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Workreport 2018-32



Pumping Tests in Drillholes OL-KR49, -KR50, and -KR56 at Olkiluoto in 2012–2014


Pentti, E., Vaittinen, T., Pekkanen, J., Karvonen, T.



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Two pumping tests were carried out during 2012–14 in the eastern investigation area of Olkiluoto to improve the understanding of the hydrogeological conditions. The first one was a cross-hole interference test in drillholes OL-KR49 and ‑KR50 in October–December 2012, and the second one a pumping test in OL-KR56 that lasted from October 2013 to March 2014. The part of the latter test where zone HZ146 was affected was also simulated by numerical modelling.

In the cross-hole interference test of OL-KR49 and ‑KR50, the drillholes were pumped in turns, and during each pumping, a PFL DIFF flow logging was carried out in the other drillhole. Because in both drillholes, there are sections in such a bad condition that there is a risk of the logging equipment getting stuck, flow logging had to be limited to the uppermost 630 m in OL-KR49 (total length 1060.22 m) and the uppermost 380 m in OL-KR50 (total length 939.33 m). According to the results, there are several fractures in both drillholes above elevation −80 m with a hydraulic connection to the other hole. At greater depths, no connections were observed.

In the pumping test of OL-KR56, the head decrease was focused on a chosen drillhole section by installing inflatable packers in the drillhole and pumping water from between them. The effect of the pumping was monitored in the surrounding packed-off drillholes with the standard automatic head monitoring equipment and by flow logging of the neighbouring OL-KR57. Two sections were pumped: first at drillhole lengths 370–375 m and then at 119–139 m. The former pumping section was chosen at the modelled intersection of HZ146, the prominent hydrogeological zone of the eastern area. The pumping caused the largest drawdowns in monitoring sections L3 of OL-KR51 (5.6 m at the end of pumping) and L1 of OL-KR52 (4.2 m), both with a modelled HZ146 intersection. The latter pumping caused much smaller drawdowns, detectable only in sections L3–L5 of OL-KR50.

The primary goal of the modelling was to evaluate the responses of OL-KR56 pumping from section 370–375 m on drawdowns in the drillholes OL-KR50, -KR51 and OL-KR52 and find possible reasons for small drawdown in OL-KR50 as compared to OL-KR52 even though the distances from pumping section do not differ much from each other and measurement depths are also close to each other. Various responses to pumping in OL-KR50 and OL-KR52 can be partly explained by differences in surface driven hydraulic gradient between OL-KR56 and OL-KR50 and OL-KR56 and OL-KR52, respectively. The second possible explanation is that there are local fractures around OL-KR50 extending to the depth of around 400 m. For the third, different response can be caused by ductile deformation zone RDZ intersecting hydraulic connection between OL-KR56 and OL-KR50.


Hydrogeology, pumping test, final deposition


WR 2018-32_web (pdf) (32.7 MB)


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