Workreport 2018-21



Flow measurements in ONKALO at Olkiluoto, Probe Holes in ONK-TR-TT-4505, Investigation Holes ONK-KR17 and ONK-PP408 and Pilot Hole ONK-PH28


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 reported measurements started on October 23, 2015 and they were completed on October 10, 2016.

The probe hole measurements presented in this report were conducted at the vehicle access tunnel ONK-TR-TT-4505 (AJYH17). The probe hole measurements were carried out with a manual device PFL MFD. The flow along the probe hole was measured using a manual measurement setup with a 1.0 m point interval.

In addition to the probe holes, core-drilled drillholes were also measured in ONKALO. The drillholes discussed in this report are ONK-KR17, ONK-PP408 and a pilot hole ONK-PH28. In drillhole ONK-PH28, in addition to the flow measurements, water loss measurement was conducted. All of the water conducting fractures detected on the basis of the flow measurements were chosen as targets of a fracture specific water loss test. The water loss measurement was conducted using the PFL Water Loss Equipment (PFL WL1) combined with a modified setup of PFL Double Packer Pressure Probe (PFL DOPP). These measurements at ONK-PH28 were the first time when the aforementioned device setup was utilized in the field.

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 flow 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 2018-21_web (pdf) (47 MB)


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