侵蚀性流体作用下石灰岩渗透性变化规律

Limestone permeability evolution under the infiltration of erosion fluid

为研究侵蚀性流体渗透过程中完整石灰岩石渗透性的变化规律,设计3组不同的渗透溶液化学侵蚀条件和应力条件下的石灰岩芯渗透实验,通过测量每种工况下不同时刻渗出液流量、渗出液中含有的离子浓度等数据,分析完整石灰岩渗透特性的主要影响因素和演化机理。实验结果表明:渗透液体侵蚀和应力施加对岩石渗透性演变存在不同作用。由于加压(围压、轴压、渗透压)对岩芯渗透性具有时效性,在实验初期(0~50 h)3种工况下岩芯渗透率都急剧下降,应力作用是引起岩石渗透率变化的主要因素;随着实验过程的进展,岩芯内部孔隙喉道逐渐闭合,大约50 h之后,渗透流体的化学侵蚀作用开始显现,在之后的330 h中,渗透液为蒸馏水时岩芯渗透率基本趋于稳定,渗透溶液为p H=6的硫酸钠溶液或硫酸溶液时岩芯渗透率则持续下降,表明实验后期渗透液的化学侵蚀作用对岩芯渗透率演变起主要作用。3种工况实验过程中岩芯渗出液中始终有离子溶出,但是不同的渗透液体对岩芯矿物质的溶解效果有差异,显著改变渗出液的离子浓度和离子浓度比值。当渗透溶液中存在促进矿物质溶解的成分并且渗透压力较小时,渗透液中离子逐渐积累变多但不能及时被运移到岩芯外,从而可能产生沉淀堵塞岩芯渗透通道。实验过程中,完整石灰岩石渗透性的演变特性是渗透溶液的侵蚀作用、应力作用和溶质运移沉淀共同作用的结果。

In order to study the complete limestone rocks＇permeability evolution law during the process of erosive fluid infiltration, three different penetrant experiments of the limestone core under the conditions of chemical erosion and stress of the infiltration solution were designed. By measuring the flow rate of ex- udate and the ion concentration contained in the exudate at different times in each working condition, the main influencing factors and evolutionary mechanism of the complete limestone permeability were ana- lyzed. The experimental results show that the infiltration of liquid and the application of stress have di- verse effects on the evolution of rock permeability. At the beginning of the experiment （0 - 50 h） , since the pressurization （surrounding pressure, axial pressure, osmotic pressure） has a time -dependent permeability to the core, the core permeability decreased sharply under the three conditions, and stress effect was the main factor that caused the change of rock permeability. As the experimental process pro- gresses, the pore throat inside the core gradually closes. The chemical erosion of the permeable liquid be- gan to appear after about 50 h. In subsequent 330 h, the permeability of the core was basically stable if penetrant was distilled water. When the permeation solution was sodium sulfate solution or sulfuric acid solution with pH = 6, the core permeability decreased continuously which indicated that at the end of the experiment chemical erosion played a key role in the evolution of core permeability. In the three working conditions, ion dissolution happened in the core exudate all the time, but different permeation liquids had different dissolution effects on the minerals of the core, with significant changes in exudates of ion con- centration and ion concentration ratio. When there were components promoting the dissolution of the min- eral and a low osmotic pressure in the permeate solution, the ions gradually accumulated but cannot be transported out of the core in time, which caused precipitation to block the core permeation channel. During the experiments, the evolution of permeability of the complete limestone is a result of the com- bined action of erosion of the permeate solution, stress interaction and the solute precipitation.