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DEVELOPMENT OF A SURVEILLANCE METHOD DURING DRY-DRILLING OF A 600 M DEEP BOREHOLE IN SALT AND PERFORMANCE OF GEOTECHNICAL MEASUREMENTS IN THE 600 M HOLE

Objective

1. DRILLING OF THE BOREHOLE.
2. SURVEILLANCE METHOD.
3.1. ISOTHERMAL CONVERGENCE MEASUREMENTS.
3.2. NON-ISOTHERMAL LITHOSTATIC PRESSURE MEASUREMENTS.
3.3. ISOTHERMAL LITHOSTATIC PRESSURE MEASUREMENT.
In situ experiments in the Asse II salt mine in Germany were conducted. Measurement devices for measurement of rock mechanical parameters have been developed and were made operational. For the drilling of the boreholes a new technique has been developed.

An on line method to determine the gas content in the flushing air during drilling operation was developed. The method used worked satisfactorily and the test showed that this surveillance method could be used during dry drilling of deep emplacement boreholes in a future repository.

The possibility to perform measurements was reduced due to drilling problems when drilling the intended 600 m deep boreholes. One borehole of 100 m depth and 2 boreholes of approximately 300 m depth have been drilled. In one of these 300 m deep boreholes convergence measurements have been performed during a 10 months period. The convergence measuring devices have been operating satisfactorily. The experimental results will be used to validate analytical techniques and computer models for the prediciton of salt behaviour; the analytical techniques are summarized.

The variable pressure device (VPD) has been constructed to measure the elastic and time dependent response of the salt to pressure changes. The VPD was placed in a 300 m deep borehole since a 600 m deep borehole could not be drilled. the construction is described in detail and thermomechanical analyses are reported of the behaviour of the VPD under realistic measurement conditions. A summary of constitutive models for rock salt is given.
THE EXPERIMENTS PERFORMED IN THE ASSE II SALT MINE IN THE FRG UNDER THE CONTRACT WITH THE CEC DURING THE PREVIOUS PROGRAMME (1980-1984) WERE CARRIED OUT IN A DRILLED HOLE OF 30 CM IN DIAMETER AND 300 M IN DEPTH; SINCE THEN A DRY DRILLING TECHNIQUE WAS DEVELOPED FOR LARGER DIAMETER HOLES AND GREATER DEPTHS. IN THIS PROJECT THIS TECHNIQUE WILL BE TESTED BY DRILLING A BOREHOLE WITH A DIAMETER OF 60 CM, TYPICAL FOR A DISPOSAL HOLE, AND A DEPTH OF 600 M.

AN ALTERNATIVE FOR THE RECONNAISSANCE DRILLING WHCIH TAKES PLACE BEFORE THE ACTUAL DRILLING, WILL BE DEVELOPED WITH GSF.
THE FREE CONVERGENCE MEASUREMENTS OF THE SALT AS A FUNCTION OF DEPTH OF THE HOLE, WILL BE CARRIED OUT. IN A SUBSEQUENT PHASE OF THE PROGRAMME, NON-ISOTHERMAL PRESSURE (ISOTHERMAL LITHOSTATIC MEASUREMENTS) WILL BE PERFORMED. BECAUSE OF THE COMPLEXITY OF THE TOTAL CONSTRUCTION THE MEASUREMENTS WILL BE DONE IN TWO BOREHOLES.

ALL THESE RESULTS WILL BE USED FOR THE VALIDATION OF ANALYTICAL TECHNIQUES AND COMPUTER CODES.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

ENERGY RESEARCH CENTRE OF THE NETHERLANDS
Address
Westerduinweg 3
Petten
Netherlands

Participants (1)

GSF-Forschungszentrum für Umwelt und Gesundheit GmbH
Germany
Address
Theodor-heuss-straße 4
38122 Braunschweig