基于原位溶蚀模拟实验的四川盆地二叠系栖霞组-茅口组白云岩孔隙演化

Pore evolution of the Permian Qixia-Maokou Formations dolomite in Sichuan Basin based on in-situ dissolution simulation experiment

利用水热金刚石压腔装置结合激光拉曼光谱和光学显微镜设备,实现了碳酸盐矿物/岩石-流体的原位模拟实验。结合四川盆地实际地质条件,针对栖霞组-茅口组白云岩进行了封闭-开放-封闭的连续变化体系原位模拟实验,通过乙酸酐的水解实现了封闭压腔内乙酸的原位生成。实验结果表明,封闭体系-阶段性开放体系中,碳酸盐岩样品边缘及解理处发生溶蚀,溶蚀规模与酸性流体通量有关。进入封闭体系后,溶液离子相对浓度的拉曼半定量结果显示趋于沉淀方向。实验结果结合四川盆地二叠系实际地质条件,表明川西南地区栖霞组-茅口组中粗晶白云岩晶间孔-晶间溶孔的演化符合实验模拟的封闭-开放-封闭体系,构造断裂与酸性流体对离子的搬运作用对体系内的孔隙和物质实现了溶蚀-胶结的再分配。

A hydrothermal diamond anvil cell(HDAC)equipped with a laser raman spectroscopy(LRS)and an optical microscope was used in an in-situ simulation experiment of dissolution-precipitation process between carbonate minerals(rocks)and pore fluid under continuous closed-open-closed cell(system)conditions that are typical of a deep burial process.In line with the actual geological conditions,the experiment was carried out on the Qixia-Maokou Formations dolomite samples from the Sichuan Basin and successfully generated acetic acid in closed cell through hydrolysis of acetic anhydride.The results show that dissolution occurs at the edge and cleavage of carbonate rock samples in a closed but periodically open system,and that the dissolution range is related to acid fluid flux.After entering the closed system,the relative ion concentration of solution was measured with the(semi-quantitative)Raman spectroscopy and indicates a precipitation tendency.The experimental results and the actual geological conditions of the Permian in the Sichuan Basin jointly indicate that the evolution of intergranular pores and intergranular dissolution pores of coarse-grained dolomites in the Qixia-Maokou Formations in southwestern Sichuan Basin conforms to the experimental simulation result and that transportation of ions in acidic fluids through tectonic fractures facilitates the redistribution of pores and materials through dissolution-cementation in the system.