Pressure-varying CO 2 distribution affects the ultrasonic velocities of synthetic sandstones

We performed a novel experiment in which three synthetic sandstones – manufactured using a common method but having different porosities – were saturated with brine and progressively flooded with CO2 under constant confining pressure. The fluid pressure was varied around the critical pressure of CO2 and repeated measurements were made of resistivity, in order to assess the saturation, and elastic wave velocity during the flood. The measured saturated bulk moduli were higher than those predicted by the Gassmann–Wood theory, but were consistent with behaviour described by a recently derived poroelastic model which combines “patch” and “squirt” effects. Measurements on two of the samples followed a patch-based model while those on the highest porosity sample showed evidence of squirt-flow behaviour. Our analysis suggests that the appropriate fluid mixing law is pressure dependent, which is consistent with the notion that the effective patch size decreases as fluid pressure is increased. We derive simple empirical models for the patch dependence from fluid pressure which may be used in seismic modelling and interpretation exercises relevant to monitoring of CO2 injection

Environmental variability and heavy metal concentrations from five lagoons in the Ionian Sea (Amvrakikos Gulf, W Greece)

Background: Coastal lagoons are ecosystems of major importance as they host a number of species tolerant to disturbances and they are highly productive. Therefore, these ecosystems should be protected to ensure stability and resilience. The lagoons of Amvrakikos Gulf form one of the most important lagoonal complexes in Greece. The optimal ecological status of these lagoons is crucial for the well-being of the biodiversity and the economic prosperity of the local communities. Thus, monitoring of the area is necessary to detect possible sources of disturbance and restore stability. New information: The environmental variables and heavy metals concentrations, from five lagoons of Amvrakikos Gulf were measured from seasonal samplings and compared to the findings of previous studies in the area, in order to check for possible sources of disturbance. The analysis, showed that i) the values of the abiotic parameters vary with time (season), space (lagoon) and with space over time; ii) the variability of the environmental factors and enrichment in certain elements is naturally induced and no source of contamination is detected in the lagoons

Abnormal auditory ERP N100 in children with dyslexia: comparison with their control siblings

<p>Abstract</p> <p>Background</p> <p>Recent research has implicated deficits of the working memory (WM) and attention in dyslexia. The N100 component of event-related potentials (ERP) is thought to reflect attention and working memory operation. However, previous studies showed controversial results concerning the N100 in dyslexia. Variability in this issue may be the result of inappropriate match up of the control sample, which is usually based exclusively on age and gender.</p> <p>Methods</p> <p>In order to address this question the present study aimed at investigating the auditory N100 component elicited during a WM test in 38 dyslexic children in comparison to those of 19 unaffected sibling controls. Both groups met the criteria of the International Classification of Diseases (ICD-10). ERP were evoked by two stimuli, a low (500 Hz) and a high (3000 Hz) frequency tone indicating forward and reverse digit span respectively.</p> <p>Results</p> <p>As compared to their sibling controls, dyslexic children exhibited significantly reduced N100 amplitudes induced by both reverse and forward digit span at Fp1, F3, Fp2, Fz, C4, Cz and F4 and at Fp1, F3, C5, C3, Fz, F4, C6, P4 and Fp2 leads respectively. Memory performance of the dyslexics group was not significantly lower than that of the controls. However, enhanced memory performance in the control group is associated with increased N100 amplitude induced by high frequency stimuli at the C5, C3, C6 and P4 leads and increased N100 amplitude induced by low frequency stimuli at the P4 lead.</p> <p>Conclusion</p> <p>The present findings are in support of the notion of weakened capture of auditory attention in dyslexia, allowing for a possible impairment in the dynamics that link attention with short memory, suggested by the anchoring-deficit hypothesis.</p

CO2‐Brine substitution effects on ultrasonic wave propagation through sandstone with oblique fractures

Seismic monitoring of injected CO2 plumes in fractured storage reservoirs relies on accurate knowledge of the physical mechanisms governing elastic wave propagation, as described by appropriate, validated rock physics models. We measured laboratory ultrasonic velocity and attenuation of P and S waves, and electrical resistivity, of a synthetic fractured sandstone with obliquely aligned (penny‐shaped) fractures, undergoing a brine‐CO2 flow‐through test at simulated reservoir pressure and temperature. Our results show systematic differences in the dependence of velocity and attenuation on fluid saturation between imbibition and drainage episodes, which we attribute to uniform and patchy fluid distributions, respectively, and the relative permeability of CO2 and brine in the rock. This behavior is consistent with predictions from a multifluid rock physics model, facilitating the identification of the dispersive mechanisms associated with wave‐induced fluid flow in fractured systems at seismic scales

