Gas bubble in aquatic sediments has a significant effect on its geophysical and geomechanical pro... more Gas bubble in aquatic sediments has a significant effect on its geophysical and geomechanical properties. Recent studies have shown that methane gas and hydrate can coexist in gas hydrate–bearing sediments. Accurate calibration and understanding of the fundamental processes regarding such coexisting gas bubble dynamics is essential for geophysical characterization and hazard mitigation. We conducted high-resolution synchrotron imaging of methane hydrate formation from methane gas in water-saturated sand. While previous hydrate synchrotron imaging has focused on hydrate evolution, here we focus on the gas bubble dynamics. We used a novel semantic segmentation technique based on convolutional neural networks to observe bubble dynamics before and during hydrate formation. Our results show that bubbles change shape and size even before hydrate formation. Hydrate forms on the outer surface of the bubbles, leading to reduction in bubble size, connectivity of bubbles, and the development o...
SUMMARY Knowledge of the effect of methane hydrate saturation and morphology on elastic wave atte... more SUMMARY Knowledge of the effect of methane hydrate saturation and morphology on elastic wave attenuation could help reduce ambiguity in seafloor hydrate content estimates. These are needed for seafloor resource and geohazard assessment, as well as to improve predictions of greenhouse gas fluxes into the water column. At low hydrate saturations, measuring attenuation can be particularly useful as the seismic velocity of hydrate-bearing sediments is relatively insensitive to hydrate content. Here, we present laboratory ultrasonic (448–782 kHz) measurements of P-wave velocity and attenuation for successive cycles of methane hydrate formation (maximum hydrate saturation of 26 per cent) in Berea sandstone. We observed systematic and repeatable changes in the velocity and attenuation frequency spectra with hydrate saturation. Attenuation generally increases with hydrate saturation, and with measurement frequency at hydrate saturations below 6 per cent. For hydrate saturations greater than...
Interest in natural gas hydrates has been steadily increasing over the last few decades, with the... more Interest in natural gas hydrates has been steadily increasing over the last few decades, with the understanding that exploitation of this abundant unconventional source may help meet the ever-increasing energy demand and assist in reduction of CO2 emission (by replacing coal). Unfortunately, conventional technologies for oil and gas exploitation are not fully appropriate for the specific exploitation of gas hydrate. Consequently, the technology chain, from exploration through production to monitoring, needs to be further developed and adapted to the specific properties and conditions associated with gas hydrates, in order to allow for a commercially and environmentally sound extraction of gas from gas hydrate deposits. Various academic groups and companies within the European region have been heavily involved in theoretical and applied research of gas hydrate for more than a decade. To demonstrate this, Fig. 1.1 shows a selection of leading European institutes that are actively invo...
Gas hydrates are ice–like compounds found in marine sediments and permafrosts. A significant frac... more Gas hydrates are ice–like compounds found in marine sediments and permafrosts. A significant fraction of all known hydrocarbons in nature is in the form of hydrate. Gas hydrates are a potential energy resource, with possible roles in seafloor slope stability and climate change. As such, improved geophysical methods are needed to identify and quantify in situ natural hydrates to better study their potential impacts. Current estimates of the distribution and volume of gas hydrates vary widely, by orders of magnitude, largely because of uncertainties in geophysical inversion results. The presence of hydrate affects the geophysical properties of the host sediment, creating anomalies that can be detected by seismic or electrical methods measurements. However, the precise relationships between measured geophysical properties and hydrate content (and distribution) are not fully understood, leading to uncertainties in hydrate estimates. Previous studies have shown that both the hydrate satu...
Gas Hydrates are considered as a viable source of energy, especially in energy starved countries.... more Gas Hydrates are considered as a viable source of energy, especially in energy starved countries. The role of gas hydrates in climate change, geo hazard and energy source has led to its study in various countries. With present scientific understand the detection of gas hydrates is done quite accurately using various geophysical exploration methods but the volume estimation or distribution of gas hydrate in a particular site is not well understood. Bottom simulating reflector (BSR) is easily identified in seismic but the upper boundary is not clear due to low impedance contrast in the upper boundary. In this thesis an attempt has been made to identify the volume distribution of hydrates in Vestenesa Ridge using seismic attributes. P cable seismic data from University of Tromso were used and the attributes were calculated. Attributes like Instantaneous Quality, Bandwidth, RMS Amplitude, Envelope were able to differentiate the hydrate zone but there were other zones of low amplitude wh...
