Analysis of in situ stress and fault reactivation potential for a major candidate storage aquifer

Within the Moray Firth, the Lower Cretaceous Captain Sandstone has been proposed as a prospective storage reservoir, with storage potential in depleting hydrocarbon fields, and more significantly, within the greater saline aquifer. Previous simulation studies of CO2 injection into the Captain Sandstone aquifer suggest storage capacities in the range 358 to 2495 Mt over a range of sensitivity scenarios. Storage at this scale will introduce the risk of fault reactivation as a consequence of elevated reservoir pressures. The transmissibility of previously stable faults may be enhanced due to reactivation, increasing the risk of CO2 migration from the storage reservoir. By studying both the geometry of faults and the contemporary stress field affecting the basin, it is possible to resolve the shear and normal stresses acting on faults which cut the reservoir formation and extend into the overburden towards the seabed, and to determine which faults (or parts of faults) are most susceptible to becoming reactivated under elevated pressure conditions. In order to do so, detailed knowledge of the pore pressure conditions at depth and the magnitude and orientations of the principal stresses are required, as are the properties of the faults themselves. Such an analysis is presented here at the basin-scale, focusing on the Captain Sandstone of the Inner Moray Firth Basin

Use of borehole imaging to improve understanding of the in-situ stress orientation of Central and Northern England and its implications for unconventional hydrocarbon resources.

New interest in the potential for shale gas in the United Kingdom (UK) has led to renewed exploration for hydrocarbons in the Carboniferous age Bowland–Hodder shales under Central and Northern England. Following an incidence of induced seismicity from hydraulic fracturing during 2010 at Preese Hall, Lancashire, the publically available databases quantifying the in-situ stress orientation of the United Kingdom have shown to be inadequate for safe planning and regulation of hydraulic fracturing. This paper therefore reappraises the in-situ stress orientation for central and northern England based wholly on new interpretations of high-resolution borehole imaging for stress indicators including borehole breakouts and drilling-induced tensile fractures. These analyses confirm the expected north northwest – south southeast orientation of maximum horizontal in-situ stress identified from previous studies (e.g. Evans and Brereton, 1990). The dual-caliper data generated by Evans and Brereton (1990) yields a mean SHmax orientation of 149.87° with a circular standard deviation of 66.9°. However the use of borehole imaging without incorporation of results from older dual-caliper logging tools very significantly decreases the associated uncertainty with a mean SHmax orientation of 150.9° with a circular standard deviation of 13.1°. The use of high-resolution borehole imaging is thus shown to produce a more reliable assessment of in-situ stress orientation. The authors therefore recommend that the higher resolution of such imaging tools should therefore be treated as a de-facto standard for assessment of in-situ stress orientation prior to rock testing. Use of borehole imaging should be formally instituted into best practice or future regulations for assessment of in-situ stress orientation prior to any hydraulic fracturing operations in the UK

Carbon dioxide storage in the Captain Sandstone aquifer: determination of in situ stresses and fault-stability analysis

