We use the TOUGH+HYDRATE code to assess the production potential of some particularly challenging hydrate deposits, i.e., deposits that are characterized by any combination of the following factors: absence of confining boundaries, high thermodynamic stability, low temperatures, low formation permeability. Using high-resolution grids, we show that a new horizontal well design using thermal stimulation coupled with mild depressurization yields production rates that appear modest and insufficient for commercially viable production levels. The use of parallel horizontal wells (with the lower one providing thermal stimulation through heat addition, direct injection or circulation of warm water, and the upper one producing under a mild depressurization regime) offers tantalizing possibilities, and has the potential of allowing commercial production from a very large number of hydrate deposits that are not currently considered as production candidates if the problem of the corresponding large water production can be solved.

No abstract

We analyze 153 bursts of earthquakes in southern California and Japan. The burst patterns are similar in southern California and Japan; they fill a spectrum between “swarm‐like” sequences without obvious mainshocks and mainshocks with Omori‐law‐abiding aftershocks. In agreement with our previous work, the “swarm‐like” sequences in Japan have more events, are more voluminous, and tend to expand with time, when compared to “mainshock‐aftershock” type sequences. In both regions, we find that the sequences starting with their largest events tend to be much shorter in duration. Bursts within 50 km of volcanoes are similar in character to those elsewhere except they tend to have longer duration. We hypothesize that swarminess is a proxy for fluid pressure redistribution and/or aseismic slip driving the seismicity bursts, and conversely, the mainshock‐aftershock‐style sequences have end‐member behavior that results solely from a cascade of elastic failures. The complexity of the spatial seismicity distribution does not correlate with the style of swarm observed, indicating that fluid conditions and composition are likely more influential than geometry in determining the patterns we observe.

No abstract

The quantity of hydrocarbon gases trapped in natural hydrate accumulations is enormous, leading to significant interest in the evaluation of their potential as an energy source. It is known that large volumes of gas can be readily produced at high rates for long times from some types of methane hydrate accumulations by means of depressurization-induced dissociation with conventional horizontal or vertical well configurations. However, most assessments of hydrate production use simplified or reduced-scale 3D or 2D production simulations. In this study, we use the MPI-parallel TOUGH+HYDRATE code (pT+H) to make the first field-scale assessment of a large, deep-ocean hydrate reservoir. Systems of up to 2.5M gridblocks, running on thousands of supercomputing nodes, are required to simulate such large systems at the highest level of detail. The simulations begin to reveal the challenges inherent in producing from deep, relatively cold systems with extensive water-bearing channels and connectivity to large aquifers, mainly the difficulty of achieving depressurization and the problem of water production. Also highlighted are new frontiers in large-scale reservoir simulation of coupled flow, transport, thermodynamics, and phase behavior, including the construction of large meshes, the computational scaling of larger systems, and the complexity and resource-intensiveness of large-scale volume visualization of unstructured meshes.