Gas bubble in aquatic sediments has a significant effect on its geophysical and geomechanical pro... more Gas bubble in aquatic sediments has a significant effect on its geophysical and geomechanical properties. Recent studies have shown that methane gas and hydrate can coexist in gas hydrate–bearing sediments. Accurate calibration and understanding of the fundamental processes regarding such coexisting gas bubble dynamics is essential for geophysical characterization and hazard mitigation. We conducted high-resolution synchrotron imaging of methane hydrate formation from methane gas in water-saturated sand. While previous hydrate synchrotron imaging has focused on hydrate evolution, here we focus on the gas bubble dynamics. We used a novel semantic segmentation technique based on convolutional neural networks to observe bubble dynamics before and during hydrate formation. Our results show that bubbles change shape and size even before hydrate formation. Hydrate forms on the outer surface of the bubbles, leading to reduction in bubble size, connectivity of bubbles, and the development o...
SUMMARY Knowledge of the effect of methane hydrate saturation and morphology on elastic wave atte... more SUMMARY Knowledge of the effect of methane hydrate saturation and morphology on elastic wave attenuation could help reduce ambiguity in seafloor hydrate content estimates. These are needed for seafloor resource and geohazard assessment, as well as to improve predictions of greenhouse gas fluxes into the water column. At low hydrate saturations, measuring attenuation can be particularly useful as the seismic velocity of hydrate-bearing sediments is relatively insensitive to hydrate content. Here, we present laboratory ultrasonic (448–782 kHz) measurements of P-wave velocity and attenuation for successive cycles of methane hydrate formation (maximum hydrate saturation of 26 per cent) in Berea sandstone. We observed systematic and repeatable changes in the velocity and attenuation frequency spectra with hydrate saturation. Attenuation generally increases with hydrate saturation, and with measurement frequency at hydrate saturations below 6 per cent. For hydrate saturations greater than...
Interest in natural gas hydrates has been steadily increasing over the last few decades, with the... more Interest in natural gas hydrates has been steadily increasing over the last few decades, with the understanding that exploitation of this abundant unconventional source may help meet the ever-increasing energy demand and assist in reduction of CO2 emission (by replacing coal). Unfortunately, conventional technologies for oil and gas exploitation are not fully appropriate for the specific exploitation of gas hydrate. Consequently, the technology chain, from exploration through production to monitoring, needs to be further developed and adapted to the specific properties and conditions associated with gas hydrates, in order to allow for a commercially and environmentally sound extraction of gas from gas hydrate deposits. Various academic groups and companies within the European region have been heavily involved in theoretical and applied research of gas hydrate for more than a decade. To demonstrate this, Fig. 1.1 shows a selection of leading European institutes that are actively invo...
Gas hydrates are ice–like compounds found in marine sediments and permafrosts. A significant frac... more Gas hydrates are ice–like compounds found in marine sediments and permafrosts. A significant fraction of all known hydrocarbons in nature is in the form of hydrate. Gas hydrates are a potential energy resource, with possible roles in seafloor slope stability and climate change. As such, improved geophysical methods are needed to identify and quantify in situ natural hydrates to better study their potential impacts. Current estimates of the distribution and volume of gas hydrates vary widely, by orders of magnitude, largely because of uncertainties in geophysical inversion results. The presence of hydrate affects the geophysical properties of the host sediment, creating anomalies that can be detected by seismic or electrical methods measurements. However, the precise relationships between measured geophysical properties and hydrate content (and distribution) are not fully understood, leading to uncertainties in hydrate estimates. Previous studies have shown that both the hydrate satu...
Gas Hydrates are considered as a viable source of energy, especially in energy starved countries.... more Gas Hydrates are considered as a viable source of energy, especially in energy starved countries. The role of gas hydrates in climate change, geo hazard and energy source has led to its study in various countries. With present scientific understand the detection of gas hydrates is done quite accurately using various geophysical exploration methods but the volume estimation or distribution of gas hydrate in a particular site is not well understood. Bottom simulating reflector (BSR) is easily identified in seismic but the upper boundary is not clear due to low impedance contrast in the upper boundary. In this thesis an attempt has been made to identify the volume distribution of hydrates in Vestenesa Ridge using seismic attributes. P cable seismic data from University of Tromso were used and the attributes were calculated. Attributes like Instantaneous Quality, Bandwidth, RMS Amplitude, Envelope were able to differentiate the hydrate zone but there were other zones of low amplitude wh...
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