A review of geothermal reservoir properties of Triassic, Permian and Carboniferous sandstones in Northern Ireland

This report presents the results of a review of the available porosity and permeability data for potential deep geothermal sandstone reservoirs in Northern Ireland. It is based on information from published and unpublished sources and data collected as part of a GSNI reservoir characterisation project involving a detailed petrography study borehole core and sample material by one of the authors (Dr R Raine). The geology of the north-eastern part of Northern Ireland is characterised by a number of deep sedimentary basins largely concealed below the extensive outcrop of Palaeogene basalts covering most of County Antrim and parts of counties Londonderry, Tyrone, Armagh and Down. The Larne, Lough Neagh, Rathlin and Foyle basins contain thick sequences of sedimentary rocks of Carboniferous to Cretaceous age, including Carboniferous, Permian and Triassic sandstones which are potential hydrocarbon and/or hydrogeothermal reservoirs. Sandstones of similar age and types are being used to produce heat in geothermal energy systems in the Netherlands, Denmark, Germany and Great Britain. There is the potential to develop similar geothermal energy systems in Northern Ireland. Geothermal energy systems can play a role in the decarbonisation of heat and are characterised by their high deliverability and availability approaching 24/7, 365 days a year. Deep geothermal energy systems involve relatively high initial capex associated with the drilling of deep boreholes so it is important to be able to predict accurately the nature and performance of the target geothermal aquifers. In particular, we are interested in the thickness, depth of these sandstones and the temperature of the formation fluids they contain, how much fluid is stored within them and how easily it can move through the rocks. This report focuses on the porosity and permeability of the reservoir rocks, i.e. their storage capacity and fluid flow characteristics. Surface outcrops of these sandstones are very limited in extent so that most of the information about them has been derived from rock samples collected from deep boreholes. This report draws together data included from previous published and unpublished data together with the results from recent laboratory analyses and petrographic studies carried out on core and cuttings samples by GSNI geologists or by external contractors on behalf of GSNI. Overall the results reinforce earlier observations that the Permo-Triassic sandstones are potentially productive geothermal aquifers, albeit with significant variations in porosity and permeability both within individual borehole sequences and between boreholes from the same and different sedimentary basins. The Sherwood Sandstone Group (SSG) is a prolific aquifer at shallow depths in the Lagan Valley and Newtownards Trough and, although reservoir quality generally decreases with depth, the available data indicate that some intervals within the upper part of the SSG could be productive geothermal aquifers at depths below 1500m. When the results from pumping tests in water production boreholes are compared to laboratory derived permeabilities this suggests that fracture flow is important in the SSG. There is very limited information from the Carboniferous sandstones – mostly from outcrops, shallow boreholes and moderate depths – but some of the samples exhibit surprisingly good reservoir properties, even below 1000 m depth. However, the petrographic analysis suggests that the porosity and permeability might be expected to reduce significantly at greater depths. These are the oldest reservoirs considered and, as a result, a better understanding of the distribution of sandstones with the greatest potential for the preservation of primary porosity or creation of secondary porosity would be helpful. The Permian outcrop in Northern Ireland is very limited in extent and most of the available information about Permian sandstones has been obtained from core samples in a relatively small number of boreholes, both shallow and deep. Permian sandstones exhibit a wide variation in sedimentary characteristics and consequently in reservoir quality, although some borehole samples yield good porosity and permeability values. vi Available temperature data from deep boreholes in Northern Ireland yield geothermal gradients of about 34oC/km, 32oC/km and 28oC/km for the Rathlin, Lough Neagh and Larne sedimentary basins, respectively, significantly higher than the average (26oC/km) for Upper Palaeozoic and Mesozoic sedimentary basins in Great Britain. The geothermal gradients for the Lough Neagh and Larne basins may be underestimates because the temperatures may not have reached thermal equilibrium with the formation fluids at the time of measurement. As a result formation fluids are likely to be close to 80oC at depths of 2000 metres, temperatures suitable for large scale direct heating uses. A temperature of 97.8oC was recorded from a depth of 2565 m in the Ballinlea No. 1 well in the Rathlin Basin. Gravity modelling has been used with seismic survey and borehole data to predict the depths of the potential geothermal aquifers in the deepest parts of the sedimentary basins. Although gravity modelling cannot give unique or definitive depth solutions, they do indicate that the Sherwood Sandstone should lie below 2000 metres depth beneath the northeast corner of Lough Neagh and below 1500 metres in the Rathlin Basin near Ballymoney and Ballycastle, with the Permian and Carboniferous sandstones at still greater depths. Magnetotelluric (MT) surveys are a relatively low-cost geophysical method for determining the subsurface distribution of rocks with low electrical resistivity and are routinely used in exploration for deep geothermal energy resources. In Northern Ireland MT surveys have been carried out in the Rathlin Basin and the northern part of the Lough Neagh Basin that show low resistivity rocks (potential geothermal aquifers) extending down below 2000 metres depth, thus increasing confidence in the results of the gravity modelling. The results from this review of reservoir quality, taken together with the information on temperatures, geothermal gradients and likely depths of potential geothermal sandstone aquifers, show that there are several areas in Northern Ireland where deep geothermal energy resources may be suitable for direct heating use. Heat demand mapping will indicate where in Northern Ireland geothermal energy could provide the energy source for heat networks

