Estimating Pore Space Hydrate Saturation Using Dissociation Gas Evolution Measurements: In Relevance to Laboratory Testing of Natural or Artificially Synthesised Hydrate-Bearing Soil Specimens

Physical properties of gas hydrate-bearing soils are known to be greatly affected by the pore space hydrate saturation. The accuracy of most saturation estimation methods is affected by hydrate growth habit and pore space distribution. We highlight the usefulness of dissociation gas evolution measurement (DGEM) method as a reference laboratory method to calibrate most other methods. The DGEM method is based on the concept of mass balance and properties of volume compatibility between two distinct states of a closed system. The accuracy of the estimation depends on (1) the precision with which the laboratory measurements of temperature, pressure, and volumetric properties are obtained (2) and the ability of theoretical models used in the calculation to closely represent the true nature of the system. We perform an analysis to evaluate the sensitivity of the estimation (1) to various laboratory measurements and (2) to the use of different theoretical models to generate a feel for the appropriateness of various assumptions associated with DGEM. The comprehensive guide to available resources useful in the hydrate saturation estimation also serves as one of the major contributions of the work presented. 1. Introduction Gas clathrate hydrates (herein called “hydrate” or “hydrates”) are nonstoichiometric compounds of water and low molecular weight hydrocarbons. Methane is the most common form of hydrocarbon found in natural hydrate systems. Hydrates are formed as a result of encapsulation of gas molecules within parent lattices of hydrogen bonded water molecules. Since the first discovery of naturally occurring gas hydrates in the Siberian Messoyakha gas field in 1960s [1], the investigations carried out over the decades have generated evidence for abundant existence of hydrates in marine sediments as well as in on shore permafrost regions where suitable pressure/temperature ( ) conditions exist in addition to sufficient methane flux. Of interest to this communication is the pore volume fraction of given sediment occupied by hydrate (termed hydrate saturation, ) and its quantification. The role of hydrate saturation in determining the host sediment behavior is explained followed by various techniques for determination of hydrate saturation. The dissociation gas evolution measurement (DGEM) method for hydrate saturation estimation is then presented as a reference method for calibrating and overcoming the challenges associated with most other methods. The discussion then proceeds to provide leads to sources of information which are required in the determination