Saline Aquifer CO2 Storage (SACS2). Final report, geological characterisation of the Utsira Sand reservoir and caprocks (Work Area 1)

This report summarises the results and highlights the main findings of SACS Work Area 1, the geological and reservoir characterisation of the Utsira Sand and its caprock. For more detailed technical information on each topic, the reader is directed to the relevant SACS Technical Reports and, in particular, two earlier Work Area 1 interim reports, Holloway et al. (1999) and Chadwick et al. (2000). The Utsira Sand comprises a basinally-restricted deposit of Mio-Pliocene age forming a clearly defined seismic unit, pinching out to east and west, and seismically distinct from overlying and underlying strata.The reservoir is highly elongated, extending for more than 400 km from north to south and between 50 and 100 km from east to west, with an area of some 26100 km2. Its eastern and western limits are defined by stratigraphical lap-out, to the southwest it passes laterally into shaly sediments, and to the north it occupies a narrow channel deepening towards the More Basin. Locally, particularly in the north, depositional patterns are quite complex with some isolated depocentres, and lesser areas of non-deposition within the main depocentre. The top Utsira Sand surface generally varies relatively smoothly, mainly in the range 550 to 1500 m, but mostly from 700 to 1000 m. The base of the sand is more irregular, disturbed by diapirism of the underlying shales. Isopachs of the reservoir sand show two main depocentres. One is in the south, around Sleipner, where thicknesses range up to more than 300 m. The second depocentre lies some 200 km to the north of Sleipner. Here the Utsira Sand is locally 200 m thick, with an underlying sandy unit adding further to the total reservoir thickness. Macroscopic and microscopic analysis of core and cuttings samples of the Utsira Sand show that it consists of a largely uncemented fine-grained sand, with medium and occasional coarse grains. The grains are predominantly angular to sub-angular and consist primarily of quartz with some feldspar and shell fragments. Sheet silicates are present in small amounts (a few percent). The sand is interpreted as being deposited by mass flows in a marine environment in water depths of 100 m or more. The porosity of the Utsira Sand core ranges generally from 27% to 31%, but reaches values as high as 42% Regional log porosities are quite uniform, in the range 35 to 40% over much of the reservoir. Geophysical logs show a number of peaks on the -ray, sonic and neutron density logs, and also on some induction and resistivity logs. These are interpreted as mostly marking thin (~1m thick) intrareservoir shale layers. The shale layers constitute important permeability barriers within the reservoir sand, and have proved to have a significant effect on CO2 migration through, and entrapment within, the reservoir. The proportion of clean sand in the total reservoir thickness varies generally from about 0.7 to nearly 1.0. The caprock succession overlying the Utsira reservoir is rather variable, and can be divided into three main units. The Lower Seal forms a shaly basin-restricted unit, some 50 to 100 m thick. The Middle Seal mostly comprises prograding sediment wedges of Pliocene age, dominantly shaly in the basin centre, but coarsening into a sandier facies both upwards and towards the basin margins. The Upper Seal comprises Quaternary strata, mostly glacio-marine clays and glacial tills. The Lower Seal extends well beyond the area currently occupied by the CO2 injected at Sleipner and seems to be providing an effective seal at the present time. Cuttings samples comprise dominantly grey clay silts or silty clays. Most are massive although some show a weak sedimentary lamination. XRD analysis typically reveal quartz (30%), undifferentiated mica (30%), kaolinite (14%), K-feldspar (5%), calcite (4%), smectite (4%), albite (2%), chlorite (1%), pyrite (1%) and gypsum (1%) together with traces of drilling mud contamination. The clay fraction is generally dominated by illite with minor kaolinite and traces of chlorite and smectite. The cuttings samples are classified as non-organic mudshales and mudstones. Although the presence of small quantities of smectite may invalidate its predictions, XRD-determined quartz contents suggest displacement pore throat diameters in the range 14 to 40 nm. Such displacement pore throat diameters are consistent with capillary entry pressures of between about 2 and 5.5 MPa capable of trapping a CO2 column several hundred metres high. In addition, the predominant clay fabric with limited grain support resembles caprocks which are stated in the literature to be capable of supporting a column of 35 API oil greater than 150 m in height. Empirically, therefore, the caprock samples suggest the presence of an effective seal at Sleipner, with capillary leakage of CO2 unlikely to occur. Around and east of the injection point, a layer of sand, 0 - 50 m thick, lies close to the base of the Lower Seal and is termed the Sand-wedge. The geometry of this unit is likely to prove important in determining the long-term migration behaviour of the CO2. Fluid flow in the Utsira Sand, based on limited pressure measurements and basin-modelling, is likely to be low, in the range 0.3 – 4 metres per year, depending on assumed permeabilities. The total pore-space within the Utsira Sand is estimated at 6.05 x 1011 m3. However not all of this can necessarily be utilised for CO2 storage. The simplest assumption is that long-term storage of CO2 can only be accomplished in structural traps at the top of the reservoir. A detailed study around Sleipner indicates that 0.3% of the reservoir porosity is actually situated within structural closures such as this. In practical terms moreover, with a small number of injection wells, it is unlikely that all of the small traps could be utilised in any case. Around Sleipner the most realistic estimate of the pore-space situated within accessible closed structures is just 0.11% of the total pore-volume. On the other hand, trapping of CO2 beneath the intra-reservoir shales could significantly increase realisable storage volumes, particularly if it encouraged dissolution of CO2 into the groundwater. Similarly trapping of CO2 in the Sand-wedge, as well as beneath the top of the Utsira Sand, will increase the overall storage capacity significantly. In conclusion, the theoretical storage capacity of the Utsira Sand is very high, but how much of this can be utilised in reality is uncertain, and a function of several complex parameters. Migration models have been constructed with 30 x 106 m3 of CO2, injected into the Utsira Sand (approximating to the expected final injected mass of 20 million tonnes). They show that if the CO2 is trapped at the top of the Utsira Sand it will migrate generally northwestward, reaching a maximum distance from the injection site of about 12 km. However, if the CO2 is trapped within the Sand-wedge, migration is less well constrained, being northwards then northeastwards. Data limitations to the east of the injection point preclude quantitative estimates of the maximum migration distance in this case

