A new global gas hydrate budget based on numerical reaction-transport modeling and a novel parameterization of Holocene and Quaternary sedimentation

This study provides new estimates for the global methane hydrate inventory based on reaction-transport modeling [1]. A multi-1D model for POC degradation, gas hydrate formation and dissolution is presented. The model contains an open three-phase system of two solid (organic carbon, gas hydrates), three dissolved (methane, sulfates, inorganic carbon) and one gaseous (free methane) compounds. The reaction module builds upon the kinetic model of POC degradation [2] which considers a down-core decrease in reactivity of organic matter and the inhibition of methane production via accumulation of metabolites in sediment pore fluids. Global input grids have been compiled from a variety of oceanographic, geological and geophysical data sets including a parameterization of sedimentation rates in terms of water depth (Holocene) and distance to continents (Quaternary).The world's total gas hydrate inventory is estimated at 1.74 x 1013 m3 – ~2 x 1015 m3 CH4 (STP) or, equivalently, 8.3 – ~900 Gt of methane carbon. The first value refers to the present day conditions using the relatively low Holocene sedimentation rates; the second value corresponds to a scenario of higher Quaternary sedimentation rates along continental margins. This increase in the POC input could be explained by re-deposition process at the continental rise and slope due to erosion of continental shelf sediments during glacial times. Our results show that in-situ POC degradation is at present not an efficient hydrate forming process. Significant hydrate deposits are more likely to have formed at times of higher sedimentation during the Quaternary or/and as a consequence of active upward fluid transport

GH-3PAD – a new numerical solver for multiphase transport in porous media - new insights on gas hydrate and free gas co-existence

Gas Hydrate-3 Phase Advanced Dynamics (GH-3PAD) code has been developed to study the geophysical and biochemical processes associated with gas hydrate as well as free methane gas formation and dissolution in marine sediments. Biochemical processes influencing in-situ organic carbon decay and, therefore, gas hydrate formation, such as Anaerobic Oxidation of Methane (AOM), sulfate reduction, and methanogenesis have been considered. The new model assumes a Lagrangian reference frame that is attached to the deposited sedimentary layers, which compact according to their individual lithological properties. Differential motion of the pore fluids and free gas is modeled as Darcy flow. Gas hydrate and free gas formation is either controlled by 1) instant gas hydrate crystallization assuming local thermodynamical equilibrium or by a 2) kinetically controlled rate of gas hydrate growth. The thermal evolution is computed from an energy equation that includes contributions from all phases present in the model (sediment grains, saline pore fluids, gas hydrate, and free gas). A first application of the GH-3PAD model has been the Blake Ridge Site, offshore South Carolina. Here seismic and well data points to the out-of-equilibrium co-existence of gas hydrate and free gas. It has been reported that these two distinct phases appear within sediment column with a gaseous phase tending to migrate upwards throughout the Gas Hydrate Stability Zone (GHSZ) until it reaches the seafloor despite relatively low gas hydrate content (4 – 7 vol. % after Paull et al., 1996). With the GH-3PAD model we quantify the complex transport- reaction processes that control three phase (gas hydrate, free gas, and dissolved CH4) out-of-equilibrium state. References: Paull C. K., Matsumoto R., Wallace P. J., 1996. 9. Site 997, Shipboard Scientific Party. Proceeding of the Ocean Drilling Program, Initial Reports, Vol. 164

Transport- reaction modeling of marine gas hydrate deposits- global results

We have developed a multi-1D numerical model of gas hydrate formation and dissolution processes in anoxic marine sediments and, by this model, we have estimated the new global gas hydrate inventory (BURWICZ E. B. et al., 2011). The reaction-transport model contains various chemical compounds (solid organic carbon, dissolved methane, inorganic carbon, and sulfates, gas hydrates, and free methane gas). The rates of POC degradation, anaerobic methane oxidation, sulfate reduction, and methanogenesis are kinetically controlled. Gas hydrate stability zone (GHSZ) is defined as a combination of pressure, temperature, and (to a smaller degree) salinity conditions. The lower boundary of the GHSZ is defined as the intersection of gas hydrate and methane gas solubilities. The diffusion equations are solved using a fully-implicit finite-differences method, while all transport processes are resolved by a Semi-Lagrangian scheme. Global input data sets (1°x1° resolution) were compiled from various oceanographic, geological and geophysical sources. The entire model was implemented in Matlab

A Spectroscopic and Photometric Investigation of the Mercury-Manganese Star KIC 6128830

