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Workreport 2017-18



Flow Measurements in ONKALO at Olkiluoto, Investigation Holes ONK-PP414-PP415 and ONK-PVA11


Pekkanen, J.



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The Posiva Flow Log, Difference Flow Method (PFL DIFF) uses a flowmeter that incorporates a flow guide and can be used for relatively quick determination of hydraulic conductivity and hydraulic head in fractures/fractured zones in cored drillholes. This report presents the principles of the method and the results of measurements carried out in several drillholes at underground research facility ONKALO at Olkiluoto. The measurements started on January 20, 2014 and they were completed on February 27, 2014.

The shallow core-drilled drillholes discussed in this report are ONK-PP414-PP415 and -PVA11.

The PFL DIFF probe was used to detect flow within single fractures in a drillhole. The method utilizes rubber disks to isolate the flow in a test section from that in the rest of the drillhole. The core-drilled holes were measured using a 0.5 m section length (the distance isolated with the rubber disks). Alternatively, the flow along the drillhole was measured without the lower rubber disks. The measurements were conducted with a 0.1 m point interval.

The PFL DIFF probe includes a sensor for single point resistance (SPR). SPR was measured in connection with the flow measurements. The flow measurements and the single point resistance measurements were used to locate flowing fractures and evaluate their transmissivity.

Electrical conductivity (EC) and temperature of water were registered during automatic flow logging. The conductivity values are temperature corrected to 25 °C.


Groundwater, flow, measurement, bedrock, probe hole, drillhole, electrical conductivity, Posiva Flow Log, flow logging


WR 2017-18_web (pdf) (3.8 MB)


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