水岩化学作用对黑色页岩的化学损伤及力学劣化试验研究

为模拟黑色页岩化学风化中酸性水-页岩化学作用过程,本文对其进行氧化条件下的不同pH值H2SO4溶液的非平衡流动态腐蚀性试验,获得了黑色页岩化学腐蚀前后矿物变化、相对质量损失、次生孔隙率、纵波波速变化及微观结构特征的变化。通过单轴压缩试验,获得黑色页岩在不同浸泡时段的变形和强度特性规律,探讨了酸性水对黑色页岩化学作用的化学损伤和力学劣化的腐蚀效应及机制。研究表明,页岩试件在化学腐蚀后,易溶性矿物成分减小,黏土矿物增加,同时矿物胶结变得松散,矿物边缘变得模糊;页岩试件的相对质量损失与次生孔隙率随pH值减小和浸泡时间的增长而增大,而纵波波速则减小;其力学特性有从脆性破坏向延性破坏转化的趋势,单轴抗压强度和弹性模量有随pH值减小和浸泡时间的增长而减小的趋势。基于次生孔隙率,构建化学损伤变量来描述试件化学-力学损伤演化过程。分析酸性水-页岩化学作用的机理主要为:溶解作用、氧化作用、水解作用及离子交换吸附作用。

Experimental Study of Chemical Damage and Mechanical Deterioration of Black Shale Due to Water-Rock Chemical Action

In order to simulate the acidic water-rock chemical reaction process in chemical weathering of black shale, corrosion experiment was carried out by soaking black shale into H2SO4 acidic water with different pH values, under oxidation and dynamic non-equilibrium flow conditions. The change of mineralogical compositions, the relative qualities loss, the secondary porosity, and the change of longitudinal wave velocity and micro-structural characteristics of black shale before and after chemical corrosion were obtained. Through uniaxial compression experiment, the deformation and strength characteristics of black shale subjected different soaking time were also obtained; therefore, the corrosion effects, such as chemical damage and mechanical deterioration, and its mechanism were explored. Results indicate that (1) after corrosion, the soluble mineralogical composition decreases, but clay mineral composition increases; (2) the mineral cementation becomes loose and mineral edge becomes blur; (3) the relative mass loss and secondary porosity of shale specimens increase with the decrease of pH value and the increase of soaking time, but the velocity of longitudinal wave decreases with the decrease of pH value and the increase of soaking time; (4) the uniaxial compression strength and elastic modulus decrease with the decrease of pH value and the increase of soaking time. Chemical corrosion results in the transformation of brittle failure to ductile failure of black shale. Based on the secondary porosity, chemical damage variable was constructed to describe the evolution of specimens'' chemical damage and mechanical deterioration. After analysis, the main mechanisms of acidic water-black shale chemical reaction include dissolution, oxidation, hydrolysis, and ion exchange adsorption.