In order to recover the natural gas trapped deep below the surface in rock formations, Cuadrilla’s wells reach depths of over 10,000 feet. All of our wells are designed with safety as the foremost concern.
Before drilling begins, the site is lined with a thick impermeable membrane and the drilling rig (around 30 metres in height) is set up.
Each well we drill is lined with layers of steel casing which are cemented in to place, completely sealing the well from the rock formations.
Importantly, Cuadrilla always has at least three layers of steel casing at depths where the aquifer is found. These casings are cement-sealed and extend hundreds of feet below the aquifer. This is a comprehensive safety feature of our well designs and prevents contamination of the ground water.
Cuadrilla also always uses an intermediate casing as part of its well design. The intermediate casing creates a second steel, cement-sealed layer of well protection extending well below the level of the aquifer, ensuring environmental safety. In the US, this was recently made a requirement by New York as part of the state’s recommendation to allow fracturing to resume.
For more detail on the construction of Cuadrilla’s wells, along with the safety mechanisms in place, refer to the Wellbore Integrity document.
Directional drilling and horizontal wells
The concept of horizontal drilling is not new. The first patent for this was issued in 1891 to Robert E. Lee, for the drilling of a horizontal ‘drainhole’ for a vertical well. Since then, significant advances in technology and knowledge have led to increasingly effective directional drilling and the ability to create horizontal wells.
Hundreds of thousands of horizontal wells have been drilled safely and successfully onshore in the UK and across the world for many decades.
One of the most notable examples in the UK is at Wytch Farm, on the southern shore of Poole Harbour in Dorset.
At the Wytch Farm site, which is the largest onshore oil field in Western Europe, natural gas and oil is extracted from deep beneath the surface. In 2008, a record-breaking horizontal well was drilled by BP at the Dorset site.
Planning and safety
For any horizontal well that Cuadrilla drills, the path is determined in advance by Cuadrilla’s expert geologists and engineers, who each have decades of experience in the drilling of wells.
We also use the same stringent environmental and safety measures on our horizontal wells as we do with our vertical wells, including using steel casing cemented in place.
How we do it
Drilling a horizontal well involves curving the path of the well, gradually moving from a vertical to a horizontal path. The well itself is very narrow, usually only 8.5 inches in diameter.
Technological advances in drilling allow us to steer our equipment away from the straight line that traditional wells take, deviating to reach a point that is not directly under the entry site.
One of the key tools is measurement-while-drilling technology, or borehole telemetry. This technology allows our engineers and geologists to monitor in real-time how the drilling is progressing deep beneath the surface. Using this technology we are able to plot and manage the path of the well as it curves from a vertical to a horizontal path.
Another important tool, which has been developed over many years, is the steerable downhole motor assembly.
Conventional drilling of vertical wells occasionally requires downhole motors, placed above the drill bit, to help penetrate particularly hard rock formations. Adding the ability to steer these motors means that well’s path can be controlled while continuing to drill. This allows us to introduce the deviation in the wells path, carefully steering the drill bit into a horizontal path.
Cuadrilla is currently undertaking an exploration programme in Lancashire which seeks to understand whether it is viable to recover the natural gas held within Shale rock deep beneath the surface.
By drilling an exploratory horizontal well, we are able to discover much more information about the geology and quality of the gas reservoir.
This is because we are able to direct the well to pass through formations which are of interest on a horizontal path. Because the width and length of a formation is usually significantly greater than its depth, the well comes in to contact with much more of the formation along a horizontal path than if we simply drilled vertically through it. As a result, we have many more opportunities to test and sample the rock and can attain a good understanding of a much larger area of a target formation.
This greater information helps us to advance our exploration programme and brings us closer to potentially unlocking this significant natural resource
Horizontal wells also have important benefits for a production programme, where gas is extracted on a commercial scale.
In terms of impact, using horizontal wells allow for multiple horizontal wells, to branch off underground from a single vertical well bore, thereby minimising the number of vertical wells and sites required and reducing the surface impact of factors like land use, visual impact and service vehicle movements. Moreover, we can avoid any negative impact in environmentally, visually or historically sensitive sites by locating well sites away from these areas.
Horizontal wells also improve the recoverability and productivity of a reservoir. The U.S. Department of Energy indicates that using horizontal drilling can lead to an increase in reserves in place by 2% and finds that the productivity of horizontal wells can be almost 400 per cent higher than vertical wells.