|Mechanisms for Methane Transport and Hydrate Accumulation in Coarse-Grained Reservoirs
||Last Reviewed 6/24/2014
The project goal is to evaluate whether the transport of methane, and the specific mechanism by which it is transported, are the primary controls on the development of persistent, massive hydrate accumulations in sediments below the seabed. The dissolved methane flux and time required to develop the accumulations observed at WR 313 by long-distance updip migration or by short-distance local migration will be studied and defined within the scope of this research. Researchers will also determine 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.
University of Texas at Austin, Austin, TX 78713-7726
Ohio State University, Columbus, OH 43210
Lamont-Doherty Earth Observatory (Columbia University), Palisades, NY 10964
Massive hydrate deposits, defined as thick (>5 feet) accumulations of high hydrate saturation (>50 percent), have been encountered in many regions worldwide. This project will focus specifically on accumulations found at Walker Ridge Block 313 in the northern Gulf of Mexico during the 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 buoyancy as in the case of conventional oil and gas. Hydrates form most easily within coarse-grained sediments within the methane hydrate stability zone, 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. The focus will be 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 methane generation sites and hydrate reservoirs.
Successful completion of this project will provide valuable insight into conditions necessary for the development of massive gas hydrate accumulations and the role of free gas in their persistence. This, in turn, will advance understanding of the transport and fate of methane in the subsurface; carbon cycling associated with hydrates; and role of a free gas phase in the formation and persistence of hydrate deposits.
Preliminary 1-D modeling work has shown that short migration may only be a feasible mechanism of generating massive hydrate deposits when the ratio of the coarse-grained layer thickness to the fine-grained layer thickness is smaller than some threshold. This threshold is a function of microbial methanogenesis rates and local solubility conditions and is therefore site-specific. These results were presented at the Gordon Research Conference on Natural Gas Hydrate Systems in March 2014.
Detailed petrophysical analysis has shown that pore size may be determined by a simple relationship involving resistivity and porosity. This is an important development because it will allow us to determine pore size and methane equilibrium conditions in the Walker Ridge area. These results were presented at the Offshore Technology Conference in May 2014 (paper OTC 25252) and the 6th International Conference on Porous Media (Interpore) in May 2014.
Current Status (June 2014)
Reservoir model development and 1-D modeling of microbial methanogenesis is ongoing. The reservoir model is being updated to include the salinity effect, microbial methanogenesis, and sedimentation components. Researchers are assessing reservoir geometry by analyzing 3-D seismic data recently collected by the U.S Geological Survey. They have also developed a 1-D reaction-transport model to analyze microbial methanogenesis and hydrate formation in a subsiding coarse-grained layer, the results of which will be used to constrain methanogenesis rates in the reservoir model.
Project Start: October 1, 2013
Project End: September 30, 2017
Project Cost Information:
DOE Contribution: $1,679,137
Performer Contribution: $448,001
NETL – John Terneus (John.Terneus@netl.doe.gov or 304-285-4254)
University of Texas at Austin – Hugh Daigle (firstname.lastname@example.org or 512-471-3775)