In many conventional natural gas reservoirs, a few vertical wells every 2.5 square kilometres (around one square mile) are enough to produce the resources available. In contrast, tight and shale gas does not flow easily and resources are often spread over a much larger area, making it harder to access.

We drill wells in different directions from a central location that penetrate the reservoir vertically, often in an S-shape, or horizontally. This limits the number of drilling locations – known as well pads – and reduces our overall surface impact.

Well pads can be spaced up to five kilometres (three miles) apart. Some accommodate up to 50 wells or more. Mobile drilling rigs allow us to avoid dismantling and reassembling drilling equipment at each pad, making the process quicker and saving resources.

Wells can stretch several kilometres underground. For example, in Groundbirch, Canada, we drilled a well 6.3km (3.9 miles) long. In Changbei, China, we drilled an extensive network of wells up to two kilometres (1.2 miles) long to open up a much greater area for gas extraction. This increased potential production as much as ten times compared with conventional techniques.

Opening up rock

When we have completed a well we need to coax the gas from the very tight rock. We pump fluids into the well to make fractures in the rock that allow the gas to flow. This typically takes place a kilometre (several thousand feet) beneath supplies of drinking water, at pressures high enough to create fractures.

The fracturing fluids comprise around 99% water and sand (or ceramic particles), and 1% chemical additives. Sand and ceramic particles have large pores which keep the fractures open, allowing gas to flow. The chemical additives help to keep pipes cool and prevent scale build-up.

During this process, we sometimes place a string of sensors in a nearby well to pick up the popping and creaking of the controlled opening of the rock deep underground. The sounds help us to map out the contours of the cracked rock.

Temperature-sensitive fibre-optic strands help us monitor inside the wells. Cooler zones show us where gas is flowing freely into the wells so that we can adjust operations and improve efficiency. We use software to map out fields below the surface and better target fracturing.

Tight and shale gas plant in Canada

Safety steps

At Shell, we believe we can explore, develop and produce these tight and shale resources safely and responsibly. Shell’s efforts are underpinned by the Shell Onshore Tight Sand or Shale Oil and Gas Operating Principles that we believe provide a framework for protecting water, air, wildlife and the communities in which we operate.

We line the wells with steel pipes and cement them in place from the surface to below the level of the drinking water. These barriers help to contain the fracturing fluid and, along with the depth at which we fracture, prevent the fluid from mingling with drinking water close to the surface.

During operations we monitor wells with pressure sensors to check they are firmly sealed. We also monitor the fractures and the fluids, which helps make production as efficient as possible and protects the environment.

Proven techniques

The oil and gas industry has used hydraulic fracturing worldwide for more than 60 years in vertical wells and for almost 20 years in horizontal wells to recover natural gas (and oil). Globally, hydraulic fracturing has been used in more than two million oil and gas wells to date.

Studies by the US Environmental Protection Agency (EPA) and the Ground Water Protection Council have shown that the process is safe.

A 2012 study by the Royal Society and Royal Academy of Engineering for the UK government also concluded that hydraulic fracturing is safe “as long as operational best practices are implemented and robustly enforced through regulation”. A European Parliament report on the environmental impacts of shale gas and shale oil extraction, supports its findings.

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