The non-destructive measurement of the radio frequency properties of hard rock borehole cores

Rutschlin, Marc (2005)

Thesis (PhD) -- Stellenbosch University, 2005.

Thesis

ENGLISH ABSTRACT: The effective use of borehole radar in geophysical exploration requires accurate knowledge of the dielectric properties of the geological system in which it is employed. The attenuation and propagation velocity of pulses through rock must be known in order to plan and interpret experimental data. Conventional destructive methods for the measurement of hard rock cores require the careful preparation of samples. This firstly necessitates the selection of sampling position and the resulting estimation of rock properties based on sparse measurements, and secondly results in the loss of material and thus data. The ready availability of cylindrical borehole core samples invites the use of a nondestructive means of measuring their properties. A novel design for a flexible guarded capacitor which conforms to a core's cylindrical surface is presented here. T he proposed device has numerous advantages over previous methods. No material is lost to sample preparation and a detailed characterisation of the entire core, including inclusions and transitions between rock types, may be performed. A detailed methodology for the rapid construction of a robust capacitor is given. Guidelines for its operation to achieve repeatable and accurate measurements of the complex dielectric constant of samples of varying homogeneity in the 1- 25 MHz frequency range are presented. The increased amount of data collected from complete core samples is analysed statistically, and amongst other things allows the estimation of the rock's homogeneity. Comparisons of the dielectric properties measured in the laboratory to propagation velocity estimates obtained from crosshole borehole shoots show that a more homogeneous sample is a better predictor of bulk propagating conditions. Detailed studies of the dielectric properties of economically important diamondiferous and platiniferous geological systems show that borehole radar is a feasible tool for the high resolution delineation of ore bodies and other geological targets.

AFRIKAANSE OPSOMMING: Die effektiewe gebruik van boorgatradar in geofisiese eksplorasie benodig akkurate kennis van die dielektriese eienskappe van die geologiese sisteme waarin dit gebruik word. Kennis van die verswakking en voortplantingsnelheid van pulse deur die rots word benodig om eksperimente te beplan en gemete data te interpret eer. Vir konvensionele destruktiewe meetmetodes van harde rotskerne is noukeurige voorbereiding van monsters noodsaaklik. Hierdie proses vereis eerstens 'n keuse van meetposisies en die afskatting van rotseienskappe gebaseer op verspreide metings, en lei tweedens tot die verlies van materiaal en dus data. Die beskikbaarheid van silindriese bom·gat kernmonsters maak dit moontlik om die kerneienskappe op n nie-destruktiewe manier te meet. Die ontwerp van 'n nuwe buigbare afgeskermde kapasitor wat op 'n silindriese kernoppervlak pas, word hier voorgestel. Die toestel het verskeie voordele bo huidige metodes. Geen materiaal word gedurende monstervoorbereiding verloor nie, en 'n volledige beskywing van die eienskappe van die hele kern , met insluitings en oorgange tussen rotstipes, kan verkry word. 'n Gedetaileerde prosedure vir die vinnige konstruksie van 'n robuuste kapasitor word gegee. Die gebruik van die toestel vir herhaalbare en akkurate metings van die komplekse dielektriese konstante van verskillend homogene monsters in die 1- 25 MHz frekwensie bereik word beskryf. Die groter hoeveelheid data wat deur middel van hierdie metode van hele kernmonsters verkry kan word , word statisties geanaliseer, en laat onder andere 'n skatting van die rots se homogeniteit toe. Vergelykings van laboratoriumgemete rotseienskappe met veldskattings van voortplant ingsnelhede wys dat 'n meer homogene monster tot 'n beter afskatting van werklike voortplantingstoestande lei. Studies van die dielektriese eienskappe van ekonomies belangrike diamanthoudende en platinumryk geologiese sisteme wys dat boorgatradar geskik is vir hoe resolusie uitkenning van ertsligame en ander geologiese teikens.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/50504
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