MEASUREMENTS IN THE 300 METRE DEEP DRY DRILLED BOREHOLE AND FEASIBILITY STUDY ON THE DRY DRILLING OF A 600 METRE DEEP BOREHOLE IN THE ASSE-II SALT MINE
In 1980 a borehole with a diameter of 300 millimetres and a depth of 300 metres was drilled with a dry drilling technique in the Asse-II salt mine in the Federal Republic of Germany. This borehole was used to perform a series of in-situ experiments to establish the constitutive behaviour of rocksalt, to measure the temperature induced compression on a heated tube and to validate the computer codes for the thermo mechanical behaviour. Three types of experiments are performed and described in this report: (i) free isothermal convergence measurements, (ii) temperature induced pressure measurements, (iii) free non-isothermal convergence measurements. It is shown that the thermo mechanical behaviour of rocksalt can be described accurately with a set of constitutive equations based upon elastic behaviour (E = 7 600 MPa; upsilON = .3) and secondary creep (A = 4.8 10**- 10-MPa**-n.days -1 ; n = 5.5). It is measured that the state of stress at a depth of 830 metres deviates significantly from the lithostatic pressure. This deviation is shown to be caused by the stress redistribution due to the large excavations in the mine. The maximum compression on a heated tube is measured to be about 35 MPa for a lithostatic pressure of 17 MPa and a maximum salt temperature of 175 degrees C. In this report the results are given of a feasibility study on the dry drilling of a 600 metre deep borehole in Asse II. This study is based on the classic roller bit configuration. Parallel, the GSF has developed a more advanced drilling technique, which will be pursued for the 600 metre hole experiment. The study under consideration must therefore be seen as a "backing up solution"' in the improbable situation that the advanced GSF system will not fulfil its promises.
Bibliographic Reference: EUR 10737 EN (1986) FS, 262 P., BFR 800, EUROFFICE, LUXEMBOURG, POB 1003
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Record Number: 1989125029800 / Last updated on: 1987-03-01
Available languages: en