Pore-Scale Controls on Permeability, Fluid Flow, and Methane Hydrate Distribution in Fine-Grained Sediments
Permeability in fine-grained sediments is governed by the surface area exposed to fluid flow and tortuosity of the pore network. I modify an existing technique of computing permeability from nuclear magnetic resonance (NMR) data to extend its applicability beyond reservoir-quality rocks to the fine-...
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| Format: | Others |
| Language: | English |
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2012
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| Online Access: | http://hdl.handle.net/1911/64415 |
| Summary: | Permeability in fine-grained sediments is governed by the surface area exposed to
fluid flow and tortuosity of the pore network. I modify an existing technique of
computing permeability from nuclear magnetic resonance (NMR) data to extend its
applicability beyond reservoir-quality rocks to the fine-grained sediments that comprise
the majority of the sedimentary column. This modification involves correcting the NMR
data to account for the large surface areas and disparate mineralogies typically exhibited
by fine-grained sediments. Through measurements on resedimented samples composed of
controlled mineralogies, I show that this modified NMR permeability algorithm
accurately predicts permeability over 5 orders of magnitude. This work highlights the
importance of pore system surface area and geometry in determining transport properties
of porous media.
I use these insights to probe the pore-scale controls on methane hydrate
distribution and hydraulic fracturing behavior, both of which are controlled by flux and
permeability. To do this I employ coupled poromechanical models of hydrate formation
in marine sediments. Fracture-hosted methane hydrate deposits are found at many sites
worldwide, and I investigate whether pore occlusion and permeability reduction due to
hydrate formation can drive pore fluid pressures to the point at which the sediments
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fracture hydraulically. I find that hydraulic fractures may form in systems with high flux
and/or low permeability; that low-permeability layers can influence the location of
fracture initiation if they are thicker than a critical value that is a function of flux and
layer permeability; that capillary-driven depression of the triple point of methane in finegained
sediments causes hydrate to form preferentially in coarse-grained layers; that the
relative fluxes of gas and water in multiphase systems controls hydrate distribution and
the location of fracture initiation; and that methane hydrate systems are dynamic systems
in which methane flux and hydrate formation cause changes in fluid flow on time scales
of hundreds to thousands of years. My results illustrate how pore-scale processes affect
macro scale properties of methane hydrate systems and generally affect fluid flow and
transport from pore to basin scale. |
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