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Summary:
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Working report: ABSTRACT
Front, K., Okko, O. & Hassinen, P., 1997. Interpretation of geophysical logging of
boreholes KI-KR10 and KI-KR11 at the Kivetty site at Äänekoski and revision of the
bedrock model based on data from boreholes KI-KR10 - KI-KR13. Posiva, Work
Report 97-57, 63 p. + 9 app.
The Finnish power companies Teollisuuden Voima Oy and Imatran Voima Oy are
preparing for final disposal of the high-level nuclear fuel waste deep into the bedrock. The
Kivetty research site at Äänekoski is one of the four candidates selected for the detailed site
characterization conducted by Posiva Oy. This report describes the processing and
interpretation of standard single hole geophysical borehole logging carried out in the 600 m
long boreholes KR10 and KR11 cored in 1996 and geological description of the recently
cored boreholes KR12 and KR13 at the Kivetty site at Äänekoski.
Furthermore, the structural bedrock model of the Kivetty site was reviewed according to
the hydraulic conductivity measurements, and oriented fracture data of dipmeter, applied in
the 76 mm diameter borehole KR10 as well as according to the reflections obtained by
oriented borehole radar and VSP surveys.
Lithological units, different types of porphyritic granodiorite and granite with associated
dykes and short amphibolitic sections, are classified by the use of combined natural gamma
radiation, density and magnetic susceptibility information. Fracturing is analysed by the
interpretation of different types of acoustic, density, resistivity and temperature logs. There
are typically 1 - 3 tight fractures per meter in the drilled borehole cores. Typically, the main
fracturing is associated within the uppermost 150 - 200 m of the core samples. In this depth
section, rusty and weathered fractures occur, especially along the borehole KR11. The few
fractured sections are typically only 1 - 2 m long sections. They are located and described
along the boreholes KR10 and KR11 by combining the logs of fluid temperature and
salinity together with the porosity and modulus of elasticity derived from the full wave
form sonic log and the visual observations at the core samples. The main exceptions in
length of fracturing are the 30 - 40 m long hydrothermally altered and weathered section at
the depth interval of 290 - 330 m in the borehole KR12 and the altered fracturing with core
loss associated with the contact zone of amphibolitic rock and porhyritic granite at the core
depth of 320 - 325m in the borehole KR13
According to hydraulic conductivity tests and attenuation of both body and tube waves in
the full waveform acoustic logs, 2 - 3 individual sections were considered locally
significant fractured zones. Geometrically, oriented fractures, the adjoining borehole radar
and VSP reflections of the fractured sections, and the hydraulic interference tests give
incoherent information. Therefore, the bedrock model is re-evaluated according to the
large-scale hydraulic connections and similarities in the tectonic and geological character in
fractured sections in different boreholes.
Key words: Geophysical, structural bedrock model, lithological unit, fracturing, hydraulic
conductivity
ABSTRACT
Front, K., Okko, O. & Hassinen, P., 1997. Interpretation of geophysical logging of
boreholes KI-KR10 and KI-KR11 at the Kivetty site at Äänekoski and revision of the
bedrock model based on data from boreholes KI-KR10 - KI-KR13. Posiva, Work
Report 97-57, 63 p. + 9 app.
The Finnish power companies Teollisuuden Voima Oy and Imatran Voima Oy are
preparing for final disposal of the high-level nuclear fuel waste deep into the bedrock. The
Kivetty research site at Äänekoski is one of the four candidates selected for the detailed site
characterization conducted by Posiva Oy. This report describes the processing and
interpretation of standard single hole geophysical borehole logging carried out in the 600 m
long boreholes KR10 and KR11 cored in 1996 and geological description of the recently
cored boreholes KR12 and KR13 at the Kivetty site at Äänekoski.
Furthermore, the structural bedrock model of the Kivetty site was reviewed according to
the hydraulic conductivity measurements, and oriented fracture data of dipmeter, applied in
the 76 mm diameter borehole KR10 as well as according to the reflections obtained by
oriented borehole radar and VSP surveys.
Lithological units, different types of porphyritic granodiorite and granite with associated
dykes and short amphibolitic sections, are classified by the use of combined natural gamma
radiation, density and magnetic susceptibility information. Fracturing is analysed by the
interpretation of different types of acoustic, density, resistivity and temperature logs. There
are typically 1 - 3 tight fractures per meter in the drilled borehole cores. Typically, the main
fracturing is associated within the uppermost 150 - 200 m of the core samples. In this depth
section, rusty and weathered fractures occur, especially along the borehole KR11. The few
fractured sections are typically only 1 - 2 m long sections. They are located and described
along the boreholes KR10 and KR11 by combining the logs of fluid temperature and
salinity together with the porosity and modulus of elasticity derived from the full wave
form sonic log and the visual observations at the core samples. The main exceptions in
length of fracturing are the 30 - 40 m long hydrothermally altered and weathered section at
the depth interval of 290 - 330 m in the borehole KR12 and the altered fracturing with core
loss associated with the contact zone of amphibolitic rock and porhyritic granite at the core
depth of 320 - 325m in the borehole KR13
According to hydraulic conductivity tests and attenuation of both body and tube waves in
the full waveform acoustic logs, 2 - 3 individual sections were considered locally
significant fractured zones. Geometrically, oriented fractures, the adjoining borehole radar
and VSP reflections of the fractured sections, and the hydraulic interference tests give
incoherent information. Therefore, the bedrock model is re-evaluated according to the
large-scale hydraulic connections and similarities in the tectonic and geological character in
fractured sections in different boreholes.
Key words: Geophysical, structural bedrock model, lithological unit, fracturing, hydraulic
conductivity
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