Physical properties of sediment from the Mount Elbert Gas Hydrate Stratigraphic Test Well, Alaska North Slope

Abstract

a b s t r a c tThis study characterizes cored and logged sedimentary strata from the February 2007 BP Exploration Alaska, Department of Energy, U.S. Geological Survey (BPXA-DOE-USGS) Mount Elbert Gas Hydrate Stratigraphic Test Well on the Alaska North Slope (ANS). The physical-properties program analyzed core samples recovered from the well, and in conjunction with downhole geophysical logs, produced an extensive dataset including grain size, water content, porosity, grain density, bulk density, permeability, X-ray diffraction (XRD) mineralogy, nuclear magnetic resonance (NMR), and petrography.This study documents the physical property interrelationships in the well and demonstrates their correlation with the occurrence of gas hydrate. Gas hydrate (GH) occurs in three unconsolidated, coarse silt to fine sand intervals within the Paleocene and Eocene beds of the Sagavanirktok Formation: Unit D-GH (614.4 m-627.9 m); unit C-GH1 (649.8 m-660.8 m); and unit C-GH2 (663.2 m-666.3 m). These intervals are overlain by fine to coarse silt intervals with greater clay content. A deeper interval (unit B) is similar lithologically to the gas-hydrate-bearing strata; however, it is water-saturated and contains no hydrate.In this system it appears that high sediment permeability (k) is critical to the formation of concentrated hydrate deposits. Intervals D-GH and C-GH1 have average ''plug'' intrinsic permeability to nitrogen values of 1700 mD and 675 mD, respectively. These values are in strong contrast with those of the overlying, gas-hydrate-free sediments, which have k values of 5.7 mD and 49 mD, respectively, and thus would have provided effective seals to trap free gas. The relation between permeability and porosity critically influences the occurrence of GH. For example, an average increase of 4% in porosity increases permeability by an order of magnitude, but the presence of a second fluid (e.g., methane from dissociating gas hydrate) in the reservoir reduces permeability by more than an order of magnitude.Published by Elsevier Ltd.

X-ray computed-tomography imaging of gas migration in water-saturated sediments: From capillary invasion to conduit opening

“…[8] The porosity of the sand sample under confining stresses is 0.39 (Table 1), which is within the typical range for natural sandy sediments (0.26-0.47) at depths typical of both arctic [Winters et al, 2011] and marine [Fujii et al, 2009] gas hydrate systems. The porosity of the silt sample is 0.54, which seems to be above the usual range of porosity values for natural silt-sized sediments, although very high nominal porosity values have been reported previously for natural sediments with substantial clay-size fractions [Riedel et al, 2006].…”

Geologic controls on gas hydrate occurrence in the Mount Elbert prospect, Alaska North Slope

“…The stratigraphically highest occurrence of gas hydrate (as inferred from the CMR log data) within the D unit occurs at 614.7 m (2016.2 ft), which corresponds closely to the transition from LS II to the overlying clay-rich LS I. The overlying LS I is more than 12 m (40 ft) thick and is characterized by relatively low density porosity (27-30%) and low permeability (0.1-10 md: Winters et al, 2011).…”

“…In the following sections, log data are reviewed and compared to sediment lithologic and physical property data as reported in Rose et al (2011) and Winters et al (2011) to describe the nature of, and inferred geologic controls on, gas hydrate occurrence in both the C and D units within the Mount Elbert accumulation.…”

“…7). Nonetheless, porosity remains relatively high in the unit (w38%) with intrinsic permeabilities (defined as permeability of the reservoir with no gas hydrate present) of 100 md or more (Winters et al, 2011).…”

DEM simulations of methane hydrate exploitation by thermal recovery and depressurization methods

“…To study the dissociation process, previous in-situ tests [23,24] have only investigated the change of modulus by measuring the shear wave propagation velocities through the MHBS, while other mechanical properties, such as stress-strain relationships, could not be studied during the in-situ MH dissociation. It is not practical to carry out laboratory tests either, because the occurrence conditions of MH are too difficult to maintain and samples are easily disturbed during transportation.…”