Modeling Gas, Hydrates, and Slope Stability on the U.S. Atlantic Margin during Pleistocene Glaciations

Dissociation of methane hydrates in shallow marine sediments due to increasing global temperatures can lead to the venting of methane gas or seafloor destabilization. Along the U.S. Atlantic margin there is a well-documented history of slope failure and numerous gas seeps have been recorded. Several studies have linked slope failure to gas seepage and hydrate dissociation driven by glacial-interglacial transitions, but this linkage has not been quantitatively demonstrated. Along the shelf edge, in an area where shallow methane gas seeps have been identified, we modeled methane gas and hydrate formation over the last 120,000 to simulate a glacial-interglacial cycle. The development of hydrate and gas during this time was modeled using the PFLOTRAN software from Sandia National Laboratories, a parallel subsurface flow code. At 100-year intervals during this simulation, we calculated the factor of safety throughout the modeled sediment column. Factor of safety compares the shearing and resisting stresses of a slope and can be used to determine if sediment failure is likely to occur in an area. Modeling seafloor depths between 200-1000 m we predicted gas and hydrate development and calculated the associated factor of safety over time to determine if sediment failure was likely to be caused by hydrate dissociation. Parallelizing this code, we used Lonestar6 to run the one-dimensional fluid flow model and factor of safety model at 16044 individual locations in the region between 29°N – 45°N and 82°W – 66°W at a resolution of 1 x 1 arcminutes. We found that hydrate dissociation alone is unlikely to cause sediment failure in the region, implying that an additional driving force would be necessary for failure to occur. In addition, we see a shift down slope of when the minimum factor of safety is likely to occur and the depth below seafloor at which this minimum occurs.Texas Advanced Computing Center (TACC

Predicting the geomechanical response of marine sediments to hydrate dissociation using machine learning and fluid flow modeling

With increasing global and ocean temperatures, the dissociation of methane hydrates at the feather edge of the of the gas hydrate stability zone (GHSZ) has become a greater concern to the scientific community. Possible responses to hydrate dissociation including seafloor methane venting and slope failure have been associated with gas generation and hydrate dissociation and have been used to create predictive maps of hydrate and gas locations around the world. Recently there has been a more concerted effort to model seafloor characteristics using machine learning methods to better estimate the global location of hydrate and gas formation. Seafloor total organic carbon (TOC) can be used to predict where methane hydrate and gas are likely to occur beneath the seafloor. I used a k-nearest neighbor machine learning model to predict global TOC at the seafloor. Within the region around the U.S. Atlantic margin (29°N–45°N and 82°W–66°W), I focused specifically on an area with high TOC predictions along the continental slope from (35.4°N, 75.0°W) to (39.0°N, 72.0°W). My research aims to model the geomechanical response of sediments to hydrate dissociation caused by increasing seafloor temperatures, specifically focused on areas along the upper continental slope. At nine locations – five hydrate bearing locations along the feather edge of the hydrate stability zone, one gas location up-dip of the feather edge, and three hydrate bearing locations down-dip of the feather edge – I modeled hydrate and gas formation due to burial over a 120,000 year time period. At each of these locations, hydrate and gas formation were modeled by sampling TOC, sedimentation rate, and heat flux. At the five locations along the feather edge, I modeled hydrate dissociation at the base of the hydrate stability zone (BHZ) due to an increase in temperature. I found that in a purely drained loading environment, no failure is expected to occur due to hydrate dissociation. However, in an undrained loading environment, shear failure is expected to occur during the hydrate dissociation process, even at low hydrate saturations (0.1% – 0.3%).Petroleum and Geosystems Engineerin

The Effect of Fluorine on the Viscosity of Jadeite-Leucite Melts

Glasses were synthesized along the jadeite-leucite (NaAlSi2O6 – KAlSi2O6) join with various amounts of dissolved fluorine (up to 4 wt.%). Na:K ratios synthesized include Jd100, Jd75Lct25, Jd62.5Lct37.5, Jd50Lct50, and Jd25Lct75, all of which have a nominal ratios of non-bridging oxygen to tetrahedrally-coordinated cations (NBO/T) of 0. For Jd50Lct50, we synthesized glasses with 0, 0.27, 0.54, 0.93, and 1.83 wt.% F. For all other Na:K ratios, we only synthesized two compositions of glass. For each Na:K ratio, glass with no fluorine was synthesized. In addition, Jd100(1.27F), Jd75Lct25(1.29F), Jd62.5Lct37.5(0.36F), and Jd25Lct75(0.25F) were synthesized. We measured the viscosity of each melt by parallel-plate viscometry at temperatures between 655 ◦C and 980 ◦C. We use the temperature at which the viscosity is 1012 Pa·s (T12) to compare the effect of F on the different composition of melts. Although melt viscosity, and thus T12 temperature, increases with decreasing Na:K ratios, the change in T12 with the addition of fluorine is similar for each melt. The addition of fluorine decreases the density and T12 of each melt relative to its F-free equivalent. However, as more F is added to a given composition, T12 decreases at a decreasing rate. With the addition of 0.5 wt.% F, T12 decreases by about 75 ◦C. With the addition of another 0.8 wt.% F (1.3 wt.% F total), T12 only decreases by an additional 50 ◦C. We conclude that increasing Na:K ratio and wt.% F both decrease the viscosity of the melts in this. Our results are consistent with the observed effect of Na:K ratio in more silica rich melts, with albite melt having a viscosity nearly 3 orders of magnitude lower than orthoclase melt at around 925 ◦C. Our results also show a similar effect of F on the viscosity of jadeite and albite melts, with a reduction in T12 for 2 wt.% F of about 130 ◦C in both melts. Further, as Jd50Lct50 becomes more depolymerized with the addition of F, the F has a smaller effect on viscosity