b'Minerals geophysics Minerals geophysicsgeophysical logging programme toaccess to the deeper sections of the drill-generate systematic data unbiasedhole The logging itself was all carried out by sample selection With such detail,open-hole Drill-hole inclinations were we reasoned it should be possibletypically quite steep, although at their to recognise subtle trends in datadeepest, some drill-holes flattened to less properties within particular rock units,than 300, limiting the depth to which the which in a best-case scenario might beprobe could be loweredrelated to mineralising processes To expedite survey conduct, we supplied To generate a comprehensive petro- the logging crew with a comprehensive physical database, we selected a suitesuite of information on each drill-hole of geophysical logging techniquesincluding collar location, total depth, comprising magnetic susceptibility,drillers surveys, in-hole location of Terry Harveydensity, inductive conductivity, IP- major fault zones and zones of poor Associate Editor resistivity, spectral gamma-ray androck quality, details of any surface for Minerals geophysics seismic velocity, plus acoustic and opticalcasing and stranded in-hole casing, terry.v.harvey@glencore.com.au televiewers for structural informationand, for the acoustic and optical There are some excellent sites on the netteleviewers and sonic logging tools with information on geophysical drill-holewhich employ centralising spacers, logging, some sponsored by geophysicaldepths of hole diameter changes Drillers Drill-hole logging logging companies and down-holewere requested to flush drill-holes on sonde manufacturers, and some linked tocompletion to remove grease, etc, but As an adjunct to a recent drillingthis wasnt always successful; in several programme we undertook extensiveuniversities and professional associationsinstances rigs had to be recalled to site geophysical drill-hole logging, andPetroWiki (Society of Petroleumto undertake further cleaning Drill-hole I thought Id share some of theEngineers), for instance, is a good sitewater turbidity prevented the successful practicalities of such an endeavour for the fundamentals of geophysicalapplication of the optical televiewer in logging; not unexpectedly, it does havemost drill-holesThe principal aim of the drill-holean oil and gas bias Table 1 provides a logging was to assemble a databasesummary of the operational parametersFinally, did everything run smoothly? of petrophysical properties of thefor each logging technique SomeFor the most part, yes, but in the last principal rock types and mineralisationconcern was expressed about the use ofphase of the programme, while in-filling styles This knowledge was expected toa radioactive source in the density tool;missing coverage, we did lose one benefit future exploration programmesstrict radiation handling protocols wereprobe, jammed in a drill-hole As luck through selection of more appropriateenforced and the risk of block sterilisationwould have it, the drill-pad was small geophysical techniques and surveyaround a stranded probe was deemedand uneven, requiring a track-mounted parameters and a more informedacceptably small rig for safe access Unfortunately, this interpretation of results Specifically, arig had moved off-site, so an attempt better understanding of petrophysicalThe diamond drill-holes selected forat probe recovery was not immediately properties could improve geophysicalgeophysical logging ranged in depth frompossible Given that a track-mounted rig modelling and constrained inversion of400 m to over 1800 m Most drill-holeswould have to be specifically sourced geophysical survey results Our databasewere logged with the drill-rig off-siteand brought back on site, recovery was could have been assembled fromHowever, in several instances, a drilldeemed economically unviable at this measurements on selected drill-corerig remained on-site with rods in-holetime And, no, it was not the radioactive samples, but we opted for a drill-holecovering zones of caving to ensure loggingprobe!Table 1.Geophysical logging operating parametersGeophysical method Sonde type Petro-physicalRadioactiveSpacer DryWetSteelPVCCommentsparameter source hole hole casing casingGravity Sidewall gamma density Density Yes Caliper Yes Yes Yes* Yes *Dimished sensitivityMagnetics Magnetic susceptibility Magnetic susceptibility No No Yes Yes No YesRadioactivity Gamma-ray and spectralNatural radioactivity No No Yes Yes Yes* Yes *Dimished sensitivitygamma-rayResistivity Dual guarded resistivity Electical resistivity No No No Yes No Yes* *Must be slottedIP-Resistivity Dual spacing IP IP effect and resistivity No No No Yes No Yes* *Must be slottedElectro-magnetics EM induction conductivity Electical conductivity No No Yes Yes No YesSeismics Full waveform sonic Seismic velocity No Sprung spacers No Yes Yes* Yes** *Cement log only **Diminished sensitivityGeology and structure Optical tele-viewer Colour No Sprung spacers Yes Yes* No No *Clean waterGeology and structure Sonic tele-viewer Seismic impedance No Sprung spacers No Yes No Yes* *Limited sensitivity33 PREVIEW OCTOBER 2022'