122 research outputs found
Estimating geological CO2 storage security to deliver on climate mitigation
Full text linkACKNOWLEDGEMENTS Juan Alcalde and Clare Bond were supported by NERC Grant NE/M007251/1 on interpretational uncertainty; Stephanie Flude and Stuart M V Gilfillan were supported by EPSRC Grant EP/K036033/1; R Stuart Haszeldine was supported by Scottish Funding Council, EPSRC Grants EP/P026214/1, EP/K000446/2 and NERC Grant NE/L008475/1; Gareth Johnson was supported by EPSRC Grant EP/P026214/1; Vivian Scott was supported by NERC GHGR programme Grant NE/P019749/1; Katriona Edlmann was supported by H2020 Grant 636811.Peer reviewe
Conceptual model development using a generic Features, Events, and Processes (FEP) database for assessing the potential impact of hydraulic fracturing on groundwater aquifers
Full text linkHydraulic fracturing for natural gas extraction from unconventional reservoirs has not only impacted the global energy landscape but has also raised concerns over its potential environmental impacts. The concept of features, events and processes (FEP) refers to identifying and selecting the most relevant factors for safety assessment studies. In the context of hydraulic fracturing we constructed a comprehensive FEP database and applied it to six key focused scenarios defined under the scope of FracRisk project (http://www.fracrisk.eu, last access: 17 August 2018). The FEP database is ranked to show the relevance of each item in the FEP list per scenario. The main goal of the work is to illustrate the FEP database applicability to develop a conceptual model for regional-scale stray gas migration
Experimental and numerical investigations of geomechanical controls on petrophysical changes of carbonates during fluid flow
Full text linkIn flooding experiments, porosity and permeability of carbonate rocks is enhanced
through the dissolution of the rock matrix, which further increase the
permeability as well as the inter-connection of the pre-existing porosity. Authors
often refer to this process as wormholing or channelling, which define preferential
pathways for any fluid circulating through the rock’s matrix (Hoefner and Fogler,
1988; Fredd and Fogler, 1998; Golfier et al., 2002). A wormhole’s shape and size
ranges from face dissolution at very low fluid flow rates (where the reactive fluid
is rapidly consumed after the injection point), to uniform dissolution (where the
acid is brought to far-ends within the rock matrix, which allows the creation of a
large network of connected pores). Authors have studied the factors influencing
the relationship between dissolution fronts, injection rate, rock nature, and
acidity of the circulating fluid (Frick et al., 1994a; Bazin et al., 1995; Fredd et al.,
1996; Fredd and Fogler, 1998; Golfier et al., 2002; Egermann et al., 2006; Luquot
and Gouze, 2009; Menke et al., 2015; Ott and Oedai, 2015; Barri et al., 2016;
Luquot et al., 2016; Teles et al., 2016; Zhang et al., 2016). The current status of
knowledge present strong connections between the reaction rate and the diffusion
rate (referred to as the Damköhler number – Da Bekri et al. (1995); Egermann
et al. (2010)), as well as the study between the fluid velocity and the ability
for a medium to diffuse into a solvent (referred to as the Péclet number – Pe
Golfier et al. (2002); Menke et al. (2015)). The Da number measures the relative
importance of the reaction rate constant versus advection over some length
scale, while the Pe number gives the ratio of advective to dispersive flux for a
given length scale (Zhang and Kang, 2004; Steefel and Lasaga, 1990). Large Da
correspond to rapid chemical reaction in comparison to all other processes. On
the other hand, smaller Da testify of very slow chemical reactions in comparison
to all other processes taking place during fluid flow (Zhang and Kang, 2004). A
low Péclet number suggests that transport is governed by diffusion and not by
convection, and inversely at high Pe number (De Boever et al., 2012).
