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摘要:
研究表明碳酸盐岩的溶蚀过程可用溶解速率方程进行表征，但表征的形式存在较大差别，主要体现在远离平衡的欠饱和态下。为进一步确定碳酸盐岩在欠饱和态下的溶解特征及溶蚀速率的表征形式，首先开展了碳酸盐岩裂隙溶蚀试验研究，探讨了CO2及溶液初始Ca2+浓度对溶蚀过程的影响，并基于试验结果构建了欠饱和态下的溶解速率方程；而后采用碳酸盐岩裂隙渗流-溶解耦合模型，通过数值模拟对量化模型的参数进行率定和检验。结果表明：（1）CO2的参与加快了碳酸盐岩的溶蚀扩展，溶液初始Ca2+浓度越高，对碳酸盐岩的溶解抑制程度就越高；（2）CO2作用下碳酸盐岩裂隙溶蚀扩展的平均溶蚀速率增加了1.82～2.29倍；（3）溶液不同初始Ca2+浓度在同等区间流量条件下，蒸馏水为溶蚀溶液的样品中Ca2+浓度差值下降了0.0915 mmol/L，溶液初始Ca2+浓度为0.352，0.476，0.581 mmol/L的溶蚀溶液中，Ca2+浓度差值分别下降了0.0742，0.0536，0.0474 mmol/L；（4）在高度欠饱和状态下溶解动力学由线性速率定律控制，随着溶液中Ca2+浓度的升高，溶解动力学将变为非线性关系，此时Ca2+浓度为0.4倍的平衡时Ca2+浓度。研究结果可为定量评价岩溶发育演化提供数据支撑。
Abstract:Previous researches show that the dissolution of carbonate rocks can be characterized by dissolution rate equation, but the form of characterization is quite different, which is mainly reflected in the undersaturated state far from equilibrium. In order to further determine the dissolution characteristics of carbonate rocks in the undersaturated state and the characterization form of dissolution rate, first of all, the fracture dissolution test of carbonate rocks was carried out, and the influence of CO2 partial pressure and initial concentrations of Ca2+ on dissolution was discussed. Based on the test results, the dissolution rate equation in the undersaturated state was constructed. Then, the carbonate rock fracture seepage dissolution coupling model was used, calibrating and verifying the parameters of the quantitative model through numerical simulation. The results indicate that: (1) The participation of CO2 accelerates the dissolution expansion of carbonate rocks, and the higher the initial Ca2+ concentration of the solution, the higher the degree of dissolution inhibition of carbonate rocks. (2) The average dissolution rate of carbonate rock fractures under the action of CO2 increased by 1.82−2.29 times. (3) Under the same interval flow rate conditions for different initial Ca2+ solutions, the difference of Ca2+ concentration in distilled water decreased by 0.0915 mmol/L, and the initial Ca2+ concentration of 0.352, 0.476, 0.581 mmol/L decreased by 0.0742, 0.0536, 0.0474 mmol/L, respectively. (4) The dissolution kinetics is controlled by the linear rate law under the highly undersaturated state. With the increase of the concentration of Ca2+ in the solution, the dissolution kinetics becomes nonlinear, and the threshold of Ca2+ concentration between the two is 0.4 times the saturated of Ca2+ concentration. The study provides a reference for quantitative evaluation of karst development and evolution.
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Key words:
- dissolution widening /
- dissolution rate /
- undersaturation /
- carbonate rock /
- dissolution kinetics
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