Interpreting temperature-strain data from mesoscale clathrate experiments

Gas hydrates may play an important role in global climate change, carbon sequestration, energy production and seafloor stability. However, formation and dissociation pathways in geologically complex systems are poorly defined. We present a new approach to processing large amounts of data from a LUNA distributed sensing system (DSS) in the seafloor process simulator (SPS) at Oak Ridge National Laboratory to monitor and visualize gas hydrate formation and dissociation in heterogeneous sediments. The DSS measures relative temperature/strain change with a high spatial resolution allowing the heat of reaction during gas hydrate formation/dissociation to be used to locate clathrate processes in space and time within the vessel. Optical fibers are placed in the sediment following an Archimedean spiral design and the position of each sensor is determined iteratively over the arc length using Newton's method. The DSS data are then gridded with a natural neighbor interpolation algorithm to allow contouring. The locations of sensors on the fiber were verified with hot and cold stimuli in known locations. Software was developed to produce temperature/strain linear and polar plots, which aid in locating significant hydrate formation/dissociation events. Results from an experiment using a vertically split column of sand and silt clearly showed initial hydrate formation in the sand, followed by slow encroachment into the silt. Similar systems and data processing techniques could be used for monitoring of hydrates in natural environments or in any situation where a hybrid temperature/strain index is useful. (C) 2011 Elsevier Ltd. All rights reserved.