Along with these dynamically controlled numbers, studies have tried to unpick
the relationship between rock-fluid interaction for a variety of injection fluid,
as well as rock-stress interaction. These studies have been done through the
analysis of key variables (resistivity, porosity, permeability, etc.), using acidic
and non-acidic fluids (Hoefner and Fogler, 1988; Frick et al., 1994b; Bazin
et al., 1995; Fredd et al., 1996; Fredd and Fogler, 1998; Golfier et al., 2002;
Egermann et al., 2006; Luquot and Gouze, 2009; Menke et al., 2015; Ott and
Oedai, 2015; Barri et al., 2016; Luquot et al., 2016; Teles et al., 2016; Zhang
et al., 2016). The experimental rationales of these studies usually implies
large changes in the variables representing the reservoirs conditions, such as
the temperature, confining pressure, and the effective stress. A large gap has
been found between the actual state of knowledge and the absolute impact
of effective stress on reservoir rock alteration, at steady reservoir condition
of pressure and temperature. In this study, we have created an experimental
matrix where the variable representing the reservoir conditions are kept constant
during an experimental flooding, while varied between experiments. By doing
so, we can isolate and cross-compare the effect of each variable on the rock
alteration. We have flooded a total of twelve 38 mm large diameter carbonate
cores of different nature (Indiana limestones, Saturnia travertines, and pre-salt
shrubs) under constant geo-reservoir condition of P-T: Pc = 50 MPa, and T= 60
◦C. The effective stress and pore volume rate was varied between experiments
while kept constant during each experimental flooding. We used porosity,
permeability, Ca-Mg analysis, and μCT scanning as proxies for stress state
related rock matrix alteration. While it is agreed that injection rate plays a major
role in carbonate dissolution, through a higher dissolution rate corresponding
to a high injection rate, and our work confirms this, we also demonstrate
that for a constant given confining pressure, the effective stress can have a
stimulant role in rock matrix alteration and wormhole development (Indiana
limestone). Inversely, effective stress has a reverse role in less consolidated,
more heterogeneous rocks (travertines). The pre-salt rock samples have shown
interesting and mixed results, whose behaviour falls in between the Indiana
limestone’s ones and the travertines’ ones: the chemical response behaved like
an Indiana limestone while the physical response can be compared to a travertine.
We think that our results highlight the importance of the stress state in a reservoir,
and while the confining pressure cannot be varied during injection or depletion
of a reservoir, the pore pressure can be affected. The processes involved behind
this are not yet clarified by the experimental work, but we believe that they
are time and chemistry related, with further study by the authors indicating
that our results are energy-dependent. Therefore, in a carbonate sample, the
expected wormhole shape and spread can be predicted thanks to the reservoir
conditions, the experimental conditions, and the rock’s petromorphology. Finally,
our numerical work further demonstrates that the heterogeneities within the
porosity arrangement and geometry drive the fluid flow and could represent the
main driving variable for the creation of pore space and carbonate dissolution
Supercritical CO2 flow through fractured low permeability geological media: experimental investigation under varying mechanical and thermal conditions
Full text linkTo ensure secure geological storage of carbon dioxide it is necessary to establish the
integrity of the overlying sealing rock. Seal rock fractures are key potential leakage
pathways for storage systems; understanding their behaviour in the presence of CO2
under reservoir conditions is therefore of great importance. This thesis presents experimental
investigations into the hydraulic behaviour of discrete fractures within low
permeability seal rocks during single phase supercritical CO2 flow, under varying mechanical
and thermal conditions representative of in-situ conditions.
An experimental rig was designed and built to enable the controlled study of supercritical
CO2 flow through 38 mm diameter samples under high pressures and temperatures.
Samples are placed within a Hassler-type uniaxial pressure cell and CO2 flow is controlled
via high precision syringe pumps. Flow experiments with supercritical CO2
within the pressure range 10-50 MPa were undertaken at temperatures of 38°C and
58°C with confining pressures of 35-55 MPa. The effects of stress loading and temperature
change on the hydraulic properties of the fractured sample were studied; continuous
differential pressure measurement enabled analysis of hydraulic response.
Experiments were undertaken on a pre-existing Wissey field Zechstein Dolomite fracture
and three artificial fractures (two East Brae field Kimmeridge Clay samples and
one Cambrian shale quarry sample). Fracture permeabilities ranged from 8 X 10-14 m2
to 6 X 10-11 m2 with higher permeabilities observed within the harder rock samples.
A broadly linear flow regime, consistent with Darcy's law, was observed in the lowest
permeability sample (East Brae). A Forchheimer-type non-linear flow regime was
observed in the other samples.
Transmissivity variations during experiments were used to infer the mechanical impact
of stress and temperature changes. An increase in effective stress resulted in transmissivity
reduction, suggesting fracture aperture closure. During initial stress loading
cycles, and subsequent higher temperature stress loading, a component of this transmissivity
reduction was found to be inelastic, suggesting permanent modification of fracture
geometry during closure. Pre- and post-experiment fracture surface characterisation
provides further evidence for the occurrence of plastic deformation. Transmissivity-stress
relationships were elastic during subsequent external stress-loading cycles, suggesting
elastic closure and opening of fractures without additional permanent fracture
geometry changes.
The impact of fluid property variations on fracture hydraulic conductivity, Kfrac, was
also analysed. Under constant effective stress Kfrac was found to be higher within high
temperature and low fluid pressure scenarios, due to higher density/viscosity ratios.
