Effects of Confining Stress on the Semipermeability of Siliceous Mudstones: Implications for Identifying Geologic Membrane Behaviors of Argillaceous Formations

Abstract

The semipermeability arising from filtration effects on ionic species at the pore spaces in clay minerals has been recognized as a fundamental transport property of argillites. However, little is known about the dependence of the semipermeability on the confining stress that controls the pore sizes. Thus, we investigated the evolution of the semipermeability during cyclic loading by performing chemical osmosis experiments on siliceous mudstones. Results show that the semipermeability irreversibly increases with increasing confining stress, but once the stress exceeds the past maximum effective burial stress, it reversibly changes in accordance with the change in the stress. The net increase in the semipermeability from the first loading cycle to the last unloading cycle implies the irreversible shrinking of pores that should have expanded owing to stress relief before testing. The reversible change in the semipermeability probably reflects the reversible pore deformation due to the elasticity of argillites in the overconsolidated state.

Cyclic confining pressure and rock permeability: Mechanical compaction or fines migration

“…With each subsequent cycle it does not recover to the initial values and this phenomenon is also known as a permeability hysteresis [ [1] , [2] , [3] , [4] , [5] , [6] ]. According to the classical poromechanics theory, the apparent permeability degradation and hysteresis occur as a result of mechanical compaction by plastic deformations, and microcracks closure [ [7] , [8] , [9] , [10] , [11] , [12] , [13] , [14] , [15] , [16] , [17] , [18] , [19] , [20] , [21] , [22] , [23] , [24] , [25] , [26] , [27] , [28] , [29] , [30] , [31] , [32] , [33] , [34] , [35] , [36] , [37] , [38] , [39] , [40] , [41] , [42] , [43] ] which agrees well with rock mechanics [ [44] , [45] , [46] , [47] , [48] , [49] , [50] , [51] , [52] , [53] , [54] , [55] ]. In addition, during compaction, crushing of mineral grains can occur within the rocks as a result of which a certain amount of detrital material can form [ 56 ] with a size from a few microns (colloids) to tens of microns (fines) which is especially typical for higher loads.…”

Study on the Strength and Failure Characteristics of Silty Mudstone Using Different Unloading Paths

“…Moreover, Wang et al [ 10 ] analyzed how the confining pressure and unloading rate impacted crack propagation; the results indicated that under greater confining pressure, crack formation post-failure, and the rate of crack expansion, increased with higher unloading rates. Takeda et al [ 11 ] examined the semi-permeability evolution of Wakkanai mudstones during cyclic loading and unloading, emphasizing the importance of considering the applied stresses when estimating argillite semi-permeability. In response to stress evolution induced by activities such as excavation and mining, Zhang et al [ 12 ] executed a multi-level axial stress triaxial unloading test that defined the alteration law of mechanical parameters (friction, cohesion, and dilatancy angle) using an unloading factor representing rock specimen damage mechanisms.…”