단열암반층에서 단열 및 수리 특성과 지하수 유동차원과의 상관성 연구

Abstract

When evaluating the flow dimensions of the groundwater in the fractured rocks, the data from the pumping test are used as important flow dimension parameters. Recently, a method to determine the groundwater flow dimension with the generalized radial flow (GRF) model (Barker, 1988) was developed, But it is hard to conceptualize the flow model for the non-integer flow dimension. So, fractional flow dimension, which appears as characteristic flow patterns displayed by the drawdown derivative data, is important because a flow dimension is the geometry of the flow streamlines in the fractured rocks. In particular, this study used the drawdown derivative formulated by Bourdet's (1983) and Spane & Wurstner's (1993) methods in order to interpret diverse flow dimensions based on the drawdown data from the pumping test. Since the slope of drawdown derivative appears as the fractional flow dimension, diverse fractional flow dimensions in the fractured rocks were easily interpreted by modified flow regime identification (MFRID) and flow type curve match (FTCM) method. In an attempt to analyze the correlation of groundwater flow dimensions with fracture density and hydraulic properties, this study analyzed the data about fracture dimension (Cantor dust method), fracture orientation, step drawdown and constant rate pumping tests and borehole logging. Analyses of fracture dimension using Cantor Dust method (fracture density) and fracture orientation were used to interpret density and connectivity of fracture in both single and double wells. As a result, SB-2 well (8.290) showed high connectivity of fracture in general, while the other pumping and observation wells were well connected only at the upper intervals. In addition, this study utilized the FASTEP program to calculate aquifer loss, well loss and its exponentials in real numbers in the step-drawdown test. As a result, the well loss exponentials ranged from 2.390 to 8.290. The large drawdown of 64.2m at the interval of step 5 for CBP-2 well (8.290) was found to reduce fracture and cause hydraulic head loss by turbulent flow. In interpretation of the flow dimensions with the data from the constant rate pumping tests (CBP-2, PBP-1), 1.0～1.9 dimension accounted for 61.54%, 2.0 dimension accounted for 3.84% and 2.1～3.0 dimension accounted for 34.62%. In the case of the step-drawdown test, 1.0～1.9 dimension stood at 53.01%, 2.0 dimension stood at 9.64% and 2.1～3.0 dimension stood at 37.35%. In other words, 1.0～1.9 dimension was as much as 8.53% higher in constant rate pumping test than step-drawdown test. This study also analyzed well reservoir effect, dual-porosity, channeling and constant head interval occurring at the pumping late times, permeable and impermeable interval, flow pattern of pseudo-steady state, and the like. Furthermore, this study found out that MFRID and FTCM are useful to analyze the flow dimension in comparatively analyzing the borehole logging. With a view to analyzing the correlation of groundwater flow dimensions with fracture density and hydraulic properties, this study comparatively analyzed scale dependency effect of hydraulic conductivity, flow dimensions and patterns, fracture and flow dimensions, and specific capacity and flow dimensions. As a result, groundwater flow dimensions differed much depending on the secondary porosity and heterogeneity of fracture. When the fracture rock layer was more heterogeneous, 1.0～1.9 dimension took 68.75～83.33% (CBP-1, PBP-1). On the other hand, when the fracture rock layer was less heterogeneous, 2.0～3.0 dimension made up 60% due to development of the secondary porosity. From the comparative analyze of flow dimensions and patterns, and specific capacity and flow dimensions, it was found that 1.0～1.9 dimension prevailed at the intervals with smaller specific capacity, while 2.0～3.0 dimension prevailed at the intervals with larger specific capacity. Besides, dual-porosity patterns and channeling were observed. Additionally when the yield of groundwater was small, the correlation between fracture dimensions and flow dimensions was higher (R=0.9070～0.9529) because flow dimension well reflects characteristics of fracture regardless of fracture density. Moreover, when fracture density and groundwater yield were higher, the correlation was lower due to the flow dimensions diversified by variation characteristics of fracture. All in all, this study confirmed that groundwater flow dimension is very useful to analyze fracture density and hydraulic properties in studying the correlation of groundwater flow dimensions with fracture density and hydraulic properties in fractured rocks.