Workreport 2011-86

Pressure, Flow and Hydraulic Interference Measurements in ONKALO at Olkiluoto, Drillholes ONK-PP262 and ONK-PP274

Hurmerinta, E., Pekkanen, J., Komulainen, J. & Rouhiainen, P.

English

66

The general purpose of these studies is to characterize the fracture network and groundwater flow properties in a volume of rock, which is representative of the rock close to deposition holes. As a part of the studies hydraulic tests and flow measurements were applied in two drillholes in hydraulically poorly conductive bedrock.

This report presents the principles of the methods as well as the results of the measurements carried out in the underground facilities of ONKALO. The measurements were conducted in drillholes ONK-PP262 and ONK-PP274 between May 9, 2010 and  June 9, 2011.

The aim of the measurements was to obtain pressure in the closed drillholes, to detect water yielding fractures by flow measurements, to obtain transmissivity with overpressure and drawdown tests and to study hydraulic interference between the drillholes by cross-hole hydraulic tests.

The PFL DIFF probe was used to detect flow within single fractures in the drillhole. Transmissive water yielding fractures were found at depths 17.9 m, 16.9 m and 16.4 m in ONK-PP262 and at depths 19.8 m and 19.5 m in ONK-PP274.

The cross-hole hydraulic tests included three basic phases. Flow was measured in one drillhole when the other drillhole was open, closed or overpressurized. The cross-hole hydraulic tests were carried out to both directions in the two drillholes.

Groundwater, flow, measurement, bedrock, drillhole, hydraulic interference, Posiva Flow Log.

Pressure, Flow and Hydraulic Interference Measurements in ONKALO at Olkiluoto, Drillholes ONK-PP262 and ONK-PP274 (pdf) (12.3 MB)