Introduction to special section on the rock physics contribution to the energy transition challenge

Rock physics connects with geophysics, petrophysics and geomechanics to adequately characterize geological reservoirs, optimize monitoring operations in the field, interpret in situ and laboratory test data, and develop accurate predictive models for extraction/injection activities. The application of rock physics is crucial to achieving net-zero carbon emissions worldwide, as we need to combine large-scale mitigation technologies like carbon capture usage and storage, together with an increasing use of renewables such as geothermal and underground hydrogen storage (UHS)

Core-scale geophysical and hydromechanical analysis of seabed sediments affected by CO2 venting

Safe offshore Carbon Capture Utilization and Storage (CCUS) includes monitoring of the subseafloor, to identify and assess potential CO2 leaks from the geological reservoir through seal bypass structures. We simulated CO2-leaking through shallow marine sediments of the North Sea, using two gravity core samples from ∼1 and ∼2.1 m below seafloor. Both samples were subjected to brine−CO2 flow-through, with continuous monitoring of their transport, elastic and mechanical properties, using electrical resistivity, permeability, P-wave velocity and attenuation, and axial strains. We used the collected geophysical data to calibrate a resistivity-saturation model based on Archie’s law extended for clay content, and a rock physics for the elastic properties. The P-wave attributes detected the presence of CO2 in the sediment, but failed in providing accurate estimates of the CO2 saturation. Our results estimate porosities of 0.44 and 0.54, a background permeability of ∼10−15 and ∼10-17 m2, and maximum CO2 saturation of 18 % and 10 % (±5 %), for the sandier (shallower) and muddier (deeper) sample, respectively. The finer-grained sample likely suffered some degree of gas-induced fracturing, exhibiting an effective CO2 permeability increase sharper than the coarser-grained sample. Our core-scale multidisciplinary experiment contributes to improve the general interpretation of shallow sub-seafloor gas distribution and migration patterns

CO2-brine flow-through on an Utsira Sand core sample: Experimental and modelling. Implications for the Sleipner storage field

Sleipner (North Sea) is the world’s first commercial-scale carbon capture and storage (CCS) project, active since 1996, with ∼17 million tonnes of CO2 stored. The main reservoir, Utsira Sand, constitutes an ideal host formation of exceptionally high porosity-permeability and large lateral extent. However, the extensive seismic time-lapse, gravity and electromagnetic monitoring surveys deployed at Sleipner have not been well-supported by laboratory measurements. Here, we investigate the geophysical and geomechanical response of an Utsira core sample for the first time, using controlled inflation/depletion cycles at variable CO2-to-brine fractional flow rates. Ultrasonic P-wave velocities and attenuations are measured together with electrical resistivity (converted into CO2-saturation), along with continuous axial and radial strain monitoring. Ultrasonic velocity and attenuation data were simultaneously inverted and results extrapolated to field-scale seismic-frequencies using a new rock physics theory, which combines patchy fluid distribution and squirt flow effects. It provides a velocity-saturation relationship of practical importance to CO2 plume monitoring. Furthermore, by combining ultrasonic and deformation data, we report empirical relations between pore pressure changes and geomechanical effects in the reservoir, for different saturation ranges. Our dataset complements and constrains existing geophysical monitoring surveys at Sleipner and, more generally, improves the understanding of shallow weakly-cemented sand reservoirs

Detecting Complexity Abnormalities in Dyslexia Measuring Approximate Entropy of Electroencephalographic Signals

Dyslexia constitutes a specific reading disability, a condition characterized by severe difficulty in the mastery of reading despite normal intelligence or adequate education. Electroencephalogram (EEG) signal may be able to play an important role in the diagnosis of dyslexia. The Approximate Entropy (ApEn) is a recently formulated statistical parameter used to quantify the regularity of a time series data of physiological signals. In this paper, we initially estimated the ApEn values in signals recorded from controls subjects and dyslectic children. These values were firstly used for the statistical analysis of the two groups and secondly as feature input in a classification scheme. We also used the cross-ApEn methodology to get a measure of the asynchrony of the signals recorded from different electrodes. This preliminary study provides promising results towards correct identification of dyslexic cases, analyzing the corresponding EEG signals