碳酸盐岩单裂隙渗流-溶蚀耦合模型及其参数敏感性分析

Coupled fluid flow and dissolution model and associated parameter sensitivity analysis in a single carbonate rock fracture

岩溶地下水系统是由碳酸盐岩裂隙含水介质演化形成的,系统初始的裂隙网络介质特征及边界条件决定了其演化过程。为揭示岩溶系统演化过程中裂隙介质特征和边界条件的影响程度,建立了裂隙溶蚀扩展的渗流-溶蚀耦合模型,并对不同边界条件下不同隙宽的单裂隙溶蚀扩展特征进行了模拟分析。结果表明:裂隙溶蚀扩展受水的侵蚀性(CO2分压)、水动力条件(水力梯度)、裂隙介质特征(裂隙初始隙宽)等综合作用影响,Ca2+的平衡浓度、水力梯度以及裂隙初始隙宽等参数的增加均能促进裂隙的快速扩展。在这些参数中,初始隙宽B0对岩溶发育的影响最为敏感,水力梯度J和Ca2+平衡浓度Ceq对岩溶发育具有相同的敏感性;此外,随着各参数值的不断增大,参数变化对岩溶发育的敏感程度越来越低。

Karst groundwater system is evolved from fracture water bearing medium of carbonate rock; the evolution process of this system is determined by the initial fracture network characters and boundary condi tions. In order to reveal the influence degree of fracture medium and boundary conditions on the evolution of karst system, the fracture dissolution model which coupled fluid flow and dissolution was established, and the characteristics of single fracture propagation under different boundary conditions were simulated and ana- lyzed. The results show that the increase of fracture aperture due to karst water dissolution process, rise of hydraulic gradient, initial fracture aperture and equilibrium calcium concentration will accelerate the karst evolution. Among these parameters the initial fracture aperture influences the process most significantly, while hydraulic gradient and equilibrium calcium concentration have the same remarkable impact. Moreover, with the increase of the parameter values, the parameter sensitivity gets much smaller.