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Title: Linking basin-scale and pore-scale gas hydrate distribution patterns in diffusion-dominated marine hydrate systems: DIFFUSION-DRIVEN HYDRATE GROWTH IN SANDS

Abstract

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 to 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 ofmore » 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. As a result, we find that hydrate in fine-grained material can preserve high hydrate saturations in nearby thin sands with burial.« less

Authors:
ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [2];  [3]; ORCiD logo [4]
  1. Department of Petroleum and Geosystems Engineering, University of Texas at Austin, Austin Texas USA
  2. School of Earth Sciences, Ohio State University, Columbus Ohio USA
  3. School of Earth Sciences, Ohio State University, Columbus Ohio USA; GEOMAR Helmholtz Centre for Ocean Research, Kiel Germany
  4. Lamont Doherty Earth Observatory of Columbia University, Palisades New York USA
Publication Date:
Research Org.:
Univ. of Texas at Austin, Austin, TX (United States)
Sponsoring Org.:
USDOE Office of Fossil Energy (FE)
OSTI Identifier:
1343742
Grant/Contract Number:
FE0013919
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Geochemistry, Geophysics, Geosystems
Additional Journal Information:
Journal Volume: 18; Journal Issue: 2; Journal ID: ISSN 1525-2027
Publisher:
American Geophysical Union
Country of Publication:
United States
Language:
English
Subject:
03 NATURAL GAS; gas hydrate; reservoir simulation; short migration; basin simulation

Citation Formats

Nole, Michael, Daigle, Hugh, Cook, Ann E., Hillman, Jess I. T., and Malinverno, Alberto. Linking basin-scale and pore-scale gas hydrate distribution patterns in diffusion-dominated marine hydrate systems: DIFFUSION-DRIVEN HYDRATE GROWTH IN SANDS. United States: N. p., 2017. Web. doi:10.1002/2016GC006662.
Nole, Michael, Daigle, Hugh, Cook, Ann E., Hillman, Jess I. T., & Malinverno, Alberto. Linking basin-scale and pore-scale gas hydrate distribution patterns in diffusion-dominated marine hydrate systems: DIFFUSION-DRIVEN HYDRATE GROWTH IN SANDS. United States. doi:10.1002/2016GC006662.
Nole, Michael, Daigle, Hugh, Cook, Ann E., Hillman, Jess I. T., and Malinverno, Alberto. Wed . "Linking basin-scale and pore-scale gas hydrate distribution patterns in diffusion-dominated marine hydrate systems: DIFFUSION-DRIVEN HYDRATE GROWTH IN SANDS". United States. doi:10.1002/2016GC006662. https://www.osti.gov/servlets/purl/1343742.
@article{osti_1343742,
title = {Linking basin-scale and pore-scale gas hydrate distribution patterns in diffusion-dominated marine hydrate systems: DIFFUSION-DRIVEN HYDRATE GROWTH IN SANDS},
author = {Nole, Michael and Daigle, Hugh and Cook, Ann E. and Hillman, Jess I. T. and Malinverno, Alberto},
abstractNote = {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 to 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. As a result, we find that hydrate in fine-grained material can preserve high hydrate saturations in nearby thin sands with burial.},
doi = {10.1002/2016GC006662},
journal = {Geochemistry, Geophysics, Geosystems},
number = 2,
volume = 18,
place = {United States},
year = {Wed Feb 01 00:00:00 EST 2017},
month = {Wed Feb 01 00:00:00 EST 2017}
}

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  • We explore the gas hydrate-generating capacity of diffusive methane transport induced by solubility gradients due to pore size contrasts in lithologically heterogeneous marine sediments. Through the use of 1D, 2D, and 3D reactive transport simulations, we investigate scale-dependent processes in diffusion-dominated gas hydrate systems. These simulations all track a sand body, or series of sands, surrounded by clays as they are buried through the gas hydrate stability zone. Methane is sourced by microbial methanogenesis in the clays surrounding the sand layers. In 1D, simulations performed in a Lagrangian reference frame demonstrate that gas hydrate in thin sands (3.6 m thick)more » can occur in high saturations (upward of 70%) at the edges of sand bodies within the upper 400 meters below the seafloor. Diffusion of methane toward the center of the sand layer depends on the concentration gradient within the sand: broader sand pore size distributions with smaller median pore sizes enhance diffusive action toward the sand’s center. Incorporating downhole log- and laboratory-derived sand pore size distributions, gas hydrate saturations in the center of the sand can reach 20% of the hydrate saturations at the sand’s edges. Furthermore, we show that hydrate-free zones exist immediately above and below the sand and are approximately 5 m thick, depending on the sand-clay solubility contrast. A moving reference frame is also adopted in 2D, and the angle of gravity is rotated relative to the grid system to simulate a dipping sand layer. This is important to minimize diffusive edge effects or numerical diffusion that might be associated with a dipping sand in an Eulerian grid system oriented orthogonal to gravity. Two-dimensional simulations demonstrate the tendency for gas hydrate to accumulate downdip in a sand body because of greater methane transport at depth due to larger sand-clay solubility contrasts. In 3D, basin-scale simulations illuminate how convergent sand layers in a multilayered system can compete for diffusion from clays between them, resulting in relatively low hydrate saturations. All simulations suggest that when hydrate present in clays dissociates with burial, the additional dissolved methane is soaked up by nearby sands preserving high hydrate saturations.« less
  • Marine pore-water sulfate profiles measured in piston cores are used to estimate methane flux toward the sea floor and to detect anomalous methane gradients within sediments overlying a major gas hydrate deposit at the Carolina Rise and Blake Ridge (U.S. Atlantic continental margin). Here, sulfate gradients are linear, implying that sulfate depletion is driven by methane flux below, rather than by the flux of sedimentary organic matter from above. Thus, these linear gradients can be used to quantify and assess in situ methane flux, which is a function of the methane inventory below. 37 refs., 3 figs.
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  • The creation of the deep-water Aleutian Basin (Bering Sea) is inextricably linked to the formation of the three co-genetic arcs that structurally frame the basin--the active Aleutian arc subduction zone (SZ), and the fossil submarine Shirshov and Bowers arcs. The origin of these arcs is tied to an early Eocene episode of accelerated tectonism and terrane movement that affected the north Pacific rim from British Columbia westward to Kamchatka. Transpressive tectonism was driven by rapid northward movement of the Kula plate into terrane-clogged SZs of southern Alaska and Kamchatka. A clogged Kamchatka SX and N-S compression of southern Alaska extrudedmore » interior Alaska southwestward along regional strike-slip shear zones toward the Beringian sector of the Pacific rim. Circum-north Pacific continental deformation transmitted shortening stresses to the adjacent Kula plate and formed the offshore family of SZs and arcs that cordoned off the Aleutian Basin from the Pacific Basin. The basin`s sedimentary sequence (4-12 km) is largely terrigenous in character, but dominantly diatomaceous deposits characterize turbidite beds that seismic relection data reveal host localized massive deposits of methane gas hydrate velocity structures termed VAMPs, which are detected at a subsurface depth of 400-500 m as anaomalous velocity pull-up domes (high velocity hydrate masses) overlying a high-amplitude BSR reflection and velocity push-down depressions below (low velocity gas). VAMPs record sealing of porous beds with hydrate deposits that block vertically migrating thermogenic gases generated from underlying Miocene and older basinal deposits. The volume of hydrated and free gas at a typical VAMP can exceed 0.3 TCF. A conservative estimate of the basin-wide ({approximately}400,000 km {sup 2}) volume of methane associated with VAMPs is 1100-900 TCF.« less