Mechanisms for Methane Transport and Hydrate Accumulation in Coarse-Grained Reservoirs
The distribution of natural methane hydrate within high saturation reservoirs and mechanisms that control the migration of methane are an active area of research. In this project, we studied methane migration mechanisms and associated hydrate accumulation rates in coarse-grained sands of the Terrebo...
| Main Authors: | , , , , |
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| Language: | unknown |
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2018
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| Online Access: | http://www.osti.gov/servlets/purl/1457393 https://www.osti.gov/biblio/1457393 https://doi.org/10.2172/1457393 |
| Summary: | The distribution of natural methane hydrate within high saturation reservoirs and mechanisms that control the migration of methane are an active area of research. In this project, we studied methane migration mechanisms and associated hydrate accumulation rates in coarse-grained sands of the Terrebonne Basin, located in Walker Ridge Block 313 (WR313), northern Gulf of Mexico. Hydrate in this area is distributed heterogeneously within ~900 m of methane hydrate stability zone, in both thick (10-25 m) and thin (< 3 m) sand layers, and in units of subvertical hydrate-filled fractures. We investigated hydrate formation from diffusively and advectively supplied methane using one-, two-, and three-dimensional basin modeling with inputs from well log and seismic data. The hydrate accumulations at WR313 can mostly be explained by short, diffusive migration of methane as well as short-range advective transport of methane from clays into neighboring coarser-grained layers. This is likely enhanced by small-scale lithologic variations, including local microbial methanogenesis in interbedded clays. Furthermore, our work shows overpressure in clay sediments surrounding sand reservoirs may enhance short-range diffusive migration. Long-range migration of dissolved methane and gas mainly influence hydrate saturation right at the base of the hydrate stability zone, although the dissolved phase can be channeled upwards along sands by compaction-driven flow. Capillary effects can allow gas bubbles to migrate appreciable distances above the predicted base of gas hydrate stability, possibly reaching a few tens of meters into the hydrate stability zone. Recycling methane from hydrate buried beneath the base of the hydrate stability zone can concentrate hydrate at large saturations within a few tens of meters of the base of hydrate stability. |
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