Borehole instrumentation

Pro­ject and ob­jec­ti­ves

Svensk Kärnbräns­lehan­te­ring AB (the Swe­dish nu­c­le­ar fu­el and was­te ma­na­ge­ment com­pa­ny) nee­ded a con­sul­ting com­pa­ny which could ta­ke me­a­su­re­ments on its behalf in two loca­tions: Os­karshamn and Fors­mark. The me­a­su­ring equip­ment had to me­et ve­ry high stan­dards. Af­ter ha­ving in­ve­s­ti­ga­ted and re­jec­ted a num­ber of com­mer­ci­al op­tions, the cont­ract was awar­ded to Ge­o­sig­ma, which de­ve­lo­ped a new and uni­que me­a­su­ring in­stru­ment espe­ci­al­ly for the pur­po­se. The prin­cip­le and de­sign of the in­stru­ment is ba­sed on our 30 ye­ars’ ex­pe­ri­en­ce of de­ve­lo­ping bo­reho­le in­s­tal­la­tions which ha­ve been con­s­tant­ly im­pro­ved and re­fi­ned over this pe­ri­od.

The equip­ment was de­sig­ned to mo­ni­tor ground­wa­ter pres­su­re, flow and che­mistry. The me­a­su­re­ments had to be ta­ken in around ten sec­tions of a nar­row bo­reho­le (76 mm in di­a­me­ter). The me­a­su­re­ments had to con­ti­nue over a pe­ri­od of at le­ast 5 ye­ars in bo­reho­les up to 1000 m deep without the equip­ment be­ing re­mo­ved du­ring this ti­me.

The ob­jec­ti­ve of the in­ve­s­ti­ga­tion was to un­ders­tand the hyd­rau­lic con­di­tions in the area, in­clu­ding wa­ter mo­ve­ments and ground­wa­ter che­mistry, and to be­gin a ti­me se­ri­es of me­a­su­re­ments, so that any chang­es cau­sed by the fu­tu­re fi­nal re­po­si­to­ry for nu­c­le­ar was­te could be iden­ti­fi­ed and qu­an­ti­fi­ed. It was the­re­fo­re es­sen­ti­al to be ab­le to re­pla­ce da­ma­ged sen­sors without re­mo­ving the en­ti­re pie­ce of equip­ment.

De­scrip­tion

The ob­jec­ti­ve was to al­low da­ma­ged sen­sors to be ex­chang­ed without lif­ting the en­ti­re me­a­su­ring in­stru­ment out of the bo­reho­le. This was ma­de pos­sib­le by ope­ning up the up­per part of the bo­reho­le which enab­led me­a­su­ring equip­ment, such as pres­su­re sen­sors and pumps, to be lo­we­red down nar­row tu­bes that we­re con­nec­ted to dee­per sec­tions of the bo­reho­le.

The equip­ment was in­s­tal­led in a to­tal of around 40 deep co­re-dril­led bo­reho­les (300-1000 m) and around 40 per­cus­sion-dril­led bo­reho­les (100 m). The equip­ment in the ol­dest bo­reho­le has now (2010) been in pla­ce for over 8 ye­ars and is still ful­ly fun­c­tio­ning.