Experimental Study on Seepage Characteristics of Jurassic Weakly Cemented Sandstone under Water-Rock Interaction

Abstract

As unconventional water-bearing rocks, the hydraulic conductivity of weakly cemented sandstones can increase by several orders of magnitude during drainages or pumping tests, posing great challenges to water prevention and control of coal mines in northwestern China. In this study, seepage experiments on Jurassic weakly cemented sandstones were performed and the hydraulic conductivity during the seepage process was analyzed. Combined with laboratory test and theoretical analysis methods, the relation between the permeability and micropore structures was studied, and the permeability evolution mechanism of the weakly cemented sandstones was eventually clarified. According to the experimental results, the seepage process can be divided into the saturated seepage stage, the stable seepage stage, and the seepage mutation stage. The hydraulic conductivity increases as the porosity and the mercury extrusion rate increase, but there is no obvious correlation between them that can be identified. In contrast, there is a linear positive correlation between the hydraulic conductivity and the average pore-throat radius. The variation trend of the pore-throat ratio can be used as the main reference indicator for judging whether the seepage mutation occurs in weakly cemented sandstone. Based on the correlation analysis of micropore structures and the hydraulic conductivity, a seepage model of straight capillary was constructed and the theoretical permeability equations of stable seepage stage and seepage mutation stage were proposed. It is concluded that the specific permeability of weakly cemented sandstones is directly proportional to porosity and the square of the average pore-throat radius. A theoretical equation to calculate the specific permeability during the latter two stages was also presented in this paper. Theoretical calculation results are roughly consistent with actual values obtained in the experiments.

Mechanical Properties of the Hard Sandstone Fracture Surface under Hydrochemical Corrosion

“…Strength. Appropriate damage variables should be selected to study the damage and describe the influence of damage state change and its influence on the mechanical characteristics of specimens, and appropriate state variables are selected from microscopic and macroscopic angles in common definitions of damage variables [14,18,19]. The porosities of rock specimens relatively increased after corrosion using hydrochemical solution, and the internal pore structure also changed.…”

“…where 0 is initial porosity and is porosity after corrosion. Li Peng [14] obtained linear relations of damage variables with cohesive force and internal frictional angle through regression analysis. When the normal force is fixed, the shear strength of the fracture surface is related to damage variables.…”

“…Chemical composition had controlling effect on crack propagation, and ductile damage value under wet conditions was lower and with faster crack propagation than that under dry conditions. Li Peng [14] carried out shear strength tests under different erosion conditions using solutions and analyzed the influence of action on sandstone microstructure. The chemical kinetics method was used by introducing rock hydrochemical damage degree to simulate the time-dependent process of sandstone damage degree under given hydrochemical environmental conditions to predict evolution laws of its shear strength.…”

Experimental Study of the Pore Structure Deterioration of Sandstones under Freeze‐Thaw Cycles and Chemical Erosion

“…Corrosion due to hydrochemical solutions can cause changes in mineralogical composition and structure of rocks leading to the transformation of the physical mechanical properties of rocks. erefore, the hydrochemically altered state of rock can pose a great threat to the long-term stability of rock engineering structures [1,2]. e chemical elements in solution can drive the expansion of cracks and the rate of the crack expansion.…”

Mechanical Properties of Tonalite Subjected to Combined Effects of Chemical Corrosion and Freeze-Thaw Cycles

“…Some research has focused on the changes in physical characteristics and micro-mechanical properties of rock subjected to chemical corrosion. The mechanical properties have been investigated using the uniaxial compression test, tri-axial compression test and direct shear test [21][22][23][24][25][26][27].…”