Modeling Fluid Flow Effects on Shallow Pore Water Chemistry and Methane Hydrate Distribution in Heterogeneous Marine Sediment

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dc.contributor.advisor Hirasaki, George J.
dc.contributor.advisor Chapman, Walter G.
dc.creator Chatterjee, Sayantan 2012-09-06T04:17:20Z 2012-09-06T04:17:26Z 2012-09-06T04:17:20Z 2012-09-06T04:17:26Z 2012-05 2012-09-05 May 2012
dc.description.abstract The depth of the sulfate-methane transition (SMT) above gas hydrate systems is a direct proxy to interpret upward methane flux and hydrate saturation. However, two competing reaction pathways can potentially form the SMT. Moreover, the pore water profiles across the SMT in shallow sediment show broad variability leading to different interpretations for how carbon, including CH4, cycles within gas-charged sediment sequences over time. The amount and distribution of marine gas hydrate impacts the chemistry of several other dissolved pore water species such as the dissolved inorganic carbon (DIC). A one-dimensional (1-D) numerical model is developed to account for downhole changes in pore water constituents, and transient and steady-state profiles are generated for three distinct hydrate settings. The model explains how an upward flux of CH4 consumes most SO42- at a shallow SMT implying that anaerobic oxidation of methane (AOM) is the dominant SO42- reduction pathway, and how a large flux of 13C-enriched DIC enters the SMT from depth impacting chemical changes across the SMT. Crucially, neither the concentration nor the d13C of DIC can be used to interpret the chemical reaction causing the SMT. The overall thesis objective is to develop generalized models building on this 1-D framework to understand the primary controls on gas hydrate occurrence. Existing 1-D models can provide first-order insights on hydrate occurrence, but do not capture the complexity and heterogeneity observed in natural gas hydrate systems. In this study, a two-dimensional (2-D) model is developed to simulate multiphase flow through porous media to account for heterogeneous lithologic structures (e.g., fractures, sand layers) and to show how focused fluid flow within these structures governs local hydrate accumulation. These simulations emphasize the importance of local, vertical, fluid flux on local hydrate accumulation and distribution. Through analysis of the fluid fluxes in 2-D systems, it is shown that a local Peclet number characterizes the local hydrate and free gas saturations, just as the Peclet number characterizes hydrate saturations in 1-D, homogeneous systems. Effects of salinity on phase equilibrium and co-existence of hydrate and gas phases can also be investigated using these models. Finally, infinite slope stability analysis assesses the model to identify for potential subsea slope failure and associated risks due to hydrate formation and free gas accumulation. These generalized models can be adapted to specific field examples to evaluate the amount and distribution of hydrate and free gas and to identify conditions favorable for economic gas production.
dc.format.mimetype application/pdf
dc.language.iso eng
dc.subject Gas hydrate
marine sediment
continental slopes
focused fluid flow
lithologic heterogeneity
local fluid flux
sulfate‐methane transition
anaerobic oxidation of methane
organoclastic sulfate reduction
numerical modeling
dc.title Modeling Fluid Flow Effects on Shallow Pore Water Chemistry and Methane Hydrate Distribution in Heterogeneous Marine Sediment
dc.contributor.committeeMember Zygourakis, Kyriacos
dc.contributor.committeeMember Dickens, Gerald R.
dc.contributor.committeeMember Dugan, Brandon 2012-09-06T04:17:26Z
dc.identifier.slug 123456789/ETD-2012-05-126
dc.type.genre thesis
dc.type.material text Chemical and Biomolecular Engineering Chemical and Biomolecular Engineering Rice University Doctoral Doctor of Philosophy
dc.identifier.citation Chatterjee, Sayantan. (2012) "Modeling Fluid Flow Effects on Shallow Pore Water Chemistry and Methane Hydrate Distribution in Heterogeneous Marine Sediment." Doctoral Thesis, Rice University.

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