Quantifying extreme behaviour in geomagnetic activity

Understanding the extremes in geomagnetic activity is an important component in understanding just how severe conditions can become in the terrestrial space environment. Extreme activity also has consequences for technological systems. On the ground, extreme geomagnetic behavior has an impact on navigation and position accuracy and the operation of power grids and pipeline networks. We therefore use a number of decades of one-minute mean magnetic data from magnetic observatories in Europe, together with the technique of extreme value statistics, to provide a preliminary exploration of the extremes in magnetic field variations and their one-minute rates of change. These extremes are expressed in terms of the variations that might be observed every 100 and 200 years in the horizontal strength and in the declination of the field. We find that both measured and extrapolated extreme values generally increase with geomagnetic latitude (as might be expected), though there is a marked maximum in estimated extreme levels between about 53 and 62 degrees north. At typical midlatitude European observatories (55–60 degrees geomagnetic latitude), compass variations may reach approximately 3–8 degrees/minute, and horizontal field changes may reach 1000–4000 nT/minute, in one magnetic storm once every 100 years. For storm return periods of 200 years the equivalent figures are 4–11 degrees/minute and 1000–6000 nT/minute

The HLA System and Primary Open-Angle Glaucoma

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66382/1/j.1399-0039.1978.tb01313.x.pd

Displacement timer pins: An experimental method for measuring the dynamic deformation of explosively loaded plates

The measurement of dynamic deformation of an explosively loaded plate is an extremely onerous task. Existing techniques such as digital image correlation are expensive and the equipment may be damaged by explosively driven debris/ejecta, particularly if it is necessary to locate such equipment close to loaded elements which are likely to fail. A new, inexpensive and robust measurement technique for use in full-scale blast testing is presented, which involves the placement of displacement timer pins (DTPs) at pre-defined distances from the rear surface of the centre of a plate. A strain gauge on the perimeter of each pin records the time at which the plate comes into contact with the end of each DTP and hence has deformed to that value of displacement, giving a direct measure of the time-varying deformation at a discrete point on the plate. An experimental proof-of-concept was conducted and the results are compared with numerical displacements determined using LS-DYNA. The numerical and experimental results were in very good agreement, which suggests that the proposed experimental method offers a valuable means for determining the full-scale response of structures subjected to blast loads in aggressive environments. Further improvements to the experimental procedure are outlined, along with applications where the DTPs are particularly suited. 2015 Elsevier Ltd. All rights reserved

Predicting the role of geotechnical parameters on the output from shallow buried explosives

Experiments have been conducted to quantify the effect the geotechnical conditions surrounding a buried charge have on the resulting output. From the results obtained the critical importance of moisture content in governing the magnitude of impulse delivered is highlighted. This has led to the development of a first-order predictive model for the impulse delivered from a buried charge, based on bulk density and moisture content, allowing rapid assessment of the effect of varying the geotechnical conditions. The work utilised a half-scale impulse measurement apparatus which incorporated a deformable target plate. Impulse, peak and residual target deflections were recorded for each test. No variations the charge geometry, mass of explosive, burial depth or stand-off were considered, with the focus solely being on the effect of the geotechnical conditions on the magnitude of loading and structural response. Five different types or grades of soils were used in the work, with both cohesive and cohesionless soils represented. The effect of air voids on the impulse generated was also investigated which showed that while strongly correlated, air voids alone is a poorer predictor of impulse than moisture content

The physical parameters, excitation and chemistry of the rim, jets and knots of the planetary nebula NGC 7009

We present long-slit optical spectra along the major axis of the planetary nebula NGC 7009. These data allow us to discuss the physical, excitation and chemical properties of all the morphological components of the nebula, including its remarkable systems of knots and jets. The main results of this analysis are the following: i) the electron temperature throughout the nebula is remarkably constant, T_e[OIII] = 10200K; ii) the bright inner rim and inner pair of knots have similar densities of N_e = 6000cm^{-3}, whereas a much lower density of N_e = 1500cm^{-3} is derived for the outer knots as well as for the jets; iii) all the regions (rim, inner knots, jets and outer knots) are mainly radiatively excited; and iv) there are no clear abundance changes across the nebula for He, O, Ne, or S. There is a marginal evidence for an overabundance of nitrogen in the outer knots (ansae), but the inner ones (caps) and the rim have similar N/H values that are at variance with previous results. Our data are compared to the predictions of theoretical models, from which we conclude that the knots at the head of the jets are not matter accumulated during the jet expansion through the circumstellar medium, neither can their origin be explained by the proposed HD or MHD interacting-wind models for the formation of jets/ansae, since the densities as well as the main excitation mechanisms of the knots, disagree with model predictions.Comment: Figure 1 was changed because features were misidentified in the previous version. 17 pages including 5 figures and 3 tables. ApJ in press. Also available at http://www.iac.es/galeria/denise