The upper continental crust, an aquifer and its fluid: hydaulic and chemical data from 4 km depth in fractured crystalline basement rocks at the KTB test site

Geofluids - Tập 5 Số 1 - Trang 8-19 - 2005
Ingrid Stober1, Kurt Bucher2
1Geological Survey Baden‐Württemberg (LGRB), Freiburg, Germany
2Institute of Mineralogy (IMPG), University of Freiburg, Freiburg, Germany

Tóm tắt

AbstractDetailed information on the hydrogeologic and hydraulic properties of the deeper parts of the upper continental crust is scarce. The pilot hole of the deep research drillhole (KTB) in crystalline basement of central Germany provided access to the crust for an exceptional pumping experiment of 1‐year duration. The hydraulic properties of fractured crystalline rocks at 4 km depth were derived from the well test and a total of 23100 m3 of saline fluid was pumped from the crustal reservoir. The experiment shows that the water‐saturated fracture pore space of the brittle upper crust is highly connected, hence, the continental upper crust is an aquifer. The pressure–time data from the well tests showed three distinct flow periods: the first period relates to wellbore storage and skin effects, the second flow period shows the typical characteristics of the homogeneous isotropic basement rock aquifer and the third flow period relates to the influence of a distant hydraulic border, probably an effect of the Franconian lineament, a steep dipping major thrust fault known from surface geology. The data analysis provided a transmissivity of the pumped aquifer T = 6.1 × 10−6 m2 sec−1, the corresponding hydraulic conductivity (permeability) is K = 4.07 × 10−8 m sec−1 and the computed storage coefficient (storativity) of the aquifer of about S = 5 × 10−6. This unexpected high permeability of the continental upper crust is well within the conditions of possible advective flow. The average flow porosity of the fractured basement aquifer is 0.6–0.7% and this range can be taken as a representative and characteristic values for the continental upper crust in general. The chemical composition of the pumped fluid was nearly constant during the 1‐year test. The total of dissolved solids amounts to 62 g l−1 and comprise mainly a mixture of CaCl2 and NaCl; all other dissolved components amount to about 2 g l−1. The cation proportions of the fluid (XCa approximately 0.6) reflects the mineralogical composition of the reservoir rock and the high salinity results from desiccation (H2O‐loss) due to the formation of abundant hydrate minerals during water–rock interaction. The constant fluid composition suggests that the fluid has been pumped from a rather homogeneous reservoir lithology dominated by metagabbros and amphibolites containing abundant Ca‐rich plagioclase.

Từ khóa


Tài liệu tham khảo

10.2118/2466-PA

Boonstra J, 1989, SATEM: Selected Aquifer Test Evaluation Methods, a Microcomputer Program, 80

10.1007/978-94-017-1816-5_7

10.1029/91EO00190

10.1029/TR027i004p00526

10.1029/WR003i001p00263

10.1029/GL015i009p01029

10.1029/96JB03945

Emmermann R, 1995, KTB Hauptbohrung Results of Geoscientific Investigation in the KTB Field Laborarory, Final Report: 0‐9101 m

10.2118/2864-PA

Frape SK, 1987, Saline Water and Gases in Crystalline Rocks, 19

Frape SK, 2004, Surface and Ground Water, Weathering, and Soils, 541

10.1016/0009-2541(82)90045-6

10.1016/0040-1951(94)90040-X

Gale J, 1987, Hydrogeological Characterization of the Stripa Site, 126

10.1007/PL00014651

10.1007/PL00014663

Horner DR, 1951, Pressure build‐up in wells, Engineer Journal Bulletin, 3, 503

Ingebritsen SE, 1998, Groundwater in Geologic Processes

10.1016/0098-3004(92)90029-Q

Krusemann GP, 1991, Analysis and Evaluation of Pumping Test Data, 377

10.1029/1998RG900002

Matthews CS, 1967, Pressure Buildup and Flow Tests in Wells, 167, 10.2118/9780895202000

Miller CC, 1950, The estimation of permeability and reservoir pressure from bottom hole pressure builtup characteristics, Petroleum Transactions AIME, 189, 91

10.1029/96JB02899

Nagra, 2002, Projekt Opalinuston, Synthese der geowissenschaftlichen Untersuchungsergebnisse, 659

10.1029/WR016i002p00423

10.2475/ajs.272.3.234

10.1029/WR003i001p00241

Parkhurst DL, 1980, PHREEQE – A Computer Program for Geochemical Calculations, 210

Patzak M, 1991, Die Metabasite der KTB‐Vorbohrung, Oberpfalz (NE‐Bayern), 103

10.1016/0016-7037(93)90387-C

10.1007/PL00014652

Stober I, 1986, Strömungsverhalten in Festgesteinsaquiferen mit Hilfe von Pump‐ und Injektionsversuchen, Geologisches Jahrbuch, 42, 204

10.1029/96EO00062

10.1046/j.1365-3121.1999.00241.x

10.1111/j.1468-8115.2004.00078.x

10.1029/TR016i002p00519

10.2475/ajs.277.10.1315

10.1007/PL00014661

Thông tin
Thông tin xuất bản

Geofluids

Tập 5 Số 1

8-19

Thông tin tác giả