Formation history and physical properties of sediments from the Mount Elbert Gas Hydrate Stratigraphic Test Well, Alaska North Slope

Sheng Dai, Changho Lee*, Juan Carlos Santamarina

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

54 Scopus citations

Abstract

The synthesis of available geological information and surface temperature evolution in the Alaska North Slope region suggests that: biogenic and deeper thermogenic gases migrated through fault networks and preferentially invaded coarse-grained layers that have relatively high hydraulic conductivity and low gas entry pressures; hydrate started forming before the beginning of the permafrost; eventually, the permafrost deepened and any remaining free water froze so that ice and hydrate may coexist at some elevations. The single tested specimen (depth 620.47-620.62 m) from the D unit consists of uncemented quartzitic fine sand with a high fraction of fines (56% by mass finer than sieve #200). The as-received specimen shows no evidence of gas present. The surface texture of sediment grains is compatible with a fluvial-deltaic sedimentation environment and shows no signs of glacial entrainment. Tests conducted on sediments with and without THF hydrates show that effective stress, porosity, and hydrate saturation are the major controls on the mechanical and geophysical properties. Previously derived relationships between these variables and mechanical/geophysical parameters properly fit the measurements gathered with Mount Elbert specimens at different hydrate saturations and effective stress levels. We show that these measurements can be combined with index properties and empirical geomechanical relationships to estimate engineering design parameters. Volumetric strains measured during hydrate dissociation vanish at 2-4. MPa; therefore, minimal volumetric strains are anticipated during gas production at the Mount Elbert well. However, volume changes could increase if extensive grain crushing takes place during depressurization-driven production strategies, if the sediment has unexpectedly high in situ porosity associated to the formation history, or if fines migration and clogging cause a situation of sustained sand production.

Original languageEnglish (US)
Pages (from-to)427-438
Number of pages12
JournalMarine and Petroleum Geology
Volume28
Issue number2
DOIs
StatePublished - Feb 1 2011

Keywords

  • Conductivity
  • Gas hydrate
  • Gas production
  • Mount Elbert
  • Permafrost
  • Permittivity
  • Seismic waves
  • Stress-volume response

ASJC Scopus subject areas

  • Oceanography
  • Geophysics
  • Geology
  • Economic Geology
  • Stratigraphy

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