1,720,962 research outputs found
Impact of subsurface fluid flow on sediment acoustic properties, implications for carbon capture and storage
No full textGeological Carbon Capture and Storage (CCS) is a promising climate change mitigation technology, which allows the reduction of anthropogenic carbon dioxide (CO2) emissions into the atmosphere. Although CCS is considered to have a significant potential in tackling climate change, several uncertainties remain, including the efficiency and permanency of carbon sequestration, and notably risks of CO2 leakage from the storage reservoir. A better understanding of fluid flow activity within the sedimentary overburden and the identification of the best monitoring techniques are crucial for increasing societal confidence in sequestration.This thesis reports findings from two different offshore CCS projects: a controlled sub-seabed CO2 release experiment completed in Ardmucknish Bay, Oban (Quantifying and Monitoring Potential Ecosystem Impacts of Geological Carbon Storage, QICS), and a multidisciplinary research project conducted in the vicinity of Sleipner CCS site, in the Central North Sea (Sub-seabed CO2 Storage: Impact on Marine Ecosytems, ECO2).During the QICS project, a borehole was drilled from land, allowing 37 days of CO2 release in unconsolidated marine sediments. Analysis of the time-lapse high- resolution seismic reflection data reveals development of acoustic anomalies within the overburden and water column, caused by CO2 fluxing in the vicinity of the injection site. The impacts of CO2 injection on sediment acoustic properties are investigated, where changes in seismic reflectivity, seismic attenuation, acoustic impedance and P-wave seismic velocity are detected on high-resolution seismic reflection data. CO2 migration within the overburden is interpreted to be controlled by sediment stratigraphy and injection rate/total injected volume throughout the gas release, and by the sediment stratigraphic geometry post-release. Seismic quantification of the gaseous CO2 indicates that most of the injected CO2 is trapped below a stratigraphic boundary, located at 4 m depth below the seafloor, or dissolved, throughout the gas release. These observations are in agreement with seabed gas flux measurements by passive hydroacoustics and water column bubble sampling, which suggest that only 15% of the injected CO2 emerges at the seabed, towards the end of gas release.Within the scope of the ECO2 project, increased fluid flow activity is detected along, and in the vicinity of a seabed fracture, the Hugin Fracture. Although there is no evidence of anthropogenic CO2 leakage in the Central North Sea from the current dataset, biogenic and thermogenic gas leakage at the Hugin Fracture suggest a well-established hydraulic and structural connection. The origin of the Hugin Fracture is proposed to be controlled by an E-W transtensional stress regime, and differential compaction above a buried tunnel valley system
First controlled sub-seabed CO2 release experiment: qualitative and quantitative analysis of high-resolution seismic reflection data
No full textCarbon Capture and Storage is a promising climate change mitigation technology which allows the reduction of carbon dioxide emissions into the atmosphere. To assure a safe and permanent CO2 storage, it is vital to adapt efficient monitoring technologies allowing to better understand the fate of the injected CO2 within the subsurface, including its impact on sediment acoustic properties and migration into the overlying layers. The first-controlled sub-seabed CO2 release experiment, Quantifying and Monitoring Potential Ecosystem Impacts of Geological Carbon Storage (QICS), was completed in Ardmucknish Bay, Oban, where 4.2 tonnes of CO2 were injected into unconsolidated shallow marine sediments over 37 days. High-resolution seismic reflection data acquired syn-release reveal many CO2-related acoustic anomalies including seismic chimneys and enhanced reflectivity within the overburden, and bubbles within the water column. CO2 migration is interpreted to be controlled by sediment stratigraphy in the early stages of the experiment, whereas CO2 injection rate/ total injected volume overrode the stratigraphic control towards the end of gas release. Post-release seismic reflection data reveal that injected CO2 was mostly trapped below an erosional unconformity, Horizon 2, where a dip of 3.5° was found to significantly control the up-dip migration of the gaseous CO2 after the cessation of injection. The in situ CO2 content above Horizon 2 is also determined using the syn-release seismic reflection data combined with the Anderson and Hampton geaocoustics model, confirming that most of the injected CO2 was trapped below Horizon 2, or dissolved, during the QICS experiment
Gas migration pathways, controlling mechanisms and changes in sediment acoustic properties observed in a controlled sub-seabed CO2 release experiment
Full text linkCarbon capture and storage (CCS) is a key technology to potentially mitigate global warming by reducing carbon dioxide (CO2) emissions from industrial facilities and power generation that escape into the atmosphere. To broaden the usage of geological storage as a viable climate mitigation option, it is vital to understand CO2 behaviour after its injection within a storage reservoir, including its potential migration through overlying sediments, as well as biogeochemical and ecological impacts in the event of leakage.The impacts of a CO2 release were investigated by a controlled release experiment that injected CO2 at a known flux into shallow, under-consolidated marine sediments for 37 days. Repeated high-resolution 2D seismic reflection surveying, both pre-release and syn-release, allows the detection of CO2-related anomalies, including: seismic chimneys; enhanced reflectors within the subsurface; and bubbles within the water column. In addition, reflection coefficient and seismic attenuation values calculated for each repeat survey, allow the impact of CO2 flux on sediment acoustic properties to be comparatively monitored throughout the gas release. CO2 migration is interpreted as being predominantly controlled by sediment stratigraphy in the early stages of the experiment. However, either the increasing flow rate, or the total injected volume become the dominant factors determining CO2 migration later in the experiment
