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Title: Permeability and porosity of hydrate-bearing sediments in the northern Gulf of Mexico

Hydrate-bearing sands are being actively explored because they contain the highest concentrations of hydrate and are the most economically recoverable hydrate resource. However, relatively little is known about the mechanisms or timescales of hydrate formation, which are related to methane supply, fluid flux, and host sediment properties such as permeability. We used logging-while-drilling data from locations in the northern Gulf of Mexico to develop an effective medium theory-based model for predicting permeability based on clay-sized sediment fraction. The model considers permeability varying between sand and clay endpoint permeabilities that are defined from laboratory data. We verified the model using permeability measurements on core samples from three boreholes, and then used the model to predict permeability in two wells drilled in Walker Ridge Block 313 during the Gulf of Mexico Gas Hydrate Joint Industry Project Leg II expedition in 2009. We found that the cleanest sands (clay-sized fraction <0.05) had intrinsic (hydrate-free) permeability contrasts of 5-6 orders of magnitude with the surrounding clays, which is sufficient to provide focused hydrate formation due to advection of methane from a deep source or diffusion of microbial methane from nearby clay layers. In sands where the clay-sized fraction exceeds 0.05, the permeability reduces significantlymore » and focused flow is less pronounced. In these cases, diffusion of dissolved microbial methane is most likely the preferred mode of methane supply for hydrate formation. In conclusion, our results provide important constraints on methane supply mechanisms in the Walker Ridge area and have global implications for evaluating rates of methane migration and hydrate formation in hydrate-bearing sands.« less
Authors:
 [1] ;  [2] ;  [3]
  1. Univ. of Texas at Austin, Austin, TX (United States)
  2. The Ohio State Univ., Columbus, OH (United States)
  3. Lamont-Doherty Earth Observatory of Columbia Univ., Palisades, NY (United States)
Publication Date:
OSTI Identifier:
1223537
Grant/Contract Number:
FE0013919
Type:
Accepted Manuscript
Journal Name:
Marine and Petroleum Geology
Additional Journal Information:
Journal Volume: 68; Journal Issue: PA; Journal ID: ISSN 0264-8172
Publisher:
Elsevier
Research Org:
Univ. of Texas at Austin, Austin, TX (United States)
Sponsoring Org:
USDOE Office of Fossil Energy (FE)
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES Walker Ridge; methane hydrates; permeability; effective medium theory; Integrated Ocean Drilling Program