Saline Aquifer CO2 Storage phase 2 (SACS2) : a demonstration project at the Sleipner Field : work area 1 (Geology). Progress report 1 April to 31 December 2000

1.1 Summary · Preliminary depth and thickness maps produced of Utsira Sand over its entire subsurface extent. · Total Utsira reservoir storage volume estimated. · Potential storage volume in traps estimated around Sleipner. · Preliminary map of caprock around Sleipner produced. · Seismic amplitude anomalies mapped in caprock around Sleipner. · Samples of caprock obtained and preliminary analysis made. · Core from possible caprock analogue at Ekofisk examined and analysed. · 2-D basin modelling carried out to assess major controls on the regional fluid flow regime. Task 1.3 Stratigraphy and structure of the Greater Sleipner Area The reprocessed CNST82RE survey has been loaded. Interpretation of the Utsira Sand transferred onto the reprocessed data and extended onto previously unavailable seismic lines. Transferred reprocessed CNST82RE dataset to GEUS. Received additional Norwegian well information from GEUS. This completed the initial Greater Sleipner interpretation

A ‘quiet revolution’? The impact of Training Schools on initial teacher training partnerships

This paper discusses the impact on initial teacher training of a new policy initiative in England: the introduction of Training Schools. First, the Training School project is set in context by exploring the evolution of a partnership approach to initial teacher training in England. Ways in which Training Schools represent a break with established practice are considered together with their implications for the dominant mode of partnership led by higher education institutions (HEIs). The capacity of Training Schools to achieve their own policy objectives is examined, especially their efficacy as a strategy for managing innovation and the dissemination of innovation. The paper ends by focusing on a particular Training School project which has adopted an unusual approach to its work and enquires whether this alternative approach could offer a more profitable way forward. During the course of the paper, five different models of partnership are considered: collaborative, complementary, HEI-led, school-led and partnership within a partnership

Mineralogical and geochemical analysis of Fe-phases in drill-cores from the Triassic Stuttgart Formation at Ketzin CO₂ storage site before CO₂ arrival

Reactive iron (Fe) oxides and sheet silicate-bound Fe in reservoir rocks may affect the subsurface storage of CO2 through several processes by changing the capacity to buffer the acidification by CO2 and the permeability of the reservoir rock: (1) the reduction of three-valent Fe in anoxic environments can lead to an increase in pH, (2) under sulphidic conditions, Fe may drive sulphur cycling and lead to the formation of pyrite, and (3) the leaching of Fe from sheet silicates may affect silicate diagenesis. In order to evaluate the importance of Fe-reduction on the CO2 reservoir, we analysed the Fe geochemistry in drill-cores from the Triassic Stuttgart Formation (Schilfsandstein) recovered from the monitoring well at the CO2 test injection site near Ketzin, Germany. The reservoir rock is a porous, poorly to moderately cohesive fluvial sandstone containing up to 2–4 wt% reactive Fe. Based on a sequential extraction, most Fe falls into the dithionite-extractable Fe-fraction and Fe bound to sheet silicates, whereby some Fe in the dithionite-extractable Fe-fraction may have been leached from illite and smectite. Illite and smectite were detected in core samples by X-ray diffraction and confirmed as the main Fe-containing mineral phases by X-ray absorption spectroscopy. Chlorite is also present, but likely does not contribute much to the high amount of Fe in the silicate-bound fraction. The organic carbon content of the reservoir rock is extremely low (<0.3 wt%), thus likely limiting microbial Fe-reduction or sulphate reduction despite relatively high concentrations of reactive Fe-mineral phases in the reservoir rock and sulphate in the reservoir fluid. Both processes could, however, be fuelled by organic matter that is mobilized by the flow of supercritical CO2 or introduced with the drilling fluid. Over long time periods, a potential way of liberating additional reactive Fe could occur through weathering of silicates due to acidification by CO2