Seismicity and accretion processes along the Mid-Atlantic Ridge south of the Azores using data from the MARCHE autonomous hydrophone array
No full textThe seismicity of the South Atlantic Ocean has been recorded by the MARCHE network of 4 autonomous underwater hydrophones (AUH) moored within the SOFAR channel on the flanks of the Mid-Atlantic Ridge (MAR). The instruments were deployed south of the Azores Plateau between 32° and 39°N from July 2005 to August 2008. The low attenuation properties of the SOFAR channel for earthquake T-wave propagation result in a detection threshold reduction from a magnitude completeness level (Mc) of ~4.3 for MAR events recorded by the land-based seismic networks to Mc=2.1 using this hydrophone array. A spatio-temporal analysis has been performed among the 5600 events recorded inside the MARCHE array. Most events are distributed along the ridge between lat. 39°N on the Azores Platform and the Rainbow (36°N) segment. In the hydrophone catalogue, acoustic magnitude (Source Level, SL) is used as a measure of earthquake size. The source level above which the data set is complete is SLc=205 dB. We look for seismic swarms using the cluster software of the SEISAN package. The criterion used are a minimum SL of 210 to detect a possible mainshock, and a radius of 30 km and a time window of 40 days after this mainshock (Cevatoglu, 2010, Goslin et al., 2012). 7 swarms with more than 15 events are identified using this approach between 32°et 39°N of latitude. The maximum number of earthquake in a swarm is 57 events. This result differs from the study of Simao et al. (2010) as we processed a further year of data and selected sequences with fewer events. Looking at the distribution of the SL as a function of time after the mainshock, we discuss the possible mechanism of these earthquakes : tectonic events with a "mainshock-aftershock" distribution fitting a modified Omori law or volcanic events showing more constant SL values. We also present the geophysical setting of these 7 swarms, using gravity, bathymetry, and available local geological data. This study illustrates the potential of hydrophone data to monitor segment-scale ridges processes in the vicinity of the Lucky Strike seafloor observatory (lat. 37°20'N), the Azores node of the EMSO (European Multidiciplinary Subsea Observatory) system
Autonomous Underwater Vehicle survey design for monitoring carbon capture and storages sites
No full textLong-term monitoring of sub-seabed Carbon Capture and Storage (CCS) sites will require systems that are flexible, independent, and have long-endurance. In this presentation we will discuss the utility of autonomous underwater vehicles equipped with different sensor packages in monitoring storage sites. We will present data collected using Autosub AUV, as part of the ECO2 project, from the Sleipner area of the North Sea. The Autosub AUV was equipped with sidescan sonar, an EM2000 multibeam systems, a Chirp sub-bottom profiler, and a variety of chemical sensors. Our presentation will focus on survey design, and the simultaneous use of multiple sensor packages in environmental monitoring on the continental shelf
First controlled sub-seabed CO2 release experiment: Insights into gas migration pathways and impacts on sediment physical properties
No full textCarbon Capture and Storage (CCS) is a key technology to potentially mitigate global warming by reducing the amount of carbon dioxide (CO2) from industrial facilities and power generation that escapes into the atmosphere. In order to broaden the usage of geological storage as a safe and reliable climate change mitigation option, it is vital to understand CO2 behaviour after its injection within a storage reservoir, including its migration through overlying sediments, as well as its biogeochemical and ecological impacts in the event of leakage at the seafloor. To address these issues, the first controlled CO2 release experiment, entitled 'Quantifying and Monitoring Potential Ecosystem Impacts of Geological Carbon Storage (QICS)', took place in Ardmucknish Bay, Oban, in May-July 2012. This experiment involved the injection of CO2 of known flux under shallow unconsolidated marine sediments over 36 days and repeated monitoring using geophysical and geochemical techniques. High resolution seismic reflection data (chirp and boomer), covering both pre-release and release stages, allows the detection of various CO2-related anomalies including seismic chimneys, enhanced reflectors within the sediment overburden and bubbles into the overlying water column. CO2 migration pattern is predominantly controlled by the stratigraphy in the early stages of the experiment. However, the increasing flow rate becomes the dominant factor determining CO2 migration, towards the end of the experiment. In addition, analysis of reflection coefficients and seismic attenuation indicates the effect of CO2 on sediment physical properties
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
- …
