What we do
Egdon is involved in the exploration for, and production of, conventional oil and gas in the UK. We also have a portfolio of licenses relating to unconventional oil and gas resources.
We directly manage all aspects of conventional oil and gas activity, from seismic surveying, building sites, drilling exploration wells, testing and long-term production through to decommissioning and restoring sites to their former use. We comprise of a small core team and contract out many activities to specialist contractors, whilst maintaining overall control and responsibility for all operations.
The first stage of the exploration for oil and gas is to understand the geology of the licence area.
An important tool in mapping the geology, deep in the sub-surface, is seismic reflection. This non-invasive technique enables us to obtain an image of the sub-surface to determine the potential for in-place hydrocarbons.
Seismic reflection surveys use a small explosive charge in a shallow borehole or a vibrator truck to generate a low-level seismic signal which penetrates deep into the earth. These seismic waves are reflected from different rock layers and a series of sensitive recorders called geophones record these reflections at the surface.
Image above: Vibrator truck
Seismic surveys can be recorded along a single profile for example along a road (2D seismic) or cover a larger surface area to generate a volume of information (3D seismic).
The information in seismic surveys is recorded by reference to the time it takes for a sound wave to be reflected back to the surface and must be converted into depth using well and rock velocity information.
The data is then evaluated to determine whether or not a sub-surface area has the potential to contain hydrocarbons and whether there is enough potential to drill an exploration well.
Once we have determined a suitable surface site location, the stringent planning and environmental permitting application processes start.
Our sites are built to ensure the long-term protection of the local environment. The proposed site design is an important consideration for local authority and environmental permitting processes, so our sites are subject to a thorough design assessment which is verified and approved by the Environment Agency.
During construction, we include robust environmental protection measures including an impermeable (non-porous) membrane that lines the full site to prevent any surface water and potential contaminants from leaking down into the land or groundwater systems.
Containment ditches around the edge of the site capture any rainfall run-off and prevent any discharge from the site area during any drilling operation. A surface water interceptor may be installed to ensure that only clean and uncontaminated water is allowed to drain from site. The interceptor, and its installation, has to be approved and verified by the Environment Agency.
To ensure that there is no risk of flooding from significant storm rainfall on the site, the surface of the site is set below raised bunds, sized to retain water than may fall on the site from a ‘one in 100 year’ storm event (plus climate change factor).
Pictured: Biscathorpe 2018
Exploration – drilling
How a well is drilled
Drilling an exploration well is a highly skilled operation, using specialised equipment and techniques.
The well is drilled using specialist drilling ‘mud’ to cool the drill bit, carry the cuttings (the rock drilled out) back to the surface and to keep the well bore stable while drilling takes place. The recipe for this drilling mud depends on the location and the type of rock which is being drilled and has to be assessed and approved by the Environment Agency.
How we construct the well
Well integrity is critical to the operation and is achieved by drilling through any groundwater-bearing formations with water-based drilling fluid and then cementing steel pipes in place, known as casings, to provide a multi-layered barrier to protect freshwater aquifers.
A smaller drill bit is then used to drill through the bottom of the casing section, down to the next pre-determined depth, and smaller-diameter casing section is cemented into place.
This process is then repeated down to the final depth of the well, creating multiple layers of cement and steel to create an impermeable barrier between the well and any aquifers.
Each casing section is subject to pressure tests before the next section is drilled to confirm that the casing is effectively sealed into place.
Once completed, integrity tests are applied through the life of the well to ensure that it retains its integrity and doesn’t leak.
Once the well is drilled the specialist data that has been acquired is evaluated to determine if hydrocarbons are present and of commercial interest. If they are the well is “completed” for a flow test to determine if commercially viable volumes can be produced. If not then the well is sealed with cement barriers (“plugs”) and decommissioned.
Exploration – testing
Once the drilling results are known, a decision is made as to whether to flow test the well.
If indications are good, then the well casing would be perforated by puncturing through the steel into the rock formations where hydrocarbons are present.
In some flow test cases, the natural pressure in the rock formation allows oil or gas to flow naturally to the surface. Where the pressure below ground is low, a ‘nodding donkey’ pump may be used to bring the oil to surface.
Test equipment would be on site, including storage tanks. If required, a small enclosed ground flare would manage any gas produced over the short duration of the test. The flare is technically assessed and approved by the Environment Agency, and the Environmental Permit limits the volumes of gas that can be flared.
If tests prove that oil or gas is commercially recoverable, we would apply for new planning permissions and environmental permits to cover long term production.
If these permissions are granted, permanent production facilities would be designed to include for storage tank containment bunds, loading facilities, pump systems and a mains electricity supply.
Where gas is present in sufficient quantities, we would aim to use this to generate electricity for the site, with surplus electricity exported back to the distribution network.
Production sites operate with automatic production controls and integrated safety systems that enable them to safely operate 24/7.
Typically, produced oil is taken by road tanker to the closest refinery.
We have existing production sites that operate safely and successfully without adversely impacting on local communities – most sites are remote from local properties and it’s true to say that many people in areas local to our sites aren’t aware they exist.
Restoration and aftercare
If an exploration well doesn’t find oil or gas or where volumes from an existing well decline, the well would be decommissioned and the site restored to its former use.
Any decommissioning programme is independently inspected, and approval sought from the Health and Safety Executive.
Specialist cement plugs seal the well and the casing is cut off two metres below ground level and completed with a metal plate bearing the well number. Throughout the process, pressure and integrity tests are applied to ensure that the wellbore is completely sealed.
The site is restored in accordance with Egdon procedures, best practice and in compliance with any Planning and Environmental Permit conditions.
The site is always restored to the satisfaction of the landowner and the Environment Agency before the Permit can be relinquished. The Local Planning Authority also conducts inspections to verify compliance with Planning Conditions, and that the restoration is to an acceptable standard.