|article dans une revue internationale avec comité de lecture|
|Song Yang; Davy Catherine A.; Bertier P.; Skoczylas Frédéric; Talandier Jean|
|Microporous and Mesoporous Materials (Microporous and Mesoporous Materials)|
|272 – 286|
|An original method for porosity assessment is proposed, which uses gas injection into dried or partially-dried claystone under hydrostatic stress. For these materials, accurate porosity assessment is complicated by the interactions of clay with water, by its crack sensitivity and by the fineness of the pores (ranging from a few nm to hundreds of nm). The hydrostatic stress limits the sample volume changes and favors crack closure. Our method is compared with water vapor equilibration or injection, with ethanol injection, and tested with two different gases (argon and helium). It is applied to COx claystone from five different cores and to a sandstone devoid of swelling clay. In addition, relative pore volumes for partially water-saturated rock are obtained. Contrarily to helium pycnometry, this method may be coupled with fluid transport assessment.
Contrarily to sandstone, a significantly greater porosity is obtained for dry COx claystone with argon gas injection, when compared to water, ethanol or helium gas. The adsorption of argon gas on the surface of clay particles is attested as the main phenomenon responsible for these differences. Hydrostatic stress, sample drying temperature (65 or 105oC) and sample thickness do not affect results significantly.
For partially water-saturated claystone, the total porosity measured by gas injection is adequate with argon or helium, but only in a given relative humidity (RH) range (RH = [0;85%] for helium, and RH = [40;75%] for argon). Argon adsorption and a limited accessibility of gas to the pore network in highly saturated medium explain these limits.
|Porosity; Claystone; Permeability; Gas adsorption; Ideal gas law|