Permeability identification of a weakly permeable partially saturated porous rock

Abstract

The present paper deals with the determination of permeability in partially saturated conditions for weakly permeable porous continua such as argillites or deep clayey formations. The permeability can be deduced from measurements of transient weight loss of a sample submitted to a laboratory drying test: a decrease of relative humidity is imposed by saline solution in an hermetic chamber. Assumptions of constant gas pressure equal to atmospheric pressure and of negligible Fickean diffusive transport of vapour are adopted. The only transport phenomenon taken into account inside the sample is the Darcean advective transport of the water liquid. The forward problem is solved by following two modelling approaches: a linear one and a nonlinear one. The parameter identification procedure is based upon the solution of corresponding inverse problems. In the two cases, the Levenberg-Marquardt algorithm has been used for the minimization problem. In the linear approach, the solution of the forward problem is explicit. In the non linear approach, finite volume method for the spatial discretization combined with a Newton-Raphson algorithm has been used to solve the non linear forward problem. The identification method enables variations of permeability and capillary capacity to be estimated. Comparisons between linear and non linear approaches show that the first one is useful to give mean values and order of magnitude of permeability and capacity. A more complete information is deduced from the non linear approach as variations of equivalent capacity and permeability during a test are significant in most cases. The analysis of the obtained results shows that the basic modelling assumption of constant gas pressure inside the sample would not be relevant for lower range of relative humidities and liquid permeability than those investigated.

Hydromechanical behavior of Tournemire argillites: Measurement of the poroelastic parameters and estimation of the intrinsic permeability by œdometric tests

“…Different kinds of identification methods can be used in geomechanics, a review of which can be found in Gioda et al [32]. Owing to the time required for one simulation deterministic methods such as the gradient-based methods [33,34], which consist of minimizing a cost-functional by calculating its gradient, seem to be well adapted in the case of the oedometric test. However, there are problems of local minima with these methods which means that the initial set of parameters (i.e.…”

Study of the soil–atmosphere moisture exchanges through convective drying tests in non‐isothermal conditions

“…Several experimental methods exist in order to reproduce such conditions. The saturated saline solution method is used to impose the relative humidity in a hermetic chamber [6,17] where the sample is lying. In a convective drying device, the relative humidity and the wind velocity are imposed through the convection of a humid air around the material [14].…”

“…Inverse method allows determining the relative permeability evolution from the weight loss measurements of samples submitted to a decrease in relative humidity [5][6][7][8]. Moisture is actually removed from the materials through the water evaporation occurring at the surface of the sample.…”

“…The first way to analyse experimental convective drying data is based on the sample weight loss evolution with the drying time, for stable drying conditions [6,12,15]. This classical curve, mainly used for the study of the drying kinetic, emphasizes different drying periods depending on the shape of the curve: a linear evolution during a first period and a non-linear one for a second period of drying.…”

“…Drying experiments are frequently performed on porous medium samples at ambient temperature [5][6][7][8]. Moisture is removed from materials through evaporation occurring at the sample surfaces.…”