial guarantee is worthless if the bond is smaller than the cost of sealing a well.

Investigating a fracking site

Much of the environmental management of fracking is an investigation, and Paper 2 expects you to plan one. The central question is nearly always the same: has this site changed the water? The method is a before-and-after survey with a control. Identify the water supplies people actually use - boreholes, springs, farm wells - and sample each one before drilling starts, then repeat the sampling on the same dates in each season after work begins. Sample both up-gradient and down-gradient of the pad, and sample a similar aquifer that no company is working, so that you have a control to compare against. Test the water for the things fracking changes: methane, chloride, conductivity, pH, total dissolved solids, heavy metals and hydrocarbons.

A water survey on its own is not a complete investigation, and the other measurements are worth marks. Record the volume of fresh water taken with a meter on the supply, and the volumes of flowback and produced water in the storage tanks, so that the water balance can be calculated - how much goes in, how much comes back, and how much is recycled. Install seismometers around the site so that the size and position of any tremor is recorded, and agree a traffic light threshold in advance. Count the traffic movements on the access road, take noise readings at the nearest houses at the same times each day, and sample air downwind of the pad for methane and volatile organic compounds. Inspect the casing and cementing records, and photograph the tanks and bunds on every visit.

The limitations are the interesting part, and writing about them is what earns the investigation marks. If there is no baseline, a change cannot be proved, and methane occurs naturally in many aquifers, so finding methane is not the same as proving the well caused it. One sample taken on one day tells you nothing about a variable body of water, so readings must be repeated and a range quoted rather than a single figure. Access to the pad is controlled by the operator and some data are commercially confidential, so an independent investigator has to rely on the published environmental impact assessment, the regulator's monitoring reports and the company's own figures. Groundwater also moves slowly and can take years to show a change, so a fortnight of fieldwork cannot settle the question on its own.