Effect of noise on microseismic event detection and imaging using ICOVA statistical noise modelling method

Despite the evidence that noise does not conform to the White Gaussian Noise (WGN) assumption, the robustnessof new processing and imaging algorithms are still tested with WGN. This paper presents an alternative noise modelling method, based on multivariate statistics, to generate realistic noise for incorporation in synthetic datasets. The realistic noise model captures the complex nature of noise arising from multiple sources and the varying signal-to-noise (SNR) observed at the different stations across the array. This complex noise structure results in microseismic events being detected at lower SNR than would be implied using a WGN model. It also successfully re-creates smearing of energy during imaging of microseismic events at low SNRs. This modelling method provides an opportunity to test the robustness of new algorithms under realistic noise conditions prior to recording data in the field

Assessment of the limitations on the seismic detectability of injected CO2 within a deep geological reservoir

Aquistore is a deep saline CO2 storage research and demonstration project located near Estevan, Saskatchewan where CO2 is transported via pipeline and injected into a sandstone reservoir ∼3200 m below the surface. A pre-injection time-lapse analysis performed on two sparse 3D seismic datasets was used to characterise the background time-lapse signal-to-noise level at the storage site. The time-lapse analysis revealed that the lowest global nRMS was 0.07 which was taken to represent the level above which CO2 would be detectable in the reservoir. We investigate the conditions under which the injected CO2 can be detected above the defined minimum noise level through Gassmann fluid substitution and 3D seismic forward modelling. Additionally, Wave Unix was used to simulate the seismic response of the reservoir due to the injected CO2 by generating the synthetic surface reflection seismic data from an explosive surface P-wave source. We generated noise-free synthetic seismograms for the baseline model as well as for the 2-phase fluid replacement of brine with CO2 for CO2 concentrations up to 100% within the target zone – the monitors. The baseline and monitor traces from the 3D seismic survey at Aquistore are used as the noise traces in this study, and were added to their respective baseline and monitor synthetic traces. The nRMS within the reservoir was then computed for the noisy baseline and various noisy monitor surveys and was used in the assessment of the limitation to the detection of the injected CO2 in the reservoir under the background noise level at the site. We are able to conclude that the time-lapse repeatability will not limit the ability to monitor the CO2 induced changes in the reservoir at the Aquistore storage site

Preparing Christian health workers for international work: Evaluating a short global health course

Improving global health education to ensure health professionals are prepared and competent in the world's increasingly interconnected health-scape is a vital need. For many health professionals, global health education is facilitated through short, pre-departure courses in cross-cultural health and development work. There is currently limited literature on both the availability and the effectiveness of such courses. Our research aim was to explore the impact of a short course in global health education, designed and delivered by an Australian not-for-profit organisation, Intermed SA (Intermed). We conducted a short online survey of Intermed graduates, followed by semi-structured interviews with selected participants. The results indicate that Intermed's International Health and Development course was effective in achieving the course objectives as assessed by graduates, whilst also having a positive practical impact on the graduates' professional development

Initial 4D seismic results after CO 2 injection start-up at the Aquistore storage site

The first post-CO2-injection 3D time-lapse seismic survey was conducted at the Aquistore CO2 storage site in February 2016 using the same permanent array of buried geophones used for acquisition of three previous pre-CO2-injection surveys from March 2012 to November 2013. By February 2016, 36 kilotons of CO2 have been injected within the reservoir between 3170 and 3370 m depth. We have developed time-lapse results from analysis of the first post-CO2-injection data and three pre-CO2-injection data sets. The objective of our analysis was to evaluate the ability of the permanent array to detect the injected CO2. A “4D-friendly simultaneous” processing flow was applied to the data in an effort to maximize the repeatability between the pre- and post-CO2-injection volumes while optimizing the final subsurface image including the reservoir. Excellent repeatability was achieved among all surveys with global normalized root-mean-square (Gnrms) values of 1.13–1.19 for the raw prestack data relative to the baseline data, which decreased during processing to Gnrms values of approximately 0.10 for the final crossequalized migrated data volumes. A zone of high normalized root-mean-square (nrms) values (0.11–0.25 as compared with background values of 0.05–0.10) is identified within the upper Deadwood unit of the storage reservoir, which likely corresponds to approximately 18 kilotons of CO2. No significant nrms anomalies are observed within the other reservoir units due to a combination of reduced seismic sensitivity, higher background nrms values, and/or small quantities of CO2 residing within these zones

Seismic arrival enhancement through the use of noise whitening

A constant feature in seismic data, noise is particularly troublesome for passive seismic monitoring where noise commonly masks microseismic events. We propose a statistics-driven noise suppression technique that whitens the noise through the calculation and removal of the noise’s covariance. Noise whitening is shown to reduce the noise energy by a factor of 3.5 resulting in microseismic events being observed and imaged at lower signal to noise ratios than originally possible - whilst having negligible effect on the seismic wavelet. The procedure is shown to be highly resistant to most changes in the noise properties and has the flexibility of being used as a stand-alone technique or as a first step before standard random noise attenuation methods

Lower Aperiodic Activity is Associated with Reduced Verbal Fluency Performance Across Adulthood

Age-related cognitive decline associations with human electroencephalography (EEG) have previously focused on periodic activity. However, EEG is primarily made up of non-oscillatory aperiodic activity, which can be characterised with an exponent and offset value. In a secondary analysis of a cohort of 111 healthy participants aged 17 to 71 years, we examined the associations of the aperiodic exponent and offset with a battery of cognitive tests assessing processing speed and response inhibition, working memory, verbal learning and memory, psychomotor speed, and verbal fluency. Using Principal Component Analysis and K-Means Clustering, we identified clusters of electrodes that exhibited similar aperiodic exponent and offset activity during resting-state eyes-closed EEG. Robust linear models were then used to model how aperiodic activity interacted with age and their associations with performance during each cognitive test. Exponent by age and offset by age interactions were identified for the verbal fluency model where flatter exponents and smaller offsets were associated with poorer performance in adults as early as 30 years of age. Steeper exponents and greater offsets become increasingly related to verbal fluency performance and executive functioning in adulthood

Rapid porosity and permeability changes of calcareous sandstone due to CO₂-enriched brine injection

Reservoir injectivity and storage capacity are the main constraints for geologic CO2 sequestration, subject to safety and economic considerations. Brine acidification following CO2 dissolution leads to fluid-rock interactions that alter porosity and permeability, thereby affecting reservoir storage capacity and injectivity. Thus, we determined how efficiently CO2-enriched brines could dissolve calcite in sandstone cores and how this affects the petrophysical properties. During computerized tomography monitored flow-through reactor experiments, calcite dissolved at a rate largely determined by the rate of acid supply, even at high flow velocities which would be typical near an injection well. The porosity increase was accompanied by a significant increase in rock permeability, larger than that predicted using classical porosity-permeability models. This chemically driven petrophysical change might be optimized using injection parameters to maximize injectivity and storage

Epidemiology and long-term clinical and biologic risk factors for pneumonia in community-dwelling older Americans analysis of three cohorts

Preventing pneumonia requires better understanding of incidence, mortality, and long-term clinical and biologic risk factors, particularly in younger individuals