The Lower Cretaceous Captain Sandstone Member of the Inner Moray Firth has significant potential for the injection and storage of anthropogenic CO2 in saline aquifer parts of the formation. Pre-existing faults constitute a potential risk to storage security owing to the elevated pore pressures likely to result from large-scale fluid injection. Determination of the regional in situ stresses permits mapping of the stress tensor affecting these faults. Either normal or strike-slip faulting conditions are suggested to be prevalent, with the maximum horizontal stress orientated 33°–213°. Slip-tendency analysis indicates that some fault segments are close to being critically stressed under strike-slip stress conditions, with small pore-pressure perturbations of approximately 1.5 MPa potentially causing reactivation of those faults. Greater pore-pressure increases of approximately 5 MPa would be required to reactivate optimally orientated faults under normal faulting or transitional normal/strike-slip faulting conditions at average reservoir depths. The results provide a useful indication of the fault geometries most susceptible to reactivation under current stress conditions. To account for uncertainty in principal stress magnitudes, high differential stresses have been assumed, providing conservative fault-stability estimates. Detailed geological models and data pertaining to pore pressure, rock mechanics and stress will be required to more accurately investigate fault stability. Large-scale deployment of CO2 storage as a strategy for reducing greenhouse gas emissions will rely on the integrity of sealing strata overlying the storage reservoirs to ensure that the captured CO2 is permanently isolated from the atmosphere (IPCC 2005; Chadwick et al. 2009a; Holloway 2009). The existence of pre-existing fault systems of varying dimensions is a common feature throughout the subsurface, and the efficacy of seals may potentially be compromised by any enhanced transmissibility associated with fault zones. Within the Moray Firth, the Lower Cretaceous Captain Sandstone Member of the Wick Sandstone Formation has been proposed as a suitable storage reservoir candidate (SCCS 2011; Shell 2011a; Akhurst et al. 2015). Storage potential exists within depleting hydrocarbon fields (Marshall et al. 2016), while significant additional capacity is available in the surrounding saline aquifer volume. Regional top seals include the Cretaceous Rodby, Carrack and Valhall formations. Simulation studies of CO2 injection identified the storage capacity of the Captain Sandstone to be between 358 and 2495 Mt (Jin et al. 2012). As the injection of CO2 is reliant on the displacement of existing pore fluids, large-scale injection results in increased pore-fluid pressure, the effects of which will be felt across large areas in well-connected aquifer systems (Chadwick et al. 2009b; Jin et al. 2012; Noy et al. 2012). It is well documented that some faults are transmissible to fluid flow, while others act as effective capillary seals (Caine et al. 1996; Aydin 2000; Faulkner et al. 2010). Whether cross-fault flow occurs depends on the juxtaposition of lithologies in the footwall and hanging-wall blocks, as well as the composition of the fault zone and any differential pressure across the fault. In addition, reactivation of previously stable faults caused by increasing pressure, and therefore a reduction in the effective stress, could allow faults to become transmissive to buoyant fluids, such as supercritical CO2, due to the opening of flow pathways during failure (Streit & Hillis 2004). It is this aspect of fault stability that forms the focus of this study, with respect to the Captain Sandstone of the Inner Moray Firth, and utilizing an adaptation of the geological model presented by Jin et al. (2012). Analysis of the geomechanical stability of faults offsetting the Captain Sandstone requires the contemporary stress field affecting the basin to be characterized, in order to resolve the shear and normal stresses acting on mapped faults and to determine which faults, or segments of faults, are most susceptible to becoming reactivated if pore-fluid pressures in the basin are increased as a result of CO2 injection. In order to do so, detailed knowledge of the pore-pressure conditions at depth, the magnitude and orientations of the principal stresses, and the properties of the faults is required

Defining in-situ stress magnitude and the responses of geology to stress anisotropy in heterogeneous lithologies for the United Kingdom

Newly calculated in-situ stress magnitude data has improved the UK database of this important data, vital for understanding how rocks may behave under hydraulic fracturing or "fracking." As this process is controversial in the UK, all new data adds to our understanding of the potential risks of this process. The mode of deformation that rocks experience are highly dependent upon their detailed geology. New data from the highly variable UK Coal Measures Group highlights the degree of lithological control on these processes

Pressure control for managing and optimizing adjacent subsurface operations in large scale CCS

Injecting CO2 in to the subsurface for safe storage of CO2 the pressure propagates far away from the injection point and this can be a potential problem if the overpressure extents to neighbouring subsurface activities or potential leakage pathways. For structural closure trap configurations the CO2 plume is captured within the local structural closure but the pressure footprint is on a more regional scale. This rise the question on, how large the storage complex needs to be for any individual storage operations and how large an area monitoring activities have to cover. The EC CCS guidance document addresses the issues with statements on competitions between subsurface operations but returns no absolute values. Pressure modelling of CO2 injection process with state of the art reservoir simulation tools is challenges by use of realistic model boundary conditions in order to model a realistic pressure level. Combined use of models on a site scale and on a regional scale can instruct how boundary conditions are set-up for a site scale model. Pressure management through pressure release wells could be an option to mitigate undesirable over-pressure developments. For local structural closures the pressure release wells can be placed outside the closure hereby mitigate the overpressure without introducing a potential leakage by drilling inside the trap. The paper addresses the issue of selecting model boundary conditions and modelling mitigation of pressure development by use of a large regional model with local structural traps in the Bunter Sandstone Formation in the UK Southern North Sea

Assessing carbon dioxide storage integrity of an extensive saline aquifer formation: East Irish Sea Basin, UK

Accurately determining the contemporary pore pressure and in situ stress conditions is critical to the safe planning and development of subsurface operations such as CO2 storage. According to the UK storage capacity atlas, CO2STORED (Bentham et al. 2014), the East Irish Sea Basin (EISB) has a significant storage capacity of nearly 4 Gt (P50) within saline aquifer parts of the Triassic-aged Ormskirk Sandstone Formation (OSF). The OSF is present over a significant part of the EISB, and where buried deeply enough to be considered for CO2 storage is overlain by the Mercia Mudstone Group (MMG), a thick sequence comprising up to 3200 m of interbedded mudstones, siltstones and evaporites. As a result of Tertiary inversion, the Jurassic and younger succession is absent over most of the basin, and so the MMG represents the vast majority of the overburden succession. The presence of numerous gas accumulations, including the Morecambe South Gas Field with its ~400 m gas column, is testament to the sealing capacity of the MMG. Where halite formations within the MMG directly overly the OSF, the sealing capacity of the MMG is significantly increased

