Mechanisms for methane transport and hydrate accumulation in coarse-grained reservoirs

Hugh Daigle in collaboration with Kishore Mohanty, Steven Bryant, Alberto Malinverno (Lamont-Doherty Earth Observatory, Columbia University) and Ann Cook (School of Earth Sciences, Ohio State University), with PhD Student Michael Nole (UT PGE)


Migration mechanisms in marine hydrate reservoirs represent some of the least understood processes in hydrate systems, but at the same time represent a crucial link between sites of methane generation and hydrate reservoirs.

We investigate the hypothesis that the transport of methane, and the mechanism by which it is transported, are the primary controls on the development of persistent, massive hydrate accumulations in deep sediments below the seabed. Several methane (circles) migration mechanisms are associated with the development and persistence of massive hydrate deposits (squares). Short migration of dissolved microbial methane moves methane from fine-grained (brown) layers into adjacent coarser-grained (yellow) layers to form hydrate. Long migration of dissolved methane moves methane from some distance into the MHSZ. Methane migration in free gas phase can move methane around within the methane hydrate stability zone (MHSZ), either locally produced in fine-grained units or through fractures connected to the base of the MHSZ where gas may accumulate as hydrate-bearing units are buried, or updip from the base of the MHSZ within a coarse-grained unit.

Massive hydrate deposits, defined as thick accumulations of high hydrate saturation, have been encountered in many regions worldwide. We focus specifically on accumulations found at Walker Ridge Block 313 in the northern Gulf of Mexico during Gulf of Mexico Gas Hydrate Joint Industry Project Leg 2. Hydrates may be thought of broadly within a petroleum systems framework, requiring a methane source, migration mechanisms, a reservoir, and an appropriate seal.

Hydrate reservoirs and seals are defined by thermodynamics rather than by buoyancy, as in the case of conventional oil and gas. Hydrates form most easily within coarse-grained sediments within the methane hydrate stability zone (MHSZ), the depth interval in which pressure and temperature favor hydrate as the stable phase. Methane sources may include microbial activity as well as thermogenic sources.

In this proposed research, we focus on migration mechanisms in marine hydrate reservoirs as they represent some of the least understood processes in hydrate systems, but at the same time represent a crucial link between sites of methane generation and hydrate reservoirs.

The objectives of this research are to define:
    1. The dissolved methane flux, organic matter abundance, and time required to develop the accumulations observed at Walker Ridge Block 313 by short-distance migration of methane into adjacent coarser-grained layers;
    2. The dissolved methane flux and time required to develop the accumulations observed at Walker Ridge Block 313 by long-distance, updip migration;
    3. Whether there is enough methane in the dissolved phase in the fine-grained sediments to form the observed hydrate deposits or whether a gas phase is present, and if so what the conditions are     for three-phase equilibrium;
    4. The fate of hydrate that subsides beneath the base of the MHSZ, gas accumulation below the base of the MHSZ, and overpressure generation associated with gas accumulation.

Mechanisms for methane transport and hydrate accumulation in coarse-grained reservoirsIllustration of methane (circles) migration mechanisms associated with development and persistence of massive hydrate deposits (squares). Yellow layers represent coarser-grained units; brown represents finer-grained, clay-rich units. Short migration of dissolved microbial methane moves methane from fine-grained layers into adjacent coarser-grained layers to form hydrate. Long migration of dissolved  methane moves methane from some distance into the MHSZ. Methane migration in free gas phase can move methane around within the MHSZ, either locally produced in fine-grained units or through fractures connected to the base of the MHSZ where gas may accumulate as hydrate-bearing units are buried, or updip from the base of the MHSZ within a coarse-grained unit.

Research supported by the Research Partnership to Secure Energy for America/United States Department of Energy
For more information, please contact: Hugh Daigle (hugh_daigle@mail.utexas.edu)