Gospel Choir

KSU School of Music presents Gospel Choir.https://digitalcommons.kennesaw.edu/musicprograms/1166/thumbnail.jp

KSU Chamber Singers and Men\u27s Ensemble

KSU School of Music presents Chamber Singers and Men\u27s Ensemble.https://digitalcommons.kennesaw.edu/musicprograms/1157/thumbnail.jp

Linking basin-scale and pore-scale gas hydrate distribution patterns in diffusion-dominated marine hydrate systems

The goal of this study is to computationally determine the potential distribution patterns of diffusion-driven methane hydrate accumulations in coarse-grained marine sediments. Diffusion of dissolved methane in marine gas hydrate systems has been proposed as a potential transport mechanism through which large concentrations of hydrate can preferentially accumulate in coarse-grained sediments over geologic time. Using one-dimensional compositional reservoir simulations, we examine hydrate distribution patterns at the scale of individual sand layers (1-20 m thick) that are deposited between microbially active fine-grained material buried through the gas hydrate stability zone (GHSZ). We then extrapolate to two-dimensional and basin-scale three-dimensional simulations, where we model dipping sands and multilayered systems. We find that properties of a sand layer including pore size distribution, layer thickness, dip, and proximity to other layers in multilayered systems all exert control on diffusive methane fluxes toward and within a sand, which in turn impact the distribution of hydrate throughout a sand unit. In all of these simulations, we incorporate data on physical properties and sand layer geometries from the Terrebonne Basin gas hydrate system in the Gulf of Mexico. We demonstrate that diffusion can generate high hydrate saturations (upward of 90%) at the edges of thin sands at shallow depths within the GHSZ, but that it is ineffective at producing high hydrate saturations throughout thick (greater than 10 m) sands buried deep within the GHSZ. Furthermore, we find that hydrate in fine-grained material can preserve high hydrate saturations in nearby thin sands with burial

Characterizing the petrophysical properties of shallow marine environments and their potential as methane hydrate reservoirs

In shallow marine sedimentary environments, characterization of sediment petrophysical and thermodynamic properties is imperative for understanding the subsurface transport of fluids and their chemical constituents. This work first presents an objective method of scanning electron microscope image analysis that directly quantifies microporosity in clay-rich, fine-grained sediments typical of the shallow marine subsurface. The method is powerful because it is fast, easy, and provides a direct microporosity estimation technique to augment or replace experimental data. When used appropriately, the method can be implemented on microporous sediments and sedimentary rock in general. With an understanding of how microporosity manifests in shallow marine sediments, the impact of small pore sizes on methane hydrate solubility is then examined for core samples taken from 3 sites in the Nankai Trough offshore Japan, an area that has been heavily surveyed in recent years for its potential to host economically recoverable deposits of methane hydrate for use as a natural gas resource. Small pores in fine-grained shaley intervals are shown to significantly increase the aqueous solubility of methane in pore water relative to surrounding coarser-grained sediment strata, which can have broad implications for methane hydrate formation, including lack of formation in the clayey intervals and strong diffusive fluxes of methane into coarser sediment layers. Finally, an existing methane hydrate reservoir simulator is modified to model methane hydrate accumulations in marine environments with heterogeneous layered sediments. The impact of pore size on solubility is included in the model along with steady state microbial methanogenesis and diffusion of salt in the pore water. The simulator is then used to successfully model methane hydrate accumulations in 1D and 2D at Walker Ridge Site 313 in the Gulf of Mexico, where well logs and seismic surveys throughout the region abound. This work is an important step in building a general 3D methane hydrate reservoir simulator for shallow marine environments around the globe.Petroleum and Geosystems Engineerin

The interdependence of lithologic heterogeneity and methane migration on gas hydrate formation in marine sediments

Despite the ubiquity of methane hydrate in the pore space of shallow marine sediments worldwide, the processes governing the transport of methane from source to reservoir are still poorly understood. Methane migration mechanisms constitute important links in the evolution of a natural gas hydrate system because they control how gas hydrate distributes in sediment pore space as well as the quantities in which gas hydrate forms. Without a thorough understanding of methane migration, it is impossible to accurately predict how a methane source interacts with a reservoir, which makes it very difficult to reliably predict where hydrate will form in a given environment. When trying to understand a gas hydrate system as a potential natural gas prospect, as a geohazard, or as an agent of global climate change, it is essential to accurately characterize the distribution and volume of hydrate present. Thus, methane migration mechanisms must be properly understood if a hydrate system is to be evaluated for any of these purposes. The work presented here develops 3D, multiphase, multicomponent fluid transport simulation software to investigate the impact of three different methane migration mechanisms on the transport dynamics and distribution of gas hydrate in marine geosystems: diffusion, short-range advection, and methane recycling. I find that the expressions of gas hydrate systems in nature are sensitive to small-scale heterogeneities in sediment lithology and capillary effects. Properties of a hydrate-bearing unit including pore size distribution, unit thickness, dip, and proximity to other layers in multilayered systems all contribute to preferential flux of methane toward and within certain hydrate-bearing sediment strata, which impact the distribution of hydrate throughout these units. When sediments are overpressured, permeability contrasts can focus methane-charged fluids along high permeability pathways and precipitate hydrate through short-range advection. Capillary phenomena can produce a region near the base of the hydrate stability zone where hydrate, water, and free gas coexist over a range of pressures and temperatures, which can drive recycling of free gas derived from dissociated hydrate back into the hydrate stability zonePetroleum and Geosystems Engineerin

