| For fractured rock masses commonly found in rock engineering,the internally developed fracture network is the main channel for water and other fluid flows.The underground water-sealed oil storage is a typical rock engineering that uses groundwater flow to realize its function.The analysis accuracy of flow field is demanded to be high.The study of fluid flow characteristics has a very important and direct effect on the performance evaluation of the storage.At the same time,it is of great significance for water conservancy and hydropower,underground disposal of nuclear waste,geotechnical environmental protection and other major projects.Also,the commonly used linear fracture flow theory is difficult to apply in complex rock mass fracture networks under high hydraulic gradients for many engineering practices.The nonlinear flow of the fracture network has become one of the key research topics in the fields of rock mechanics and hydrogeology.In this paper,the rock fracture network is divided into single fractures and intersecting fractures.The non-linear characteristics of fraracture flow are comprehensively analyzed by means of laboratory experiment,theoretical analysis and numerical simulation.In this paper,a non-linear flow calculation model of intersecting fracture is proposed,and the nonlinear flow calculation method of fracture network is applied and verified.The major results of this study are summarized below:(1)The influence of roughness on single fracture flow was studied,and a single fracture flow model considering roughness was established.The fracture flow test instrument was customized,and 9 rough single fracture models were fabricated by 3D printing technology.The flow experiments of different rough single fractuers under large Reynolds number conditions were carried out.The linear flow model of single fracture was deduced and analyzed,and the applicable conditions of the linear seepage model were explained theoretically.The nonlinear characteristics of rough single fracture flow with different geometrical parameters were analyzed and compared,and the relations between non-Darcy coefficient P,critical Reynolds number Rec and roughness,and the variation characteristics of non-Darcy effect factor E and friction factor λ were obtained.(2)A non-linear flow calculation model for intersecting fracture was proposed.Taking the influence range of intersecting fractuer as the research object,considering the intersecting-angle,aperture and roughness of intersection,a non-linear flow calculation model of typical intersecting fractuers was proposed and verified by numerical simulation,which provided a general theoretical method for the study of non-linear flow characteristics of intersecting fractures.The model was unified in form and simple in structure,which was convenient for summarizing and comparing the flow characteristics of different intersecting fracture cases.The characteristics of critical Reynolds number and microscopic flow structure of intersecting fracture non-linear flow were further studied.(3)The parametric expressions of non-linear flow calculation model for intersecting fracture were obtained.The intersecting fracture cases with different characteristics were set,and the variation of nonlinear parameters in calculation model was compared and analyzed.The parametric expressions of non-linear flow calculation model with respect to the intersecting fracture characteristics were obtained and verified by combined cases.(4)The nonlinear flow calculation method for two-dimensional discrete fracture network was applied and verified.Based on the study of flow characteristics of single fracture and nonlinear flow calculation model of intersecting fracture,the nonlinear flow calculation method of discrete fracture network was applied to analyze the flow calculation of fracture network and a case study on containment properties of underground oil storage.The feasibility and accuracy of the nonlinear flow calculation method for fracture network were verified by comparison with different methods such as numerical simulation.It was shown that the influence of intersecting fracture and the nonlinear characteristics of fracture network flow should be considered in the flow analysis of fracture network. |
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