مدل سازي جريان سيال در محيط ناپيوسته ي سنگي با استفاده از شبكه ي شكستگي مجزا

Fluid Flow Modeling in Discontinuous Rock Media using a Distinct Fracture Network .

در اين نوشتار، ضمن تشريح مباني جريال سيال و روش‌هاي مدل‌سازي رفتار هيدروليك در محيط‌هاي سنگي، مطلوب‌ترين روش براي مدل‌سازي جريان سيال در محيط ناپيوسته‌ي سنگي و براي مسايل ميدان نزديك، انتخاب و توسعه داده شده است. بدين منظور، يك كد محاسباتي به نام F‌N‌E‌T‌F براي ساخت شبكه‌ي شكستگي مجزا و تحليل عددي جريان سيال در شبكه‌ي شكستگي توسعه داده شده است. در ادامه، اين كد محاسباتي با استفاده از داده‌هاي ميداني مربوط به وضعيت شكستگي‌ها و آب زيرزميني در اطراف مغار نيروگاه پروژه‌ي تلمبه‌ي ذخيره‌يي سياه‌بيشه اعتبارسنجي و درنهايت، با استفاده از اين كد محاسباتي و داده‌هاي ميداني، رفتار جريان آب ورودي به داخل مغار نيروگاه مدل‌سازي شده است. نتايج اين مدل‌سازي با نتايج ميداني تطابق خوبي را نشان مي‌دهد.

This paper presents the fundamentals of groundwater modeling in fractured media and also the technical details of a desirable modeling method in discontinuous rocks. In this paper, the modeling of fluid flow in rock mass is studied using the distinct fracture network (DFN) concept. A new computational code, ‘‘FNETF”, has been developed for generating DFN and fluid flow analysis. The FNETF computational code uses a Monte Carlo approach to generate two-dimensional discrete fracture networks, based on the statistics of the geometrical characteristics of the fracture, in terms of location in the generated region, orientation with respect to the coordinate axes, length, and aperture. In this case, individual realizations of hydraulic attribute distribution, which are formed by discrete fractures, are generated from a set of probability distributions describing the geometry of the fractures. Because the generated fractures are finite, a relatively large number of fractures in the network may not be perfectly connected and some do not contribute to the flow process. These hydraulically inactive fractures should be removed from the domain and can be recognized as isolated sub-networks, singly connected fractures, and dead end fractures, which have not complete interconnection between other percolating fractures or flow domain boundaries. Once a fracture network is regularized, a finite element mesh is generated for the percolating graphs, consisting of nodes and elements that are fracture intersections and fracture segments between nodes, respectively. The hydraulic head at each node and steady state flow rate in each element are calculated using a flow network technique, based on the mass continuity equations and cubic law. The validity of the developed computational code is explored by predicting the groundwater inflow to the powerhouse cavern of the Siahbisheh pump storage project in the North of Iran. The main input data for fluid flow modeling through a fracture network were captured from site investigation, detailed measurements of groundwater level, and geometrical characteristics of fracture. A flow domain, 122m wide and 129.75m high, was used to simulate water inflow into the Siahbisheh powerhouse cavern. The simulation of water inflow into the powerhouse cavern for 0+071 to 0+085 chainages was done using the FNETF computational code and field data. Based on direct aperture back calibration, the equivalent hydraulic aperture is considered to be 0.452mm. Comparison of results indicates that there is appropriate correspondence between inflow simulations through the DFN model and those measured. Therefore, DFN models can be utilized for fluid flow analysis in the near-field domains in discontinuous media, showing the appropriate results of rock mass hydraulic modeling.