Abstract
The LArge Reservoir Simulator (LARS) was developed to investigate various processes during gas hydrate formation and dissociation under simulated in situ conditions of relatively high pressure and low temperature (close to natural conditions). To monitor the spatial hydrate distribution during hydrate formation and the mobility of the free gas phase generated during hydrate dissociation, a cylindrical Electrical Resistivity Tomography (ERT) array was implemented into LARS. The ERT contains 375 electrodes, arranged in 25 circular rings featuring 15 electrodes each. The electrodes were attached to a neoprene jacket surrounding the sediment sample. Circular (2D) dipole-dipole measurements are performed which can be extended with additional 3D cross measurements to provide supplemental data. The data quality is satisfactory, with the mean standard deviation due to permanent background noise and data scattering found to be in the order of 2.12%. The measured data are processed using the inversion software tool Boundless Electrical Resistivity Tomography to solve the inverse problem. Here, we use data recorded in LARS to demonstrate the data quality, sensitivity, and spatial resolution that can be obtained with this ERT array.
Highlights
Gas hydrates are naturally occurring crystalline solids formed from water and small gas molecules (< 1 nm)
As the four formation conditions are fulfilled at all active and passive continental margins, deep inland seas, and permafrost areas, gas hydrates exist in quantities large enough to be considered as a potential energy resource
The results show that each mineral play individual interaction with water and gas hydrate
Summary
Gas hydrates are naturally occurring crystalline solids formed from water and small gas molecules (< 1 nm). Kneafsey et al. performed experiments in a pressure vessel on sand samples using X-ray computed tomography (CT) to monitor local density changes during the formation and dissociation of methane hydrates They observed significant water migration and possible shifting of mineral grains in response to hydrate formation and dissociation, respectively. Hydrate formation, like ice formation, consumes water but excludes dissolved salt ions, meaning the electrical conductivity of the pore fluid increases with increasing hydrate saturation when using brine as a pore fluid This builds up a high resistivity contrast between the forming hydrate crystals and the remaining fluid within the pore space. This study presents a multi-electrode system composed of 375 electrodes to perform a cylindrical Electrical Resistivity Tomography (ERT) measurement to investigate the formation and dissociation of gas hydrates on a laboratory scale
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