There are a number of distinct stages in the development of a shale gas exploration site, many of which most people probably won't even know about. We thought it might be useful to have a quick look at them.
Planning and Permitting
Decommissioning and Restoration
The first thing that fracking companies need to do is choose their sites carefully. There will be a number of things that they specifically look for: good road access; not in a groundwater Source Protection Zone 1 (SPZ1) area; limited residential dwellings nearby; not in a National Park or Area of Outstanding Natural Beauty (AONB); away from underground faults; and above rock with good "prospectivity" (i.e. likely to contain a sizeable quantity of gas) to name a few.
They search Ordnance Survey maps, publicly available environmental registers and the record from earlier geological survey work and any previous drilling activity. They will also obtain 3D images of the sub-surface to identify the thickest bands of shale rock and to avoid faults.
Planning and Permitting
Once they've selected a site location, they'll first negotiate access rights with the landowner before applying for planning permission and environmental permits.
As anyone that's paid attention to the UK shale gas debate in recent years will know, this is a lengthy and detailed process. In Cuadrilla's case, for instance, it submitted 4,000 pages of environmental statements to support its planning application at Preston New Road covering everything from site ecology to local traffic impacts.
The planning and permit applications are publicly consulted on, often more than once, giving all relevant stakeholders an opportunity to comment.
A decision is then taken by the relevant planning authority and the environmental regulator.
Up until now, there's been no visible activity at the proposed site.
Armed with planning permission and the necessary environmental permits, fracking companies can get on with building their sites.
This will see groundwork contractors strip off the top soil and form the shape of the "pad". Access roads will be built, security fencing erected, and an impermeable membrane installed to capture any surface spills before compacted stone is laid on top to form a stable base for the drilling equipment.
During this phase of work, a shale gas site will resemble a typical construction or civil engineering site, with diggers and tipper trucks.
With the site built, the drilling rig and associated equipment will be delivered and erected. This will include drill pipe, steel well casing, and ancillary equipment used to deal with the rock "cuttings" that return to the surface as the drill bit rotates and cuts through the various layers of rock.
The drill bit is attached to hollow drill pipe which turns slowly. Fluids are pumped down through the drill pipe and around the bit to keep it cool and help flush the rock fragment to the surface. Length after length of drill pipe are attached together as the drilling gets deeper and deeper, and then removed while special tools are inserted into the hole to measure things like rock density and porosity at each stage. This is known as "wireline logging" and uses a special, sealed radioactive source lowered into the wellbore.
The surface casing is installed, and drilling continues progressively in the same manner to the required depth. The drill bit gets smaller and successively smaller diameter casing is fitted, all with cement in between to form a good seal and multiple leak barriers between the inside of the well and the outer environment.
All the while, geologists are collecting core samples of the rock that the drill passes through.
It is during the drilling activity that the site will be most visible to people because of the 30-50 metre height of the drilling rig. But it's a short-term affair and the rig is soon demobilised and removed.
During the drilling of the well, safety mechanisms called a Blow Out Preventer (BOP) and the "Christmas Tree" wellhead are installed.
Once the well is built, and the drilling equipment has been removed, fracking can start.
Fracking involves pumping a mixture of mostly water and sand (99.95%) and chemical additives that are non-hazardous to groundwater (0.05%) into the shale rock to create a network of tiny hairline cracks. The sand is used to prop them open so that the gas can flow out.
First, a device called a "perforating gun" is lowered into the well, manoeuvred into position and used to punch holes in the steel production casing where the well reaches the target shale rock. These holes allow fracking fluid to exit the well and returning fluid and gas to enter it.
Fracking is carried out in discreet stages. You'll hear opponents refer to "High Volume Hydraulic Fracturing" or "HVHF" and how it might use over 18,000 cubic metres of water per well, but that isn't all pumped underground at once - it's done in segments, each using anything from around 300 m3 to 800 m3.
After each frack stage, pumping pressure at the surface is removed allowing gas and fracking fluid to flow into and up the well. You'll hear this called "flowing the well" and it's where the name "flowback fluid" comes from.
The gas is separated from the liquid and any sand that returns.
As well as gaining a better understanding of the geology and "rock mechanics" (which is what determines how much fracking fluid is used and at what pumping pressure), the fracking companies want to know how much gas they can get to flow to the surface and so they test it.
The "Initial Well Test" takes around 90 days during which they will attempt to maintain a constant flow of gas from the well.
Another goal of the well testing is to measure the quality and composition of the gas, to determine its suitability for delivery into the gas distribution grid should shale gas development and production follow the exploration phase.
In this 90 day testing period per exploration well, any gas that's found will probably be burnt in a flare.
Decommissioning and Restoration
As the term implies, after all the exploratory work has been completed, the site gets returned back to its original condition.
The well is sealed with special cement and mechanical "plugs" and capped off below the surface. All the other equipment is removed, and you're soon left with a farmer's field that looks no different than before.
Of course, it's possible that an exploratory site could be repurposed to become a production site at some later date, which would delay the final stage of the lifecycle - but that would require the fracking company to go right back to the start and make a new application for planning permission as a production site.
What you'll see from this brief overview is that the appearance of a fracking pad will differ at different times in its lifecycle. Sometimes it will resemble a construction site, at other times you probably won't even notice it's there.
There are essentially three traffic peaks: (1) during the site preparation when hardcore is being delivered to create the pad surface; (2) during the delivery of the drilling rig; and (3) during the fracking operations when flowback wastewater is being removed from site in road tankers. But these are spread out, and take place consecutively not concurrently, and in between, localised traffic levels will be similar to the background norm.
Any noise is most likely to be associated with the drilling and fracking stages - although, as we've seen at Cuadrilla's Preston New Road site, drilling is actually a lot quieter than people had been expecting and it's likely that fracking will be the same when that starts.
So there you have it - the seven stages of a shale gas pad's lifecycle and an idea of what to expect during each one.