Turbulence modulation by large ellipsoidal particles: Concentration effects

We use laboratory measurements to study how suspended ellipsoidal particles affect the velocity statistics of a turbulent flow. The ellipsoids have size, time, and velocity scales corresponding to the inertial subrange of the turbulence and are nearly neutrally buoyant. These characteristics make them likely candidates for two-way interactions with the fluid (i.e.; they influence the flow and are influenced by it). We vary the volume fraction of suspended ellipsoids and observe the effects on one- and two-point velocity statistics in the fluid phase. Measurements at two different heights indicate that particle buoyancy (0.5 % denser than the ambient fluid) significantly changes volume fraction. We see that particles' effect on turbulent kinetic energy is a non-monotonic function of the volume fraction. We also find that particles' presence causes a redistribution of velocity variance from large scales to small scales within the inertial subrange, i.e.; the slope of power spectra is flatter than in the single-phase case. © 2013 Springer-Verlag Wien

Burial-driven methane recycling in marine gas hydrate systems

Natural gas hydrate may be buried with sediments until it is no longer stable at a given pressure and temperature, resulting in conversion of hydrate into free gas. This gas may migrate upward and recycle back into the hydrate stability zone to form hydrate. As of yet, however, no quantitative description of the methane recycling process has been developed using multiphase flow simulations to model burial-driven gas hydrate recycling. In this study, we present a series of 1D multiphase transport simulations to investigate the methane recycling process in detail. By invoking the effects of capillary phenomena on hydrate and gas formation in pores of varying size, we find that a free gas phase can migrate a significant distance above the bulk base of hydrate stability. Since the top of the free gas occurrence is often identified as the base of the hydrate stability zone from seismic data, our results demonstrate that not only could this assumption mischaracterize a hydrate system, but that under recycling conditions the highest hydrate saturations can occur beneath the top of the free gas occurrence. We show that the presence of pore size distributions requires a replacement zone through which hydrate saturations progressively decrease with depth and are replaced with free gas. This replacement zone works to buffer against significant gas buildup that could lead to fracturing of overlying sediments. This work provides a framework for simulating flow and transport of methane within the 3-phase stability zone from a mass conservation perspective

Gas hydrate reservoirs and gas migration mechanisms in the Terrebonne Basin, Gulf of Mexico

Highlights • Identify new fine-grained hydrate filled fracture units in the Terrebonne Basin. • Identify new hydrate bearing thin sands, mostly within fractured muds. • Present detailed seismic amplitude maps of the new hydrate bearing units. • Discuss methane migration mechanisms and hydrate formation in thin sands. • Identify and discuss source-reservoir relationships between thick muds and thin sands. Abstract The interactions of microbial methane generation in fine-grained clay-rich sediments, methane migration, and gas hydrate accumulation in coarse-grained, sand-rich sediments are not yet fully understood. The Terrebonne Basin in the northern Gulf of Mexico provides an ideal setting to investigate the migration of methane resulting in the formation of hydrate in thin sand units interbedded with fractured muds. Using 3D seismic and well log data, we have identified several previously unidentified hydrate bearing units in the Terrebonne Basin. Two units are >100 m-thick fine-grained clay-rich units where gas hydrate occurs in near-vertical fractures. In some locations, these fine-grained units lack fracture features, and they contain 1–4-m thick hydrate bearing-sands. In addition, several other thin sand units were identified that contain gas hydrate, including one sand that was intersected by a well at the location of a discontinuous bottom-simulating reflector. Using correlation of well log data to seismic data, we have mapped and described these new units in detail across the extent of the available data, allowing us to determine the variation of seismic amplitudes and investigate the distribution of free gas and/or hydrate. We present several potential source-reservoir scenarios between the thick fractured mud units and thin hydrate bearing sands. We observe that hydrate preferentially forms within thin sand layers rather than fractures when sands are present in larger marine mud units. Based on regional mapping showing the patchy lateral extent of the thin sand layers, we propose that diffusive methane migration or short-migration of microbially generated methane from the marine mud units led to the formation of hydrate in these thin sands, as discontinuous sands would not be conducive to long-range migration of methane from deeper reservoirs