Influence of Hydrate- and Ice Formation on the Gas Permeability of Modelling Unconsolidated Reservoirs

The change in gas permeability during phase transitions of pore moisture into ice and hydrate of model unconsolidated reservoirs, represented by sandy-argillaceous rocks has been carry out in the course of experimental modeling. For experiments a complex technique developed by the authors for studying the gas permeability of rocks under conditions of hydrate and ice saturation has been used. Result of the experimental work has been presented that the decrease in gas permeability of sandy rocks during freezing is significantly influenced not only by the quantity, but also by the mineral composition of the clay component. For samples containing clay particles of kaolinite composition, permeability decreased more strongly than for samples with bentonite particles, both in frozen and thawed state. Thus, with an increase in the content of kaolin from 0 to 7%, the permeability of frozen samples decreased almost 14-fold, and when 7% of bentonite was added, the permeability decrease was less than 1.5 times. Hydrate formation of silty-sand rocks at a given moisture content (W = 14–18%) revealed that the gas permeability decreased by 1–2 orders of magnitude with the transition to 70–80% of pore moisture to hydrate. When hydrate-saturated samples freezed, their gas permeability is further reduced several times or more. This is due to the freezing out of residual pore moisture, as well as additional hydrate formation during water-ice phase transitions.