Databank

Databank

Posiva publishes Working Reports and Posiva Reports. From the year 2006 nearly all the reports have been published on our webpage and they can be found in the databank. In the databank you can also find our Annual Reviews and some other publications as well. You can also find print-quality pictures and useful links in the databank.

Recent publications


POSIVA Report 2017-4

Back

Name:

Quality Assessment of PFL Transmissivity Data Identified in Subsurface Drillholes of ONKALO

Writer:

Tammisto, E., Ahokas, H., Komulainen, J., Pekkanen, J.

Language:

English

Page count:

212

ISBN:

978-951-652-267-1

Summary:

As part of the Posiva’s investigation programme for the final disposal of the spent nuclear fuel, Posiva Oy investigates the prevailing hydrogeological conditions at Olkiluoto Island. The location and hydraulic properties of fractures are of interest for example in the groundwater flow modelling.

This report assesses the applicability of the PFL DIFF (and PFL MFD) methods to characterise flow of rock fractures intersecting subsurface holes drilled from ONKALO, which is an underground rock characterisation facility that extends approximately to the depth of 450 m. So-called PFL transmissivity can be determined at flowing fracture intersections in drillholes with the aid of Posiva Flow Log (PFL DIFF/MFD) measurements. 

Representativeness of the PFL flow logging data measured under large drawdown in ONKALO drillholes has been a topic for discussions, especially due to a doubt that large drawdowns in the subsurface drillholes could lead to turbulent flow.

Functionality of the PFL DIFF tool has been tested at laboratory and also at field to verify functionality at authentic conditions in ONKALO. The tests in ONKALO included, for example, PFL DIFF measurements in different pressure conditions. 

In this report, the data obtained with PFL measurements were also analysed against the other existing data. This consisted of the comparison of PFL DIFF data and injection test data in ONKALO and statistical analysis of PFL transmissivities from surface based drillholes and ONKALO pilot holes within certain rock domain. Additionally, the analyses also included comparisons between the sum of flows detected with the PFL DIFF tool in the ONKALO pilot holes and outflows from probe holes located at the same tunnel section.  The PFL flow anomalies that were not possible to correlate with the fractures mapped from the drillcore or drillhole wall images were also studied in detail.

This study shows that the PFL DIFF tool is working well in the subsurface ONKALO-holes. There are no clear signs of turbulent flow under a large drawdown. Large gradient of the hydraulic head does not cause any additional technical problems for the PFL DIFF tool. The reported PFL DIFF flow logging results represent flows from single fractures or a network of fractures intersecting the subsurface drillholes during steady flow conditions.

Keywords:

Hydrogeology, ONKALO, subsurface drillholes, PFL, transmissive fractures, hydraulically conductive fractures, groundwater flow

File(s):

POSIVA 2017-04_web (pdf) (35 MB)
Appendix 1_correlated_fractures_web (xlsx) (82.7 KB)
Appendix 1_PFL data in ONKALO-holes_web (xlsx) (190.4 KB)


Back


Share article:
This website stores cookies on your computer. These cookies are used to improve our website and provide more personalised services to you.
Close

Cookies

To make this site work properly, we sometimes place small data files called cookies on your device. Most big websites do this too.

1. What are cookies?

A cookie is a small text file that a website saves on your computer or mobile device when you visit the site. It enables the website to remember your actions and preferences (such as login, language, font size and other display preferences) over a period of time, so you don’t have to keep re-entering them whenever you come back to the site or browse from one page to another.

2. How do we use cookies?

A number of our pages use cookies to remember your actions and preferences (such as login, language, font size and other display preferences.)

Also, some videos embedded in our pages use a cookie to anonymously gather statistics on how you got there and what videos you visited.

Enabling these cookies is not strictly necessary for the website to work but it will provide you with a better browsing experience. You can delete or block these cookies, but if you do that some features of this site may not work as intended.

The cookie-related information is not used to identify you personally and the pattern data is fully under our control. These cookies are not used for any purpose other than those described here.

3. How to control cookies

You can control and/or delete cookies as you wish – for details, see aboutcookies.org. You can delete all cookies that are already on your computer and you can set most browsers to prevent them from being placed. If you do this, however, you may have to manually adjust some preferences every time you visit a site and some services and functionalities may not work.

Close