Transient Self Potential Inversion for the Simultaneous Estimation of Hydraulic Conductivity and Specific Storage

<p>Storage options for the energy storage in the subsurface includes the injection and storage of the &#8220;energy gas&#8221; (e.g., methane, hydrogen, compressed air) or thermal water into the underground formations. The heterogeneous structure of the storage formations could play a crucial role on the potential storage capacity, as well as the formulation of post treatment strategy. Hence, innovative techniques are required for characterizing the high-resolution formation heterogeneity and monitoring the gas or heat plume distribution in the subsurface after their injections. &#160;Previous studies have shown that flow properties can vary as the gas or thermal water being injected into the aquifer. In this study, we propose a time-lapse hydraulic tomography (HT) method for characterizing the baseline hydraulic information and depicting the hydraulic property changes through a series of cross-well pumping tests. These tests were implemented in two pilot sites for methane and hot water injection tests at Wittstock, Germany. In order to generate a three-dimensional tomographical configuration, each pumping test was conducted at certain depth in a testing well, accompanying with multiple observation points at other wells. Depth-variant pumping and observation segments were formed by the double-packer system. As a result, we achieved 198 and 135 baseline drawdown curves for the methane and heat sites, respectively. For these measured data, we initially evaluated the effective hydraulic conductivity and specific storage of the aquifer according to certain analytical fitting methods. Furthermore, the vertical anisotropy of the hydraulic conductivity was also estimated. Sequentially, the fitted hydraulic parameters and analytical drawdown curves were utilized for correcting the well skin effects on hydraulic traveltimes and attenuations, as they have an unneglectable impact on them. &#160;The corrected hydraulic traveltimes and attenuations were used for the inversion of the baseline hydraulic diffusivity and specific storage, respectively. Hydraulic conductivity distribution was then estimated through these two parameters. After we achieved the baseline information, HT was executed again by repeating the tomographical pumping tests after methane and hot water injections. The same data processing and inversion techniques were applied to the drawdown curves derived from the post-injection period. Inverted hydraulic diffusivity, specific storage, and hydraulic conductivity were compared to the baseline inversion results. Changes on these hydraulic properties could provide the information of the spatial distribution of methane or heat plume.</p>

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Hydrologic Characteristics and Response of Fractured Till and Clay Confining a Shallow Aquifer

Canadian Geotechnical Journal ◽

10.1139/t75-003 ◽

1975 ◽

Vol 12 (1) ◽

pp. 23-43 ◽

Cited By ~ 68

Author(s):

G. E. Grisak ◽

J. A. Cherry

Keyword(s):

Hydraulic Conductivity ◽

Fractured Rock ◽

Nuclear Research ◽

Pumping Test ◽

Shallow Aquifer ◽

Ratio Method ◽

Clay Loam ◽

Specific Storage ◽

Groundwater Movement ◽

Lacustrine Clay

Fractures in glacial till and glaciolacustrine clay were observed in excavations up to 20 ft (6.1 m) in depth and in drill cores at the Whiteshell Nuclear Research Establishment (WNRE) in southeastern Manitoba. The fractures are characteristically coated with carbonate and oxide precipitates, which indicate groundwater movement through the fractures. The fractures impart an effective bulk hydraulic conductivity to the clay–loam till and lacustrine clay, as evidenced by tritium tracer experiments and piezometer responses in the till and clay to pumping of an underlying sandy aquifer.The intergranular hydraulic conductivity of clay–loam till and glaciolacustrine clay in the Interior Plains, as determined from laboratory consolidation test data, is in the range of 2 × 10−10 to 9 × 10−11 ft s−1 (6 × 10−9 to 2.7 × 10−9 cm s−1). The bulk hydraulic conductivity of the fractured clay–loam till at WNRE, as determined from finite-element mathematical modeling, is about 6 × 10−9 ft s−1 (1.8 × 10−7 cm s−1). The model value represents the effective hydraulic conductivity imparted to the till by the fractures.Seven pumping tests, ranging in duration from 8.75 to 120 h were conducted on the sandy aquifer and drawdown data in the aquifer were analyzed to obtain the hydraulic conductivity and storativity of the aquifers.A 32 day pumping test on the aquifer showed that many of the piezometers in the till and clay respond quickly and strongly to the aquifer drawdown, while others show no noticeable response. The responding piezometers intersect open fractures whereas the others do not. Analysis of the piezometer drawdowns during the long-term pumping test using the Neuman and Witherspoon ‘ratio’ method indicates that the rapid piezometer drawdowns in the confining layers can be accounted for by assigning specific storativity values in the range of 1 × 10−5 to 5 × 10−6 ft−1 (3 × 10−5 to 1.5 × 10−5 m−1) to the clay–loam till and lacustrine clay. These values are typical of fractured rock. If intergranular specific storage values are used, the calculated piezometer drawdowns are very small or negligible.

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