Project Reach: Implementation of Evidence-Based Psychotherapy Within Integrated Healthcare for Hurricane Harvey Affected Individuals

Project Reach was established to deliver evidence-based mental healthcare services to children and adults affected by Hurricane Harvey and its aftermath. Through Project Reach, an innovative multi-component assessment and treatment service is utilized to identify and treat in integrated healthcare settings both children and adults exhibiting significant behavioral health concerns in Houston. The aim is to provide sustainable, integrated mental health services through primary care and school-based settings to post-Harvey affected individuals whose emotional needs remain unmet. This paper describes the design and implementation of Project Reach as well as special considerations for implementation. The overall goal of Project Reach is to form a platform for expanding integrated services for those affected by Harvey that will maximize behavioral health outcomes while reducing cost and improving access

Effect of sedimentary heterogeneities in the sealing formation on predictive analysis of geological CO₂ storage

Numerical models of geologic carbon sequestration (GCS) in saline aquifers use multiphase fluid flow-characteristic curves (relative permeability and capillary pressure) to represent the interactions of the non-wetting CO2 and the wetting brine. Relative permeability data for many sedimentary formations is very scarce, resulting in the utilisation of mathematical correlations to generate the fluid flow characteristics in these formations. The flow models are essential for the prediction of CO2 storage capacity and trapping mechanisms in the geological media. The observation of pressure dissipation across the storage and sealing formations is relevant for storage capacity and geomechanical analysis during CO2 injection. This paper evaluates the relevance of representing relative permeability variations in the sealing formation when modelling geological CO2 sequestration processes. Here we concentrate on gradational changes in the lower part of the caprock, particularly how they affect pressure evolution within the entire sealing formation when duly represented by relative permeability functions. The results demonstrate the importance of accounting for pore size variations in the mathematical model adopted to generate the characteristic curves for GCS analysis. Gradational changes at the base of the caprock influence the magnitude of pressure that propagates vertically into the caprock from the aquifer, especially at the critical zone (i.e. the region overlying the CO2 plume accumulating at the reservoir-seal interface). A higher degree of overpressure and CO2 storage capacity was observed at the base of caprocks that showed gradation. These results illustrate the need to obtain reliable relative permeability functions for GCS, beyond just permeability and porosity data. The study provides a formative principle for geomechanical simulations that study the possibility of pressure-induced caprock failure during CO2 sequestration

Efficacy of beta radiation in prevention of post-angioplasty restenosis

Restenosis remains a major limitation of coronary angioplasty in spite of major advances in techniques and technology. Recent studies have demonstrated that ionizing radiation may limit the degree of this problem. Gamma radiation has been shown to be effective in reducing in stent restenosis in humans, and beta radiation following encouraging results in animals has been shown to be feasible in humans. The objective of this study was to assess the feasibility of a 5 F non-centered catheter to deliver beta radiation emitting seeds to the lesion site post angioplasty and its effect on restenosis. Following successful angioplasty, patients were randomized to treatment with 12, 14 or 16 Gy at the angioplasty site. This was delivered with a 5 F non-centered catheter. Twelve beta radiation emitting seeds (90Sr/Y) were delivered to an area 3 cm in length to cover the angioplasty site. Angiographic follow-up was performed at 6 months. Baseline and follow-up angiograms were performed by blinded investigators at a core laboratory. This interim report comprises the first 35 patients to complete 6-month angiographic follow-up. There were no major radiation incidents. Four patients had evidence of angiographic restenosis. The MLD (mm) and percent stenosis were 0.77 +/- 0.27/72.5 +/- 8.6 pre angioplasty, 2.08 +/- 0.4/25.7 +/- 9.8 post angioplasty and radiation and 2.05 +/- 0.59/25.7 +/- 19.8 at follow-up respectively. CONCLUSION: Beta radiation can be feasibly and safely delivered post coronary angioplasty with a very encouraging reduction of restenosis

Vector meson production and nucleon resonance analysis in a coupled-channel approach for energies m_N < sqrt(s) < 2 GeV I: pion-induced results and hadronic parameters

We present a nucleon resonance analysis by simultaneously considering all pion- and photon-induced experimental data on the final states gamma N, pi N, 2 pi N, eta N, K Lambda, K Sigma, and omega N for energies from the nucleon mass up to sqrt(s) = 2 GeV. In this analysis we find strong evidence for the resonances P_{31}(1750), P_{13}(1900), P_{33}(1920), and D_{13}(1950). The omega N production mechanism is dominated by large P_{11}(1710) and P_{13}(1900) contributions. In this first part, we present the results of the pion-induced reactions and the extracted resonance and background properties with emphasis on the difference between global and purely hadronic fits.Comment: 54 pages, 26 figures, discussion extended, typos corrected, references updated, to appear in Phys. Rev.