Accumulation of gas hydrates in marine sediments

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dc.contributor.advisorHirasaki, George J.en_US
dc.creatorBhatnagar, Gauraven_US
dc.date.accessioned2009-06-03T19:54:32Zen_US
dc.date.available2009-06-03T19:54:32Zen_US
dc.date.issued2008en_US
dc.description.abstractGeneralized numerical models for simulating gas hydrate and free gas accumulation in marine sediments have been developed. These models include several physical processes such as phase equilibrium of gas hydrates, multiphase fluid flow in porous media, biogenic methane production, and sedimentation-compaction of sediments over geologic timescales. Non-dimensionalization of the models lead to the emergence of important dimensionless groups controlling these dynamic systems, such as the Peclet number, Damkohler number, and a sedimentation-compaction group that compares permeability to sedimentation rate. Exploring the entire parameter space of these dimensionless groups helps in delineating different modes of gas hydrate and free gas occurrence, e.g., no hydrate and hydrate with or without underlying free gas. Scaling schemes developed for these systems help in summarizing average gas hydrate saturation for hundreds of simulation results into two simple contour plots. The utility of these contour plots in predicting average hydrate saturation is shown through application to different geologic settings. The depth to the sulfate-methane transition (SMT) is also developed as an independent proxy for gas hydrate saturation for deep-source systems. It is shown through numerical modeling that scaled depth to the SMT correlates with the average gas hydrate flux through the gas hydrate stability zone (GHSZ). Later, analytical theory is developed for calculating steady-state concentration profiles as well as the complete gas hydrate saturation profile from the SMT depth. Application of this theory to several sites along Cascadia Margin indicates that SMT depth can be used as a fast and inexpensive proxy to get a first-order estimate of gas hydrate saturation, compared to expensive deep-drilling methods. The effect of overpressure development in low permeability gas hydrate systems is shown to have an important effect on gas hydrate and free gas saturations. Specifically, overpressure development decreases the net amount of gas hydrate and free gas in the system, in addition to extending the base of the hydrate stability zone below the seafloor by a relatively small depth. We also study the role of upward free gas migration in producing long, connected free gas columns beneath the gas hydrate layer. Finally, two-dimensional models are developed to study the effect of heterogeneities on gas hydrate and free gas distribution. Simulation results show that hydrate as well as free gas accumulates in relatively high saturations within these high permeability sediments, such as faults/fracture networks, dipping sand layers, and combinations of both, due to focused fluid flow.en_US
dc.format.extent266 p.en_US
dc.format.mimetypeapplication/pdfen_US
dc.identifier.callnoTHESIS CH.E. 2008 BHATNAGARen_US
dc.identifier.citationBhatnagar, Gaurav. "Accumulation of gas hydrates in marine sediments." (2008) Diss., Rice University. <a href="https://hdl.handle.net/1911/22258">https://hdl.handle.net/1911/22258</a>.en_US
dc.identifier.urihttps://hdl.handle.net/1911/22258en_US
dc.language.isoengen_US
dc.rightsCopyright is held by the author, unless otherwise indicated. Permission to reuse, publish, or reproduce the work beyond the bounds of fair use or other exemptions to copyright law must be obtained from the copyright holder.en_US
dc.subjectGeologyen_US
dc.subjectPhysical oceanographyen_US
dc.subjectChemical engineeringen_US
dc.subjectGeochemistryen_US
dc.titleAccumulation of gas hydrates in marine sedimentsen_US
dc.typeThesisen_US
dc.type.materialTexten_US
thesis.degree.departmentChemical Engineeringen_US
thesis.degree.disciplineEngineeringen_US
thesis.degree.grantorRice Universityen_US
thesis.degree.levelDoctoralen_US
thesis.degree.nameDoctor of Philosophyen_US
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