The advent of space-based photometry provides the opportunity for the first precise characterizations of variability in Mercury-Manganese (HgMn/CP3) stars, which might advance our understanding of their internal structure. We have carried out a spectroscopic and photometric investigation of the candidate CP3 star KIC 6128830. A detailed abundance analysis based on newly-acquired high-resolution spectra was performed, which confirms that the star's abundance pattern is fully consistent with its proposed classification. Photometric variability was investigated using four years of archival Kepler data. In agreement with results from the literature, we have identified a single significant and independent frequency $f_1$=0.2065424 d$^{-1}$ with a peak-to-peak amplitude of $\sim$3.4 mmag and harmonic frequencies up to $5f_1$. Drawing on the predictions of state-of-the-art pulsation models and information on evolutionary status, we discuss the origin of the observed light changes. Our calculations predict the occurrence of g-mode pulsations at the observed variability frequency. On the other hand, the strictly mono-periodic nature of the variability strongly suggests a rotational origin. While we prefer the rotational explanation, the present data leave some uncertainty.Comment: 13 pages, 13 figures, accepted for publication in MNRA

Openness and communication effects on relationship satisfaction in women experiencing infertility or miscarriage : a dyadic approach

Openness and communication between partners are key elements of dyadic coping with stress. Our main research question is: what is the impact of these factors on relational satisfaction in spouses struggling with infertility or miscarriage? In the current study, by applying the actor - partner interdependence model to 90 heterosexual couples (N = 180), we examined the link between the spouses’ openness (the Giessen Test), communication (Flexibility and Cohesion Evaluation Scales) and relationship satisfaction (the Marriage Success Scale). Controlling for relevant covariates (communication, own openness and type of stress experienced by the spouses: infertility or miscarriage), a dyadic analysis revealed significant actor (-0.24; p < 0.001) and partner effects (-0.20; p < 0.001). We conclude that the relationship between the perception of the partner’s openness and the relationship satisfaction in women is strong, in the context of the analyzed potential confounding variables. We also observe that the relationship satisfaction in women from the group of infertile spouses is 6.06 points lower compared to women from the group of marriages after miscarriage (p = 0.034)

Gas hydrate dynamics at the Green Canyon Site, Gulf of Mexico - recovery prospects based on new 3-D modeling study

Due to their favorable P-T conditions and organic-rich deposits, sub-seafloor sediments in the northern Gulf of Mexico are known to have a large potential for gas hydrate accumulations. The presence of gas hydrates within sediments of the Green Canyon block has been proven by various methods, incl. seismic imaging, geochemical analysis, and drilling conducted mainly as a part of Joint Industry Project (JIP) Phase II. Gas hydrates reported therein usually occur as tens up to hundreds of meters thick sections with moderate to high concentrations within a range of 50 – 70 vol. % of pore space, and hence, seem to offer a considerable natural deposit of methane gas. The main focus of this study was to explore the complex effects of a set of control- parameters responsible for hydrocarbon migration and storage within the Gas Hydrate Stability Zone (GHSZ) on the accumulation of gas hydrates. To investigate the processes of basin formation and its subsidence history, source rock maturation, hydrocarbon migration and expulsion, and to quantify the gas hydrate accumulation potential, 3-D numerical study has been conducted using PetroMod. The area of interest extends over ~14 km x 33 km and covers the edge of the Sigsbee Escarpment representing the main salt mobility front in the region. The simulation contains full depositional history of the Green Canyon block, incl. salt deposition and re-mobilization as well as its further implications for temperature field, fluids migration and sedimentary layers distribution. Methane generation has been resolved by in-situ POC degradation and deep thermogenic mobilization from two distinct hydrocarbon sources. As a result, we present a number of likely scenarios of gas hydrate formation and accumulation in the study area that have been calibrated against available data

3-D basin-scale reconstruction of natural gas hydrate system of the Green Canyon, Gulf of Mexico

Our study presents a basin-scale 3D modeling solution, quantifying and exploring gas hydrate accumulations in the marine environment around the Green Canyon (GC955) area, Gulf of Mexico. It is the first modeling study that considers the full complexity of gas hydrate formation in a natural geological system. Overall, it comprises a comprehensive basin re-construction, accounting for depositional and transient thermal history of the basin, source rock maturation, petroleum components generation, expulsion and migration, salt tectonics and associated multi-stage fault development. The resulting 3D gas hydrate distribution in the Green Canyon area is consistent with independent borehole observations. An important mechanism identified in this study and leading to high gas hydrate saturation (> 80 vol. %) at the base of the gas hydrate stability zone (GHSZ), is the recycling of gas hydrate and free gas enhanced by high Neogene sedimentation rates in the region. Our model predicts the rapid development of secondary intra-salt mini-basins situated on top of the allochthonous salt deposits which leads to significant sediment subsidence and an ensuing dislocation of the lower GHSZ boundary. Consequently, large amounts of gas hydrates located in the deepest parts of the basin dissociate and the released free methane gas migrates upwards to recharge the GHSZ. In total, we have predicted the gas hydrate budget for the Green Canyon area that amounts to ∼3,256 Mt of gas hydrate which is equivalent to ∼340 Mt of carbon (∼7 x 1011 m3 of CH4 at STP conditions), and consists mostly of biogenic hydrates