Geometric Factors for Common Electrode Arrays used in Resistivity Logging of Inclined Drill Holes

The placement of an in-hole electrode array into a mineral exploration drill hole gives rise to complicated geometric factor (G.F.) relationships. For the same arrays placed at the surface of the earth the G.F. relationships are relatively simple. This paper presents a set of nomograms giving the G.F. for three commonly used exploration logging arrays: the two (normal) array, equispaced three array and dipole-dipole array (n=1), for inclined drill holes. The nomograms may be used to compute the G.F. for drill holes of constant inclination or for deviating drill holes, by considering the deviating drill path as a series of segments of constant inclination. The disturbing influence of the air/earth interface on the G.F. for the in-hole arrays is least for the dipole dipole array and greatest for the two-array.