Man and the Last Great Wilderness: Human Impact on the Deep Sea

The deep sea, the largest ecosystem on Earth and one of the least studied, harbours high biodiversity and provides a wealth of resources. Although humans have used the oceans for millennia, technological developments now allow exploitation of fisheries resources, hydrocarbons and minerals below 2000 m depth. The remoteness of the deep seafloor has promoted the disposal of residues and litter. Ocean acidification and climate change now bring a new dimension of global effects. Thus the challenges facing the deep sea are large and accelerating, providing a new imperative for the science community, industry and national and international organizations to work together to develop successful exploitation management and conservation of the deep-sea ecosystem. This paper provides scientific expert judgement and a semi-quantitative analysis of past, present and future impacts of human-related activities on global deep-sea habitats within three categories: disposal, exploitation and climate change. The analysis is the result of a Census of Marine Life – SYNDEEP workshop (September 2008). A detailed review of known impacts and their effects is provided. The analysis shows how, in recent decades, the most significant anthropogenic activities that affect the deep sea have evolved from mainly disposal (past) to exploitation (present). We predict that from now and into the future, increases in atmospheric CO2 and facets and consequences of climate change will have the most impact on deep-sea habitats and their fauna. Synergies between different anthropogenic pressures and associated effects are discussed, indicating that most synergies are related to increased atmospheric CO2 and climate change effects. We identify deep-sea ecosystems we believe are at higher risk from human impacts in the near future: benthic communities on sedimentary upper slopes, cold-water corals, canyon benthic communities and seamount pelagic and benthic communities. We finalise this review with a short discussion on protection and management methods

4D seismic imaging of an injected CO2 plume at the Sleipner Field, central North Sea

CO2 produced at the Sleipner field is being injected into the Utsira Sand, a major saline aquifer. Time-lapse seismic data acquired in 1999, with 2.35 million tonnes of CO2 in the reservoir, image the CO2 plume as a number of bright sub-horizontal reflections. These are interpreted as tuned responses from thin (< 8 m thick) layers of CO2 trapped beneath intra-reservoir shales. A prominent vertical ‘chimney’ of CO2 appears to be the principal feeder of these layers in the upper part of the reservoir. Amplitude – thickness scaling for each layer, followed by a layer summation, indicates that roughly 80% of the total injected CO2 is concentrated in the layers. The remainder is interpreted to occupy the feeder ‘chimneys’ and dispersed clouds between the layers. A prominent velocity pushdown is evident beneath the CO2 accumulations. Velocity estimation using the Gassmann relationships suggests that the observed pushdown cannot readily be explained by CO2 present only at high saturations in the thin layers; a minor proportion of low saturation CO2 is also required. This is consistent with the layer volume summation, but significant uncertainty remains

Review of monitoring issues and technologies associated with the long-term underground storage of carbon dioxide

Large-scale underground storage of CO2 has the potential to play a key role in reducing global greenhouse gas emissions. Typical underground storage reservoirs would lie at depths of 1000 m or more and contain tens or even hundreds of millions of tonnes of CO2. A likely regulatory requirement is that storage sites would have to be monitored both to prove their efficacy in emissions reduction and to ensure site safety. A diverse portfolio of potential monitoring tools is available, some tried and tested in the oil industry, others as yet unproven. Shallow-focused techniques are likely to be deployed to demonstrate short-term site performance and, in the longer term, to ensure early warning of potential surface leakage. Deeper focused methods, notably time-lapse seismic, will be used to track CO2 migration in the subsurface, to assess reservoir performance and to calibrate/validate site performance simulation models. The duration of a monitoring programme is likely to be highly site specific, but conformance between predicted and observed site performance may form an acceptable basis for site closure