However, under constant confining pressure, fluid pressure changes are coupled both to
mechanical effects (from effective stress alteration) and hydraulic effects (from viscosity
variation), with opposing impacts on fracture hydraulic conductivity. At lower effective
stresses mechanical effects were found to be dominant, with fluid pressure increase
resulting in a notable increase to Kfrac due to aperture opening. At higher effective
stresses, mechanical changes are much smaller due to increased contact area between
fracture surfaces, and thus increased stiffness of fractures. Under such conditions hydraulic
effects may be dominant and result in a small Kfrac reduction as fluid pressure
increases, due to a reduction in the density/viscosity ratio. These results highlight that
CO2 fluid property variation can have a notable influence on hydraulic conductivity
under certain in-situ conditions.
The single phase CO2 fracture flow experiments undertaken during this study were designed
to enable a study of hydraulic and mechanical processes in isolation, without the
influence of chemical processes. In-situ, the additional presence of brine and thus multiphase
fluid behaviour and associated chemical processes makes the hydraulic behaviour
of fractures considerably more complex. Coupled process modelling enables the relative
influence of these processes to be simulated, but relies on experiments for validation.
These unique experimental findings are of great value for enabling validation of such
models as well as for informing analyses of geological and field studies
Hydrogen recovery from porous media decreases with brine injection pressure and increases with brine flow rate
No full textZero carbon energy generation from renewable sources can reduce climate change by mitigating carbon emissions. A major challenge of renewable energy generation is the imbalance between supply and demand. To overcome the energy imbalances, subsurface storage of hydrogen in porous mediais suggested as a large-scale and economic solution, yet its mechanisms are not fully understood. Important unknowns are the effect of the high migration potential of the small and mobile hydrogen molecule and the volume of recoverable hydrogen.We conducted non-steady state, cyclic hydrogen and brine injection experiments at 2-7 MPa and flow rates of 2-80 µl min-1 using water-wet Clashach sandstone cylinders of 4.7 mm diameter and 53-57 mm length (Clashach composition: ~96 wt.% quartz, 2% K-feldspar, 1% calcite, 1% ankerite). Two sets of experiments were performed using our new transparent flow-cell designed for x-ray computed microtomography: 1) Experiments using a laboratory x-ray source (University of Edinburgh) imaged the flow, displacement and capillary trapping of hydrogen by brine as a function of saturation after primary drainage and secondary imbibition. 2) Experiments using synchrotron radiation (Diamond Light Source, I12-JEEP tomography beamline) captured time-resolved hydrogen and brine flow and displacement processes. Pressure and mass flow measurements across the experimental apparatus complemented the microtomography volumes in both sets of experiments.Results from a water-wet rock show that hydrogen behaves as a non-wetting phase and sits in the centre of the pore bodies, while residual brine sits in corners and pore throats. Hydrogen saturation in the pore volume is independent of the injection pressure and increases with increasing hydrogen/brine injection ratio up to ~50% saturation at 100 % hydrogen. Capillary trapping of hydrogen during brine imbibition occurs via snap off and is greatest at higher brine injection pressures, with 10 %, 12% and 21% hydrogen trapped at 2, 5 and 7 MPa, respectively. Higher brine flow rates reduce capillary trapping and increase hydrogen recovery at any given injection pressure. Based on these results, future hydrogen storage operations should inject 100% hydrogen and manage the reservoir pressure to avoid high pressures and minimize capillary trapping of hydrogen during brine reinjection.Ongoing analysis of time-resolved experimental data will provide further insight into the critical pore-scale processes that ultimately influence the potential for geological hydrogen storage and recovery
A GIS Study on Estimating the Solar Power Potential in Urban Places: A Rooftop Analysis in Edinburgh, Scotland
No full textDue to the increased threat from climate change, it is getting more important to transition to renewable energy and reduce our CO2 emissions. Solar has potential to support urban areas and domestic users. Furthermore, as the price of solar energy continues to decrease and with the increasing electricity prices, solar becomes more attractive to a wider group of people. This GIS based study aims to investigate the solar power potential of Edinburgh, the way it can support neighbourhoods and the way it can play an important role in reaching the city’s net zero targets. Solar irradiance was measured over a year using the Area Solar Radiation tool available in ArcGIS. This study found differences between demographics by identifying the 20 most and the 20 least deprived neighbourhoods in terms of their solar power potential. More affluent areas could support their electricity demand and generate enough electricity to be stored or exported. On the other hand, the most deprived neighbourhoods do not have the potential to cover their electricity consumption and would require further support. Overall results show that around 90% of the domestic electricity consumption, and about 40% of the total electricity demand of the city could be covered with a city-wide roof solar program. Moreover, it was estimated that 397,926.57 tonnes of carbon could be avoided annually
