Abstract
The assessment of the groundwater flow rate around the cavern periphery is a critical requirement for the design of underground water-sealed oil storage caverns and commonly made through seepage analysis, where a reasonable estimation of the hydraulic conductivity of the host rock is the key issue. However, it is a challenge to accurately determine the hydraulic conductivity of natural rock masses owing to their heterogeneous and anisotropic nature. The underground storage cavern project has a unique favorable condition in that there is a water curtain system that can provide considerable hydraulic test data for inferring hydraulic parameters; however, no well-established method has ever been proposed to exploit these data for characterizing heterogeneity in hydraulic conductivity. This study presents a new approach to evaluate the spatial variation of hydraulic conductivity using water curtain borehole data. This approach treats the peripheral region of each borehole as a homogenous unit with a particular equivalent permeability coefficient that can be back-calculated from the measured injection flow rate of the borehole using a numerically established empirical formula. Besides, the impact of curtain gallery drainage, occurring in the construction stage, on the seepage field was investigated while the effect of the rock fracture configuration on hydraulic conductivity assessment was examined. The proposed method enables robust and accurate mapping of heterogeneity in the hydraulic conductivity of host rocks and provides a new idea of effectively utilizing hydro-geological test data to derive the hydraulic conductivity of rock masses surrounding water-sealed storage caverns.
Highlights
Compared with an above-ground container tank, the underground water-sealed oil/gas storage cavern has many advantages in cost, land consumption, environmental protection, and operation safety and, has become an important means for oil/gas storage
The underground water-sealed storage cavern project has a higher demand for accurate determination of the flow rate, which relies upon reasonable estimation of the rock hydraulic conductivity
There is a lack of an effective and well-established method of exploiting these borehole data to characterize the heterogeneity in the hydraulic conductivity of host rocks
Summary
Compared with an above-ground container tank, the underground water-sealed oil/gas storage cavern has many advantages in cost, land consumption, environmental protection, and operation safety and, has become an important means for oil/gas storage. The fairly high expenses related to in situ tests usually lead to a limited number of tests being implemented on several selected locations in rock masses By exploiting these hydro-geological test data, many methods have been proposed to characterize the heterogeneity in the hydraulic conductivity of fractured rock masses, such as kriging of small-scale hydraulic test data [27,28], stochastic simulation [27,29,30], geostatistical inverse modeling of a single cross-hole pumping or injection test [31], and hydraulic tomography [32]. The method presented in this study can serve as an effective idea of utilizing hydro-geological test data to robustly and accurately map the heterogeneity in the hydraulic conductivity of host rocks surrounding water-sealed storage caverns
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