A multi‐disciplinary approach to marine shallow geohazard assessment

Marsset, Bruno; Thomas, Y.; Sultan, Nabil; Gaillot, Arnaud; Stéphan, Y.

doi:10.3997/1873-0604.2012012

Cited by 6 publications

(5 citation statements)

References 28 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The first step of the sequence involves the determination of the velocity field. We use a migration velocity analysis (MVA) procedure that is based on iterative prestack Kirchhoff depth migration using a layer‐stripping method (Al‐Yahya, ; Marsset et al, ). The principle of this seismic imaging procedure is to compare migration results obtained for a range of velocities at given locations called common image gathers (CIG).…”

Section: Methodsmentioning

confidence: 99%

Anomalously Deep BSR Related to a Transient State of the Gas Hydrate System in the Western Black Sea

Ker

Thomas

Riboulot

et al. 2019

Geochem Geophys Geosyst

Self Cite

View full text Add to dashboard Cite

A comprehensive characterization of gas hydrate system offshore the western Black Sea was performed through an integrated analysis of geophysical data. We detected the bottom‐simulating reflector (BSR), which marks, in this area, the base of gas hydrate stability. The observed BSR depth does not fit the theoretical steady state base of gas hydrate stability zone (BGHSZ). We show that the disparity between the BSR and predicted BGHSZ is the result of a transient state of the hydrate system due to the ongoing reequilibrium since the Last Glacial Maximum. When gas hydrates are brought outside the stability zone due to changes in temperature and sea level, their dissociation generates an increase in interstitial pore pressure. This process is favorable to the recrystallization of gas hydrates and delays the upward migration of the hydrate stability zone explaining the anomalously deep BSR. The BSR depth, which is commonly used to derive geothermal gradient values by assuming steady state conditions, is used here to derive the maximum excess pore pressure at the BGHSZ. Derived excess pore pressure values of 1–2 MPa are probably the result of the low permeability of hydrate‐bearing sediments. Higher pore pressure values derived at the location of a fault system could cause hydrofracturing enabling the free gas to cross the gas hydrate stability zone and emerge at the seafloor, forming the flares observed in close vicinity to where the shallow gas hydrates were sampled.

show abstract

Section: Methodsmentioning

confidence: 99%

Anomalously Deep BSR Related to a Transient State of the Gas Hydrate System in the Western Black Sea

Ker

Thomas

Riboulot

et al. 2019

Geochem Geophys Geosyst

Self Cite

View full text Add to dashboard Cite

show abstract

“…Data editing and updating of the fold map are performed at the end of each line to assess the homogeneity of the data and to adjust the acquisition program to acquire additional in-fill lines to cover gaps in the fold map. Considering the relatively shallow water depth on the survey area, additional 2D HR seismic data recorded using longer source-receiver offset (490 m compared to the 375 m maximum offset of the 3D layout) has allowed to constrain the velocity field within the upper sedimentary layers of interest (Marsset et al, 2012). A two-layer velocity model, 1515 m/s for the water column, and a constant gradient of 400 m/s increasing for the sediments was then applied to perform 3D stacking following by constant velocity two-pass Stolt time migration.…”

Section: Data Base and Processingmentioning

confidence: 99%

Repeated fluid expulsions during events of rapid sea-level rise in the Gulf of Lion, western Mediterranean Sea

Gay

Cavailhès

Grauls

et al. 2017

Bull. Soc. géol. Fr.

View full text Add to dashboard Cite

Based on a High-Resolution 3D seismic block acquired in the Gulf of Lion in 2004–2005 we investigated fluid pipes and pockmarks on the top of the interfluve between the Hérault canyon and the Bourcart canyon both created by turbidity currents and gravity flows from the shelf to the deep basin in the north-western Mediterranean Sea. Combining the geometry of the potential fluid pipes with the induced deformation of surrounding sediments leads then to the ability to differentiate between potential fluid sources (root vs source) and to better estimate the triggering mechanisms (allochtonous vs. autochtonous cause). We linked together a set of derived attributes, such as Chaos and RMS amplitude, to a 3D description of pipes along which fluids may migrate. As previously shown in other basins, the induced deformation, creating cone in cone or V-shaped structures, may develop in response to the fluid pipe propagation in unconsolidated sediments in the near surface. The level at the top of a cone structure is diachronous. It means that stratigraphic levels over this surface are deformed at the end of the migration. They collapse forming a depression called a pockmark. These pipes are the result of repeated cycles of fluid expulsion that might be correlated with rapid sea-level rise instead of sediment loading. The most recent event (MIS 2.2 stage) has led to the formation of a pockmark on the modern seafloor. It has been used as a reference for calculating the effect of a rapid sea-level rise on fluid expulsion. As all physical and geometrical parameters are constrained, we were able to define that a + 34 m of sea level rise may account for triggering fluid expulsion from a very shallow silty-sandy layer at 9 m below seafloor since the last glacial stage. This value is consistent with a sea level rise of about 102 m during this period. This study shows that the episodic nature of fluid release resulted from hydromechanical processes during sea-level rise due to the interactivity between high pressure regimes and principal in situ stresses.

show abstract

“…Currently, natural gas-hydrate accumulations are regarded as a double-edged sword: while they are considered as both a potential energy resource [8][9][10][11][12][13] and huge carbon dioxidestorage reservoirs [14][15][16][17][18][19][20], they are also defined as a geohazard [21][22][23][24][25] and often presented as a potential climate-change contributor [26][27][28][29][30][31][32]. This makes its study a timely topic as reflected by the increasing number of related articles available from scientific reviews.…”

Section: Introductionmentioning

confidence: 99%

Exploring methane-hydrate formation and dissociation in geologic materials through laboratory experiments: Kinetic behavior and morphology

Ruffine

2015

Fuel

View full text Add to dashboard Cite

To gain in-depth understanding of natural gas hydrate behavior it is necessary to identify key parameters that affect their formation, distribution and destabilization within sediments. Hydrate formation kinetics in porous media is amongst the aspects which deserve important considerations as it may provide useful information on the formation history and the formation mechanisms of natural gas hydrate accumulations. Yet, it is at its early stage. In this paper, experiments on methane hydrate formation and dissociation in porous media are reported and discussed. The first part of this work is devoted to the investigation of the kinetics of methane hydrate formation within silica sand using a custom-design apparatus. The latter is suitable for investigating small hydrate-bearing cores. The influence of the methane injection flow-rate is examined, and then a straightforward method is proposed to quantify the amount of hydrate-bound gas. In the second part, three mixtures of clays and sand are used as geologic matrix to study the influence of clay content on the hydrate morphology for a predetermined amount of injected water. Visual observations showed that the morphology shifts from disseminated through massive to moussy hydrates with increasing proportion of clays. Highlights ► A novel apparatus for studying hydrate formation in geologic matrices is presented. ► Kinetics of methane-hydrate formation in sand was investigated. ► Influence of methane injection rate was studied. ► Repeated experiments at constant methane injection flow rate showed different formation patterns. ► Morphology of hydrates in sand-clay mixtures changes with the proportion of clay.

show abstract

A multi‐disciplinary approach to marine shallow geohazard assessment

Cited by 6 publications

References 28 publications

Anomalously Deep BSR Related to a Transient State of the Gas Hydrate System in the Western Black Sea

Anomalously Deep BSR Related to a Transient State of the Gas Hydrate System in the Western Black Sea

Repeated fluid expulsions during events of rapid sea-level rise in the Gulf of Lion, western Mediterranean Sea

Exploring methane-hydrate formation and dissociation in geologic materials through laboratory experiments: Kinetic behavior and morphology

Contact Info

Product

Resources

About