A GIS study to determine the potential for Lined Hard Rock Cavern Hydrogen Storage in Northwest Scotland
No full textThe geological storage of hydrogen in lined rock caverns is a relatively novel concept which has been tested and demonstrated successfully through projects in Sweden like Skallen and HYBRIT. This project investigates suitable locations in the Northwest of Scotland to construct LRCs for hydrogen storage, along with integrating the storage with nearby wind farms with high energy curtailment output to reduce wastage of energy and utilise it effectively. An area with competent rock was studied to demonstrate how a hydrogen storage facility in an LRC would be planned through various screening methods using ArcGIS Pro. The values of the hydrogen capacity estimates of the facility were 37843 m3(single cavern), 49195900 m3(cavern system), 692754 kg (overall system mass) and 27.29 GWh (energy capacity of the system). This methodology can be applied to other areas in Scotland where salt and porous formations are absent, taking into account the curtailed renewable energy in the country, and storing energy in enormous amounts to minimise the impact of energy generation and help achieve Scotland and the UK its net zero targets sooner
Geological storage of hydrogen: natural analogues, flow cell experiments and mass transport modelling
No full textDecarbonising the global energy mix is crucial to lowering greenhouse gas emissions and combating climate change. The introduction of renewable (low carbon) energy sources and the removal of fossil fuel energy sources creates uncertainty in energy supply and energy security, particularly across seasonal timescales. Many types of energy storage schemes could store large amounts (up to TW) of excess energy for use when demand is high (e.g. Pumped Hydropower, Batteries), however only the geological storage of hydrogen has the capability to sustain energy demand over seasonal timescales, while also decarbonising multiple energy sectors (e.g. heat, transport, power and industry). Currently, to sustain hydrogen production at large scale requires the use of fossil fuels (steam methane reformation, SMR) and to be low carbon, requires carbon capture, utilisation and storage (CCUS). This research explores the potential of coupling hydrogen production from SMR with CCUS, using the produced CO₂ as the cushion gas for the hydrogen storage reservoir. State of the art 1D hydrogen flow experiments coupled with analytical and numerical models are used to characterise how hydrogen and CO₂ mixtures behave in porous media. The results show that the type of cushion gas influences the speed which hydrogen flows through porous rock and that the key mass transport processes in operation are dispersion and matrix diffusion. The results highlight the need for better characterisation of hydrogen properties to understand how hydrogen would behave under subsurface storage conditions. The large-scale deployment of hydrogen as a low carbon energy vector will require further in-situ pilot projects to demonstrate a safety case, appropriate site suitability assessments, supportive policy frameworks and crucially a positive public image
Pore-scale imaging of hydrogen displacement and trapping in porous media
Full text linkHydrogen can act as an energy store to balance supply and demand in the renewable energy sector. Hydrogen storage in subsurface porous media could deliver high storage capacities but the volume of recoverable hydrogen is unknown. We imaged the displacement and capillary trapping of hydrogen by brine in a Clashach sandstone core at 2–7 MPa pore fluid pressure using X-ray computed microtomography. Hydrogen saturation obtained during drainage at capillary numbers o
Mapping hydrogen storage capacities of UK offshore hydrocarbon fields and exploring potential synergies with offshore wind
Full text linkEnergy storage is an essential component of the transitioning UK energy system, a crucial mechanism for stabilizing intermittent renewable electricity supply and meeting seasonal variation in demand. Low-carbon hydrogen provides a balancing mechanism for variable renewable energy supply and demand, and a method for decarbonizing domestic heating, essential for meeting the UK's 2050 net-zero targets. Geological hydrogen storage in porous rocks offers large-scale energy storage over a variety of timescales and has promising prospects due to the widespread availability of UK offshore hydrocarbon fields, with established reservoirs and existing infrastructure. This contribution explores the potential for storage within fields in the UK Continental Shelf. Through comparison of available energy storage capacity and current domestic gas demands, we quantify the hydrogen required to decarbonize the UK gas network. We estimate a total hydrogen storage capacity of 3454 TWh, significantly exceeding the 120 TWh seasonal domestic demand. Multi-criteria decision analysis, in consultation with an expert focus group, identified optimal fields for coupling with offshore wind, which could facilitate large-scale renewable hydrogen production and storage. These results will be used as inputs for future energy system modelling, optimizing potential synergies between offshore oil and gas and renewables sectors, in the context of the energy transition
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