How did the GeoEnergy Test Bed (GTB) develop in 2016?
November – December: Drilling boreholes 4 to 8
In November, the fourth borehole was drilled and fully cored to a depth of 282m. The core was raised from the borehole in 3m segments and, once at the surface, cut into two ready for storage in our on-site core container. Collecting a full depth core from a borehole gives our researcher’s physical samples from which they can analyse the strata at the GTB, characterise the different rock types present and provides empirical confirmation of the wireline logging data. A further four boreholes were drilled during November and December; two deep boreholes of depths 274m and 279m plus two shallow boreholes both at depths of 25m. Both deep boreholes and one shallow borehole have had sensors installed into them.
November: Cone Penetration Testing
In-Situ Site Investigation performed a Cone Penetration Test (CPT) in early November. This technique is used to provide data on the acoustic properties of the site to a depth of 10m. A track mounted rig is driven across the site and an instrumented rod with a cone on the end of it is driven into the ground at a constant speed. Readings of the stroke are recorded in quick successive intervals.
October: Downhole Imaging and Pumping/Recovery Test
Downhole imaging of the first drilled borehole (2015) was used to help determine the nature of the borehole wall to a depth of approximately 30m. A slim diameter imaging sonde, attached to a winch, is lowered down the borehole to its maximum depth and retrieved whilst images are recorded onto a laptop. A pumping/recovery test was conducted in the third drilled borehole to determine approximation of the Triassic Sandstone permeability. A slim borehole pump connected to a hose is lowered into the borehole and a column of water is removed to ascertain the rate of drawdown and recovery. The water is discharged to a tank (universal bulk container.) Subsequently a short pumping regime enables the permeability of the sandstone formation to be determined at depth. Both of these activities were carried out by the Groundwater team at the British Geological Survey.
September: Microbiology Baseline Survey
In September a microbiology survey was conducted by the British Geological Survey. Approximately 20 soil samples were augered to 50cm below the surface. This survey will be conducted quarterly (every 3 months) for one year to create a baseline.
September: Shallow Refraction Survey
A shallow seismic refraction survey was completed in September by the British Geological Survey. The shallow refraction survey is a technique which measures the speed at which seismic energy travels through different rocks. This technique can provide data on the lithology of rocks and degree of fracturing. An array of geophones are laid out across the site installed to a depth of 10cm and a very small seismic source is generated multiple times.
August: Passive Seismic Survey
In August the British Geological Survey undertook a passive seismic (H/V) survey of the GTB. This is a way of characterising the subsurface by analysing the surface waves in seismic noise. The method used is called the horizontal-to-vertical spectral ratio method and computes the ratio between the horizontal and vertical components of seismic noise measurements at a single seismometer. The H/V method is a novel and non-invasive technique that uses the seismometer, in this case a Tromino zero, to record low-amplitude vibrations of the ground produced by local sources such as traffic and other human activities.
July: Geophysical Logging of Boreholes
Geophysical logging company Robertson Geologging Ltd completed the wireline logging of boreholes 1 and 3 in July. Logging a borehole is a way of measuring, analysing and digitising the physical properties of a borehole such as its lithology, fractures and construction. Slim-hole probes attached to a winch cable are lowered into each borehole to its maximum depth and then pulled up slowly creating a continuous data log of the full height of the borehole circumference which is recorded on a laptop.
June – July: Drilling boreholes 2 and 3
The second and third boreholes were drilled during June and July to a depth of 90m and 270m respectively. Rock cuttings were taken every metre from the drilling of the third borehole to allow for characterisation of the borehole and the GTB. The borehole drilling was carried out by DrilCorp, a borehole engineering company based in County Durham.
June: Second near-surface Soil Gas Survey
A second near surface soil-gas survey was completed in June by the British Geological Survey (BGS). The BGS has a gas monitoring facility with the capability to measure concentrations of a range of gases in both the soil and atmosphere as well as determining the flux of gases across the soil/air boundary. Measuring the natural background gas variations of near surface gases at the GTB helps to establish baseline conditions prior to site creation. (The pictures below are for the purpose of illustrating technique only. They were not taken on the GTB site.)