Scale model study of a borehole pulse electromagnetic system

CIM Bulletin, Vol. 73, No. 817, 1980

DENNIS V. WOODS, Department of Geotogical Sciences, Queen's University, Kingston, Ontario, J. DUNCAN CRONE, Crone Geophysics Limited, Mississauga, Ontario

In order to determine its capabilities and to aid in the interpretation of field results, a scale model study and field tests were carried out on the Crone borehole pulse electromagnetic (PEM) system. The model results indicate that if a borehole passes in the vicinity of a tabular conductive body, the system will not only detect the presence of the body, but will also return information as to its conductivity-thickness product, size, attitude and position.The effect of variation of these electromagnetic and geometric factors on the shape of the response curve from a borehole PEM survey is displayed by a number of suites of scale-model response curves. These model curves can be used directly as type curves in the interpretation of field results. Field tests of a prototype PEM system provide a check on the scale-model results and also summarize the procedure of interpreting field data using the model type curves.The borehole pulse EM system can be effectively used as a follow-up geophysical instrument for locating and delineating known conductive bodies. It can also be profitably utilized as a primary geophysical exploration tool in areas of deep mineralization below the depth limit of conventional airborne and ground geophysical systems. The probed area of a diamond drill hole in these cases is increased from a 1-inch drill core to a zone extending hundreds of feet from the hole.
Keywords: Mineral exploration, Exploration techniques, Borehole surveys, Electromagnetic systems, PEM systems, Geophysical exploration, Scale modelling, Drilling.