Title: Physical mechanisms for multiphase flow associated with hydrate formation

Abstract

Many Arctic hydrate reservoirs such as those of the Prudhoe Bay and Kuparuk River area on the Alaska North Slope (ANS) are believed originally to be natural gas accumulations converted to hydrate accumulations after being placed in the gas hydrate stability zone (GHSZ) in response to ancient climate cooling. In this paper, the implications of a previously described mechanistic model for the transport of gaseous and aqueous phases are studied using a transient 1-D transport model during the conversion of a gas reservoir to a hydrate reservoir. The mechanistic model predicts/explains the vertical profile of hydrate saturation in “converted free gas” hydrate reservoirs. The initial gas phase saturation with depth is estimated from the profile of capillary entry pressure, which is estimated from grain size distributions measured in cores. The gas accumulation is assumed to be disconnected from its original source so that methane transport occurs only within it. As the base of the GHSZ descends through the sediment, hydrate forms within the GHSZ. The net volume reduction associated with hydrate formation creates a “sink” which drives flow of gaseous and aqueous phases to the hydrate formation zone. Mechanisms by which this fluid movement could have occurred are analyzed. Flowmore » driven by saturation gradients plays a key role in creating reservoirs of large hydrate saturations, as observed in Mount Elbert stratigraphic test well in the Milne Point Unit of Alaska North Slope (ANS). Viscous-dominated pressure-driven flow of gaseous and aqueous phases cannot explain large hydrate saturations originated from large-saturation gas accumulations. The mode of hydrate formation for a wide range of rate of hydrate formation, the rate of descent of the base of GHSZ, and host sediment characteristics are analyzed and characterized based on dimensionless groups. The proposed transport model is also consistent with field data from hydrate-bearing sand units in Mount Elbert well. Finally, results show that not only the petrophysical properties of the host sediment but also the rate of hydrate formation and the rate of temperature cooling at the surface contribute greatly to the final hydrate saturation profiles.« less

Authors:

Behseresht, Javad  ^[1];

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Bryant, Steven L. ^[2]

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1. Marathon Oil Company, Houston, TX (United States)
2. Univ. of Calgary, AB (Canada). Chemical and Petroleum Engineering Dept.

Publication Date:

Mon Apr 24 00:00:00 EDT 2017

Research Org.:

Univ. of Texas, Austin, TX (United States)

Sponsoring Org.:

USDOE Office of Fossil Energy (FE); USDOE

OSTI Identifier:

1466286

Alternate Identifier(s):

OSTI ID: 1373810

Grant/Contract Number:  

FC26-06NT43067

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Geophysical Research. Solid Earth

Additional Journal Information:

Journal Volume: 122; Journal Issue: 5; Journal ID: ISSN 2169-9313

Publisher:

American Geophysical Union

Country of Publication:

United States

Language:

English

Subject:

58 GEOSCIENCES; gas hydrate; capillary; Mount Elbert; gas hydrate stability zone (GHSZ); hydration number